detection of Poisonous Compounds. 335 



from the matters to be examined; and either reduced to 

 the metallic state by the ordinary methods, or be dissolved 

 in boiling distilled water, and the solution tested in the usual 

 way. But, if no evidence of the presence of arsenic be thus 

 obtained, then all the soft solids should be cut in small 

 pieces, and these, with the liquids, or with distilled water, 

 should have pure hydrochloric acid added to them till it is 

 decidedly in excess. The whole should then be boiled for an 

 hour till all soft solids are either dissolved or broken down 

 into fine flakes or grains : the mixture should then be strain- 

 ed through calico, brought to the boiling point, and, whilst 

 boiling, pure copper turnings, copper leaf or wire should be 

 introduced into it, and the boiling continued for about forty 

 minutes ; it being ascertained from time to time that there 

 is an excess of acid. The copper is then to be removed, 

 washed with distilled water, and dried. It is then found, if 

 arsenic had been present, to have acquired a metallic coating 

 of an iron-grey colour ; or when the arsenic is in extremely 

 small quantity, a violet or blue tint, somewhat similar to the 

 colour of watch springs.* The copper thus coated with me- 

 tallic arsenic is then to be introduced into a tube about the 

 eighth of an inch in width, and heated by a spirit lamp, when 

 a metallic sublimate will quickly be deposited in the cooler 

 part of the tube. If, however, the quantity of arsenic be very 

 minute, it is possible that it may be sublimed as white arsenic : 

 and if the sublimation be performed in a wider tube (quarter 

 or half inch,) the whole of the arsenic will be oxydized and 

 deposited as arsenious acid. When this is the case, the 

 copper being removed, the arsenious acid may be dissolved in 

 distilled water, and subjected to the three most characteristic 

 tests: the ammoniaco-nitrate of silver, the ammoniaco-sul- 

 phate of copper, and sulphuretted hydrogen. 



* The following formula represents the decomposition effected by the cop- 

 per : — 



As 03, SHCl,3 Cu. =3CuCl,SH 0, As. 



2 x 



