340 Remarks on Arse7iic. 



If it is already in the state of arsenious acid, it ought to be boiled, 

 filtered and then tried. 



But if we do not find any substantial matter of arsenic after these 

 trials, we must then conclude that the arsenic has been given in the 

 form of a fluid ; then there is, of course, the greatest necessity to 

 analyze the stomach and its contents. We cut it into very small 

 pieces, boil them in distilled water, with from one to four drachms of 

 caustic potassa, strain the fluid through a white and clean cloth and fil- 

 ter it. Then we obtain a dark fluid, to which we have to apply small 

 portions of nitric acid until the solution assumes a yellowish white 

 color, which is to be neutralized with potassa, and then we shall be 

 ready to apply the tests. 



The analytical chemist has now two methods for ascertaining 

 whether arsenic is in solution or not, these are — 



1 . The hydrochemical way, in which we use the reagents in a 

 fluid state, and then compare the color of the precipitates produced 

 by them with those of arsenic. 



2. The pyrochemical way, which is by means of fire to reduce 

 the arsenic to its metallic state. However, for a strict and correct 

 inquiry, both these methods ought to be tried, because no hydrochem- 

 ical test can serve before the court as an undeniable corpus delicti 

 while the most characteristic indication, namely, the metallic lustre 

 and the garlic smell of the arsenic, which is produced by the small- 

 est quantity of that substance on burning coals can leave no possibility 

 of doubt. 



We proceed now to the hydrochemical tests, and it is, before all, 

 necessary to prepare the precipitates of the tests out of the real arsenic 

 as a standard by which to judge of the precipitates obtained by the 

 fluid of the problematical arsenic. 



Table I, exhibits the colors of the precipitates produced with ar- 

 senious acid by the following tests. 



No. 1. The arsenious acid, in solution, brought into contact with 

 sulphuretted hydrogen, forms a yellow precipitate of sulphuret of 

 arsenic, or orpiment, which easily dissolves again in caustic potassa 

 or ammonia. The precipitate of the sulphuret presents itself very 

 soon, if we add some drops of muriatic or acetic acid. 



No. 2. Ammoniacal sulphate of copper, instantly produces in a 

 solution of arsenious acid, a grass-green precipitate of arsenide of cop- 

 per, or Scheel's green ; but if the fluid contains too much acid, no 

 precipitate is obtained. 



