PROCEEDINGS

of the Tomsk Technological Institute of Emperor Nicholas II

Vol. XXV. 1912. No. 1.

On Bronzes in General and Bell Bronzes in Particular

Bronze is one of those metals whose use for various purposes of everyday life dates back to remote antiquity. Thus, if, on the basis of those remains of ancient culture that have come down to us, we judge the time when bronze first began to be used in ancient Egypt, Assyria, and Babylonia, we must come to the conclusion that the ancient peoples of the countries named used bronze in an epoch many millennia before the Birth of Christ.

In certain pyramids, whose origin modern archaeologists assign to the time of the pharaoh Menkaure (Mencheres), who lived in 3633 B.C., the foundations of these pyramids are made of dressed granite; and for making such a foundation a hard cutting tool was necessary. Furthermore, in many ancient pyramids wooden objects and statuettes of astonishingly elegant and delicate workmanship were found. Then, in 1897–1896, Quibell found at El-Kab a cup of diorite with the inscription Snefru¹, dating to 3766 B.C. For the production of such elegant objects from wood—and all the more from very hard diorite—the corresponding hard tool was necessary; and the material for such a tool, as is clearly seen from translations of surviving inscriptions of that period of Egyptian culture, was bronze. In many papyri of ancient Egypt, bronze is mentioned as a very widespread material of that period. Thus, in the excellently preserved Harris papyrus², which is in the British Museum, there is an address by Ramses II, in the 32nd year of his reign, i.e. 1288 years B.C., to his officials and people, in which Ramses says:

“I made for him vessels of good gold; the rest, of silver and bronze, cannot be counted.”

“His doors and his pillars are of gold, overlaid with bronze,” etc. Thus, on the basis of the material available to us,

we may conclude with certainty that many millennia before the Birth of Christ bronze in Egypt was a very widely used metal.

Turning now to the ancient culture of Assyria and Babylonia and considering it with respect to the use of bronze, on the basis of the surviving remains of this culture we come to the conclusion that here, too, bronze was a very ancient metal in use. Many written monuments testify that bronze was used in Assyria and Babylonia many millennia before the Birth of Christ.

Certain bronze finds, such as, for example, two bronze figures found by Sarzec³ during excavations at Telloh, bear inscriptions dating to 2900 B.C. In the Louvre Museum in Paris there is a bronze cone⁴, the manufacture of which, according to the inscription on it, must be assigned to the period around 2000 years B.C. Later, during excavations conducted by Layard in ancient Nineveh, 28 varieties were found, of which 15 were of bronze. In short, the surviving remains of the most ancient culture of Egypt, Assyria, and Babylonia undoubtedly convince us that bronze was very widely used in these countries in the period of their most ancient development.

The ancient culture of the countries just examined spread rapidly and broadly through Asia Minor and, across the Mediterranean Sea, in the time of the power of the ancient Hittite people, rapidly spread throughout the Aegean Sea. Together with their culture the Hittites transmitted to Greece the practice of the broad use of bronze. The strong influence of ancient Greece on the ancient Romans is a generally known fact, and in the remotest antiquity the Romans used bronze for the manufacture of all kinds of articles. Later the Romans, for 200 years, from 151 B.C., used “heavy copper” as coinage in the form of ingots.

Thus, on the basis of facts from the foregoing, which constitute an extremely small share of the material possessed by the modern cultured world, we may undoubtedly conclude that in the early epoch of the centers of ancient culture bronze, in its varieties, was very widely distributed, and that subsequently from these ancient centers of culture there gradually spread, by virtue of influence and intercourse, the broad use of bronze in other centers of culture in Western Europe and the southern part of Asia. From the surviving remains of the most ancient culture of China one may with certainty—

... one may say with certainty that, 2000 years before the birth of Christ, the Chinese knew tin and copper, and copper served as coinage. There are also indications that the Chinese first became acquainted with bronze in Tibet^5).

It is now of interest to trace which metal first appeared in the ancient cultural world: bronze, or first its constituent parts—copper and tin—and after them bronze of various qualities.

Copper ores occur in many places on the globe, and in many places on the globe there have been and are deposits of native copper (in Cornwall, China, Japan, Siberia, North America, Sweden, the Urals, Australia, and other places). Not so long ago in North America, on Lake Superior, in the state of Michigan, a mass of native copper weighing about 16,800 poods was found. Native copper, owing to local natural conditions, may readily be obtained from ores, provided only that local conditions favor the reduction of copper ores; on the other hand, native copper is readily transformed into its ores under the condition of free oxidation by air, enrichment with sulfur, and combination with the carbonic acid of the air. The color of native copper attracted the attention of primitive man, and, having tested its mechanical qualities after appropriate treatment in fire, he very willingly began to use it for the manufacture of various articles, as is clearly indicated by analyses of various objects from the ancient world that are at our disposal^6).

The analyses of the objects just cited clearly show that ancient man had at his disposal pure native copper with its constant companions, which are also encountered at the present time in refined red copper, such as: iron, cobalt, nickel, sulfur, antimony, and arsenic. Native copper, by reduction, by virtue of natural conditions, may be obtained from its

^6) Skinder. Bronze. 1908. St. Petersburg.

^5) Skinder. Bronze. p. 55. 1908.

oxygen and sulfur ores, and it is always found where the above-mentioned ores occur in proximity; consequently, primitive man, in working native copper, came upon its ores all the more because one of these ores, fairly often encountered in nature—chalcopyrite ($\mathrm{Cu_2SFe_2S_3}$)—has a golden-yellow color, quite reminiscent to ancient man, in its color, of copper. From such an ore, by means of its free preliminary oxidation in fire, and then the reduction of the oxides of copper and iron by charcoal and the products of combustion in the presence of lime from limestones, among which an open hearth was built, metallic copper is obtained with an appreciable iron content. Indeed, the iron content in copper objects of the ancient world not infrequently reaches 9%⁵.

Thus it may be stated with certainty that in the ancient period of human culture man first had native copper, then learned to obtain pure copper from its ores, using the services of a simple open furnace; and this is all the more probable because the centers of the first European culture of mankind—Egypt, Assyria, Babylonia, Greece, Rome, etc.—had near them large deposits of copper, which even at the present time are renowned for their wealth (Syria, Armenia, Cyprus, the shores of the Arabian Gulf, Northern Italy and Switzerland, Spain, Cornwall, etc.).

The other component of bronze for its formation is tin. Tin in the native state was found by Damour in French Guiana and by Forbes in Bolivia⁶, and no more such native occurrences are known; nevertheless Skinder⁶ counts about eight archaeological finds made of tin. Since native tin on the earth’s surface is a great rarity, while tin objects and bronze with various contents of tin were widespread in the period of ancient culture, it must be supposed that in the period indicated man already knew how to obtain tin from its ores. The most widespread tin ore in former ancient times, and at the present time as well, is tinstone ($\mathrm{SnO_2}$), rich deposits of which even now exist in England, Australia, the Malay Peninsula, Finland, Bohemia, Galicia, the Nerchinsk district, Algeria, and elsewhere. Another very rare tin ore is tin pyrite ($(\mathrm{Cu_2,Fe,Zn})_2\mathrm{SnS_4}$), deposits of which are rarely found in the tin veins of Cornwall and Bohemia.

The most ancient, in terms of exploitation and production of tin, are the British deposits. Thus Diodorus⁷, in 30 B.C., says of them: “On the promontory of Britain, which is called Belerion (Cornwall), people prepare tin; they extract tin ore from stony earth, smelt and purify it.” Then, in the same place, there is also an indication that this tin is delivered to Gaul and to Spain (Marseille). Ancient Egypt received its tin from Asia⁸. Pliny⁹ relates of an important tin center of the ancient world: “Tin is more precious than lead. The Greeks call tin kassiteros and say that it is brought by ships from the Atlantic sea, and that the ships are built of wickerwork and covered with hide. It is now known that it is found in Lusitania (Portugal) and in Galaecia (Galicia in Spain), in sandy, dark-colored earth on the surface of the soil, and that this earth is recognized by its weight. The workers wash the sand, and what settles to the bottom they smelt in a furnace.” Thus, in this last historical datum there are even indications of the method of obtaining tin from tin-stone—the method of reduction with the aid of a simple hearth.

Thus, on the basis of the foregoing, one may conclude that in the epoch of ancient culture man knew how to mine copper and tin, made wide use of them, and distinguished them from bronze, as is clearly indicated by many inscriptions on objects of ancient Egypt, Assyria, and Babylonia¹⁰.

Of great interest to us, in the sense of confirming the proposition that pure copper and tin were known to man in remote antiquity, is the ancient Sumerian incantation of fire that has come down to us¹¹. It reads as follows:

“Fire, hero in a noble land.
Brave one, son of the watery deep, in a noble land.
Fire, thy brightly shining flame
Makes light in the valley of darkness.
To everyone who names the name, it determines fate.
Of copper and tin thou art the smelter.
Of gold and silver thou art the sound.
Companion of the goddess Ninkasi thou art,” etc.

At present we are interested in the question of what was first discovered on the earth’s surface—bronze or its constituent parts, copper and tin. The supposition that bronze was first obtained by man through the simple reduction and smelting of a mixed ore of copper and tin is not supported by the data of the most recent period, since on the earth’s surface mixed ores of copper and tin have been found only in one place, in Cornwall, from which bronze with a tin content of about 28% Sn can be obtained, whereas the bronze of archaeological excavations is extremely varied in its composition. The more probable supposition is that primitive man at first had at his disposal pure copper and tin, and later, from these two elements in different proportions, ancient man obtained bronze; in the earliest times he was struck by the characteristic change in the colors of copper caused by the addition of tin to it—from bright golden to light gray; but, beginning to use such bronze for various articles, primitive man subjected it to various manipulations in the fire (the usual ones for copper) and involuntarily became convinced of the positive advantages of bronze over pure copper. Pure copper, because during melting it strongly absorbs CO, H, and SO₂, cannot give dense castings, whereas bronze, on the contrary, possesses excellent casting properties and is much harder than copper. It did not escape the observation of primitive man that bronze has a lower melting point in comparison with copper and, in general, that this melting point gradually decreases as the tin content in copper increases. Working bronze in the fire and accidentally subjecting it, when strongly heated, to rapid cooling in water, primitive man also discovered yet another and very valuable property of bronze—to obtain tempering and then, in the opposite sense relative to steel. Bronze, upon rapid cooling, becomes darker in color, more resonant, but capable of being worked with a hammer. Making use of this last property of bronze, primitive man readily began to prepare from it various very fine ornaments for domestic use. Many archaeological finds of the ancient world were undoubtedly worked with a hammer, and yet they contain a very considerable tin content, at which bronze under ordinary working conditions is distinguished by considerable brittleness and cannot be worked in that way. Thus Skinder¹⁴) gives the following—

¹⁴) Skinder. Bronze. P. 88. 1908.

giving an analysis of archaeological sword blades, wire, and sheet metal, which undoubtedly confirm what has just been said:

Thus, on the basis of the foregoing, it may be asserted that primitive man at first had copper and tin at his disposal, then obtained bronze from them, noticed its good, distinctive casting properties (in comparison with copper), and began to use it for all sorts of castings and household articles, employing for this purpose stone crucibles, then pots and sand molds, as is indicated by archaeological inscriptions from the ancient Egyptians and Sumerians that have survived to us¹². At the same time, a very valuable property of bronze did not escape primitive man—the capacity to be worked with a hammer after strong heating and rapid cooling—and he made use of this property of bronze and began to prepare from it elegant, thin household ornaments, which not infrequently bear on their surface clear traces of hammering. Copper combines with tin within rather broad limits and gives bronze various mechanical properties and very different coloration. The melting temperature of bronze, as the tin content increases, gradually decreases and approaches the melting temperature of pure tin.

Thus, with a tin content of \(0,92\%\), it melts at \(1076,9^\circ\text{ C.}\)

\[ \begin{aligned} \text{at } 2,7\% \ \mathrm{Sn} &\ —\ 1065,5^\circ\text{ C.}\\ \text{“ } 5,69\% \ \text{”} &\ —\ 1044,6^\circ\text{ ”}\\ \text{“ } 10,78\% \ \text{”} &\ —\ 1000,4^\circ\text{ ”} \end{aligned} \]

at 18.43% Sn — 909.6° C.
” 26.24% ” — 788.8° ”
” 30.12% ” — 757.7° ”
” 33.66% ” — 738.8° ”
” 35.91% ” — 734.3° ”
” 37.50% ” — 730.8° ”
” 39.70% ” — 724.5° ”
” 42.27% ” — 714.9° ”
” 45.03% ” — 702.8° ”
” 54.47% ” — 655. etc.

As the copper content of tin increases, the mechanical properties of the latter change considerably. According to the investigations of Thurston¹³, the strength of copper, with the addition of 4% tin, increases by 16%, and with the addition of 18% tin—by 30%. If, however, the amount of tin in the bronze continues to increase, the strength of the alloy decreases considerably. With a tin content of up to 17%, the elastic limit of bronze is 50–60% of the coefficient of strength; with an increase in tin content the elastic limit rises, and at 25% tin the elastic limit and the coefficient of strength of bronze are equal. Hardness, as the tin content in the alloy increases, at first continues to rise. An alloy with 28% tin is already taken by a file only with difficulty. But, having reached the greatest hardness, the alloy, with a further increase in tin content, begins to soften, gradually approaching pure tin in hardness. Likewise, the viscosity of the alloy first decreases and then increases. An alloy with 4.75% tin can still be forged and rolled in the cold state; an alloy containing more than 5% tin, however, can be forged only when heated to a red heat. As the tin content approaches 15%, hardness and brittleness increase; such alloys are not forged at all, either in the cold or in the heated state¹⁴. The specific gravity of bronze is 8.95 on average.

In bronze alloys one can readily trace the coloring power of tin: an alloy with 10% tin, in the worked state, has a reddish-yellow color, and with 40% tin—a white-yellow color; at 40% tin—an almost white color.

All bronzes possess the property of liquation, and therefore, wherever it is required to obtain a dense casting, the casting must be made in rapidly cooling metal molds. Bronzes oxidize less than pure copper, are harder, and some of them are also stronger—

... and dense than copper. When it is desired to impart a certain toughness to bronze, it must be heated and rapidly cooled; in this case the bronze also acquires greater density. In cases where bronze is to be worked with a cutting tool, a small amount of lead is added; bronze with an admixture of lead is more easily worked by the tool, the chips separate freely, and the worked surface obtains a better appearance. But an admixture of lead to bronze increases its tendency to liquation, and therefore must be small. In order to lessen the phenomenon of liquation, zinc is sometimes added to bronze; zinc gives bronze a delicate golden tint, but increases its brittleness.

The compositions of bronzes encountered in practice are very varied, as a result of which bronzes have different purposes and bear different names.

Thus ordnance bronze (gun metal) contains from 89 to 91% copper and from 11 to 9% tin, and has a yellowish color. Coeff. of strength 20—27 kg/qmm. Ordnance bronze, as its purpose indicates, must be strong and hard; it has been found from experiments that the alloy possesses such qualities only when the amount of tin does not exceed 9–11% and when there are no other admixtures, such as zinc or lead; for this reason the admixture of zinc or lead to ordnance bronze, for the sake of cheapening the bronze itself or for the sake of greater ease of working with a cutting tool, must be carefully avoided.

In the following table is given the average composition of ordnance bronze of various countries, which widely used bronze for casting cannon:

Bell bronze must be hard and tough in order to produce a good sound and at the same time not undergo changes from the blows of the clapper. The usual composition of bell bronze varies around 20—23 parts tin to 80—77 parts copper. Accidental admixtures, which very often occur in bell bronze (antimony, zinc, lead, etc.), are certainly harmful, for they worsen the quality of the bronze. Even an admixture of silver, which is usually added to bronze for the sake of the sonority of the bell, not only does not introduce any improving qualities into the metal, but, judging by experiments...

of the Mears factory in London, diminishes the sonority of the alloy. The Japanese add a little zinc and iron to the bell alloy; Japanese cast small bells, distinguished by their special sonority, are made from an alloy of 10 parts copper, 4 parts tin, \(1/2\) part zinc, and \(1/2\) part iron.

In the most widespread compositions of bell bronzes other admixtures are rarely encountered; the bronzes consist only of copper and tin. The following table gives the composition of such bell bronzes, of rather ancient origin.

In bell bronzes in the pure form, not infrequently, as is evident from the preceding, zinc and iron are added as improving admixtures. Iron is added to bronze in the form of an iron-zinc alloy.

The use of an iron-zinc alloy as an element added to bronzes with the aim of introducing into the latter an insignificant quantity of iron was first undertaken by Dick for obtaining a special “Delta” metal, so named after him. In Dick’s opinion, zinc with iron, upon prolonged heating at temperatures of \(700\)—\(800^\circ\) C, gives an alloy of about \(8\%\) Fe. Then Bertier¹⁵, while studying the process of galvanizing sheet iron by Lorel’s method, observed that in the zinc bath, with time, as the process continued, a considerable quantity of crystals of a zinc alloy with iron was deposited on the bottom. The composition of such an alloy, according to an analysis made by Bertier, proved to be:

\[ \begin{aligned} \mathrm{Zn} &— 90.00\%\\ \mathrm{Fe} &—\phantom{0}9.50\%\\ \mathrm{Pb} &—\phantom{0}0.40\% \end{aligned} \]

F. C. Calvest and R. Jonson¹⁶, analyzing a similar alloy obtained in the form of a deposit in a zinc bath during the manufacture of galvanized iron, found that the composition of such an iron-zinc alloy fluctuates around

\[ \begin{aligned} \mathrm{Fe} &= 6.79\%,\\ \mathrm{Zn} &= 93.21\%. \end{aligned} \]

Further, Le Chatelier^20), preparing the alloy by the method indicated above, but treating it with a solution of zinc chloride, which removes the excess of pure zinc, isolated almost pure crystals of an iron-zinc alloy and found by analysis that the composition of such an alloy corresponds to the formula Fe Zn$_{10}$, requiring 7.87% Fe, with a melting temperature of about 750° C. Finally, in 1906 Vologdin^21), in Le Chatelier’s laboratory, again investigated the iron-zinc alloy and fully confirmed the data of Le Chatelier cited above.

In order to elucidate the question of the influence of iron, as an impurity, on the quality of bell bronzes, in the metallographic laboratory and mechanical workshops of the Tomsk Technological Institute we prepared pure bell bronzes, and then bell bronzes with an admixture of zinc and with an admixture of zinc and iron. The iron-zinc alloy for such an addition was prepared by prolonged melting of zinc mixed with soft iron in hermetically sealed crucibles at temperatures of 800–900° C. The melting process lasted 2–3 hours at the stated temperature, and after its completion, after cooling, particles of the iron-zinc alloy were obtained in the lower part of the crucible and had a clearly crystalline structure. An attempt to pour the alloy out of the crucible after melting, in order to separate the zinc and the particles of iron-zinc alloy from the remaining particles of soft iron, was unsuccessful, and on one occasion was accompanied by strong spattering of the liquid metal.

The average composition of the iron-zinc alloy obtained was very close to that indicated above by Le Chatelier. For the experiments, pure bell bronzes were gradually prepared first, then bronzes with an admixture of zinc, and finally with an admixture of zinc and iron. The composition, in this way, of the bell bronzes obtained, in somewhat rounded figures, was as follows (decimal places have been rounded).

^20) Vestnik Obshchestva Tekhnologov, 1906. p. 419.
^21) Le Chatelier. Notice sur les travaux scientifiques. 1897, p. 94.

It proved impossible to obtain a higher iron content in bell bronzes; moreover, the alloys obtained with an admixture of iron do not possess good casting properties: despite all precautions and repeated melting, it was only with great difficulty that dense, good specimens could be obtained. It must be supposed that, under the influence of zinc and iron, bronzes absorb gases considerably more strongly, as a result of which the castings came out porous. The specimens of melt 5 proved so hard that it was not possible to machine them with a cutter for mechanical tests. As regards the internal structure of the bronzes obtained, the appended Table I gives a fairly clear idea of the change in this structure under the influence of the chemical composition, since the cooling conditions for all the bronzes were approximately the same (slow cooling in dry molds after casting).

The bronze of the 1st melt (Fig. 1) has a very heterogeneous structure—the separation of particles richer in tin content is clearly visible. Owing to considerable liquation, the direction of the axes of crystallization can be observed. The separation of copper oxides in the form of black points can be seen over the entire field of the polished section. The etching of all polished sections was carried out with bromine water.

The bronze of the 2nd melt (Fig. 2), in its structure, rather closely resembles the bronze of the 1st melt, but the phenomena of liquation in it are less noticeable. At higher magnification one can observe that the separated particles of the alloy (the white spots in the photograph) have a complex structure depending on the tin content.

The 3rd alloy (Fig. 3) proved to be the most homogeneous in structure in comparison with the preceding ones; it has a fine binding network, and no large segregations of liquation grains are noticeable.

The 4th alloy (Fig. 4) was prepared according to a recipe very close to that indicated earlier for Japanese bronzes with an admixture of iron and zinc, the fraction of iron being replaced by zinc. The alloy is very hard and can be machined with a cutter only with great difficulty; the division into bronze and brass is distinctly visible on the polished section, the brass particles separating among the bronze particles in the form of small circles, while the structure of the particles of the bronze itself is very dense, with a weak division into separate portions.

The bronze of the 5th melt (Fig. 5) differs from the preceding one only in that part of the zinc is replaced by iron; for this purpose an iron-zinc alloy of the composition indicated earlier was added to the bronze, and the bronze was held for a long time at high temperatures after melting—

with the aim of removing part of the excess zinc in the alloying addition. As a result, a bronze was obtained that was very hard and brittle, resembling in structure bronzes with an insignificant phosphorus content. In the general dense mass of the polished section, the separation of thin, delicate fibers and veins is noticeable, evidently of a composition different from that of the main mass of the field of the polished section. In addition, over the field of the polished section the cleavage planes of individual large crystals are clearly visible; moreover, these cleavage planes are gaps filled with a black-colored substance.

The bronzes of the 4th, 5th, and 6th melts were melted under a cover consisting of a layer of magnesia and charcoal.

The bronze of the 6th melt (Fig. 6), in composition, approaches the bronzes of the 3rd melt, with a noticeable replacement of part of the copper by zinc and iron. The main mass of the polished section has a slightly pinkish tint and small inclusions of a black-colored substance. The separated particles of bronze (white spots in the photograph) are scattered rather uniformly over the field of the polished section. In external appearance the structure of the particles of the latter bronze closely resembles artistic bronze prepared according to Elster’s recipe.

The mechanical tests of the bronzes just considered gave the following results: the percentage elongation for all the bronzes is very close to 0, and the average tensile coefficient from four or five specimens had the following values:

1st melt . . . . . . . 18.17 kg/q. mm.
2nd melt . . . . . . . 16.58 ” ”
3rd melt . . . . . . . 21.36 ” ”
4th melt . . . . . . . 17.82 ” ”

The 5th melt was not tested, since, owing to its considerable hardness and brittleness, it was impossible to prepare specimens.

6th melt . . . . . . . 20.24 kg/q.mm

Thus, among the pure bell bronzes, the bronze of the 3rd melt proved to have the best mechanical properties. Bronzes prepared very nearly according to the recipe for Japanese bell bronzes had weak mechanical properties. Finally, the replacement of part of the copper in the 3rd melt by zinc and iron did not improve the mechanical properties of this bronze.

Then, in the not very distant past, bronze was widely used for the preparation of various mirrors and was known under the name of mirror bronze. Bronze for this purpose must be hard, possess good capacity for polishing, and not tarnish with

time. Bronze with an admixture of 30–33% tin possesses such qualities. Attempts were made to add arsenic and nickel to speculum bronze, but they were not successful, since the alloy quickly tarnishes from the coating of oxygen and sulfur compounds of these metals. The average chemical composition of speculum bronze encountered at the present time is given in the following table:

Finally, bronze in general has very wide application for the casting of artistic objects and for the casting of all sorts of machine parts. Without dwelling on the very broad and varied class of machine bronzes, which is set forth in sufficient detail in our course Metal Alloys, edition of 1910, we shall say a few words about artistic bronzes. The excellent qualities of bronze—its great resistance to atmospheric influence and mechanical wear, as well as its ability easily to fill delicate, graceful casting forms and to be readily worked with the chisel—were known already in remote antiquity. Thus, as early as the epoch of ancient Greek culture, tin bronze was used for casting monuments and statues, and quite often the tin was replaced by lead (lead was then considered an inferior grade of tin). By the time of the Roman emperors, a third metal began to enter into the composition of bronze—zinc¹⁷. At the present time zinc is also introduced into artistic bronze, and sometimes even in greater quantity than tin. An admixture of lead and zinc to artistic bronze is, on the one hand, even desirable: the former makes the bronze softer and more easily worked with the chisel, the latter reduces liquation of the bronze; but both metals are harmful admixtures if an object is to be cast that must be exposed to atmospheric influence. In the latter case it is required that the golden or yellowish-red color of the fresh casting gradually pass into a delicate brown basic color with a green coating, consisting of the so-called patina; and the layer of patina, as is known, consists of carbonic-acid compounds of copper. Consequently, from the indicated point of view, the layer of patina will be better and more durable the greater will be

copper in bronze; an admixture of zinc and lead to bronze gives the patina a somewhat dirty brownish color, which is highly undesirable.

As especially suitable for casting statues that are to stand in the open air, Elster¹⁸ proposes the following alloy: \(86^{2}/_{3}\) copper, \(6^{2}/_{3}\) tin, \(3^{1}/_{3}\) lead, and \(3^{1}/_{3}\) zinc. Indeed, the analysis of statues of past centuries that have been well preserved up to the present fully confirms the alloy proposed by Elster¹⁹.

Thus, briefly summarizing what has been set forth above, we arrive at the following conclusions: 1). Bronze was known in remote antiquity. Primitive man at first had at his disposal pure copper and tin, and then, by way of empirical mixing of these two elements, obtained various kinds of bronze, gradually improved their properties, and widely utilized them for his purposes.

2). Among pure bell bronzes, the bronze with a tin content of about 20% is distinguished by the best mechanical properties.

Bronzes prepared according to a formula very close to that for Japanese bell bronzes, in comparison with ordinary bell bronzes, have a lower coefficient of rupture, are harder than the latter, and, apparently, absorb gases considerably more strongly during casting.

4). The admixture of iron and zinc to bell bronzes of the best composition (about 20% tin), with the replacement by these admixtures of part of the copper, does not improve the mechanical and foundry properties of the bronze.

With regard to experimental studies in recent times concerning the addition of iron and zinc to bronze, one cannot but say that, for a definitive solution of this question, it is necessary to carry out still more extensive investigations than it was possible to do in the mechanical workshops of the Institute.

Table I.

Fig. 1. \(1 \times 100\).

Fig. 2. \(1 \times 100\).

Fig. 3. \(1 \times 100\).

Fig. 4. \(1 \times 100\).

Fig. 5. \(1 \times 100\).

Fig. 6. \(1 \times 100\).

Bell bronzes. T. Tikhonov.

1. V. Skinner. Bronze and Its History from the Most Ancient Times. p. 8. 1908. St. Petersburg. ↩

2. Skinner. Bronze. p. 12. St. Petersburg. 1908. ↩

3. De’couv. en Chaldée. 1884. Nos. 1 and 2. ↩

4. Skinder. Bronze. p. 14. 1908. St. Petersburg. ↩

5. Skinder. Bronze. p. 59. 1908. ↩

6. Ibid., p. 25. ↩↩

7. Skinder. Bronze. P. 54. 1908. ↩

8. Ibid., p. 40. ↩

9. Historia naturalis 34, 16, 47. ↩

10. Skinder. Bronze. P. 85. 1908. ↩

11. F. Hommel. Die vorsemitischen Kulturen 277, 409. Skinder. Bronze. P. 86. ↩

12. Knibert. Bronze, p. 94. ↩

13. R. H. Thurston. Report on a preliminary investigation of the properties of the copper tin alloys. Washington. 1879. ↩

14. Knaab. Foundry Practice. p. 211. 1900. ↩

15. P. Bertier, “Sur deux alliages de zinc et de fer obtenus dans la fabrication du fer galvanisé.” Ann. des Mines. T. XVII. 1840. p. 652. ↩

16. F. C. Calvest et R. Jonson, Ann. de chimie et de physique. T. XLV. 1858. p. 454. ↩

17. Ledebur. Mech. Tech., p. 20, 1900. ↩

18. Dinglers Polytechnisches Journal. \(2^{12}/_{157}\) ↩

19. Ledebur. Mech. Tech., p. 21. 1900. ↩