302 



On Chemical Tests. 



[Oci. 



the suspected substance in very dilute sulphuric acid, and introducing 

 a slip of pure zinc. The hydrogen is evolved in combination with the 

 metallic arsenic, and on examination presents most distinct and remark- 

 able phenomena. If ignited, the flume is of a leaden blue colour, and 

 diffuses a powerful smell of garlic and a dense white smoke. If the 

 flame be reduced to the size of a'pea and applied to the interior of a thin 

 glass tube, a crust of metallic arsenic is formed in the tube, surround- 

 ed by a white ring of arsenious acid. To this, by a little dexterous 

 management, the several tests may be applied, namely the ammoniacal 

 nitrates of silver and copper, and (he sulphuretted hydrogen gas. But 

 this process is not entirely distinctive of aH the arsenical poisons; and 

 tartarized antimony gives almost the same indications upon testing, as 

 the arsenical solutions. 



k. Dr. O'Shaughnessy examined the contents of the stomach of a 

 young woman who had been poisoned with crystallized yellow orpi- 

 manr, (sulphuret of arsenic) but the yellow powder which was se- 

 parated from the contents of the stomach when treated Jby the 

 above process gave no indication whatever of the presmce of arsen- 

 ic. He then converted the sulphuret into an oxide, namely, by boiling 

 the yellow matter with a few drops of nitric acid, and after the sulphu- 

 ret was thus converted into arsenious acid, the process, when applied 

 gave its proper indications. In examinations by this process the Pro- 

 fessor therefore recommends that the insoluble contents of the stomach 

 or a part of these contents in cases of poisoning, should be boiled in a 

 capsule of glass or porcelain with small quantises of nitric acid until 

 red fumes are no longer given off. The mass should then be diluted 

 with water, neutralized with carbonate of potash or soda, and lastly ex- 

 amined by Marsh's process. 



m. With respect to the indications of tartarized antimony, or tartar 

 emetic, Dr. O'Shaughnessy suggests that the encrusted tube when cold 

 should be moistened with a solution of nitrate of silver in distilled 

 water, and then be held over the mouth of a bottle containing strong 

 ammonia, so that the vapour may traverse the tube. If the crust be 

 arsenical it instantly assumes a vivid canary colour, owing to the forma- 

 tion of arsenite of silver; but no such effect is produced by antimoniai 

 compounds. This test therefore affords a simple and conclusive check 

 on Marsh's process. 



n. N^te. — The zinc of commerce often contains arsenic : the zinc 

 used should therefore be tested ; and the same zinc should not be 

 twice used for the same purpose. 



BARYTES or Bari/ta,when pure is of a greyish white colour,and 

 very friable. It slakes like lime, falling into a powder with heat 



