178 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1936 



helium. This enabled him in 1911 to observe temperatures between 

 2° and 4° K. (absolute) . By this time the original program of re- 

 searches had, of course, been amplified and extended to cover all 

 branches of physics at low temperatures. 



After the death of Kamerlingh Onnes, the researches were pursued 

 under the joint direction of Professors Keesom and De Haas. In a 

 general way, although without absolute separation, the investigations 

 carried on under the direction of Professor Keesom concerned ther- 

 modynamics, while those directed by Professor De Haas had to 

 do with magnetism and electricity. 



PRESENT ORGANIZATION OF THE LABORATORY 



The laboratory is devoted to pure research for the study of the 

 properties of substances at low temperatures and of the means of 

 producing low temperatures. 



(a) Production of cold. — The celebrated cycle by cascade (methyl 

 chloride, ethylene, oxygen, air, hydrogen, helium) is now abandoned. 

 Today the laboratory obtains almost on a commercial scale the pro- 

 duction of liquid air and liquid hydrogen. Air is compressed by a 

 machine of 60 horsepower to a pressure of 200 atmospheres. One 

 part is then expanded to 1.2 atmospheres, producing exterior work 

 which is used to compress air, and then finally further expanded to 

 1 atmosphere. The remaining part is expanded from 200 to 1 atmos- 

 phere, liquefying without having produced external work. 



In this way the laboratory is able to produce 30 liters of liquid 

 air per hour, or 13,000 liters per year. The liquid air is conserved 

 in Dewar flasks of 5 liters capacity that will keep it about 15 days. 

 In the liquid air laboratory is also an apparatus with which liquid 

 oxygen and liquid nitrogen may be obtained by separating these 

 gases from air under compression and cooling by liquid air. 



Liquid hydrogen is obtained by compressing the gas to 180 atmos- 

 pheres in an 18-kilowatt compressor, then cooling it to the tempera- 

 ture attained by liquid air boiling under reduced pressure, and finally 

 further cooling it after the method of Linde. Production of liquid 

 hydrogen may reach 16 to 18 liters per hour, or 6,000 liters per year. 

 Liquid hydrogen is preserved and transported in special Dewar flasks. 

 Helium is stored in steel cylinders. Compressed to 15 atmospheres, 

 it is then cooled in a coil bathed by liquid hydrogen at —258° C, 

 and finally liquefied by the Linde process. About 3 liters per hour 

 may be produced, and since 1923 a supply of it has been kept up for 

 the cryostats which are used in the various rooms of the laboratory. 



(5) Preparation of apparatus. — Dewar flasks (cryostats) are neces- 

 sarily much employed in the researches. Their forms, dimensions, 

 and interior construction vary with different investigations. Most 



