INTRODUCTION. xxi 



" The outer and larger part of the flame e, (?, c, which is the source of its 

 light, is caused by the full combustion of the gases derived from the oil, 

 wax, or tallow which rises into the wick, and is called the reducing flame^ 

 because, when concentrated upon the substance to be tested, it 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 be observed, &, c, which when acted 

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

 is technically called the oxidizing Jlame^ from its property of imparting 

 oxygen to the substance upon which it is directed. To produce the latter, 

 the point or jet of the blowpipe should be inserted into about a third of the 

 flame, and the assay is then to be held at the 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 the 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 following 

 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. Thin platinum wire and holder. 5th. A magnet. 6th. A few 

 small tubes of thin glass. 7th. Some small porcelain capsules or saucers. 



" Charcoal is required as a support in many cases, particularly in the 

 reduction of ores; and the following re-agents are also indispensable, the 

 three first being fluxes applicable under different circumstances : — 



" 1st. Soda, or carbonate of soda. 



" 2nd. Borax, or borate of soda. 



*' 3rd. Microcosraic salt, or phosphate of soda and ammonia. 



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

 oxides. 



"5th. Borax-glass, for the determination of phosphoric acid and of small 

 quantities of lead in copper. 



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

 oxide 01 zmc. 



" 7th. Oxide of copper for determining small quantities of chlorine in 

 compounds. 



" 8th. Fluor-spar for the recognition of lithia, boracic acid, and gypsum. 



"9th. Lead in a pure metallic state. 



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

 certain argentiferous ores). 



"11th, I2th, and 13th. Hydrochloric, sulphuric, and nitric acids. 



" 14th. Litmus-paper, blue and red, for detecting the presence of acids 

 and alkalies. 



" The experiments on an unknown mineral must be made systematically, 

 and referred for comparison to some list or table of minerals in which their 

 behaviour before the blowpipe is described, as Von Kobell's tables.* 



* Von Kobel, " Tafeln zur Bestiramung der Mineralien, Munchen ;" and the same translated 

 into English by R. Campbell. 



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