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Appendix 1 Memorandum for the People’s Commissariat of Heavy Industry in which Shubnikov formulates the tasks of the physical-technical research in cryogenics (Ref. [1], pp. 43–47). From this memorandum it is clear that Shubnikov was very much aware of the needs of industry and how his research in the low-temperature laboratory could contribute to the development of industrial processes. The UFTI Low-Temperature Laboratory The development of experimental physics in recent years is characterized by the introduction of new powerful research methods. In order to make nature talk the modern experimental physicist sets up experiments at very high stresses, colossal pressures, very low temperatures, and uses devices that have a very high sensitivity or large precision. Thanks to the fact that technology has been forced to work for science and that laboratories can use the best that technology has at present to offer, the development of modern physics proceeds at fabulous speed. Deeper knowledge of the physical processes of nature does in turn have an enormous influence on the development of technology. In recent years a number of new areas of technology have exclusively been created within the walls of physics laboratories. The area of low temperatures belongs to these extremely powerful possibilities for research in physics. Research at low temperatures is interesting for many reasons. In the first place, every new means of research leads to the discovery of completely new phenomena. One of the most well-known of these phenomena is the superconductivity of metals, implying that at very low temperatures a whole series of metals instantly loses all resistance to the passage of an electric current. The phenomenon occurs in different metals at different temperatures, while it has been found that the transition from the ordinary state to the superconducting state occurs in a temperature interval of less than 1/100,000°C, i.e. the transition is as sharp as the melting transition of a metal. In the superconducting state it has so far not been possible to measure the existence of an electrical resistance—it is infinitely small. The following experiment has been carried out: a current was induced in a superconducting coil and its strength was measured for four days. Within the limits © Springer International Publishing AG 2018 255 L. J. Reinders, The Life, Science and Times of Lev Vasilevich Shubnikov, Springer Biographies, https://doi.org/10.1007/978-3-319-72098-2 256 Appendix 1 of accuracy of the measurements, no decrease of the current was observed, from which it was concluded that the resistance of the superconductor is in any case 1020 times smaller than of the metal in the ordinary state. A qualitative explanation, let alone a theory of this phenomenon is so far lacking. Apart from exploring new phenomena, the region of low temperatures also has a specific interest. The fact is that all phenomena that occur in solid matter usually depend strongly on the temperature. Knowledge of temperature dependence is extre- mely important for analysing physical phenomena in nature and for verifying our theoretical ideas. However, the investigation of the temperature dependence at ordinary temperatures is uninteresting, since thermal motion is very strong and the phenomenon under investigation is complicated by additional phenomena, while investigations at very low temperatures at which thermal motion is small and the phenomenon becomes much simpler are of very great interest. As an example of such temperature depen- dence, whose investigation at low temperatures gave us much information on the structure of matter and the nature of thermal motion, we mention the dependence of the specific heat on the temperature. In recent years the investigation of the specificheatof gaseous hydrogen at low temperatures has led to an extremely interesting result. Contrary to other gases the specific heat of such a simple substance, like hydrogen, showed a large deviation from the values obtained by theorists. Calculations of a hydrogen molecule on the basis of quantum mechanics showed that ordinary hydrogen consists of a mixture of two different molecules and the anomalies in the specificheat are explained by the fact that we do not have a pure gas, but a gaseous mixture. These two forms of hydrogen—ortho- and para-hydrogen—have now been obtained sepa- rately and their properties are being studied. In spite of the fact that physics only recently penetrated the region of low temperatures, methods for obtaining low temperatures have been transferred rapidly from the physics laboratory to a wide range of technological applications. In technological applications low temperatures are mainly used for the separa- tion of gases. Of special interest is the separation of air into its constituent parts: extracting oxygen from it, and separating coke-oven gases, mainly extracting hydrogen from it. The need of the expanding industry for oxygen grows every year. At present oxygen is mainly used for the welding and cutting of metals, for detonation work etc. Air is separated into its constituent parts, subjecting it first to full liquefaction, and then fractionation. In this way it is in principle possible to separate air into its constituent parts: nitrogen, oxygen and noble gases: helium, neon, argon, krypton and xenon. Since the equipment is not yet perfect, air is usually separated into two components: oxygen and nitrogen, while the remaining gases are lost or remain as an impurity. These impurities, as recent research has shown, are often very harmful. For instance, an impurity of argon in oxygen decreases the speed of welding and cutting of metal approximately by a factor of ten. Noble gases find broad application in illumination engineering: half-watt lamps are filled with argon, and neon, krypton and xenon are used for manufacturing glow tubes (beacons, advertising lamps). Hydrogen is at present only of interest for the chemical industry, since mixed with nitrogen it is used for the synthesis of ammonia—a basic product for the Appendix 1 257 production of mineral fertilizer and the defence of the country. There are two procedures for obtaining hydrogen—the method of water gas1 and the method of deep cooling of coke gas. The last method was introduced in Germany by the Linde firm2 in 1923 and has spread ever wider since. In this method coke oven gas is broken down via fractional liquefaction of a higher boiling mixture, while hydrogen itself, which boils at a very low temperature, does not condense. This area of engineering is very young; both the equipment and the method of separation are far from perfected. Therefore in the near future in this area much work has to be done by engineers and physicists. In spite of the great interest of present-day physics and engineering in low temperatures, we have only a few laboratories working in this field. The reason for this is that this field of work requires extremely high technical skills, which are unavailable to most laboratories, not only in the USSR, but also abroad. A pioneer in this field is the low-temperature laboratory in Leiden (Netherlands), where Heike Kamerlingh Onnes succeeded for the first time in 1911 in obtaining liquid helium,3 which boils only at 4 °K, i.e. at −269 °C. In 1926 liquid helium was also obtained at two other laboratories: in Berlin and in Toronto (Canada). In 1926 Soviet physics could still only dream of its own laboratory of low temperatures. However, three years later the rapidly increasing technical level of the country, the growth of industry and the more serious organisation of scientific work in research institutes gave us the confidence in the necessity and possibility of founding such a laboratory in our country, in the Union. Such a laboratory was organized at UFTI in Kharkov. The size and outfit of the laboratory, as well as the scientific and technical tasks assigned to it put our laboratory on a par with the three laboratories mentioned above. This month it is three years since the birth of the institute, and we will report on three successes which we have achieved in the field of low temperatures. We obtain low temperatures by means of liquid gases that boil at these tem- peratures. Our first task was to set up a facility for liquid gases in quantities that could fully fulfil the requirements of the laboratory. In order to be able to work in the entire range of low temperatures we needed an installation for obtaining liquid nitrogen (boiling point −196 °C), liquid hydrogen (−253 °C) and liquid helium (−269 °C). At the end of 1930 we started up a facility for obtaining liquid nitrogen, with an output of 30 l/h. This facility did not present any difficulties. Its operating principle is based on the fact that compressed air, when expanding, cools down. Thus, for instance, when expanding air from 200 to 2 atm. the temperature drops by 40°C. We can use the air cooled in this way for cooling and reducing the initial 1A synthesis gas, containing carbon monoxide and hydrogen, made by passing steam over a red-hot carbon fuel such as coke. Highly flammable. 2Still the world's largest industrial gas company by market share as well as revenue, founded in 1879. The Linde Group has over 600 affiliated companies in more than 100 countries. Revenues were EUR 17 billion in 2004. 3Shubnikov is mistaken here. Kamerlingh Onnes liquified helium in 1908. In 1911 he discovered superconductivity. 258 Appendix 1 temperature of compressed air, which by subsequent expansion cools even more. The process is continued until part of the air does no longer convert into the liquid state. The facility consists of two main parts: a compressor, which compresses the air to 200 atm., and a device for liquefaction.

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