of Liquid Hydroch loric Acid. 437 



and those temperatures, when combined with the numbers 

 given in the second and fourth columns of the above Table, 

 will enable us to find the corresponding densities of the satu- 

 rated vapour. The results thus found were not very satis- 

 factory. Another way to overcome the difficulty is to make 

 use of the numbers in the third column, which give the 

 volumes of the saturated vapour just at the point of lique- 

 faction in relation to the volume occupied by the mass of the 

 gas at the temperature t° (column A*) and under the pressure 

 of one atmosphere. If the specific volume of the gas under 

 the normal circumstances be known in terms of the usual 

 units, this together with the coefficient of expansion under 

 that pressure will give us the specific volumes of the satu- 

 rated vapour at different temperatures. Now, Biot and 

 Arago f give the density of hydrochloric acid under the 

 normal circumstances to be 1*2474 in reference to air. There- 

 fore, the specific volumes under consideration will be given 

 by the following :— - 



1 1 ["fractional! •- , 



5 ~ 1-293 " VU7 ' L volume J • l 1 + aC J' 



When a long time ago I began my calculation I was not able to 

 get any information with respect to the coefficient of expansion, 

 and I assumed it perhaps not far from the value 0*003665. 

 Quite recently, however, I have found that it was determined 

 by Eegnault J as long ago as 1843 to be 0*003681, and so I 

 have proceeded to recalculate. Of course no great differences 

 were thus wrought in the final values of the heat of vaporiza- 

 tion. It is, moreover, to be remarked that Kegnault himself 

 did not put much confidence in the accuracy of his value on 

 account of an unavoidable admixture of air, very small though 

 it was, with the gas he investigated. 



The formula for the heat of vaporization (according to the 

 notation of Clausius) becomes : — 



_ 10333 1 1 ["fractional] , / <r\ dp rp 



" 425 ' 1*293* 1-247* L volume J* ^ i + a ^ 'l/ - s )'dH ' 



in which the ratio a/s is to be supplied by the numbers in 

 the second and fourth columns of the above Table. 



* As it must have been, although it is not explicitly mentioned, 

 t Wiillner, Lehrbuch der Physik, iii. p. 150. 

 \ Ann. de Chimie et Physique, serie 3, tome iv. 



