BLOWPIPE RE ACTIONS. 89 



Silver. — If the silver is in very small quantities, as in argen- 

 tiferous galena, the assay is put into a little cup made of bone 

 ashes (bone burnt white and finely pulverized), and subjected 

 to the oxidizing flame ; the lead is oxidized and sinks into the 

 bone ashes, leaving the silver a brilliant globule on the cupel. 

 Before cupellation it is often necessary to melt the assay to- 

 gether with some borax and pure lead in a hole on charcoal. 

 By this process the sand and impurities are removed, and a 

 globule of lead is obtained which contains all the silver, and 

 which may be separated from the slag and be oxidized as 

 above. 



Arsenic. — In the closed tube arsenic sublimes and coats the 

 tube with brilliant grains, or a crust, of metallic arsenic. If 

 the mineral contains sulphur as well as arsenic, sublimates of 

 the yellow and red arsenic sulphides (orpiment and realgar) are 

 often formed. In the open tube a sublimate of white arsenous 

 acid is formed, which condenses in bright crystals on the walls 

 of the tube, and a strong garlic odor is given off. On charcoal 

 the alliaceous odor is at once perceptible. 



Antimony. — In the closed tube, when sulphur is present, the 

 assay yields a sublimate which is black when hot, brown-red 

 when cold. In the open tube dense white vapors are given off 

 and a white amorphous sublimate covers the inside of the tube, 

 which, for the most part, does not volatilize when reheated. 

 On charcoal the assay yields dense, white, inodorous fumes. 



Tellurium. — In the open tube a white or grayish sublimate 

 is obtained, which may be fused to clear, colorless drops. On 

 charcoal a white coating is produced, and the reducing flame is* 

 colored green. 



Sulphur. — All sulphates, and other sulphur-bearing miner- 

 als, when heated on charcoal with soda, produce a dark, yellow- 

 ish brown sulphide of sodium ; and if a fragment of this is 

 moistened and placed on a polished plate of silver, it turns it 

 immediately brownish black, or black. Pure soda, and a flame 

 wholly free from sulphur, is needed for the trial, since the least 

 trace of sulphur in either vitiates the result. Many sulphides 

 give fumes of sulphur on charcoal. The higher sulphides afford 

 these fumes in a closed tube. The others afford fumes of sul- 

 phurous acid in an open tube, which redden a moistened bluo 

 litmus paper placed in the upper end of the tube. 



Selenium. — Selenium and many selenides afford a steel-gray 

 sublimate in an open tube, which at the upper edge appears 

 red. On charcoal '>rown fumes are given off with an odor like 

 that of decaying h( rse-radish. 



