288 Means of detecting Arsenic in the Animal Body, Sfc. 



The use of the nitric acid is to carbonize the animal matter, 

 and in that way to develope any arsenic that it may contain. 

 This process is of vast importance, as will be seen by the follow- 

 ing example. Let the liver contain the largest quantity of arse- 

 nious acid that can reach it by the process of absorption, and it 

 may be boiled for six hours, in distilled water, without giving up 

 the smallest portion of the poison ; whereas, carbonize it first by 

 the aid of nitric acid, and then pour the water upon it, and re- 

 sults of an entirely different nature will be obtained. There are, 

 no doubt, two reasons for the cause of this j the first is, that the 

 arsenious acid has undergone some chemical change, which ren- 

 ders it insoluble ; the second is, that the liver is completely broken 

 up by the nitric acid, and the arsenic, in whatever state it may 

 have existed, is now converted into arsenic acid. The nitrate of 

 potash is sometimes employed to destroy the carbon after the 

 nitric acid has acted upon the animal matter. The sulphuric acid, 

 zinc and water, are the elements of Marsh's apparatus. 



The fluid of the stomach and intestines should be first experi- 

 mented upon ; and this may be introduced into the apparatus 

 either in its crude state, or after having undergone carbonization 

 by heat or nitric acid. If it be employed uncarbonized, we may 

 expect a great quantity of froth, which may be obviated in some 

 measure by the means already mentioned. When we carbonize 

 the matter by heat, it becomes necessary to introduce a small por- 

 tion of pure caustic potash during its evaporation, which combines 

 with arsenious acid, forming arsenite of potash, a substance not 

 easily volatilized. If nitric acid be used, we first eva.porate the 

 liquid to dryness, then pour upon it two or three times its bulk of 

 nitric acid, and again evaporate to dryness, when we may ex- 

 pect an almost complete destruction of the animal substances. 

 The carbonized matter, formed either by heat or nitric acid, with 

 whatever it may contain, is digested for a little while in pure wa- 

 ter, which easily dissolves the arsenic, now in the states of arse- 

 nite of potash and arsenic acid. Filter, introduce the liquid into 

 the apparatus, when we may expect to exhibit the metal upon a 

 porcelain surface. In experimenting upon the urine, the same 

 steps are to be taken. 



The examination of the liver is conducted as follows: — Two 

 or three pounds of it are first dried by a gentle heat, and then 

 digested with about three times as much nitric acid by weight, 



