of Arsenic i?i Cases of Poisoning. 389 



where it is beyond the flame, in the shape of a shining, dark me- 

 tallic^ing, which, by gentle heating, can be driven farther for- 

 ward ; and thus more is accumulated, by which it acquires a 

 higher lustre. The small diameter of the tube prevents all cir- 

 culation of air, so that no part of the metal is reduced. It only 

 remains to determine the arsenic by its smell. This is effected, 

 if we cut the tube between the charcoal and the metal, then heat 

 it gently in the place where the metal rests, while we hold our 

 nose over it but at a little distance. 



The second case occurs, when no visible grains of arsenic are 

 present, as in those instances where death has been caused either 

 by solution of arsenic, or by finely pounded arsenious acid. 

 When the poisoning has been caused by the solution of arsenic, 

 it is often impossible to detect the arsenic, because the solution 

 has been carried off before ^ death. If, however, some portion 

 of it still remains, it is discovered by heating the contents of the 

 stomach, at a boiling heat, with caustic potash, and then with 

 muriatic acid. The filtered fluid is reduced, by evaporation, to 

 a smaller volume ; and, if necessary, again filtered, and then a 

 stream of sulphuretted hydrogen passed through it. The fluid 

 is now heated, to cause the precipitate to collect, or evaporated, 

 if it does not subside until it does, and then filtered *. If the 

 quantity of precipitate is so small that it cannot be mechanical- 

 ly removed from the filter, it must be removed from the paper 

 by means of caustic ammonia, and the fluid evaporated in a 

 watch-glass. The sulphuret of arsenic can be oxidized in twa 

 ways : either it is dissolved in a little aqua regia, until all the ar- 

 senic is converted into arsenic acid, the fluid freed from sul- 

 phur, dried by a gentle heat, then the residuum dissolved in a 

 drop of water, and supersaturated with lime-water : Or, bet- 

 ter, we mix the sulphuret of arsenic with saltpetre and defla- 

 grate the mixture at the end of a hermetically sealed glass-tube. 

 We first melt a little saltpetre in the tube, and then gradually 



• If the quantity of arsenic is very small, the fluid becomes yellow, with- 

 out precipitation ; but if it is then evaporated, the sulphuret of arsenic falls 

 in proportion as the acid concentrates during evaporation. If the fluid be- 

 comes yellow, without any precipitation of sulphuret of arsenic, during the 

 evaporation, it cannot be considered as a sign of the presence of arsenic. This 

 colour almost always occurs when the fluid contains nitric acid, which reduced 

 to the state of nitrous acid, colours the dissolved animal substances yellow. 



