474 



factor, the correction cati l)e made to the sectional area on wliich 

 the pressure acts; liie area thus coi-recled, the "functional" area, is 

 therefore according to Wagner's theoretical deductions a constant 

 for the instrument and naturally diffeis a little from the real area. 

 Wagnkr determined the functional area of his AMAGAT-gaiige b^' 

 means of experiments at low pressure, he also measured the real 

 area and found the two exaclh' ecpial ! This result is in contradiction 

 with tiie theory, and, assuming Wagnku's experinients to be trust- 

 worthy, this would indicale, thai (he theory is not so simple and 

 that there are possibly other factors which might inlluence the 

 functional area, in which case it might very well happen that the 

 functional area would turn out to be dependent on the pressure. 



Before this matter can be cleared up, i.e. before a revised theory 

 of the pressure-balance can be tested by experiment, it will be 

 necessary to study the instrument as fully as po.ssible from an 

 experimental point of view, i.e. to compare its indications over as 

 wide a range of pressures as possible with those of a standard- 

 manometer and on the other hand to make very accurate measurements 

 of the dimensions of its various parts. On the basis of these data 

 it will then perhaps be possible to build up a more exact theory. 



If it appeared that the functional area in accordance with Wagner's 

 theory were independent of the pressure over the whole range of 

 comparison, one would be justitied in extrapolating beyond the 

 region, where the comparison with the open gauge is possible (i.e. 

 above J 20 atmospheres), and thus in calculating the actual pressure 

 at 250 atmospheres from the indication of the balance with the 

 same functional area as was found say at 100 atmospheres; the 

 large pressure-balance of the van dkr WAALs-fund which has 

 a range from 250 to 5000 atmospheres could then be compared 

 with the small balance at 250 atmospheres and in this manner the 

 pressures on the isothermals of hydrogen measured by Kohnstamm 

 and Wai.stra with both instruments could be corrected using the 

 functional area thus determined. 



So far we have not gone beyond 100 atmospheres with the 

 comparison, as it was made in connection with the determination 

 of the isothermal of 20° C. dealt with in the preceding communication. 

 The range from 60 to 100 atmospheres gave sufficient data for the 

 purposes of the investigation: they show the desirability of a further 

 systematic investigation of various questions in connection with the 

 theory of the pressure-balance; but this investigation can be carried 

 out, independently of the apparatus in the possession of the laboratory. 

 We resolved to defer the continuation of the measurements, which 



