188 METALS AND THEIR COMBINATIONS. 



green). The same reagent produces in neutral arsenic acid 

 solutions a similar green precipitate of cupric arseniate. 



Instead of using for the above tests the ammonic salts, silver 

 nitrate or cupric sulphate may be added to the acid (or neutral) 



FIG. 7. 



solution of arsenic, then adding water of ammonia carefully in 

 small quantities until a neutral reaction has been obtained, when 

 the precipitate is formed. 



5. Soluble arseniates give white precipitates with soluble 

 salts of barium, calcium, magnesium, zinc, and some other 

 metals, soluble arsenites do not. 



6. Heat any dry arsenic compound, after being mixed with 

 some charcoal and dry potassium carbonate in a very narrow 

 test-tube (or, better, in a glass tube having a small bulb on one 

 end): the arsenic compound is decomposed and the metallic 

 arsenic deposited as a metallic ring in the upper part of the 

 tube. (Fig. 7.) 



7. Heat arsenious or arsenic oxide upon a piece of charcoal 

 by means of a blowpipe : a characteristic odor of garlic is 

 perceptible. 



8. Reinsch's test. A thin piece of copper, having a bright 

 metallic surface, placed in a slightly acidified solution of arsenic 

 (nitric acid should not be present) becomes, upon heating the 

 solution, coated with a film of metallic arsenic; the latter may 



