112 Mr. J. A. Wanklyn on Vapour-densities. 



cury, should consist wholly of hydrochloric acid and ammonia in 

 an uncombined state. The mean of the vapour-densities of 

 ammonia and hydrochloric acid being 0'93, whilst the vapour- 

 density of the vapours given off by chloride of ammonium when 

 heated to the boiling-point of mercury has been found to be 

 1*01 (see Deville and Troost's paper in the Comptes Rendus, 

 May 11th, 1863, page 895), it is obvious that these vapours 

 should, strictly in conformity with theory, contain some unde- 

 composed chloride of ammonium. A simple calculation will 

 show that, according to the theory, these vapours should con- 

 sist of 



By weight. 

 Chloride of ammonium .... 17'2 

 Ammonia and hydrochloric acid . . 82*8 



100-0 



On bringing together hydrochloric acid and ammonia at 

 350° C.j we should look for the development of about one-sixth 

 of the heat which would result from complete combination. 



Nothing in M. Deville' s recent paper indicates in any way 

 that there was more than this. As will be apparent on referring 

 to the paper, he agrees with M. Pebal in considering that there 

 was not the evolution of the total amount of heat which com- 

 plete combination would produce, but gives no data from which 

 we are able to form a judgment whether or not more than one- 

 sixth of that amount was evolved. 



The first point that strikes me when I turn to M. Deville's 

 account of his last experiment, is that the condition that the 

 ammonia and hydrochloric acid should have attained the tempe- 

 rature of boiling mercury before they enter the flask in which 

 they come into contact has not been satisfactorily fulfilled. 

 They were sent through the spiral at far too great a rate. 20 

 to 25 litres of each gas per hour is nearly 7 cubic centimetres of 

 each gas per second. The paper informs us that the length of 

 each tube (which was bent into a spiral) was more than 2 metres, 

 the diameter not being given at all. Unless we suppose a very 

 wide tube to have been taken, or that the length very much 

 exceeded 2 metres, each cubic centimetre of gas cannot have 

 remained in the spiral for more than two or four seconds. Is a 

 sojourn of only two or four seconds in this spiral heated to 

 350° C. sufficient to raise the temperature of a cubic centimetre 

 of gas from 20° C. up to 350° C. ? Guarantee that the ammo- 

 nia and hydrochloric acid had reached the temperature of boiling 

 mercury when they entered the flask, there is none. 



The flask in which the gases came together measured from 

 100 to 200 cubic centims. During each second 14 cubic centims. 



