338 DISSOCIATION OF SAL-AMMONIAC. 



An Experiment 



By WILLIAM A. TILDEN. 



WHEN sal-ammoniac is volatilised the vapour contains both 

 hydrochloric acid and ammonia gases in the free state^ 

 the extent to which the dissociation proceeds depending upon the 

 temperature. This fact was demonstrated originally by Pebal, by 

 means of an experiment in which advantage is taken of the 

 smaller density and, consequently, more rapid diffusibility of 

 ammonia. The following is a modification of the experiment 

 which renders it very easy and readily available for lecture 

 purposes. 



The stem of a long clay tobacco pipe is passed loosely through 

 a couple of perforated corks fitted into the two extremities of a 

 piece of ordinary combustion tubing about a foot long. The 



' tube contains in the middle a small lump of sal-ammoniac, and 

 neaDcach end a strip of blue litmus paper. When the middle of 

 the tube is heated the vapour of the sal-ammoniac surrounds a 

 portion of the pipe stem. If, now, a rapid stream of air or any 

 other indifferent gas is sent through the pipe, it is found on 



. escaping to be strongly charged with ammonia, which may be 

 recognised by all the usual tests. At the same time the litmus 

 papers contained in the glass tube become red owing to the 

 accumulation of hydrochloric acid in the residue. 



