Temperature of Hydrogen. 279 



in which Qt stands either for 7 or T according as the point of 

 intersection with the line of saturation lies on the fluid or on 

 the vapour branch. If now we suppose the " ideal " gaseous 

 laws to express the behaviour of the body at the temperature 

 T with sufficient approximation* we may put 



S = ClogT -clogR + S and88=-c-£-, . (10) 



where C, c, and S are constant quantities ; hence 



^JlM (11) 



SR KG ' [ } 



and thus the value of SQ/SR at the critical point is seen to be 

 zero. Let R c be ihe initial pressure, on the T -isothermal 

 line, which belongs to the " critical " adiabatic, i. e. to the 

 adiabatic crossing the line of saturation at the critical point. 

 Adiabatic curves with initial pressures Rj superior to R c will 

 then be found to intersect the line of saturation on the liquid 

 side and at pressures Qx satisfying the relation 



sq,_ ci| UrA 



W,- ~~n^r~ ; (U) 



consequently the pressures Q x will decrease when the R/s 

 increase. At the pressure Qi, therefore, when following the 

 course of an adiabatic, we should observe the appearance of 

 tha first bubbles of vapour ; and above Q x it will only be the 

 homogeneousness of the system which will prevent our ascer- 

 taining its liquidity. On the other hand, adiabatic curves 

 whose initial pressures R 2 are inferior to R c will intersect the 

 line of saturation on the vapour side, at pressures Q 2 such that 



sq 2 2 UH - 



SR 2 ~ R 2 r ' ^ 



so that (between the critical temperature and the temperature 

 T**) the pressures Q 2 decrease when the R 2 's decrease. 



Let us now proceed to consider ihe variations of the 

 pressures Q x on the left, and those of the Q 2 on the right of 

 the critical point. We may put SR 1 = 8R 2 ; this, in fact, is 

 what Prof. Olszewski directly realized. If we compare such 



* That for Prof. Olszewski's experiments such an assumption is 

 legitimate, may be seen from the following argument. The temperature 

 T in these experiments was —211°, i. e. 62 degrees on the absolute scale. 

 The critical temperature of hydrogen lies about -232°. Hydrogen at 

 —211° may therefore be compared with carbonic acid if taken at +187°. 



