REDUCTION TEST OF ARSENIC. 635 



is formed upon the surface of the plate, in a few seconds, sup- 

 posing the gas to contain arsenic, or if a cold object of glass be 

 held over the flame, at a small height above it, a white sublimate 

 of arsenious acid condenses upon the glass. But if the zinc 

 employed contains no arsenic, neither of these effects is produced. 

 The zinc being proved to be free from arsenic, a portion of the 

 liquor to be tested, is introduced into the lower bulb, in addi- 

 tion to the acid and zinc already there ; and when the bulb comes 

 again to be filled with hydrogen gas, the latter is burned and 

 examined precisely as before. If the liquor is loaded with 

 organic matter, as generally happens with the liquids sub- 

 mitted to examination in actual cases of poisoning, the gas may 

 be filled with froth, and the evolution of it very slow. But in 

 the course of a night, the gas is generally obtained in sufficient 

 quantity, and in a proper state, to permit of an examination of it. 

 Where the gas is evolved freely and without frothing of the 

 liquid, a plain bottle with a cork and glass jet will be sufficient 

 for this reduction experiment. Then also instead of burning the 

 gas at the jet, it may be allowed to escape by a horizontal tube, 



such as that in the figure, a por- 

 tion of which is heated to redness 

 by a spirit lamp ; the arsenic con- 

 denses within the tube, beyond 

 the flame and nearer the aperture, 

 and forms a metallic crust. Or 

 the extremity of this tube may 

 be allowed to dip in a solution of 

 nitrate of silver, by which the 

 arsenietted hydrogen is .con- 

 densed, and a black bulky pre- 

 cipitate of arseniuret of silver 

 formed. This precipitate, when dried and heated in a glass 

 tube, affords a white sublimate of arsenious acid, which may 

 afterwards be dissolved by boiling in a small quantity of dis- 

 tilled water, containing a single drop of ammonia, and the 

 solution tested for arsenious acid by nitrate of silver and sul- 

 phate of copper. (Liebig, Clark). 



When the liquid examined contains antimony, that metal 

 combines with the nascent hydrogen, and comes off as antimo- 

 nietted hydrogen, a gas which when burned, or when heated in 

 a glass tube, gives the metal and a white sublimate, in the same 



