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Sect VIIL] 



MINEHALOGY 



247 



flame, because when concentrated upon the substance to be tested, M tends 

 to abstract oxygen from it and thus to reduce it. In the lower part of 

 the flame a narrow stripe of deep blue may \ ' observed, b, c, which when 

 acted on by the current of air from the blowpipe forms a cone, 6, c (B). 

 This is technically called the oxidizing flmne, from its property of 

 imparting oxygen to the substance upon which it is directed. To pro* 

 duce the latter, the point or jet of the blowpipe should be il ned into 

 about a third of the flame, and the assay is then to be held at Ae 

 extremity of the cone of blue flame. For reduction the point of the 

 tube should scarcely penetrate the flame, and the assay should be so 

 placed as to be completely enveloped in it, and thus prevented from 



receiving oxygen. 



A little practice is sufficient to overcome tlie slight difficulty which at 



first is felt in keeping up a continual and even stream of air. The tyro 

 may begin by accustoming himself to breathe through the nostrils 

 whilst his cheeks are inflated, and will soon find it easy to maintain an 

 uninterrupted supply for several minutes. 



Of the instruments used in experimenting by the blowpipe, the follow- 

 ing are the most necessary ; — 1st. A pair of fine-pointed forceps, tipped 

 with platinum. 2nd, A small spoon of platinum. 3rd. An agate pestle 

 and mortar. 4th. Thia platinum w-ire and holder. 5th. A magnet, 

 6th, A few small tubes of thin glass. 7th. Some small porcelain cap- 

 sules or saucers. Charcoal is required as a support in many eases, par- 

 ticularly in the reduction of ores 5 and the following re-agents are also 



under 



circumstances : 



1st, Soda, or carbonate of soda, 



2nd. Borax, or borate of soda, 



3rd. Microcosmic salt, or phosphate of soda and ammonia. 



4th, Saltpetre, to increase the degree of oxidation of certain metallic 



F 



oxides. 



5th. Bovax-glass, for the determination of phosphoric acid, and of 

 small quantities of lead in copper. 



6th. Nitrate of cobalt, in solution, to distinguish alumina, 

 and oxide of zinc. 



7 th, Oxide of copper, for dr' rmining small quantities of chlorine in 



compounds. 



of lithia, boracic acid, and gypstim. 



9th. Lead in a pure metallic state. 

 10th. Bone-ashes (9th and 10th are used for separating the silver from 

 certain argentiferous ores). 



11th, 12th, and 13th. Hydrochloric, sulphuric, and nitric acids. 



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