1049 
Physics. -— “Methods and apparatus used in the cryogenic labo- 
ratory. XVII. Cryostat for temperatures between 27° K. and 
55° K”. By Prof. H. KAMERLINGH ONNes. (Communication 151a 
from the Physical Laboratory at Leiden). 
(Communicated in the meeting of June 24, 1916). 
1. Introduction. In section 1 of Comm. XVI of this series (Comm. 
N°. 147c Proc. XVIII, I, p. 507 I pointed out the importance of 
arrangements by which it would be possible to obtain constant and 
uniform temperatures in the range from about 27° K. to about 
55° K. and I mentioned that a cryostat had been constructed suit- 
able for this region of temperatures, in which for accomplishing 
this purpose a current of hydrogen warmed to the desired tempe- 
rature was made to pass through the experimental chamber '). The 
degree of constancy and uniformity of the temperatures which was 
obtained have exceeded our expectations, at least when it is pos- 
sible to adapt the arrangement of the measurements to the require- 
ments of the apparatus, as happened to be the case in the investi- 
gations which have so far been carried out with it. It is true that 
we have not succeeded in obtaining as easy and certain a regu- 
lation- of the temperature with the hydrogen-vapour cryostat as 
would be available, if substances existed suitable for liquid baths 
between 55° K. and 27° K. *). But the deviations very often remain- 
ed below 0.01 of a degree for a considerable time *) (a fuller 
account is given below in section 3). We may therefore say that the 
gap in the series of constant and uniform temperatures which still 
existed between the two regions which are easily governed by liquid 
oxygen and liquid hydrogen respectively *), has now also been filled 
1) The principle of this arrangement was already used by A. Perrier and 
H. Kamerlingh Onnes in their research on the magnetic properties of solid oxygen 
above 20° K (Comm. No. 139 c. Proc. XVI, 2, p. 894). 
2) The possibility of using neon under pressures above the normal in special 
experiments — as will probably be practically realisable between 27° K and 
34° K — is here left out of account. 
3) Compare the measurements of the vapour-pressure along the heterogeneous 
isothermals for different values of T in the investigation of the critical data of 
hydrogen (Comm. N°. 151 c). 
4) Besides for the range from 27° K—55° K the hydrogen-vapour cryostat is 
also suitable for temperatures lower than 27° K; in many experiments it will 
thus for instance be able to replace the neon-cryostat for the range from 25° K— 
27° K; this may be of some importance considering that the dimensions of the 
experimental space may have to be kept smaller in the neon-cryostat than in the 
