288 Means of detecting Arvente in the Animal Body, Se. 
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; 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. ‘T'he me of 
potash is sometimes employed to destroy the carbon after the 
nitric acid has acted upon the animal matter. The sulphuric acid, 
zine 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 evaporate 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 ¢© 
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 W® 
ter, which easily dissolves the arsenic, now in the states of ars 
nite of potash and arsenic acid. Filter, introduce the liquid into 
the apparatus, when we may expect to exhibit the metal upon ® 
porcelain surface. In experimenting upon the urine, the sam? 
steps are to be taken. | : 
The examination of the liver is conducted as follows:—TW° 
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, 
