ARSENIC. 



211 



FIG. 14. 



7. Heat arsenous 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 becomes, upon 

 heating the solution, coated with a dark steel-gray deposit of arsenic, 

 which can be vaporized by application of heat. 



9. Bettendorff's test. Add to any arsenic compound, dissolved in 

 concentrated hydrochloric acid, an equal volume of freshly prepared 

 solution of stannous chloride in hydrochloric acid, add a small piece 

 of tin-foil, and apply heat : a brown color or precipitate is formed, 

 due to the separation of arsenic. 



10. Gutzeit's test. Place a small piece (about 1 gramme) of pure 

 zinc in a test-tube, add about 5 c.c. of dilute (5 per cent.) sulphuric 

 acid and a few drops of any arsenic solution, which should not be 

 alkaline. Fasten over the mouth of the test tube a cap made of three 

 thicknesses of pure filter paper, and moisten the upper 



paper with a drop of a saturated solution of silver 

 nitrate in water, acidulated with about 1 per cent, of 

 nitric acid. (Fig. 14.) Place the tube in a box so as 

 to exclude all light, and examine the paper cap after 

 awhile. Upon it will appear a bright yellow stain, 

 rapidly if the quantity of arsenic be considerable, slowly 

 if it be small. Upon moistening the yellow stain with 

 water the color changes to brown or black. The action 

 of hydrogen arsenide upon silver nitrate in the absence 

 of water takes place with the formation of a yellow 

 compound, thus : 



AsH 3 + 6AgN0 3 = 3HN0 3 + Ag 3 As.(AgNO 3 ) 3 . 



In the presence of water metallic silver is separated, 

 showing a black or brown color : 



AsH 3 + 6AgNO 3 "+ 6H 2 O = 6HNO 3 + H 3 AsO 3 + 6Ag. 



Compounds of antimony treated in the above manner 

 produce a dark spot upon the paper, but cause no pre- 

 vious yellow color. 



11. Fleitmann^s test. This is similar to the previous 



test, the chief difference being that hydrogen is evolved in alkaline 

 solution, which has the advantage that the presence of antimony does 

 not interfere, because this metal does not form antimonetted hydrogen 

 in alkaline solutions. 



Place about 1 gramme of pure zinc in a test-tube, add about 5 c.c. 



