Medico-Legal Application of Riench/s Test for Arsenic. 247 



until it drops off. But the presence of this metal does not hinder 

 the reduction of the arsenious acid, so that they are both thrown 

 down together, the only inconvenience being that more copper 

 is required, and care must be taken that the arsenic be not lost by 

 the falling off of the deposit. If both agents be present, the 

 character of the precipitate upon the copper cannot be considered 

 as a test at all, for it will differ with the proportion of either. But 

 by carrying on the process to the second step, the separation be- 

 comes perfect, for the arsenious acid sublimes away, and the bis- 

 muth remains at the lower end of the tube. In this way, j^th 

 grain of arsenic mixed with T ^th grain of nitrate of bismuth 

 was clearly recognized after sublimation. This impurity is not 

 however often to be expected in the fluids under consideration. 



Antimony. — The entire separation of this substance from arse- 

 nic, by the method proposed, forms one of its chief advantages. 

 If tartar emetic be present, it will not in any way affect the cop- 

 per until hydrochloric acid is added. The first consequence of 

 the introduction of the acid into the fluid, is the precipitation of 

 the oxide of antimony, which it afterwards dissolves. From this 

 solution the metal is rapidly deposited in the form of a gray 

 crust, very much resembling that formed when arsenic alone is 

 present in small quantity, but unlike the latter substance there is 

 no darkening, or falling off of the antimonial crust. It is an ex- 

 ceedingly delicate test for antimony alone ; but when arsenic is 

 also present, the appearances depend upon the proportion of one 

 to the other. 



In subliming, arsenious acid is separated ; this takes place at 



380° Fall., long before the fusion of antimony at 800° Fah., which 



is nearly a red heat. In the case before us, more care than usual 

 must be devoted to the heating of the tube, so that the melting 

 point of antimony be not exceeded. This furnishes us with an 

 additional argument in favor of carrying the process to the second 

 stage, before an opinion can be formed upon sufficient grounds. 



Mercury acts much more readily on copper than any of the 

 preceding metals. If corrosive sublimate be present in the solu- 

 tion, it attacks the strips without assistance of any acid. The 

 deposition of mercury takes place without heat, but boiling has- 

 tens the process. Under these circumstances, arsenic does not 

 fall down, however great the quantity present. The mercurial 

 deposit is at first gray, and afterwards, as the amount increases, 

 presents all the physical characters of the metal, so that it can- 



