Prof. S. V. LEBEDEV

“DRY ICE”

IN THE EXPORT OF SIBERIAN BUTTER

(On replacing ordinary ice in the transportation of export Siberian butter with solid carbon dioxide—so-called “dry ice”—and on the advantages and benefits connected with this for Siberian butter-making)

Tomsk
1929

Prof. S. V. Lebedev

“DRY ICE”

in the Export of Siberian Butter

(on replacing ordinary ice in the transport of export Siberian butter with solid carbon dioxide—i.e., “dry ice,” and on the advantages and benefits connected with this for Siberian butter-making).

The prospects for Siberian agriculture are most closely connected with the growth of the marketability of its products and with the development of export possibilities for them. One of the essential aspects of this question is the creation of favorable conditions for exporting from Siberia perishable livestock products in general and Siberian butter in particular. The relative share of the Siberian Territory in butter procurements for the Union, according to data for 1926–1927, amounted to 51.8%. In relation to butter shipments from the Siberian Territory in 1913, the year 1926–1927 gave a little more than 60%. According to customs statistics for all borders of the USSR, in the indicated year 26.66 thousand tons of butter (net) were exported. Of this amount, Siberia’s export amounted to 21.44 thousand tons, i.e., 80.4% of the total export of butter actually taken abroad. The relative weight of the value significance of Siberian butter among all products of agriculture, fishing, and hunting, according to procurements in 1926–27, indicates that butter, according to SKTO data, occupied in that year second place in Siberia, making up 29.4% of the total value of Siberian exports, while first place in this respect was occupied by grain fodder, accounting for 42.1%.

It is evident that the actual value of Siberian butter on the world market is determined, besides its quality corresponding to the moment of production at the butter factories, also by the export conditions under which Siberian butter travels its long route of 3—3,500 versts from Siberian factories to the markets of world sale, chiefly in London. Because of the remoteness from the latter of the districts of Siberian butter-making, Siberian butter passes through three lengthy stages, differing in their conditions, duration, and consequences for the quality of the butter being exported. The first stage is the delivery of butter from the factories to a railway station, in individual cases to a wharf; the second is the transport of butter by railway; and the third is the sea route from a Russian port to London. The butter-shipping season from Siberia falls chiefly in the summer months. This circumstance, given the considerable remoteness of the overwhelming majority of Siberian butter factories from railway stations, is of substantial importance. Owing to the primitiveness of the means of transport by horse-drawn haulage, represented in Siberia only by the ordinary peasant cart, the delivery of butter to the railway line under Siberian conditions has a very bad effect on the quality of the butter being shipped.

The temperatures of the summer months in Siberia are very high; this can be seen below from the monthly mean and maximum temperatures for Novosibirsk, presented by the data of Table 1 for 1914.

Table 1.

°C temperature	April	May	June	July	August	September	October
Monthly average	2.0	11.0	16.7	16.1	18.1	11.4	2.0
Maximum	15.2	26.2	29.1	24.0	28.2	24.4	16.8

In order to reduce, as far as possible, the heating of the butter during cart transport, in Siberia the removal of butter from the factories is usually timed for the cool nighttime hours. In addition, the barrels of butter are covered with straw, hay, or tarpaulin. However, all this helps very little, failing to protect the butter from heating, as may be judged from the high temperature of the butter being delivered. After the cart transport is completed, the butter is usually further delayed at railway stations, remaining there while awaiting dispatch to the procurement points. The duration of such delays is sometimes very considerable and is determined by the time at which refrigerator cars are made available. In this connection, the fate of the butter brought to the railway may be threefold: either the butter is stored in cooled premises, or the butter is placed in ordinary storehouses, whose temperature differs very little from the outside temperature, or, finally, the butter simply lies under a shed in the open air, covered with tarpaulin.

Proceeding further along its route, Siberian butter reaches the procurer’s warehouse, where the duration of storage after acceptance ranges from 1 hour to 29 days, judging by the data for 1928.

According to the data of the Siberian butter-grading service, from May 1 to October 1, 1928, the temperature of the delivered butter varied as follows:

From \(+6^\circ\mathrm{C}\) and below, for 2% of the butter of the total quantity.
” \(+6.1\) to \(15.0^\circ\), for 72.0% ” ” ” ” ”
” \(+15.1\) ” \(20.0^\circ\), for 24.7% ” ” ” ” ”
” \(+20.1\) and above, for 1.3% ” ” ” ” ”

Total . . 100.0%

The average temperature of the butter at the time of its shipment was \(+7.3^\circ\mathrm{C}\). The fluctuations of the temperature maximum in individual Siberian districts, in degrees Celsius, are as follows: Chanovsky \(+24^\circ\), Slavgorodsky \(+17^\circ\), Kansky \(+17^\circ\), Ubinsky \(+18^\circ\), Rubtsovsky \(+15^\circ\), and Barnaulsky \(+15^\circ\).

With respect to the corresponding minima, the following data are available: Omsk district \(+6^\circ\), Tatarsky \(+6^\circ\), Kargatsky \(+5^\circ\), Shipunovsky \(+5^\circ\), Aleisky \(+5^\circ\). It is obvious that such temperature conditions during the cart transport and storage of Siberian butter before its dispatch by railway are highly favorable to the emergence, in the butter being exported, of various chemical-biological processes. These processes, developing and progressing during the subsequent lengthy railway transport, inevitably lead to a further deterioration in the quality of Siberian export butter, significantly reducing its value by the time it appears on the London market.

The degree of deterioration of Siberian butter is directly dependent on the temperature conditions under which it passes through the railway stage, the longest stage of its route. The lower the temperature of the butter en route, the less the deterioration of its quality during

transport, since the corresponding lowering of the temperature helps to prevent, or at least to weaken, the various chemical and biological processes that are taking place or may begin to develop in the butter being transported.

The results of transporting Siberian butter by rail indicate that the degree of cooling of butter in railway cars usually accepted in our country proves insufficient to guarantee the butter against spoilage. The refrigerator-car systems existing among us may be divided into two principal types:

a) Ice cars maintaining a temperature below 0°, with brine cooling apparatus, and

b) Ice cars above 0°, with ice cooling only.

This determines the subdivision into two principal types of normal isothermal cars.

Considering that the transport of butter from Siberia is seasonal, falling approximately within the four warmest, partly hot, months, one must conclude that ice cars cooled by ice alone are too weak to eliminate to the necessary degree the adverse influence of external heat on the butter being transported. Ice cars with brine solutions cope considerably better with their task, but there are comparatively few of them.

The significance of temperature conditions for Siberian butter transport during its railway shipment is further aggravated by the fact that the temperature of the butter arriving at the reception points is usually extremely high. According to the data of the Government Trade Inspectorate for 1927 and 1928, this temperature fluctuated by month within the limits, shown in °C and % in Table 2 below.

Table 2.

Temperature in °C of butter: / Months	May 6–15°	May 15–20°	May Above	June 6–15°	June 15–20°	June Above	July 6–15°	July 15–20°	July Above
% of total quantity of butter:
In 1928 . . .	97.1	2.9	—	95.5	3.0	1.5	60.2	37.3	2.5
In 1927 . . .	91.3	8.7	—	79.7	19.4	0.9	59.6	36.3	4.1

Temperature in °C of butter: / Months	August 6–15°	August 15–20°	August Above	September 6–15°	September 15–20°	September Above	Total 6–15°	Total 15–20°	Total Above
In 1928 . . .	72.5	26.8	0.7	89.9	9.6	0.5	74.0	24.7	1.3
In 1927 . . .	63.8	35.7	0.9	89.5	10.5	—	76.0	22.2	1.2

In view of the fact that the cooling of butter entering the railway car very often proves far from sufficient—not reaching 0°—the task of the refrigerator car is not only to maintain the temperature already established in the butter being transported, but also to

cool it during the railway journey. It is obvious that, in most cases, even the improved refrigerator cars with salt cooling by ordinary ice prove powerless to cope with this task, since they do not possess the corresponding capacity either to provide the necessary depth of cooling or to release the required amount of cold within a short interval of time. Without these conditions being met, a refrigerator car is not capable of producing the necessary cooling effect for exported butter, to protect it from the possibility of noticeable deterioration en route. In addition to all this, it should be noted that there are not enough isothermal cars to meet the needs of Siberian butter transport. The total available stock of the Republic’s isothermal rolling stock of all possible types and purposes, judging from 1923 data, consisted of 6,047 rolling units, with a very considerable number of cars defective both technically and thermally, amounting on January 1, 1924, to 27.8% of their total number. Turning to the question of the required number of refrigerator cars for transporting Siberian butter, let us take the following approximate figures: 3,000,000 poods of butter per year; average load of one car—620 poods; average run of a car with butter 3,000 versts and the same distance back, that is, 6,000 versts in all in both directions, at a daily run of 200 versts. If, in addition, one takes into account the necessary time for receiving and handing over cars between railways (about four transfers), unloading and dispatching empty cars and loading, as well as repairs, this will determine the entire turnover of a refrigerator car in the export of butter from Siberia at 40 days. If, furthermore, one assumes that about 20% of the required number of refrigerator cars for Siberian butter is also needed for transporting within Siberia all other perishable goods, then the total amount of all freight carried in isothermal cars for Siberia will be:

$$ 3{,}000{,}000 \times 1.2 = 3{,}600{,}000\ \text{poods}, $$

dividing this by 620, we obtain 5,806 refrigerator cars.

Taking the average daily load on the basis of a four-month campaign, we obtain a daily load of:

$$ 5{,}806 : (4 \times 30) = 48.4\ \text{cars per day}. $$

From this follows the requirement of the Siberian railways for an isothermal stock with a capacity of

$$ 48.4 \times 40 = 1856\ \text{refrigerator cars}. $$

The total inventory of the Siberian railways, including the Trans-Baikal, Omsk, and Tomsk railways, amounts to about 1,300 refrigerator cars.

From everything set out above it follows that, for the export of Siberian butter, according to 1923 data, calculated at 3,000,000 poods of butter per year:

a) the existing stock of isothermal cars of the Siberian railways would be insufficient—about 500 cars would be lacking;

b) the types of isothermal cars available on the Siberian railways are not sufficiently perfected to protect exported Siberian butter from deterioration of its quality en route.

According to later data received by the Administration of the Tomsk Railway as of 1/X-1928, the isothermal stock of the USSR railway network consisted of 6,695 cars, including on the Tomsk, Om—

and Trans-Baikal—1,300 cars. The number of defective cars at present does not exceed the 8% norm established by the NKPS.

The Siberian Regional Committee determines the average turnover of insulated cars for 1928/29 to Novy Port at 26 days, and to other points at 29 days. The maximum need of Siberia for insulated cars for the stated year has been calculated by the Siberian Regional Committee at 1,073 cars. Thus, with the existing need, judging by the data cited, there is even a certain surplus of about 200 insulated cars.

However, even with the apparent availability of such a temporary surplus, the year-to-year growth in the productivity of Siberian butter-making indicates that in the very near future the existing fleet will prove insufficient in number; moreover, it is unsatisfactory in its cooling capacity. This indicates that the question of improving butter transport in Siberia, both qualitatively and quantitatively, is one of the essential and urgent tasks of Siberian butter-making.

When comparing on the London market the prices of Danish, Austrian, and Siberian butter, it can be seen that Siberian butter, quite good in quality before shipment, reaches London already considerably deteriorated. This can be seen from a comparison of the quality of Siberian butter according to London data at the place of receipt and according to the data of the Siberian Government inspection at the place of shipment, that is, in Siberia:

According to inspection data in Siberia:

Table 3.

Years	Average grade I	Average grade II	Average grade III	Average score
1927 . . . .	27.7%	66.7%	5.6%	85.2%
1928 . . . .	36.9%	61.4%	1.7%	86.3%

According to London data:

Table 4.

Years	Average grade I	Average grade II	Average grade III	Average score
1927 . . . .	3.9%	95.1%	1.0%	82.2%
1928 . . . .	10.9%	83.4%	5.7%	83.9%

The percentage of butter affected by mold, according to London data, is also fairly high—in 1926 it was 5.8%, and in 1927—4.4%.

Under such conditions, Siberian butter, despite some of its generally recognized merits, such as low water content, good consistency, naturalness, and despite being of fully good quality before shipment from Siberia, is valued very low when it reaches the London market.

The ratio of prices for Siberian and Danish butter, expressed in rubles per 1 pood and as a percentage of the value of Danish butter, is determined by year as follows:

	In 1926	In 1927
Danish butter	28 rub. 49 kop.	26 rub. 88 kop.
Siberian butter	22 rub. 75 kop.	22 rub. 50 kop.
Difference in value:
In rubles	5 rub. 74 kop.	4 rub. 38 kop.
In %	79.8%	84.0%

During the years indicated, butter exported from Siberia amounted to 1,570,000 poods in 1926 and 1,770,000 poods in 1927.

Without any risk of exaggeration, it may be assumed that Siberian butter loses at least two rubles on every pood of its export, owing to the insufficient depth of cooling of the butter during the excessively long rail transport from Siberia. Given the indicated price ratio and the volume of exports from Siberia, the losses of the Siberian butter industry due to insufficient cooling of butter during its transportation by rail amounted in 1926 to 3,140,000 rubles, and in 1927 to 3,550,000 rubles.

With the steady growth of the Siberian butter industry, these losses will inevitably increase over time. This indicates that the task of intensifying the cooling of Siberian butter along its route from the place of production to the place of sale abroad is a question deserving the most serious attention.

At the same time, the simpler the appliances required for this purpose are in their construction, the more accessible they are for practical implementation. This question is of interest not only for Siberian butter, but in general for the export of perishable cargoes. In this connection, from time to time a whole series of various proposals has been put forward to replace the ordinary ice refrigerator car with more advanced systems. The overwhelming majority of these proposals comes down to the development and improvement of the devices and designs of cars with ice-salt cooling. Standing apart in this respect is Linde’s experimental refrigerated train, which is a train equipped with a mobile refrigerating installation. However, beyond experimental trips on our railways the matter has not advanced. The reasons for this are usually considered to be:

1) The considerable increase in the cost of transporting butter in this manner as compared with the cost in ordinary ice refrigerator cars.

2) The complexity of the apparatus, its high cost, and the short period of operation of such equipment during the year.

3) The need for qualified and careful maintenance, which under ordinary transport conditions—especially in our Russian conditions—is extremely difficult to provide.

The question of the admissibility of one or another device in terms of its cost depends on the profitability of the latter; in view of this, so-called expensiveness in the ordinary sense is, of course, not of decisive importance here. It must be assumed that the latter remains with the conditions of the second and, chiefly, the third of the points cited above. In this connection it is necessary to pay particular attention to the idea of applying, for cooling purposes during the export of perishable products, carbon dioxide ice, i.e. “dry ice,” which requires for its use almost no special structural appliances, machine installations, and the like.

The industrial process for obtaining solid carbon dioxide—“dry ice”—is, in principle, sufficiently simple; it consists of the following operations: 1) preparation of pure carbon dioxide gas; 2) compression of it into a liquid; 3) rapid evaporation of the resulting liquid carbon dioxide; 4) pressing the carbon-dioxide snow into blocks of a definite shape and size.

The logical basis of this idea is determined chiefly by the following properties of solid carbon dioxide:

1) the very low temperature of its evaporation, corresponding to minus 78.9°C, which makes possible extremely deep cooling as compared with ordinary ice, whose melting temperature is only 0.0°;

2) its ability, upon melting, to pass from the solid state directly into a gas, without a liquid phase and without the water that inevitably appears with ordinary ice, causing wetness, dampness, and excessive humidity in the ice-storage space.

In addition, solid carbon dioxide has still other advantages over ordinary ice, since per unit of weight it yields twice as much cold as ordinary ice; moreover, solid carbon dioxide is twice as heavy as the latter, and for this reason the cooling effect of one unit of volume of solid carbon dioxide is four times greater than that of the same volume of simple ice. Thus, so-called “dry ice” is, as it were, a concentrated source of deep cooling, occurring under conditions of an almost complete absence of moisture in the surrounding space. Both these features should attract serious attention to dry ice as a means capable of finding wide application in the transport and storage of perishable products in general. As regards the export of butter under Siberian conditions, over a distance of 3–4000 versts, when in particular cases there arises an urgent need now for especially energetic, now for prolonged, now for intensified cooling, dry ice could, under certain conditions, prove to be an exceptionally valuable source of cold.

However, the solution of this problem requires elucidation of the possibilities for the practical application of dry ice in several directions: 1) with respect to the attitude of the butter itself toward the action of deep and prolonged cooling; 2) with respect to the industrial and economic possibilities of obtaining and applying dry ice to butter transport under the conditions of Siberia; 3) from the point of view of the technical possibilities of using dry ice on the plane of a purely transport order in general and, above all, under conditions of railway transport; and, finally, 4) from the point of view of clarifying the very technique of obtaining dry ice and pure, dry, gaseous carbon dioxide free from all impurities.

The elucidation of the above propositions was carried out by the author of the present work jointly with specialists brought in from the corresponding fields. These persons were: in the physico-chemistry and biology of butter, the agronomist-chemist S. A. Ponegin; and for the theoretical substantiation of the question of the production of dry ice, its cost, and the cost of cooling during transportation, the engineer G. I. Fuks; while on questions of transport the author resorted to the assistance of engineer M. N. Bordthausen, who kindly agreed to help resolve particular aspects of the question under consideration with his authoritative opinion.

The significance of the depth of cooling both of the butter being transported and of the space surrounding it is naturally determined by the fact that

at the very highest quality of the butter being exported, it in fact cannot be unconditionally sterile, that is, it cannot be entirely free from various representatives of the microflora of butter, both in the vegetative state and in their germinal forms. Under such conditions, almost the only possible means of combating the microflora harmful to butter inside the cask is a profound lowering of the temperature of the butter.

Practically all the complex and varied phenomena of the development of microorganisms in butter and on its containers are defined by the concept of mold growth. In butter-making practice the latter is usually established by a simple inspection with the naked eye of the butter under examination and of its container. In trade and in grading, of course, the “molds” of butter are understood not as their academically separated representatives, but as the totality of all the developed microflora, which is colored in its mass and therefore clearly noticeable on the butter and on its container. In certain years in Siberian butter-making there have occurred spontaneous outbreaks of mold growth in butter, which have brought considerable losses to the Siberian national economy.

The mold that develops during the export of butter most often covers the bast matting of the cask containing the butter, the outer and inner surfaces of the stave, and its crevices; then mold appears on the parchment wrapper of the butter; sometimes it nests in the layer of butter under the bottom of the cask; and, finally, mold spreads over the surface and into the very thickness of the packed butter, penetrating it as if with veins and giving it a marbled appearance.

If, in order to combat the development of mold in the butter inside the casks, the only remaining measure is an appropriate lowering of the butter temperature, then for combating it on the surface of the container of the butter being transported, another measure is also the maintenance of the greatest possible dryness of the air in the butter-storage room. However, this requirement is difficult to carry out under the conditions of ordinary ice or salt-ice cooling, which are associated with excessive humidity, dampness, and even wetness of the premises.

But all these difficulties are easily eliminated by replacing ordinary ice with dry ice, which fully ensures the maximum dryness of the butter-storage room; this, together with the low temperature, will completely eliminate the possibility of mold appearing on the butter containers and, naturally, may contribute to some increase in the quotations of Siberian butter on foreign markets.

As regards the necessary degree of cooling of butter to protect it from mold growth, in this respect it is necessary to note the assertion of the eminent commodity expert and English specialist in butter, Professor Thomson, who assumes that some representatives of butter molds require temperatures of about minus 10°C in order to prevent their development. The usual forms of molds of Siberian export butter, according to data from the Leningrad Laboratory of Water Transport (Privatdocent Mordberg) and other investigators of them (Prof. S. V. Parashchuk), suspend their growth at a temperature somewhat higher than that indicated above.

Comparing these propositions on the degree of cooling necessary to prevent spoilage of butter with the actual temperature conditions of cooling Siberian butter in railway cars, one can see that the task of rationalizing the transport of export butter must above all proceed along the path of a significant lowering of the temperatures of the butter during its carriage, as though supercooling it in comparison with the temperatures accepted and permitted up to the present time.

standards on railways, the broad possibility of which is easily opened up by the use of dry ice.

It is not without interest to note that the Leningrad inspection office, in its excellent refrigerator, already in 1926 had a case of significant overcooling of butter, without observing any negative effects on the quality of the butter from such overcooling. Here, however, it should be pointed out that the compelling reason which forced them there to resort to strong overcooling of the butter was the insufficiency of the refrigeration installation on one of the steamships, i.e., something other than the idea advanced here of deliberately overcooling the butter en route.

The isolated nature and lack of accounting for the results of the indicated cases of overcooling of butter do not provide sufficient grounds for judging what consequences for butter may be caused by the process of its prolonged and deep cooling.

But what, then, is cow’s butter?

Schematically, one may imagine export Siberian butter as a very thoroughly mixed fine mixture of milk fat and salt solution.

The brine of butter is composed of water as such, of dairy products, and of a certain quantity of table salt from the salting of the butter. Other constituent parts of cow’s milk and residual protein substances, known under the name of “buttermilk,” are represented here in considerably smaller amounts. Salt, on the one hand, is the only preservative substance permitted in butter; on the other hand, by salting Siberian butter the tastes and requirements of the foreign buyer are satisfied. The highest permissible limit for salt content in export butter is regulated by law at 2%, and the same legislation permits in export butter a water content of no more than 16%. The percentage relationship of the salt and water contained in the butter denotes the so-called concentration (or strength) of the salt brine of the butter; water and salt, remaining in joint interaction, form the salt solution of the butter. With respect to Siberian export butter it is noted, according to data from previous years, that the concentration of the salt brine approaches 14.25%—almost constant for all the highly diverse butter-producing districts of Siberia. This fact, noted over a whole series of years and traced by the analytical material of the government Siberian butter-control laboratories, seems to signify a normally traditional brine concentration for the butters of Siberia. In questions of butter science and reforms of Siberian butter-making, every step must be cautious and experimentally studied. The reductions in the strength of the salt brine allowed in the butter seasons of 1925 and 1926 coincided precisely with the spontaneous defeat of Siberian butter by molds. According to the data of the Leningrad inspection office, the second half of 1925 is characterized by only a 12.8% concentration of salt brine, while the moldy season of 1926, according to the same report data, unfolded at an 11% strength of brine (on average for the operating year), whereas the moisture content of export butter in both these seasons was fairly close to the prescribed norm. These cases make it evident that the extreme instability of Siberian butter under real conditions is determined by insufficient cooling of the butter in the railway cars. Therefore, the very tempting prospect of increasing the moisture content of Siberian butter by adding the 2–3 percent of water lacking to reach the norm still remains unrealizable, mainly owing to insufficiently deep cooling of the butter in the ...

in our wagons. Under such conditions, the use of “dry ice” for wagon cooling would make it possible to introduce into export butter 2–3% extra water and to sell it at butter prices, since in this case we would be dealing with supercooling and therefore with butter protected against mold.

Incidentally, one should also dwell on the question of the “drying of butter” in wagons. This term dates almost from the very dawn of Siberian butter-making. However, in essence, there is no “drying of butter” in wagons, as was confirmed as early as the 15th Butter Congress in Omsk in 1913, which categorically acknowledged the problematic nature of the “drying of butter”; and in this respect the use of dry ice introduces nothing new.

Finally, in elucidating the applicability of the idea of “dry ice” for cooling butter wagons, it is necessary also to touch upon the question of the possible effects of carbon dioxide both on the butter itself and on its living microflora during the two-week period of the butter’s being in transit. It is known that carbon dioxide has no odor and, consequently, in this respect this gas, as the final product of “dry ice,” is safe for butter. Moreover, carbon dioxide, by its chemical nature, is very little active and cannot enter into any chemical compounds with such substances as butter or the butter container. As a consequence of this, “dry ice” will undoubtedly be harmless to the entire butter product as a whole.

As for the living microflora of butter, it is represented in butter by both microbiological groups: insufficiently accounted-for anaerobes and widely observed aerobes.

By giving off dry, cold carbon dioxide gas, which is a retarding and harmful factor for aerobes, dry ice should thereby contribute to suppressing the development of representatives of this group of microorganisms, while the dryness of the gaseous space surrounding the butter product and its low temperature, due to the evaporation of the dry ice, exclude in this case the possibility of anaerobes developing. Without coming into direct contact with the mass of butter, carbonic acid, naturally, can affect only the microflora of the container of the butter being transported; and, as is evident from the considerations set forth, the favorable condition of this container should be fully ensured by the combined action of the low temperature and the carbon dioxide from the dry ice. It is obvious that the ordinary dampness, occasional trickles of water, and similar phenomena that occur in refrigerator wagons are completely excluded with dry ice, which may to some extent help eliminate contingencies that reduce the value of Siberian butter on the foreign market.

As a general conclusion, in all the indicated respects concerning the butter, the butter container, and the living microflora of the butter, “dry ice” must be recognized as a harmless and desirable source of cold for butter railway wagons.

In further developing and discussing the concrete possibilities for the use of “dry ice” for the separate types of Siberian butter transport, it should first of all be pointed out that this refrigerant is applicable in the overland haulage of butter by cart. Even today, butter haulage is a “penal servitude” for Siberian butter, and here, quite literally, the “roots of evil and vice” are laid in it. More than once, both earlier and now, attempts have been proposed to design “butter carts” and thermal butter vans in general. It may be said directly that the principle of thermal insulation did not go beyond the drawing-board representation of such

projects under the harsh conditions of life and the elements. A principle of another kind—the idea of “dry ice,” in the form of its small quantity, easily solves the design and implementation of any butter van and, together with motor transport, in practice leads to rational and reliable butter service under the conditions of Siberian butter-making.

The use of “dry ice” on waterways will make it possible to transport butter in more or less simple barges or scows, towing them with ordinary hot steamships, instead of costly refrigerated ones. The point is that, when “dry ice” is used on such butter barges, the care of cooling the butter being transported will be limited only to ventilating the barges with outside air in order to eliminate local overcooling, if temperature self-regulation is not achieved by structural devices. It is easy to supply power to electric fans by running an electrical cable from the steamship’s dynamo to the butter barge.

The practical introduction into butter transport of the idea of using dry ice must take into account not only the properties and nature of the butter, but also the characteristic conditions in which this butter will remain during the course of its subsequent passage in railway cars.

In this case, for example, unlike the regime of butter in refrigerators, where the small barrels can from time to time be turned over, during transport one must note the immobility of the small butter barrels throughout the journey, which may lead to the staleness of the butter, when its upper and side layers in the barrels, over time, become relatively enriched with moisture in comparison with its lower layers. Thus, in addition to questions requiring elucidation under the conditions of the static action of dry ice, corresponding questions are also raised concerning the action of deep cold on butter under the dynamic conditions of transport.

All that has been set forth above on physical, chemical, and microbiological questions connected with butter and its transport indicates that the use of dry ice for cooling purposes in butter transport is, in its conception, entirely correct. However, the practical realization of this idea, before it is introduced into life, will require special study of a number of questions concerning the influence of deep cold on butter under static conditions, as well as in a setting, so to speak, that is dynamic—that is, under the conditions of the practical implementation of railway transport.

The possibility of producing deep cooling by means of solid carbon dioxide had long since been established by science. But the idea of applying this phenomenon to practical and industrial tasks appeared only very recently. Some information in this direction is given by engineer V. N. Rulev*) in his articles on experiments in the use of “dry ice” in the fish industry of the United States of America, where a number of separate experiments were carried out on the transport of fresh fish. The results were entirely successful for runs of up to 4–6 days and at average outside-air temperatures of 26.7° C. Thus, with respect to fish shipments these experiments indicate the applicability of dry ice; however, this question lies mainly in the plane not only of technology, but also of economics—that is, the profitability of using dry ice for the transport of one product or another. In

) Perishable Products and Refrigeration*—Rulev: 1928, April 7 and No. 15, August.

in the present case the question is considered of whether it is possible, from this side, to apply dry ice to butter transport; that is, the matter comes down above all to the problem of the cost of dry ice.

In view of the novelty and unusual nature of the production of dry ice on an industrial scale, and the extreme scarcity in the literature of indications of this kind, in this regard one can outline only approximate figures, comparing them with those isolated data that could be found concerning the price of dry ice in the U.S.A.

Enthalpy diagram of \(CO_2\)

Fig. 1.

The technique for obtaining solid carbon dioxide, or “dry ice,” is very simple. Having liquid carbon dioxide in a cylinder at a pressure of 50–70 atmospheres and at a temperature of \(10\)—\(25^\circ C\), it is passed through a narrow throttling orifice so that the pressure of the carbon dioxide falls to atmospheric; in doing so, part of the carbon dioxide evaporates, and part of it passes into the solid state. One of the essential questions in calculating the cost of dry ice is the yield of dry ice in this process. In ordinary laboratory experiments it is possible, under these conditions, to obtain only 10–15% in the form of solid carbon dioxide. In industrial installations of this kind, however, about 30% is supposedly obtained. Since the magnitude of the yield of solid carbon dioxide in the question under consideration appears to be one of the basic factors in establishing its cost, we therefore give below the corresponding calculations, worked out by engineer G. I. Fuks, proceeding from the appropriate theoretical data, based on the works of the well-known specialist Planck: “On the thermal properties of carbon dioxide in the gaseous, liquid, and solid states,” and other works by this major authority in the given field.

To make the calculations that interest us more concrete, a possible practical installation is associated with a definite capacity of 500 poods (8,000 kg) per day. As the source of carbon dioxide, it is proposed to use carbon dioxide obtained in the process of fermentation in distilling, which is usually not utilized.

As the basis of the process for obtaining solid carbon dioxide, let us take a process of three-stage compression with likewise three-stage evaporation, with heat exchange in the intermediate evaporators (intermediate coolers) assumed between the compressed vapor and the liquid flowing in through a throttle valve (see the installation diagram, drawing No. 2). Thus we have an approximation to the most advantageous regenerative process of the installation.^1)

We shall take the practical deviations from it into account by the corresponding coefficients, as is customary in the practice of calculating refrigerating installations.

Using the entropy diagram for carbon dioxide, we plot the theoretical process of compressor operation. The intermediate pressures are taken as 6 atm. and 20 atm. abs., that is, \(-50^\circ\text{C}\) and \(-20^\circ\text{C}\) (drawing No. 1).

Theoretical process^2).

When the liquid is throttled through the first regulating valve, according to the diagram one obtains:

\[ 0.41\ \text{kg of vapor and } 0.59\ \text{kg of snow}. \]

The vapor is obtained at a pressure of 1 atm. abs. and \(t=-80^\circ\text{C}\). For continuity of the process, it is necessary to add to it 0.59 kg of vapors, whose temperature we shall take as equal to the temperature of the 1st intermediate cooler, \(-50^\circ\text{C}\).

The mean temperature of the vapor drawn in by the first stage will therefore be:

\[ t=\frac{0.41\cdot(-80)+0.59\cdot(-50)}{1}\sim -60^\circ\text{C}. \]

When compressing the vapor to a pressure of 6 atm. in the 1st stage, the theoretical expenditure of work required is

\[ A L_{ag}=i_{21}-i_{11}=182-157=25\ \text{Cal}. \]

For complete conversion into liquid of the vapor compressed in the 1st stage, from each kg it is necessary to remove

\[ Q_{21}=i_{21}-i_{31}=182-72=100\ \text{Cal}. \]

^1) See G. I. Fuchs, “Regenerative Process of a Refrigerating Machine,” Izvestiya STI, vol. 48 (2), 1928.

^2) All characteristic points of the process have double numbering, the second digit indicating the number of the stage.
Meaning of the first digit:

\[ \begin{array}{ll} 1\text{—beginning of compression} & 3\text{—end of condensation}\\ 2\text{—end of compression} & 4\text{—beginning of evaporation.} \end{array} \]

For example: heat content of the mixture at the beginning of evaporation in the 3rd stage (2nd intermediate cooler).

Diagram
of an installation for obtaining solid \(CO_2\).

[Figure labels and annotations:]

• \(A\). Compressor, 1st stage. \(1\) atm. — \(6\) atm.
• \(B\). Compressor, 2nd stage. \(6\) atm. — \(20\) atm.
• \(C\). Compressor, 3rd stage. \(20\) atm. — \(65\) atm.
• \(E\). Condenser.
• \(F\).
• \(G\).
• \(H\).
• \(D\). Generator of solid \(CO_2\) (snow), \(1\) atm., \(-80^\circ\)C.
• \(R'\), \(R''\), \(R\).
• Temperatures indicated in the diagram include: \(+25^\circ\)C, \(+15^\circ\)C, \(-20^\circ\)C, \(-50^\circ\)C, \(-80^\circ\)C, \(-65^\circ\)C.

Legend:

\(E\) — condenser of liquid \(CO_2\).

\(G, H\) — first and second intermediate evaporators (liquefiers).

\(R', R'', R\) — regulating valves.

\(K_1, K_2\) — ordinary coolers of compressed \(CO_2\) between compression stages.

——— — pipelines for liquid gas.

----- — water pipeline.

Fig. 2.

Since at the end of compression the vapor is obtained at a high temperature \((+68^\circ\mathrm{C})\), part of the heat can be removed from it by cooling water. Assuming cooling to \(25^\circ\mathrm{C}\) \((i=173)\), we find that the cooling water will remove:

\[ q'_2 = 182 - 173 = 9\ \mathrm{Cal/kg}. \]

Remainder:

\[ Q_{21} - q'_2 = 110 - 9 = 101\ \mathrm{Cal/kg}. \]

must be removed by evaporation of the liquid in the 1st intermediate cooler. Since a mixture of liquid and vapor with heat content \(i_{32}=i_{41}=89\ \mathrm{Cal}\) enters the 1st intermediate cooler, while dry saturated vapor with heat content \(i=155\ \mathrm{Cal}\) is sucked off, then by one kg it is possible to remove heat:

\[ Q_{12}=i_{12}-i_{42}=155-89=66\ \mathrm{Cal/kg}. \]

It is also necessary to take into account that in the first intermediate cooler \(0.59\) kg of vapor must be cooled from \(-20^\circ\mathrm{C}\) to \(-50^\circ\mathrm{C}\), for which the following must be removed:

\[ q_1 = 0.59 \cdot 0.2 \cdot 30 \sim 3.5\ \mathrm{Cal}\quad (c_p \sim 0.2). \]

Consequently, in total in the 1st intermediate cooler it is necessary to remove:

\[ (Q_{21}-q'_2)+q_2 = 101+3.5 = 104.5\ \mathrm{Cal/kg}. \]

For one kg of carbon dioxide in the 1st stage, in the second there must be

\[ G_2=\frac{(Q_{21}-q'_2)+q_2}{Q_{12}}=\frac{104.5}{66}=1.58\ \mathrm{kg}. \]

Further analogous calculations, as well as the computed quantities for the 1st stage, are collected in Table No. 1.

Table No. 1

	I stage	II stage	III stage
Temperature at the start of compression	\(-60\)	\(-50\)	\(-20\)
Work expenditure for compression of 1 kg	25	15	12
When the compressed vapor is cooled to \(25^\circ\mathrm{C}\), removed by cooling water per 1 kg, Cal	9	1	—
In the intermediate cooler it is necessary to remove heat for complete condensation of 1 kg, Cal	101	80	—
For cooling the additional gas into the 1st stage, \(0.59\) kg per each kg of working substance of the 1st stage (heat to be removed), Cal	3.5	3.4	—
Total quantity of heat exchange in the intermediate cooler per 1 kg, Cal	104.5	83.4	—
During evaporation of 1 kg of liquid in the intermediate cooler, heat is bound, Cal	66	49	—

The following additions must be made to this table: The quantity of heat that must be removed in the second intermediate cooler for cooling the additional gas is calculated by assuming cooling in it from \(+25\) to \(-20^\circ\mathrm{C}\).

\[ q^1 = c_p G \Delta t = 0.2 \times 0.59 \cdot [25 - (-20)] \sim 5.5\ \mathrm{Cal/kg}. \]

But since for each kg of working substance of the 1st stage, 1.58 kg works in the second, then for each kg of working substance of the 2nd stage this will be:

\[ \frac{5.5}{1.58} \sim 3.4\ \text{kg}, \]

which is also entered in the table.

The quantity of working substance that must pass through the second stage per 1 kg of the first stage was calculated above as 1.58. Accordingly, the quantity of working substance of the 3rd stage falling to the share of the 1st and 2nd stages is:

\[ G_3 = \frac{83.4}{49} = 1.72\ \text{kg}. \]

Actual process.

First stage.

The actual process will differ from the theoretical one considered by a series of losses of a thermal and mechanical character.

Owing to the penetration of heat, in order to obtain the prescribed effect it will be necessary to pass through a larger quantity of working substance. Let us take, according to Koeniger, \(P = 1.2\) for the first stage, that is, let us assume that, in order to eliminate losses from the penetration of heat in the 1st stage, it is necessary to pass 20% more working substance than in the theoretical installation.

For 1 kg of carbon-dioxide snow in the 1st stage, the following must be passed:

\[ G' = \frac{P}{0.59} = 2.035\ \text{kg}. \]

Let us estimate the compressor losses by the coefficient:

\[ \eta_g = 0.8 \]

The cooling of the added vapor in the 1st intermediate cooler, to make heat transfer possible, we shall take from \(-10^\circ\mathrm{C}\) to \(-40^\circ\mathrm{C}\), that is, by \(30^\circ\mathrm{C}\), for which it is necessary to expend \(\sim 3.5\) Cal.

Initial temperature of compression:

\[ t = \frac{0.41(-80) + 0.59(-40)}{1} \sim -57^\circ\mathrm{C}. \]

Plotting this point on the \(TS\) diagram and drawing an adiabat to a pressure of 6 atm, we read off the adiabatic work of compression:

\[ AL_{ag} = 183.5 - 158 = 25.5\ \text{Cal/kg}. \]

Actual work of compression per 1 kg:

\[ AL_g = \frac{AL_{ag}}{\eta_g} = \frac{25.5}{0.8} = 31.9\ \text{Cal/kg}. \]

Actual work of compression of the 1st stage per 1 kg of carbon-dioxide snow:

\[ AL_1 = AL_g\,G^1 = 31.9 \cdot 2.035 = 65.0\ \text{Cal/kg}. \]

Heat content at the end of compression of the 1st stage:

\[ i_{22} = i_1 + AL_g = 158 + 31.9 = 189.9\ \text{Cal} \]

By cooling to \(25^\circ\text{C}\) it is possible to remove heat:

\[ 189.9 - 173 = 16.9\ \text{Cal/kg}. \]

by cooling water. For 1 kg of dry ice, consequently, the water must remove:

\[ 16.9\, g^1 = 34.3\ \text{Cal/kg}. \]

For the subsequent complete conversion into liquid it is necessary to remove, in addition:

\[ 173 - 72 = 101\ \text{Cal/kg}. \]

That is, for 1 kg of first-stage agent, theoretically (see above), 1.58 kg must be passed into the second stage; in practice, however:

\[ 158\,P = 1.58 \cdot 1.2 = 1.9\ \text{kg}. \]

And per 1 kg of solid carbon dioxide:

\[ \frac{1.90}{0.59} = 3.21/\text{kg}. \]

Estimating the thermal losses in the industrial cooler by the coefficient 1.2, it is necessary to pass into the second stage, per 1 kg of solid carbon dioxide:

\[ G'' = 3.21 \cdot 1.2 = 3.86\ \text{kg/kg}. \]

The corresponding calculations for the second and third stages are summarized in Table No. 2. The data calculated above for the first stage are also included in this same table.

Table No. 2.

	I stage	II stage	III stage	Notes
Thermal coefficient of perfection (adopted)	1.2	1.2	1.12
Quantity of working substance per 1 kg of snow, \(G\) kg	2.035	3.86	7.31
Initial compression temperature, \(t^\circ\text{C}\)	\(-57^\circ\)	\(-50^\circ\)	\(-20^\circ\)
Adiabatic work of compression, \(AL_{\text{ad}}\) Cal	25.5	15	12
Effective coefficient of compressor (adopted), \(\eta_g\)	0.8	0.8	0.8
Effective work of compression, \(AL_g\) Cal	31.9	18.75	15
Work of compression per 1 kg of snow, \(AL\)	65.0	72.3	109.5
Heat content at end of compression, \(i_2\)	189.9	174	173
Heat of compression removed by cooling water per 1 kg of snow, Cal	34.4	19.4	40.3 65.0	In the condenser In the precooler.

The total quantity of work expended on compression, reckoned per 1 kg of snow obtained:

\[ AL = 65.0 + 72.3 + 109.5 = 247\ \text{Cal/kg}. \]

The total quantity of heat transferred to the cooling water per 1 kg of snow:

\[ \sim 530\ \text{Cal/kg}. \]

The data necessary for calculating the dimensions of the compressor are summarized in Table No. 3.

Table No. 3.

	I stage	II stage	III stage	Note
Specific volume at the beginning of compression . . \(V_1\) dm³	450	60	20	Taken from the entropy diagram (Fig. 1).
Specific volume at the end of compression . . . \(V_n\) dm³	100	28	8	Taken from the entropy diagram (Fig. 1).
Required net volume swept by the piston per 1 kg of snow . . . . . . \(V''\) dm³	916	232	146	Computed by the formula \(V''=v_2 g\)
Volumetric coefficient of delivery . . . . . \(\lambda_v\)	0.82	0.95	0.92	Computed by the formula \(\lambda_v=1-\varepsilon_0\left(\dfrac{v_1}{v_2}-1\right)\), where the harmful space \(\varepsilon\) is taken as 5%
Weight coefficient of delivery . . . . . . . \(\lambda\)	0.70	0.80	0.78	\(\lambda=\lambda_v\cdot\lambda_w\)
Total gross volume swept by the piston per 1 kg of snow . . . . . . . \(V\) dm³	1310	290	188	\(\lambda_w=0.85\) (adopted)

According to the data of Tables 2 and 3, we calculate the dimensions and labor consumption of the installation, with a capacity of \(G=500\) poods per day \(\sim 8000\) kg per day of dry ice. Assuming 20-hour operation of the installation, we have the required indicated power:

\[ N_i=\frac{ALG\cdot 20}{632.3}=\frac{400\cdot 247}{632.3}=156\ \text{h.p.} \]

The mechanical efficiency of the compressor is taken as \(\eta_m=0.85\). Then the required effective power is:

\[ N_e=\frac{N_i}{\eta_m}=\frac{156}{0.85}=184\ \text{h.p.} \]

Allowing for losses in transmission, one must install a motor:

\[ N=200\ \text{h.p.} \]

The total hourly consumption of water, assuming its heating by \(14^\circ\text{C}\):

\[ G=\frac{550.0\cdot G\cdot 20}{14}=15\ \text{m}^3/\text{hour}. \]

To calculate the dimensions of the compressor, we compute the required hourly volume swept by the compressor piston by the formula:

\[ V_r=VG/20 \]

where \(V\) is taken from Table 3.

As a result we have:

Hourly volume swept by the piston of the 1st stage: \(524\cdot 10^6\ \text{cm}^3\)

” ” ” ” ” 2nd ”: \(116\cdot 10^6\ \text{cm}^3\)

” ” ” ” ” 3rd ”: \(75\cdot 10^6\ \text{cm}^3\)

To obtain an idea of the actual dimensions of the compressor, we adopt the following diagram of its construction (Fig. 3).

Taking the number of revolutions per minute as \(n = 300\) rpm, and the compressor stroke \(S = D_3\), we obtain the following compressor dimensions:

\[ D_1 = 495\ \text{mm}; \qquad D_2 = 410\ \text{mm}; \]
\[ D_3 = 175\ \text{mm}; \qquad S = 175\ \text{mm}. \]

A compressor of the indicated dimensions, according to a preliminary estimate, should cost about 15,000 rubles.

Fig. 3.

Calculation of the cost price of 1 kg of dry ice.

Proceeding from the concrete dimensions established, we draw up a preliminary estimate of the initial costs for the installation.

Preliminary estimate of initial expenditures.

Item	Amount
Stone building, volume 600 m³, reckoned at 30 rubles per cubic meter	18,000 rubles
2 three-stage compressors \(D_1 : D_2 : D_3 = 495 : 410 : 175\); stroke \(= 175\) mm, \(n = 300\) rpm (1 reserve), \(15000 \times 2 =\)	30,000 rubles
Foundation, installation (25% of cost)	7,600 rubles
2 electric motors = 200 h.p. (1 reserve), \(1200 \times 2 =\)	24,000 rubles
Foundation for them, installation (20% of cost)	4,800 rubles
3 generators of carbon-dioxide snow (evaporators)	12,000 rubles
Their installation (20% of cost)	2,400 rubles
1 condenser	10,000 rubles
2 intermediate coolers, \(5000 \times 2\)	10,000 rubles
3 hydraulic presses for 50–100 atm., \(5000 \times 3\)	15,000 rubles
Contingencies (25% of the sum)	28,900 rubles
Total full cost of the building	18,000 rubles
Total full cost of machinery and equipment	144,500 rubles

Preliminary estimate of annual expenditures.

Operating expenses.

The operation of the installation is assumed to be seasonal, over the course of 100 days per year, 20 hours per day. Drive is by an electric motor \(N = 200\) h.p. \(\sim 150\ \mathrm{kwt}\). The efficiency coefficient of the motor is taken as 0.95; the cost of current is 8 kopecks per kilowatt-hour. The annual expenditure for electric power is:

\[ \frac{0.08 \cdot 150 \cdot 20 \cdot 100}{0.95} = 25250\ \text{rubles}. \]

The annual expenditure for water, with consumption of \(15.0\ \text{m}^3/\text{hour}\) and a price of 25 kopecks per cubic meter:

\[ 0.25 \cdot 15.0 \cdot 20 \cdot 100 = 7500\ \text{rubles}. \]

Lubricating and wiping material . . . . . . . . . . 500 rubles.

For servicing the installation the following personnel are proposed:

1 shop manager.
3 production foremen.
4 machinists (3 shift and 1 reserve).

4 press operators
4 assistant press operators
7 unskilled laborers.

Valuing labor according to the tariff rates, we obtain the total annual expenditure for service personnel (see the estimate): 22,800 rubles.

Estimate of annual expenditures for service personnel.

Position title	Number	Grade, scale	Unit of grade	Coefficient	Number of months of work	Amount
Shop manager	1	Grade 7, 16-grade tariff scale for engineering and technical personnel	130	1.7	12	2650
Production foreman	3	Grade 2 of the same scale	”	1.1	12	5150
Machine operator	4	Grade 8 of the 8-grade scale	40	2.8	12	5370
Press operator	4	Grade 4 of the same scale	”	1.7	6	1630
Assistant press operator	4	Grade 2 of the same scale	”	1.2	6	1150
Unskilled laborer	7	”	”	1.2	6	2020
Total						17970

Counting 27% for supplementary expenses (social insurance, cultural needs, maintenance of the local committee, etc.), we have, in all . . . . . . . . . . . . . . . . . . . . . . . . 22,800 rubles.

The total amount of annual operating expenses, also allowing 15% for unforeseen expenses, will be . . . . . . . . . . . . . . . . . . . . . 64,500 rubles.

The total annual expenses for the installation, counting depreciation of the building at 5% and depreciation of the machinery at 10%, will be . . . . . . 80,000 rubles.

The output of dry ice is 400 kg/hour; counting 20 hours for 100 days per year:

\[ 400 \times 20 \times 100 = 800{,}000 \text{ kg/year.} \]

Counting 25% for evaporation before reaching the consumer, we have a useful output:

\[ 0.75 \times 800{,}000 = 600{,}000 \text{ kg/year.} \]

The cost price of 1 kg of dry ice:

\[ 80{,}000 : 600{,}000 = 0.1335 \text{ rub.} = 13.5 \text{ kopecks.} \]

Taking into account the cost of the principal product (gaseous carbon dioxide) at the figure of 1.5 kopecks per kg (the cost of purification, etc.), we obtain the full cost of 1 kg of dry ice at 15 kopecks per kilogram.

This cost figure is considerably—about 1.5 times—lower than those cited in the literature from American practice. Since, nevertheless, the reality of the figure given, as an approximate one, is not subject to doubt, it remains to suppose two sources of discrepancy:

1. The imperfection of the working process in the installations being used. Existing installations, as far as is known, work with compression in one stage, which must substantially reduce the yield of product for approximately the same expenditure of work.
2. High commercial profit.

The Use of Dry Ice in Transport

Having calculated the cost price of 1 kg of dry ice, let us try, as an approximation, to consider the question of its operational use as a source of cold in transporting export butter from Siberia.

At atmospheric pressure dry ice does not melt, but passes directly into vapor at \(-78.9^\circ\mathrm{C}\), and the latent heat of sublimation involved is \(136.89\ \mathrm{Cal/kg}\). The resulting carbon-dioxide vapors will have the same temperature, \(-78.9^\circ\mathrm{C}\). If measures are taken to avoid leakage of the cold vapors, then a certain additional amount of cold can also be obtained. Since for the needs of refrigerated transport we usually require a temperature only slightly below zero (by \(2\)–\(8^\circ\mathrm{C}\)), it may be assumed that the vapor will be released at a temperature of about \(-10^\circ\mathrm{C}\).

To calculate the heat that will go to warming the \(\mathrm{CO}_2\) vapors from \(-78.9^\circ\) to \(-10^\circ\mathrm{C}\), it is quite sufficient to use the approximate equation for heat capacity, treating \(\mathrm{CO}_2\) as an ideal gas. We take, according to Planck:

\[ C_p = 0.1965 + 0.00023\,t \]

Then, on being heated from \(-78.9^\circ\) to \(-10^\circ\mathrm{C}\), 1 kg of \(\mathrm{CO}_2\) will require

\[ q=\int_{-78.9}^{-10} C_p\,dt = \left[ 0.1965 + 0.00023 \frac{-10 - 78.9}{2} \right] \cdot \left[ -10 - (-78.9) \right] = \]

\[ = 12.85\ \mathrm{Cal}. \]

Consequently, in all, 1 kg of dry ice gives cold:

\[ 136.89 + 12.85 = 149.74 \quad \text{we shall take as } 150\ \mathrm{Cal/kg}. \]

Let us note that this quantity of cold is twice as great as that which 1 kg of ordinary ice can give, and the cold itself is obtained at a considerably lower temperature.

Further, in a car cooled by dry ice, carbon dioxide completely eliminates a factor very harmful to the preservation of any perishable product, namely excessive speed or humidity of the air. The following simple calculation convinces us of this.

Each kg of dry ice, on evaporating, increases considerably (570-fold) in volume. At atmospheric pressure, 1 kg of carbon-dioxide vapor occupies a volume of \(365.12\ \mathrm{dm}^3\) at \(t=-78.9^\circ\mathrm{C}\). Upon further heating to \(-10^\circ\mathrm{C}\), the volume occupied by 1 kg must increase in the ratio of the absolute temperatures, that is,

\[ \text{by } \frac{273 - 10}{273 - 78.9} = 1.35 \text{ times}. \]

Thus the volume of 1 kg of the carbon dioxide discharged will be \(495\ \mathrm{dm}^3\). If we assume that 1500 kg of dry ice will be loaded into the car, then, upon evaporation and warming, its vapor must occupy a volume of

\[ 1500 \times 0.495 = 740\ \mathrm{m}^3. \]

The total volume of an ordinary butter car is \(38.5\ \mathrm{m}^3\). From the above it is evident that the volume of the vapor obtained exceeds the volume of the car by 19 times.

Taking into account the circumstance that during the run the car must be closed as tightly as possible and, consequently, gas will escape from it only through the unavoidable leaks in the lining and insulation, one may expect that the greater part of the air present in the car during the loading of dry ice will be displaced. In this way both the admixture of water to the air and the air itself will be displaced.

We shall try to clarify the main question of the cost of cooling en route when using dry carbon-dioxide ice by the following calculation for the run of an ordinary loaded butter car from Novosibirsk to Leningrad. Let us note that, for the purpose of simplifying this approximate calculation, certain known simplifications have been introduced into it, for the most part on the side unfavorable to the new method of cooling, in order to obtain figures more reliable for comparison.

The average commercial speed of an isothermal car has been taken, according to the data of the Tomsk Railway for the 1927/28 operating year, as

\[ v = 20\ \text{km/hour}.^{1)} \]

Taking the Novosibirsk—Leningrad distance as \(L = 3620\) km, we obtain the time the car remains en route, in hours:

\[ n = \frac{L}{v} = \frac{3620}{20} = 181\ \text{hours, i.e. } \sim 7.5\ \text{days}. \]

For a comparative calculation we shall take the necessary running time of the Novosibirsk—Leningrad car, at the speed of a freight-passenger train, as 6 days. Counting, as a minimum, 4 fillings of ordinary ice en route as replenishment, we obtain a total time in motion of 7 days. To this must be added:

12 hours from the beginning of the ice filling to delivery to the refrigerator with loading of butter in Novosibirsk.

12 hours from the completion of the butter loading to departure from Novosibirsk.

24 hours from the moment of the car’s arrival in Leningrad to unloading—altogether 2 days.

Thus the total time the isothermal butter car remains under cooling is determined as 9 days, or \(= 216\) hours (when cooled with ordinary ice).

When cooled with dry ice, this time may be reduced by:

1) 12 hours in Novosibirsk, i.e. preliminary cooling of the car is not required.

2) 24 hours en route, since the need to replenish ice is eliminated. Total 26 hours, which gives the time the car remains under cooling:

\[ n_c = 180\ \text{hours}. \]

The coefficient of thermal conductivity of the car walls is taken in the subsequent calculation as \(K = 0.45\). This figure has been adopted as a certain average for the entire car, after calculation of the average coefficient of thermal conductivity of a number of isothermal cars described in the literature, and also according to the data of engineer P. I. Denisov.²) This coefficient is somewhat smaller than that obtained when the butter car was insulated only with cork, although it was reached in other cars. With modern—

¹) It fluctuates within the limits of 16.5 to 23 km/hour.

²) XXXIII Soviet Congress of Engineers of Rolling Stock and Traction. Moscow, 1924, p. 382.

types of insulation of cars with shavings, sea grass, felt, etc., the coefficient of thermal conductivity usually does not exceed the indicated value.

There is no doubt¹) that the coefficient of thermal conductivity of the car walls should be chosen on economic grounds, as the most advantageous. In this case, it is to be expected that cars cooled with dry ice should be provided with more perfect insulation, with a lower coefficient of thermal conductivity, than cars cooled with ordinary ice. Having adopted, however, the same coefficient of thermal conductivity for both types of cars, we thereby overstate the consumption of ice, that is, we calculate its quantity with a certain reserve.

The temperature of the outside air has been taken as \(22^\circ\mathrm{C}\), and the temperature inside the car when cooled with ordinary ice as \(+2^\circ\mathrm{C}\), while when cooled with dry ice it is \(-2^\circ\mathrm{C}\). Thus the calculated temperature difference when cooling with ordinary ice is:

\[ \Delta t_0 = 22 - 2 = 20^\circ\mathrm{C}. \]

When cooling with dry ice:

\[ \Delta t_c = 22 - (-2) = 24^\circ\mathrm{C}. \]

For the practice of butter export, the significance of the difference from \(+2\) to \(-2^\circ\mathrm{C}\) in the storage and transportation of butter is so obvious that it is unnecessary to dwell on it.

The thermal calculation, of course, does not take into account the “quality” of the cooling temperature, but there is no doubt that, with such a low temperature of the principal cooling agent as dry ice \((-78.9^\circ\mathrm{C})\), attaining a temperature of \(-2^\circ\mathrm{C}\) inside the car is considerably easier than attaining \(+2^\circ\mathrm{C}\) when cooling with ordinary ice, whose melting temperature is about \(0^\circ\mathrm{C}\).

We shall carry out the calculation for an ordinary “butter” car, the principal data for which are given in Table No. 4.

Table No. 4.

Number of axles	Tare	Lifting capacity	Internal dimensions	Total outside surface	Loading area
2	20	15.6 t	\(6.356 \times 2.743 \times 2.222\ \mathrm{m}^3\)	\(F = 85.98\ \mathrm{m}^2\)	\(f = 13.96\ \mathrm{m}^2\)

Cooling apparatus: number 8, at the end walls, dimensions

\[ 0.410 \times 0.410 \times 1.500\ \mathrm{m}^3. \]

The necessary amount of refrigeration for cooling the car en route, net, when cooling with ordinary ice:

\[ Q^{\mathrm{n}}_0 = K \cdot F \cdot \Delta t_0 \cdot n_0 = 0.45 \times 85.8 \times 20 \times 216 = 167000\ \mathrm{Cal}. \]

The same when cooling with dry ice:

\[ Q^{\mathrm{n}}_c = K \cdot F \cdot \Delta t_c \cdot n_c = 0.45 \times 85.8 \times 24 \times 180 = 167000\ \mathrm{Cal}. \]

When accounting for the quantity of ice, in addition to this net expenditure of refrigeration it is necessary to take into account a number of various losses of refrigeration, sometimes very considerable.

¹) Although such calculations are not made in practice.

To obtain an idea of the magnitude of these losses, the results of two experimental shipments were used:

The experimental shipment Astrakhan—Petrograd¹ and an experimental trip, Kurgan—Leningrad in the summer of 1924². In this, by plotting thermograms, the average temperature difference during the run was determined, the necessary net quantity of ice was calculated, and it was compared with the quantity actually expended. The results of the calculations are summarized in Table No. 5.

Table No. 5.

Car No.	Average temperature difference	Necessary quantity of ice, poods per day	Ice expended, poods per day	Utilization coefficient	Note
212.473	13.94	9.7	17	57%	Experimental trip Astrakhan–Petrograd, June–July 1915
119.976	21.4	14.8	27	55%	Experimental trip Astrakhan–Petrograd, June–July 1915
212.520	16.6	15.95	21	76%	Experimental trip Astrakhan–Petrograd, June–July 1915
848.540	22	21.3	53.8	39%	Experimental trip Kurgan–Leningrad, July 1924
847.323	25.9	25.1	52.7	47.5%	Experimental trip Kurgan–Leningrad, July 1924

The utilization coefficient was calculated as the ratio

\[ \eta=\frac{\text{Necessary quantity of ice}}{\text{Expended quantity of ice}}\times 100\%. \]

On the basis of these data, the utilization coefficient for cooling with ordinary ice is taken as 50%.

The necessary quantity of ordinary ice \(G_0\), taking, as is customary in cooling with salt, the latent heat of fusion as 75 Cal/kg:

\[ G_0=\frac{Q_0^{n}}{75\times \eta}=\frac{167000}{0.50\times 75}=4500\ \text{kg}. \]

In addition to this, the consumption of salt, taking an average of 10–12% by weight of the ice charge:

\[ G=0.11\,G_0=0.11\times 4500\approx 490\ \text{kg}. \]

The cost of ice in procurement, according to the data of engineer P. I. Denisov³, in the 1923/24 operating year averaged 20 rubles 30 kopecks per 1 cubic sazhen, with considerable fluctuations from 32 rubles 90 kopecks to 6 rubles 90 kopecks.

In view of the great fluctuation of these figures and their considerable instability from year to year, the average cost of ice has been adopted for the calculations according to data of the Tomsk Railway for the 1927/28 operating year. These data are as follows:

Cost of procurement . . . . . . . 1 m³ = 1 ruble.
“ loading into the car . . . 1 “ = 2 rubles.
“ salt . . . . . . . . . . . 1 “ = 26 rubles.

According to these data, the cost of 1 m³ of ice loaded into the railcar is calculated as follows. The percentage of ice melting in procurement, according to the data of engineer P. I. Denisov, is 25–50%. For Siberian conditions a figure close to the lower limit, 30%, has been adopted. Taking the specific weight of ice in procurement as 0.7, and the cost of loading as 2 rubles, we obtain the cost of 1 kg of ice in the railcar:

\[ a=\frac{\frac{100}{0.7\times(1-0.3)}+200}{1000}=0.404\ \text{kopecks/kg}. \]

the cost of all the ice for cooling, including loading:

\[ a_0 \cdot G_0 = 0.404 \times 4500 = 18\ \text{rubles}\ 20\ \text{kopecks}. \]

Cost of salt:

\[ \frac{2600}{1000}g_0 = 2.6 \times 490 = 12\ \text{rubles}\ 70\ \text{kopecks}. \]

The total cost of cooling en route:

\[ 18\ \text{rubles}\ 20\ \text{kopecks} + 12\ \text{rubles}\ 70\ \text{kopecks} = 30\ \text{rubles}\ 90\ \text{kopecks}. \]

The type of railcar adopted by us holds 150 barrels, or 8 tons of butter.

The expenditure en route for cooling one ton of butter is

\[ K_0=\frac{30\ \text{rubles}\ 90\ \text{kopecks}}{8}=3\ \text{rubles}\ 86\ \text{kopecks}. \]

When calculated for 1 ton of butter per day, this gives a cooling cost of 43 kopecks. This figure is considerably (5 times) higher than the figure of 8.1 kopecks/ton given in Hütte¹), where all expenses for refrigerated transport are included in the latter figure. Obviously, the latter figure was calculated for other (probably prewar) relations, since the cost of ice alone in procurement gives, when calculated per 1 ton of butter, a larger figure.

With cooling by dry ice, we shall find the necessary quantity from the condition that 1 kg of dry ice, evaporating and warming, will absorb 150 Cal./kg. At the same time, a considerably better utilization of cold in the railcar should be expected, since a number of factors that impair the utilization of cold disappear. In fact, the necessary quantity of dry ice for cooling in the railcar is not large and can be loaded into the railcar at once, at the sending station, without the need for its subsequent replenishment. Further, in the construction of the railcar there are no places where leaks are most probable (the cover of the loading hatches, siphon openings, and so on). In view of the considerable refrigerating capacity of dry ice and its location in the railcar above the product being cooled, the reserve of dry ice toward the end of the run may be made minimal, which, as is known, is not permitted with ordinary cooling. Trial shipments in America with dry ice, to which reference was made above, confirm this result. The quantity of dry ice loaded in them only slightly exceeded the theoretically necessary amount. Nevertheless, as a precaution, we shall introduce a coefficient of utilization of the railcar when cooling with dry ice \(\xi = 0.75\)

¹) Hütte, transport volume.

The necessary quantity of dry ice in this case is determined as

\[ G_c=\frac{Q_c^n}{150\times \eta_c} =\frac{167000}{0.75\times 150}=1500\ \text{kg}. \]

The price of dry ice was determined above at 15 kopecks per kg, or 150 rubles per ton. The cost of loading dry ice must not exceed the cost of loading ordinary ice. Let us take the cost of loading 1 ton of dry ice as 3 rubles; then the full cost of cooling the car en route will be \(1.5(150+3)=230\) rubles.

In absolute magnitude this figure is 6.5 times greater than the cost of cooling by the ordinary method—ice with salt; that is, there can be no question of applying this method of cooling where the ordinary ice-salt method is sufficiently satisfactory. But in those cases where this is not so, the principal role will be played not by the absolute cost of cooling, but by the difference in expenses for each unit of weight and the difference in selling price.

The cost of cooling 1 ton of butter with ordinary cooling has been indicated above. In calculating the cost of cooling per unit of weight with dry ice, it is necessary to take into account the increase in the capacity of the car when cooled with dry ice. This increase in capacity is due to two reasons:

1) The need for cooling pockets at the end walls of the car is eliminated; these pockets take up a rather considerable area that can be used. Calculation from the data given above gives a gain in area of 16%.

2) There is the possibility of a significantly better use of the cubature of the car, since there is no need to leave such a considerable distance between the top of the barrels and the ceiling of the car as is done with ordinary cooling for air circulation. A certain volume of the car, to be sure a very small one, will be used for placing boxes with dry ice. But they are placed above, directly under the ceiling, where loading of the transported cargo is in any case impossible.

Taking, as a minimum, the gain in loading the car in proportion to the gain in area freed from cooling devices, at 15%, we have, with dry-ice loading, the weight of transported butter:

\[ 1.15\times 8.0=9.2\ \text{tons}. \]

Under these conditions, the expense en route from Novosibirsk to Leningrad for cooling one ton of butter will be expressed as follows:

\[ K_c=\frac{230}{9.2}=25.0\ \text{rubles per ton}. \]

In comparison with cooling by ordinary ice with salt, cooling by dry ice will be more expensive by

\[ 25.0-3\ \text{r.}\ 86\ \text{k.}=21\ \text{r.}\ 14\ \text{k. per ton}, \]

or by 35.2 kopecks per pud.

The value found will be somewhat reduced upon refinement of the calculation. Without dwelling here on its numerical value, let us note only the chief grounds for this reduction. They consist in the following:

1 — in reducing the duration of the car’s turnover by at least one day,

2 — in better utilization of the car’s lifting capacity,

3 — to reducing to a minimum the attention required by the ice car with respect to concerns about replenishing the supply of ice en route.

As was established above, the use of dry ice increases the cost of refrigeration in transit for exported Siberian butter by 32.5 kopecks per pood, but at the same time ensures an increase in the valuation of Siberian butter on the London market.

This increase, cautiously taken at 2 rubles per pood, after deducting the increased expenses for the use of dry ice, gives 200—32—1 r. 67.5 kop. for each pood of butter.

If, in addition, one takes into account that deep refrigeration makes it possible to increase the moisture content of the butter by 2—3% of its weight, this gives an increase in the value of Siberian butter, judging by its prices in 1927, of 22 r. 50 × 0.2 = 45 kopecks, or of 22 r. 50 × 0.03 = 67.5 kop. for each pood.

Thus, the total increase in the value of Siberian butter in London in connection with the use of dry ice, judging by the calculations given, could rise by 165 + (45 or 67.5) kop., that is, by an amount of 2 r. 10—2 r. 32 kop.

Taking, under these conditions, the annual volume of exports of Siberian butter at 3,000,000 poods, one can see that the use of dry ice can give Siberian butter-making an additional 6.3—7.0 million rubles annually.

Let us now dwell on the question of from what raw material it is possible to obtain the so-called “dry ice.”

In this regard, engineer V. N. Rulev cites the following information from the practice of S. A. S. Shtatov:

Carbon dioxide gas is obtained by burning coke under a steam boiler lined with highly fire-resistant material. The boiler operates without a chimney, but with artificial draft, regulated in such a way that combustion would take place with a very small excess of oxygen, in order to avoid the formation of carbon oxides and hydrogen sulfide. The steam goes to the steam engine serving the compressor, fans, pumps, and other production machinery. The combustion products from under the boiler go into an economizer, where, while heating the feed water, they are cooled to a temperature of 15° C. This gas mixture, consisting of 17—18% carbon dioxide, and then, chiefly, of nitrogen and a small amount of oxygen, is washed, purified, and cooled with water in two towers filled with stones. From these towers the gases are drawn off by an exhauster, which forces them into an absorber consisting of two towers connected in series, filled with coke, which is irrigated with a 10% solution of soda. This solution absorbs carbon dioxide from the gas mixture, with 70% of it being converted into a solution of sodium bicarbonate. Nitrogen and the remaining oxygen are released from the second tower into the atmosphere. The sodium bicarbonate solution is pumped into a carbon dioxide generator heated by exhaust steam from the power plant, with a small addition of live steam up to 115° C. At this temperature, 99.9—99.95% carbon dioxide is released from the solution, and the hot regenerated soda solution, still containing some bicarbonate, is fed through a heat exchanger, which consists of two concentric pipes: through one of them flows the hot soda solution from the generator to the tower, and through the other flows the cold soda solution from the absorption tower to the carbon dioxide generator. The pure, gaseous carbon dioxide formed in the generator, at a pressure of about 2/3 atmosphere, is cooled to remove water from it and then enters a three-stage compressor with water cooling between stages, where it is liquefied under pres-

by liquefaction at 75 atmospheres. The liquid carbon dioxide thus obtained is either poured into steel cylinders for shipment, or enters an evaporator to be converted into snow. The whole of the process described above takes place almost automatically; labor is needed only for servicing the boiler furnace (feeding fuel, cleaning the grate) and for filling the cylinders.

One installation yields 1,000–1,350 kg of carbon-dioxide snow per day. The snow is pressed into pieces of two sizes: in the form of cubes with an edge of 255 mm, weighing 17–18 kg each, and in the form of cylinders 75 mm in diameter and 150–200 mm high. These pieces are sawn with a wooden saw into parts of any desired size.

The loss of snow from the moment it is removed from the apparatus until the moment it is packed in the form of pressed dry ice for shipment amounts to about 10% by weight of the snow. Dry ice is sold in America at half the price of liquid carbon dioxide.

Under Siberian conditions, the source of carbon dioxide gas for obtaining dry ice could be, following the example of America, the coke burned as indicated above. In addition, a second source could be the carbon dioxide of Siberian distilleries.

As is known, in distilling, about 20% by weight of the grain products distilled, or about 45% of the fermented starch, is converted into carbon dioxide gas, irretrievably and uselessly lost into the atmospheric air. It is precisely this gas which, after preliminary purification by washing with water to remove alcohol and other volatile impurities, could be used for the production of dry ice. How large the masses of gaseous carbon dioxide unproductively lost in distilling are may be seen from the fact that the Novosibirsk distillery alone, with an annual output of about 300,000 vedros of alcohol (40°), in 1927–28 released into the air about 60,000 poods of gaseous carbon dioxide.

The utilization of carbon dioxide at distilleries could make it possible to turn this waste into a waste product of definite value. In addition, this would provide distilling with some additional income amounting to at least one degree of alcohol per pood of grain mashed. For a plant such as the Novosibirsk one, this would amount to about 300,000° of alcohol.

In connection with the seasonality of butter exports over 4–5 months of spring, summer, and autumn, a distillery’s need for carbon dioxide would be limited in time; moreover, the greatest demand for carbon dioxide falls during the hottest season of the year, when, under present conditions, distilling cannot operate.

But if the production of dry ice is available, this situation can change substantially, since the chief difficulty in this respect lies in malting during the hot summer period of the year.

If, however, the production of dry ice is established at a distillery, then it is evident that such a plant, with its new tasks and the means connected with them, will also find within itself new possibilities, both economic and technical, for equipping itself with special installations for successful cooling during the warm season of the year.

As for the required changes in the equipment of a distillery specifically for the use of its carbon dioxide, in this respect very little will be required in the distilling process itself—only closed iron fermentation vats of the appropriate design and devices for washing the departing carbon dioxide...

acid in order to free it from the ethyl alcohol carried along with it and from other volatile impurities easily retained by water. All the remaining special equipment connected with the subsequent capture and conversion of the purified gaseous carbonic acid and its conversion into the solid state belongs already to the production of dry ice, which was considered in its place in the preceding exposition. The cost of adapting a distillery such as the Novosibirsk one would come, approximately, to 220—150,000 rubles.

The basic propositions, the essence, and the major advantages of replacing ordinary ice with dry ice in the export of Siberian butter abroad are entirely understandable and obvious. However, the conditions for the practical formulation of this task, which has only just begun to be carried out abroad in individual cases, are still very little known and accessible to us. For the time being, all information reaching us in this respect is limited only to brief reports in the specialized journal literature. Naturally, under such conditions, an undertaking so great in its significance and scale for Siberia, for its practical realization on a broad scale in Siberian butter transport, will require further serious special preparatory study, both theoretical and technical. These studies must be developed in several directions, including the following groups of basic questions:

I—a) Clarification of the chemical-technological and organizational-industrial aspects of dry-ice production.
    b) Study of the conditions of use of dry ice—its stability, evaporative capacity under various conditions of time, temperature, and so forth.

II—a) Clarification of the general effect of the influence of various degrees of depth of cooling and of its duration on Siberian butter; determination of its physicochemical constants and possible changes in its appearance, consistency, and structure.
    b) Differentiation of the general effect of cooling butter according to the influence of the individual principal factors, and determination of the optimal conditions for the action of each of them.
    d) Study of the influence on Siberian export butter of the rate of cooling.
    e) Establishment, with respect to various conditions of deep cooling, of the possibilities for the development of dangerous molds on butter.

All experiments of Section II are to be carried out under static conditions.

III—Clarification of the questions of Section II on the scale and under the conditions of ordinary railway transport.

IV—Development and coordination of transport questions—the design and construction of butter cars, their servicing, and the like, when dry ice is used.

V—Verification of all the data obtained in trial-experimental transport of butter, with comprehensive testing of the butter before and after its transport. Recording the results of trial shipments of butter cooled with dry ice and preparation of materials for the standardization of this new method of cooling for butter transport.

The idea of dry ice advanced with respect to Siberian butter transport, in its practical application, may be considerably broadened by extending it in general to the transport of perishable products exported from and imported into Siberia, such as fish, meat, eggs, fruit, and the like. Moreover, in some cases

dry ice may have the significance of a specific means required for deep cooling, whereas in other cases it may play the role of a concentrated source of a significant medium of cooling energy, which, under appropriate equipment conditions in refrigerator cars—for example, with a certain flow of outside air through the ice compartments—could serve as a convenient and reliable means of prolonged cooling for a comparatively moderate lowering of temperature.

The indicated methods of cooling with dry ice acquire special significance and value for transport in wartime, for theaters of military operations and front-line areas, where one cannot count on the regular repeated replenishment of refrigerator cars with ordinary ice.

Tomsk Siberian Technological Institute June 20, 1929.

1. Izvestia of the Committee on Refrigeration, 1917, No. 1. ↩

2. Data placed at the author’s disposal by participant Comrade Rabalchenko. ↩

3. P. I. Denisov. Refrigerated Railway Transport. Moscow. 1926. ↩