354 METALS AND THEIR COMBINATIONS. 



with a dark steel-gray deposit of arsenic, which can be vaporized by 

 application of heat. Antimony also responds to this test. 



9. Bettendorf's test, U. S. P. Add to any arsenic compound, dis- 

 FIG 45 solved in concentrated hydrochloric acid, an equal vol- 

 ume of freshly prepared saturated solution of stannous 

 chloride in concentrated hydrochloric acid, and heat in 

 boiling water for 15 minutes ; a brown color or precipi- 

 tate is formed, due to separation of the arsenic. Anti- 

 mony does not respond to this test. 



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. 45.) 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 com- 

 pound, thus : 



AsH 3 + 6AgNO 3 = 3HNO, -f Ag 3 As.(AgNO 3 ) 3 . 



In the presence of water metallic silver is separated, showing a 

 black or brown color : 



AsH 3 + 6AgN0 3 + 3H 2 =-- 6HNO, + H 3 AsO 3 + 6Ag. 



Compounds of antimony treated in the above manner produce a 

 dark spot upon the paper, but cause no previous yellow color. 



Modified Gutzeit's test, U. S. P. This is employed in nearly all 

 instances in the U. S. P. where traces of arsenic are tested for in official 

 products. It cannot be used in the case of bismuth or antimony 

 compounds, for which Bettendorf's test is employed. The test is 

 carried out as follows : 



All the tests for arsenic bearing proper names are intended to be 

 applied for the detection of minute quantities of arsenic. If arsenic 



