8 I\IM. Lecher and Pernter on the Absorption 



1 cubic inch; but as in our case the volume of M is only 

 ■\ cubic inch, the volume of the tube is 440 times that of M, 

 and the vapour must have expanded into 440 times its volume; 



so that the pressure becomes ^-. But after a repetition of 

 the process SS times (that is, after the pressure in the tube 

 has become ~ x 8*6), the total pressure in the tube, accord- 

 ing- to the tables, had become half an inch of mercury. We 

 have therefore the equation 



x 

 -jj- x 8-6 = -J inch, or ^=25*6 inches mercury. 



If we make the same calculation with the numbers which cor- 

 respond to a pressure of 1 inch in the table, we find x from 

 the equation 



£j— x 14*8 = 1, or #=29-9 inches mercury. 



We see, then, that there must have been a vapour-tension of 

 sulphide of carbon amounting to an entire atmosphere. But 

 as this is only possible at 46°, we have discovered some error, 

 the cause of which must be sought for. 



For benzol the calculations are still more surprising. The 

 table gives us the following data : — 



(Table XII.*) Benzol. Unit volume = ^ cubic inch. 

 Volumes . 1 . . . 18-0 19*0 20-0 

 Absorptions 4*5 .. . 67*0 69*0 72*0 

 Further, the absorption was 78 at a mercury-pressure of 1 inch 

 If we extrapolate a little, we find that if M were emptied 

 IZ'b times into the tube, an absorption of 78 would be ob- 

 tained which corresponds to the absorption at \ inch mercur Y . 

 A similar calculation to the former one gives 



2^ x 22-5 = 0-5, or ^ = 99*3 inches mercury ; 



that is to say, the temperature must have been about 100° C 



The explanation of these impossibilities may perhaps be as 

 follows. Regnaultt has observed that the tension of vapours is 

 ess » vacuo than m a space filled with air, and he explains 

 this as the result of condensation on the walls ; this causes a 

 diminution of the tension of the vapour; so that, whilst in a 

 vacuum compensation is instantly made by the liquid, in a 

 space filled with air this requires time, and the full vapour- 

 tension is never reached In the same way the results P f the 

 above calculations may be explained. 



* Loc tit. p. 31. f Pogg. Ann. xciii.; Memoires de VAcad. t. xxvi. 



