and its relation to Latent Heat. 11 



1st, from the absolute volumes ; Snd, from the relative volumes. 

 Do they give the same result ? 



§ 13. From Regnault^s empirical formula, the latent heat of 

 aqueous vapour at 86° F. is 1054. One cubic inch of water thus 

 heated is equivalent to one cubic inch of water at temperature 

 60° raised through 1054° x 772 x 12 inches vertical, or 9,764,256 

 cubic inches raised through one inch. 



From the capillary force we have, as above, '007577 cubic inch 

 raised through one inch as the measure of one-sixth the cohesion 

 of one layer of molecules, and "045462 cubic inch raised through 

 One inch as the integral of one layer of the cubic inch. Hence, 



9,764,256 _ 

 •045462 - 214,7/8,000 



is the number of layers of molecules in one cubic inch, and the 

 cube of the reciprocal of this is the absolute volume of one mole- 

 cule of water at the temperature 86°. 



/ 6 \^ 

 The process expressed by symbols is m^=l r^p- ) , in which L 



is the product of the latent heat by 12 times 772, Q the quotient 

 of capillarity, and m^ the molecular volume expressed with refer- 

 ence to a cubic inch as unit. 



The similar data for alcohol are as follows : — 



The latent heat of absolute alcohol at 174° F. is 376, accord- 

 ing to M^I. Fabre and Silberman {Ann. de Chim. vol. xxxvii. 

 1853, p. 466). The specific heat is 0'64. The ratio of latent to 

 sensible heat in alcohol is about the same as with water, according 

 to M. Despretz, hence 415° may be taken as the latent heat of 

 alcohol at 86^, 



[174° -86° =88°, 88°xO-64=56°-3, 56°-3x 0-695=39°, 



39° + 376=415°], 



and 415 x 772 x 12 = 3,844,560 cubic inches of alcohol raised 

 through one inch vertical. From Q = 228 we have t^= volume 



raised by a water-line one inch long : ^s = "026316 cubic inch raised 



through one inch as the cohesion integral of one layer of mole- 

 cules; hence 



M4M60_i4eo92 000 

 "026316 -i'*^^"'^-/JW 



is the number of layers of molecules of alcohol in one cubic inch, 

 and the cube of the reci])rocal of this is the absolute volume of 

 a molecule of alcohol at tlie temperature 86°. 



Comparing this absolute volume with that of water, we have 



