461 



60 atmospheres, it was quite possible, that the extrajwlatioii on 

 which tlie above ooiicliision was based woiiki turn out to be imper- 

 missible. 



It had been our intention lo carry the calibration of a working- 

 manometer for pressures above 60 atmospheres and the determination 

 of the isothermals of lijdrogen at 20^ C. up to 100 atmospheres. 

 Hut when we had reached 90 atmospiieres the connections in the 

 pressure-system turned out less perfectly tight as was desirable. The 

 mercury-surfaces were not completely still and to attain this it 

 appeared necessary' to affect certain improvements. But it was not 

 till 1915 that these were carried out (comp. next Comm. lM)/>). 

 Soon after the measurements mentioned above which were made in 

 1911, our work was interrupted by the departure of one of us and 

 remained tiius confined to a few preliminary, determinations which 

 do not extend beyond 90 atmospheres. 



2. Ari'dngement of th". divided open (jaufie for mea.sureiuenis from 

 60 to 100 atmospheres. The connections of the apparatus, already 

 roughly indicated in section 1, are shown in the Plate belonging to 

 Comm. 146c (these Proceedings below p. 472). 



The figure differs from the earlier representation of the gauge by 

 the manner in which the tubes of the open gauge which had now 

 to serve for tlie measurement of 60 to 100 atmospheres are joined 

 up : the same arrangement has been used in the measurements of 

 the next communication. As will.be seen, the first five tubes iiave 

 been left intact, while the remaining lubes were replaced by tubes 

 of greater wall-strength, destined for pressures from 60 to 100 

 atmospheres and tested to a pressure double of what tiiey are 

 intended to be used at. 



This arrangement has the advantage that the first five tubes 

 which go up to 20 atmospheres remain available as a separate open 

 gauge, and this is necessary, because they are not only used as a 

 standard-manometer, but also regularly as working-manometer for 

 the range below 20 atmospheres and in tins respect supplement the 

 manometer which we have described in previous communications, 

 going from 20 to 60 atmospiieres, which aboxe we called 3/^5„. In 

 the open gauge up to 20 atmospheres, J/„„ and il/,,„ we thus possess 

 a set of three manometers which embrace llie whole range of pres- 

 sure, through which the isothermals at low temperatures are measured 

 in the Leiden-Laboratory at the present time. 



The steel capillary on the left of tube B^ which normally is 

 coupled to the T-piece 1\ is now connected to a tube which through 



30* 



