E. A. Kroger.

Application of a Mercury–Oil Thermoregulator at High Temperatures.

(From the Laboratory of Organic Chemistry of the Siberian Technological Institute).

Working since 1925 on the activity of halogens in organic compounds, I have had, in most cases, to deal with reactions at high temperatures \((100^\circ\text{--}400^\circ C)\). At the same time, one of the principal difficulties was maintaining a constant temperature, with gas heating of the furnaces, throughout the entire course of reactions, which sometimes required hundreds of hours. Temperature fluctuations exceeding \(10^\circ C\) have a very significant effect on the rate of reactions and reduce the accuracy of the results obtained. On the other hand, the deficiency of illuminating gas, its irregular flow, and insufficient purification further intensified these temperature fluctuations and made it difficult to regulate the heating temperature of the furnaces in which the reacting substances were placed. Therefore the necessity of automatic regulation of furnace temperature had already become evident by the end of the first year of work. Since all the experiments were of a preliminary, general character, temperature fluctuations within the limits of \(8^\circ\text{--}10^\circ C\) were permissible for my purposes. On reviewing the literature on this question, the following types of thermoregulators attracted attention: the thermoregulator proposed by G. L. Andreae¹ is distinguished by the greatest simplicity. The accuracy of temperature regulation here reaches \(0.04\text{--}0.05^\circ C\), but, unfortunately, the regulator is applicable only for low temperatures. It is then of interest to note several types of regulators for low temperatures described by Ostwald–Luther² and by Oskar Hahn³. M. Bodenstein, with collaborators, proposes two types of thermoregulators for high temperatures (with electric heating). The regulator proposed by M. Bodenstein and Fr. Kranendieck⁴ is distinguished by a more complicated construction and brings the accuracy of regulation to \(1^\circ C\) (at \(800\text{--}900^\circ C\)). Another type of thermoregulator, proposed by M. Bodenstein and W. Pohl⁵, is simpler in construction and is based in its principle on the combined action of several tubes with an expanding medium (four tubes with toluene and one with air) upon a mercury valve, closing the opening of the gas-supply tube (with gas heating) and closing a contact (with electric heating). Among the disadvantages of the construction must be counted the bulkiness and great weight of this apparatus. On the other hand, this principle makes it possible (theoretically) to bring the accuracy of temperature regulation to any desired limit. For use in my work with gas-heated furnaces, I constructed in 1926/27 a thermoregulator with which I have wor—

worked for 3 years. Distinguished by its simplicity, this thermoregulator (see drawing) is based on the generally accepted principle of a mercury valve (A) closing the end of the gas-supply tube (B). The expanding medium in the knee (CC′) is a high-boiling, thoroughly dried lubricating oil. The operation of the thermoregulator was tested and gave satisfactory results even at temperatures above 400° C. The danger of poisonous mercury vapors¹) is completely eliminated, owing to the removal of the valve (A) from the furnace by 25–30 cm and to the asbestos shield (MN), thanks to which the temperature of the mercury does not exceed 30–35° C.

In conclusion I give several comparative tables of temperature fluctuations, which were obtained under the following conditions:

1. All tests were carried out for all 3 furnaces simultaneously, and consequently with identical qualitative and quantitative fluctuations of the gas (in May and November 1929).

2. The temperature of the 1st furnace was regulated automatically by means of the thermoregulator described above; the 2nd and 3rd furnaces were regulated by hand (without a thermoregulator).

3. The tests were conducted at 2 temperatures: about 150° and 250° C.

4. The volume of the expanding medium (oil) of the thermoregulator being tested was about 30 cm³.

Table No. 1

of observations of furnace temperature (with gas heating).

¹) Ostwald–Zuther. Physiko-Chem. Messungen (119).

Table No. 2
of observations of furnace temperatures (with gas heating).

Table No. 3
of observations of furnace temperatures (with gas heating).

Table No. 4

of observations of furnace temperature (with gas heating).

Table No. 5.

observations of furnace temperature (with gas heating).

Thus, as is evident from the tables, the average fluctuations of the temperature (with the thermostat) do not exceed 1° C. The sensitivity of the thermostat and the accuracy of temperature regulation can be very considerably increased by increasing the volume of the expanding medium (oil).

The tests of the thermostat were carried out in the Laboratory of Organic Chemistry of the Siberian Technological Institute; for this I express my gratitude to the Head of the Laboratory, Professor B. V. Tronov.

E. Krüger.

7 November 1929.

MERCURY–OIL THERMOREGULATOR

(drawing labels and dimensions visible on the page)

M

N

C

C′

A

B

Hg

32 cm

23 cm

1.7

7

8

16

5

4

15

5

8

7

10

E. A. Knoper
1929.

1. Annalen der Physik u. Ch. IV (1878), 64. ↩

2. Ostwald–Luther. Physiko.-Chemisch. Messungen (113). ↩

3. Zeitschrift f. Phys. Chem. 41 (1903), 525. ↩

4. Zeitschrift f. Elektrochem. 18, (1912), 447. ↩

5. Zeitschrift f. Elektroch. 11, (1905), No. 1, 375. ↩