IN CASES OF POISONING. 271 



they may be easily recognized by means of the charac- 

 teristic reactions given above, after they have been 

 dissolved in a few drops of nitric acid, and the greater 

 excess of acid has been expelled by a very gentle heat. 

 If only traces of arsenic be present, the spots are so 

 feeble that their nature may remain uncertain. The 

 only indication which is perfectly conclusive, is the 

 production, in the red-hot tube, of a metallic mirror, 

 which must volatilize when gently heated, and re-con- 

 dense upon a cool part of the tube, at the same time 

 imparting to the evolved gas the peculiar garlic odor. 



When the arsenical mirror no longer increases, and 

 the flame ceases to deposit the spots, the operation is 

 discontinued. It is then very convenient to draw the 

 tube e gently out, while it is still red-hot and soft, and 

 to close it, when the metallic mirror is obtained in a 

 tube, which may be sealed also at the other end, and 

 laid before the authorities. 



If the analyst have reason to believe that a large 

 quantity of arsenic is present, it is well not to employ 

 the whole quantity of liquid at once, but to divide it 

 into several portions, and to make use of a much lon- 

 ger tube e, so as to obtain the arsenic-mirror in several 

 places. The tube is then cut with a file into as many 

 pieces as there are mirrors of arsenic. That which 

 contains the most characteristic mirror is sealed at 

 both ends and produced in court; the remaining mir- 

 rors are subjected to the tests given at p. 260, among 

 which the ready volatility and alliaceous odor are the 

 most characteristic and decisive. 



If after heating the tube for one hour, no stain or 

 mirror make its appearance, and no traces of spots 

 have been obtained from the flame, the absence of 

 arsenic may be inferred, provided that proper care 

 has been taken in the former part of the examination, 

 so that the arsenic cannot have been lost through neg- 

 ligence or awkwardness. 



