34!^ CONTRIBUTIONS TO BLOWPIPE ANALYSIS. 



This reaction is not affected by copper ; but a precipitation of bis- 

 muth would ensue, in the absence of lead, if either zinc or iron were 

 present. These metals, however, may be eliminated from the test- 

 globule by exposing this on charcoal for some minutes, with a mixture 

 of carb-soda and borax to a reducing flame. The zinc becomes vola- 

 tilized, and the iron is gradually taken up by the borax. If a single 

 operation do not effect this, the globule must be removed from the 

 saturated dark green glass, and treated with further portions of the 

 mixture, until the resulting glass be no longer colored. 



11. DETECTION OF ANTIMONY IN TUBE-SUBLIMATES. 



In the examination of mineral bodies for antimony, the test-sub- 

 stance is often roasted in an open tube for the production of a white 

 sublimate. The presence of antimony in this sublimate may be de- 

 tected by the following process — a method more especially available 

 when the operator has only a portable blowpipe- case at bis command. 

 The portion of the tube to which the chief part of the sublimate is 

 attached, is to be cut off by a triangular file, and dropped into a test- 

 tube containing some tartaric acid dissolved in water. This being 

 warmed or gently boiled, a part at least of the sublimate will be dis- 

 solved. Some bisulphate of potash — either alone, or mixed with some 

 carb-soda and a little borax, the latter to prevent absorption — is then 

 to be fused on charcoal in a reducing flame ; and the alkaline sulphide 

 thus produced, is to be removed by the point of the knife-blade, and 

 placed in a small porcelain capsule. The hepatic mass is most easily 

 separated from the charcoal by removing it before it has time to soli- 

 dify. Some of the tartaric acid solution is then to be dropped upon 

 it, when the well known orange-colored precipitate of Sb S^ will at 

 once result. 



In performing this test, it is as well to employ a somewhat large 

 fragment of the test-substance, so as to obtain a thick deposit in the 

 tube. It is advisable also to hold the tube in not too inclined a posi- 

 tion, in order to let but a moderate current of air pass through it ; 

 and care must be taken not to expose the sublimate to the action of the 

 flame — otherwise it might be converted almost wholly into a compound 

 of Sb O^ and Sb 0^, the greater part of which would remain undis- 

 solved in the tartaric acid solution. A sublimate of arsenious acid, 

 treated in this manner, would, of course, yield a yellow precipitate, 



