588 MINERALOGY 



Sodium sulphide, Na 2 S, will be formed, soluble in water. The 

 fusion is cut away from the coal and placed on a bright silver 

 surface, a coin will answer, and moistened with a couple of drops 

 of water. The dissolved sodium sulphide attacks the silver, form- 

 ing a brown or black stain of silver sulphide. 



c. Wet test for sulphates. The substance if insoluble in acid 

 is fused on coal in O. F. with 4 parts of soda, dissolved in boiling 

 water and filtered ; to the filtrate, a few drops of barium chloride 

 are added, when, if sulphates are present, a white precipitate of 

 barium sulphate, BaSO 4 , will form. 



Illustration. For tests in a and 6, use pyrite, FeS 2 ; for c, use 

 gypsum, CaS0 4 . 2 H 2 O. 



Chlorine, Cl. Atomic weight, 35.45. Fusing point, 102 C. 



a. Flame test. Copper oxide is dissolved in the S. Ph. bead. 

 The hot bead is touched to the powdered substance to be tested 

 for chlorine ; it is now held just within the blue cone of the O. F. ; 

 if chlorine is present, an azure-blue copper chloride flame will 

 appear. 



b. Wet test: The substance to be tested is dissolved in nitric 

 acid, if insoluble it is fused with soda and boiled in water ; to the 

 clear solution a drop or two of a silver nitrate solution is added, 

 when if chlorine is present, a white precipitate of silver chloride 

 will form, which on exposure to light becomes violet and finally 

 black. Bromine and iodine yield the above reaction also, except 

 the precipitate is yellowish. 



c. Separation of chlorine, bromine, and iodine. The silver 

 precipitate is collected on a filter, and washed with dilute ammonia ; 

 silver chloride and silver bromide are dissolved, leaving the silver 

 iodide on the filter, which is tested according to d. The filtrate 

 is made acid with nitric acid ; the bromide and chloride of silver 

 filtered and tested for bromine as under bromine, c. 



Illustration. Use halite, NaCl. 



Bromine, Br. Atomic weight, 79.92. Fusing point, 7.3 C. 



a. Flame test. Compounds of bromine when treated as in 

 chlorine, a, with copper oxide also yield a blue flame. 



6. Bromides are precipitated with silver nitrate as silver bro- 

 mide, AgBr, a slightly yellowish precipitate soluble in ammonia. 



c. If silver bromide is mixed with bismuth sulphide and heated 

 gently in the closed tube, it will yield a sublimate of yellow bismuth 

 bromide directly above the assay. Silver chloride under the same 

 conditions will yield a white sublimate of bismuth chloride. 



