546 



NA TURE 



[August 13, 1896 



the second substance. Both substances arc in continual 

 circulation in metallic, self-contained cycles, which are 

 worked by two Pictet conjugated pumps. While Olszewski 

 introduced a steel cyclinder in which to liquefy oxygen, 

 Prof. Onnes devised an '"ethylene boiling flask" in which 

 oxygen (or air) is condensed in a copper spiral. The 

 glass apparatus into which the oxygen is poured is of 

 original construction, and especially adapted for experi- 

 mental work in oxygen (or air) baths of 4 to \ litre. 



Sometimes instead of the methylchloride cycle solid 

 carbonic acid is used. Experiments on the insertion of a 

 methane cycle between the ethylene and oxygen, with the 

 ultimate object of condensing hydrogen, are still being 

 carried on. Oxygen and air are taken from high-pressure 

 cylinders, into which they are compressed either by a 

 Brotherhood compressor (as used in launching torpedos) 



into a kind of model "cryogenic laboratorj'," as Prof. 

 Onnes calls his creation, with emphasis on both cryo- 

 genic and laboratory. Occasional comparisons with other 

 cryogenic installations illustrate this vividly. Dewar 

 works with quantities of ethylene up to "a hundredweight '' 

 (40 kg.), while Prof Onnes requires I'j kg., by aid of 

 which 7 to i litre of oxygen is kept liquid. Pictet 

 estimates the power required for experiments with liquid 

 air at from 30 to 40 h. p., while in the Leiden laboratory 

 only six or eight are required, even in exceptional cases. 

 Olszewski gives his power as 1-3 h.p., but it must not be 

 forgotten that his system is not a continuous one, and 

 that the largest quantity which his apparatus in its 

 enlarged form yields is 200 cc, only J of which gets 

 into his boiling-glass. His experiments require a corre- 

 spondingly smaller quantity of ethylene (i kg.). 



^ of the cryogenic departn 



i'ing the compressors destined for 

 chlormethyl conden 



: chlormethyl, ethylene, and oxygen cycle. .\t the right the 



or by a much less powerful, but in other respects highly 

 superior Cailletet compressor. This compressor as modi- 

 fied, almost re-designed by Prof. Onnes, is a most desir- 

 able laborator)' apparatus where high-pressure work with 

 pure gases is being done. The chief modification is that 

 the mercury column works in a steel U-tube, so that the 

 piston with its lubricant (glycerine) is on one side above 

 it, and the valves, &:c., on the other. This compressor 

 may be fully depended upon ; the gases remain just as 

 pure as they were, and may be compressed to 100 atmo- 

 spheres without loss. (A full description of this compressor 

 may shortly be expected.) 



It is worth noticing that the greatest possible care is 

 taken (and had to be taken) in the way of safety and of 

 economy ; these circumstances make the department 



NO. 1398, VOL. 54] 



It need hardly be said that these low figures have only 

 been arrived at by a slow process of trial and gradual im- 

 provement, and one cannot but admire the perseverance 

 and skill which the development of this system reveals. 



Now that the cryogenic department is so far com- 

 pleted that baths of liquid oxygen and air may be readily 

 prepared, no doubt the co-operation with the rest of the 

 laboratory will become more regular and fruitful. Even 

 now, in reading through the "Communications," we come 

 repeatedly across instances in which the high-pressure 

 and low temperature appliances have given invaluable 

 help. 



At one time, for instance, pure oxygen was required for 

 experiments on the magnetic rotation in gases at high 

 pressure (Nos. 7, 15). Commercial oxygen being too 



