46fi 



meter M,,„ witli (lie open standanl-gauge (as carried out in the 

 preliminary measurements of the preceding communication) afibrded 

 an opportunity for measuring the isothermal of hydrogen at 2(f C. 

 up to 100 atmospheres, with an accuracy of 1 in 3000 or 4000, 

 as required in the investigations with piezometers for low tempera- 

 tures which will go up to 100 atmospheres and first of all in the 

 investigation of the isothermal of 0° C. to 100 atmospheres mentioned 

 above. The calibration of M,^^ also served as a link in the compa- 

 rison of a pressure-balance of Schakffer and Budf.nberg with the 

 open standard-gauge which will be dealt with in the next commu- 

 nication lifif. 



2. As regards the experimental method we can be short, as it is 

 fully described in the preceding and in the next communication, the 

 latter of which also containing a plate. We only mention, that we 

 considered it advisable to compare once more the closed manometer 

 i¥j, at a few pressures with the open gauge, seeing that several 

 years had elapsed since the last comparison and that on one occasion 

 a small change of the normal volume had been noticed. 



Table I contains the results of this comparison, 0. M. standing 

 for "open manometer". 



In view of the accuracy of the two instruments it will he seen, 

 that the correspondence which is obtained must be called completely 

 satisfactory. 



The method differed from that of the preliminary determination 

 of the preceding communication by the normal volume of J/, j„ being 

 directly measured, in order to obtain a determination of the isothermal 

 as independent as possible. 



The i-esults of these measurements were as follows : 



