CHEMICAL TOXICOLOGY 287 



collected on a small filter, washed, dissolved in the minimum 

 amount of dilute nitric acid, most of the acid evaporated off, 

 and a small crystal of potassium iodide added. This gives 

 with lead yellow lead iodide as an amorphous powder, dis- 

 solving on boiling to a colourless solution, which, on cooling, 

 deposits yellow spangles of lead iodide, which are so charac- 

 teristic that their formation is the best test for lead. 



Having removed lead as the sulphide, the liquid is 

 evaporated till free of sulphuretted hydrogen, oxidised by 

 heating with a few drops of strong nitric acid, and ammonium 

 hydrate added in excess. The precipitate always formed 

 contains brown ferric hydroxide and phosphates. If the 

 phosphate is in excess, the precipitate is pale yellow, and a 

 few drops of ferric chloride must be added before the 

 ammonia. In addition to these the precipitate may contain 

 chromium hydroxide, known by its green colour. The 

 filtrate is tested for zinc and manganese by adding ammonium 

 sulphide, which gives colourless zinc sulphide and buff- 

 coloured manganese sulphide as precipitates. 



The residue left after treatment with hydrochloric acid 

 may contain free sulphur, and the black sulphides of 

 mercury, bismuth, copper, and silver. It is to be noted 

 that silver, mercury, and bismuth will have been found in 

 the Eeinsch test. 



Hot dilute nitric acid dissolves the silver, bismuth, and 

 copper. If copper is present in significant amount, the 

 solution will be of a pale, greenish-blue colour. Silver is 

 recognised by adding dilute hydrochloric acid, which pre- 

 cipitates colourless silver chloride. Ammonium hydrate 

 is now added, and precipitates bismuth hydroxide as a 

 colourless flocculent precipitate. The solution is filtered, 

 and the bismuth precipitate washed and dissolved in the 

 minimum quantity of hydrochloric acid. On adding the 

 chloride solution to water, an opalescent turbidity of 

 bismuth oxychloride is produced. The ammoniacal filtrate 

 containing the copper will have a more or less deep, pure 

 blue colour, according to the quantity of copper. It is 

 made acid with acetic acid and potassium ferrocyanide 



