286 VETEEINAEY TOXICOLOGY 



• 

 150 c.c, stirred well to disintegrate solid fatty matter, 

 allowed to cool thoroughly, filtered, and the fatty residue 

 washed with water. The pale yellow liquid now contains 

 all the poisonous metals, except barium, whose sulphate is 

 insoluble in dilute nitric acid. If barium is to be looked 

 for, the sulphuric acid must be omitted, in which case the 

 metal is in solution along with the others. 



The acid solution is now made strongly alkaline with 

 ammonia, whereby the colour changes to dark brown, and 

 pure sulphuretted hydrogen bubbled into the warm liquid. 

 A little yellow ammonium sulphide is added, and the liquid 

 is filtered. The precipitate may contain sulphur, sul- 

 phides of lead, mercury, silver (bismuth), copper, zinc, man- 

 ganese, and iron ; phosphates of calcium and magnesium, 

 and phosphate or hydroxide of chromium. Arsenic and 

 a;ntimony sulphides are soluble in ammonium sulphide, as 

 also is organic matter. After washing the precipitate, it is 

 therefore free from organic impurities, and may be dealt 

 with according to the ordinary methods of qualitative 

 analysis. 



Iron in the form of black ferrous sulphide, sulphur, and 

 phosphates (chiefly of calcium), are always present, and 

 the other compounds named above may also be in the pre- 

 cipitate. 



By passing hot dilute hydrochloric acid repeatedly through 

 the filter, there are dissolved iron, phosphates, chromium, 

 zinc, manganese, and lead. When, however, lead sulphide 

 is present in considerable quantity, the sparingly soluble 

 lead chloride forms needle-shaped colourless crystals on the 

 paper and in the filtrate. Dilute hydrochloric acid also 

 dissolves traces of copper and bismuth. 



The dilute hydrochloric acid solution is concentrated 

 until nearly all the free acid has been volatilised, the liquid 

 diluted, and sulphuretted hydrogen solution added. Lead 

 is precipitated as black sulphide, but with small quantities 

 of the order of ^^^r grain a yellow to brown coloration 

 only is produced. In order to further characterise it, and 

 to distinguish from copper and bismuth, the precipitate is 



