INSTRUMENTS AND ( IIKMK AL TESTS 585 



On the outer edge, when- tin- mat is thin, it appears bluish, due 

 to the black coal showing through the thin white film. Tin- anti- 

 mony coat is volatile and may be driven from the coal with either 

 flame, but with more difficulty than the arsenic coat, which it 

 very closely resembles. If a well-pointed O. F. about an inch 

 lon; is blown and the eoat brought up quickly to the middle of 

 the flame and in a slanting position, the coat will volatilize and 

 at the same time color the flame a yellowish green. This flame 

 coloration serves to distinguish antimony from arsenic. 



Illustration. Use stibnite, Sb 2 Ss. 



Arsenic, As. Atomic weight, 75. Fusing point, 450 C. 



(i. Compounds of arsenic when heated in the O. F. on coal 

 oxidize ; when heated in R. F. volatilize yielding a white oxide coat, 

 AszOs, which settles on the coal at a distance from the assay. It is 

 very similar to the white coat yielded by antimony, but when treated 

 with the O. F. the flame is not colored green. Arsenical vapors 

 as they rise from the assay, especially after heating in R. F., yield 

 a garlic-like odor, very characteristic. In case the mineral con- 

 tains sulphur, it is mixed with several volumes of soda to retain 

 the sulphur, when the arsenic odor is easily detected. 



6. Arsenic mirror. Fusible and volatile compounds of arsenic 

 are mixed with coal dust ; infusible compounds must be mixed 

 with soda and coal 



dust. The mixture, d 



in either case, is placed 

 in the bottom of a 

 narrow closed tube, 

 also a small fragment 

 of coal is placed on 

 top of the charge, the 

 0. F. is now directed 

 upon this fragment of i ,,,. 534. 



coal first until it glows, 



then the assay is heated. Arsenic is reduced and condenses as 

 a metallic mirror on the cold walls of the tube. If the amount 

 of arsenic is small, the closed tube should be drawn out at the 

 bottom as represented in Fig. 534, in which d is the mirror. 



The mirror may be further tested to distinguish it from anti- 

 mony, in which the bottom of the tube. is broken off; the mirror 

 is now heated in the Bunsen flame ; the arsenical odor may be 

 detected by quickly smelling the fumes as they escape from the 



