﻿320 Intelligence and Miscellaneous Articles. 



stance in the interior and when part of its heat was used in volati- 

 lizing either water or some volatile substance, enables us to calculate, 

 not exactly, perhaps, but at all events with sufficient approximation, 

 the quantity of heat consumed in each case. 



For the details of the method I must refer to the memoir which I 

 shall publish on the subject, and I limit myself here to indicating the 

 principle of the method. 



I find that the heat of volatilization of 1 gramme of sal-ammoniac 

 is 706 thermal units, with a great probability that its real value is 

 between the limits 617 and 618. 



The magnitude of this number, compared with that of the various 

 compounds for which it is known, and, on the other hand, its agree- 

 ment with that for the heat of combination of ammoniacal and hy- 

 drochloric acid gases*, make it highly probable that sal-ammoniac is 

 indeed partially decomposed into its elements when it is vaporized. 



To strengthen this conclusion, and to be certain that the high 

 numbers are not solely due to the imperfection of the method used, 

 I have endeavoured to apply it to determining the latent heats of 

 some other substances ; but having only made a few experiments 

 in each case, I shall cite the results without attaching any other im- 

 portance than that of showing that my method does not necessarily 

 lead to high results in the case of bodies which approach sal-ammo- 

 niac in their physical properties (boiling-point or solid state). 



Mercury y 103 to 106. — This must be regarded as a minimum ; 

 for a considerable quantity of mercury condenses at the orifice of the 

 tubes and falls in the interior in droplets. 



Mercurous chloride, 72 to 131, according as we do not, or do, 

 allow for the portion of salt vaporized in the tubes, but condensed 

 at their orifice. This difficulty does not occur in the case of sal-am- 

 moniac, the fumes of which, being very light, are easily carried 

 away by the motion of the air. 



Mercuric chloride, 28 to 45. — These numbers comprise both the 

 latent heat of fusion and that of volatilization. 



Monohydrated sulphuric acid, 292 to 342. — These high numbers 

 seem to justify the hypothesis of the dissociation of this acid as- 

 sumed by Messrs. Wanklyn and Robinson. It may, moreover, be 

 remarked that this heat of volatilization would exactly agree with 

 the heat of combination of anhydrous sulphuric acid and water. 



I must, in conclusion, remark that when I speak of the dissocia- 

 tion of sal-ammoniac or of sulphuric acid, I attach to this term the 

 meaning w r hich M. St. -Claire Deville has given to it — that of a par- 

 tial decomposition, the resultant of a state of equilibrium, varying 

 with the temperature, between the elements of a body and the com- 

 pound they tend to form. The principle of my experiments, and 

 the uncertainty which prevails as to their results, do not justify us 

 in concluding that there is a complete decomposition, which, more- 

 over, seems impossible within the limits of temperature attained in 

 my experiments. — Comptes Rendus, November 2, 1868. 



* This heat of combination, according to MM. Favre and Silbermann, is 

 743*5 thermal units at the ordinary temperature; it would be 715 at a 

 temperature of 350°. 





