detection of Poisonous Compounds. 339 



and in this manner escape decomposition by the copper. 

 Hence, in every case, or at any rate whenever it is suspected 

 that such changes have taken place under the influence of 

 organic matters, it is better in the first instance to acidulate 

 the substances with hydrochloric acid, and boil them with it 

 for a quarter of an hour ; by which means the organic mer- 

 curial compounds will be decomposed, and the corrosive sub- 

 limate restored : after this, all insoluble matters may be re- 

 moved by straining through calico, the copper introduced, 

 and the process proceeded with as above. On the other 

 hand it must be remembered, that calomel (subchloride) is 

 converted into corrosive sublimate (chloride) by being boiled 

 with hydrochloric acid or an alkaline chloride, such as chlo- 

 ride of sodium. Thus I have found, that when a few grains 

 of pure calomel were boiled for a quarter of an hour in a few 

 ounces of soup, with its usual quantity of salt, corrosive sub- 

 limate could be detected in solution in considerable quantity ; 

 and when submitted to decomposition by the copper turnings, 

 it gave an abundant deposit of metallic mercury in distinct 

 globules : so that, if the possibility of such a transition from 

 the insoluble to the soluble chloride be not kept in view, the 

 previous existence of corrosive sublimate in a suspected sub- 

 stance may be inferred, when in truth it contained only 

 calomel. Dr. Christison alludes to the difficulty likely to 

 arise from the conversion of calomel into corrosive sublimate, 

 in relation to other methods for the detection of mercurial 

 poisons, and says, " that this objection can be obviated solely by 

 sufficient evidence that calomel has not been administered."* 

 When the soluble salts of mercury exist in considerable 

 quantity, mercury will be deposited on copper from the acidu- 

 lated liquid, without the aid of heat ; and then the objection 

 from the possible conversion of calomel into corrosive sub- 

 limate will be entirely obviated. 



* Christison on Poisons, 4th Edit. p. 386. 



