262 EXAMINATION FOR ARSENIC 



acetate of potassa about as large as a pin's head, when 

 the indescribably offensive and characteristic odor of 

 kakodyl should be evolved. 



7. One or more fragments are finely powdered, 

 under distilled water, the powder rinsed into a small 

 beaker-glass with 20 or 30 drops of water, and the 

 mixture heated nearly to ebullition until the powder 

 is dissolved. A part of this solution is mixed, in a 

 small test-tube, with several drops of solution of nitrate 

 of silver, and afterwards with very dilute ammonia, 

 added drop by drop. In this way, if the substance 

 were arsenious acid, a considerable bright yellow pre- 

 cipitate of arsenite of silver will be produced. An- 

 other portion of the liquid, mixed with several drops 

 of a clear solution of ammonio-sulphate of copper, 

 gives a fine yellowish- green precipitate of arsenite of 

 copper. A third quantity of the solution, mixed with 

 a few drops of hydrochloric acid, and afterwards with 

 several times its volume of sulphuretted-hydrogen- 

 water, gives a bright yellow precipitate of tersulphide 

 of arsenic, which redissolves perfectly on adding am- 

 monia. 



Of all these reactions, the reduction to the metallic 

 state in Nos. 4 and 5 is the most necessary, because it 

 is most characteristic and conclusive. The others are 

 to be viewed rather in the light of superfluous confir- 

 mations, and are only employed when a considerable 

 quantity of substance is at the analyst's disposal. 



II. Arsenic can no longer be perceived by the eye, 

 or mechanically separated, in the solid state, but is 

 contained in a state of solution, or of intimate mixture, 

 in the contents of the stomach, &c. In this case, 

 which is more difficult and of more frequent occur- 

 rence than the preceding, the problem consists in dis- 

 solving and destroying, by appropriate reagents, the 

 whole mass of the organic matter composing the con- 

 tents, the vomited matters, the food, and even the 



