CHEMICAL TOXICOLOGY 285 



The delicacy of the test is extreme, especially for arsenic, 

 of which ^^ grain gives a distinct coating to a quarter 

 square inch of copper, even when mixed with 4 ounces of 

 organic matter. The test is less delicate with mercury, 

 of which quantities much below the bV grain may escape 

 deposition. 



When the coating is at all considerable, that of arsenic 

 has a steel-grey appearance, of antimony purplish -black, of 

 bismuth black, and of mercury and silver the silvery lustre 

 of those metals. When very small quantities are present, a 

 definite stain of indistinct greyish-black tint may alone be 

 given. 



A good qualitative test and distinction is now got by 

 thoroughly washing the coated copper with water and finally 

 with pure alcohol, drying, and heating in a small perfectly 

 dry ignition-tube. Arsenic forms a very characteristic sub- 

 limate of glistening octahedral crystals, easily observed under 

 a low magnification. Antimony gives a white amorphous, or 

 non-crystalline, sublimate. Mercury volatilises in globules 

 of liquid metal. Bismuth is oxidised, but not volatilised, 

 and silver remains unchanged by heat. 



2. For the second process a suitable quantity of material, 

 from 1 to 4: ounces, is mixed in a porcelain dish, with 50 per 

 cent, nitric acid, to a thin paste, and about 1 to 2 c.c of 

 strong sulphuric acid added. The mixture is then warmed 

 over a, small flame with constant stirring. A violent reac- 

 tion, accompanied by the evolution of brown oxides of 

 nitrogen, sets in, and the operation must be conducted in a 

 proper fume chamber. After from twenty minutes to half 

 an hour's heating the liquid will be nearly all evaporated, 

 and will have a brown colour and pasty consistency. No 

 organic tissue remains, but fats are not completely destroyed. 

 If heating is continued, the mass suddenly carbonises with 

 some violence. There is a slight risk of loss if this occurs, 

 but it is not a fatal objection. After carbonisation, which 

 is unnecessary, the solutions are more deeply coloured, but 

 the analysis is not hindered. 



The heated mass is diluted with water, about 100 to 



