138 POISONS I THEIR EFFECTS AND DETECTION. [§ I 42 . 
water renders it not easy of detection by dialysis ; but its very insolubility will aid 
the analyst, for the contents of the stomach may be treated with water, and thus all 
soluble salts of the alkalies extracted. On now microscopically examining the in¬ 
soluble residue, crystals of bitartrate, if present, will be readily seen. They may be 
picked up on a clean platinum wire and heated to redness in a Bunsen flame, and 
spectroscopically examined. After heating, the melted mass will have an alkaline 
reaction, and give a precipitate with platinic chloride. All other organic salts of 
potassium are soluble, and a white crystal giving such reaction must be hydro- 
potassic tartrate. 
Ammonium Salts. —If the body is fresh, and yet the salts of ammonium present 
in large amount, it is safe to conclude that they have an external origin ; but there 
might be some considerable difficulty in criminal poisoning by a neutral salt of 
ammonium, and search for it in a highly putrid corpse. Probably, in such an 
exceptional case, there would be other evidence. With regard to the quantitative 
separation and estimation of the fixed alkalies in the ash of organic substances, 
the reader is referred to the processes given in Foods, pp. 96 etseq., and in the present 
work, p. 131. 
