USE OF THE BLOWPIPE. 



59 



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The mineral is supported in the flame, either on cha>voal 

 or by means of steel forceps, (fig. 103,) with platinum ex- 

 tremities (a b) ; the forceps are opened by pressing 103 

 on the pins p p. The charcoal should be firm 

 and well burnt. Charcoal is especially necessary 

 when the reduction of the assay needs the presence 

 of carbon ; and platinum when simple heat is re- 

 quired. Platinum foil for enveloping the mineral, 

 and small platinum cups are also used. When 

 nothing better is at hand, the mineral mica or kyan- 

 ite may be employed. ■ The fragment of mineral 

 under trial should be less than half a pea incize, ' 

 and often a thin splinter is required. '£*44ts*~h\*-> 



To test the presence of water or a volatile ingre- 

 dient, the mineral is heated in a glass tube or test 

 vial. The tube may be three or four inches long 

 and as large as a quill. The flame is directed 

 against the exterior of the tube beneath the assay, 

 and the volatilized substance usually condenses in 

 the upper part of the tube. By inserting into the 

 upper end of the tube a strip of litmus or other 

 test paper, it is ascertained whether the fumes are 

 acid or not. 



Some species require for fusion the aid of what are 

 caMedjluxes. Those more commonly used are borax, 

 salt of phosphorus, and carbonate of soda. They 

 are fused to a clear globule, to which the mineral is 

 added ; or powdered and made up into a ball with 

 the moistened mineral in powder. In this way 

 some minerals are fused that cannot be attacked 

 otherwise, and nearly all species, as they melt, un- 

 dergo certain changes in color, arising Irom changes 

 in composition, which are mentioned in describing 

 minerals. 



The above mentioned fluxes also are often required in 

 order to obtain the metals from the metallic ores. On heat, 

 ing a fragment of copper pyrites with borax, a globule of 

 copper is obtained ; and tin ore heated with soda yields a 

 globule of tin. 



■ 



What instruments or appliances are used for holding minerals before 

 the blowpipe 1 How is the presence of water ascertained 1 How may 

 its acidity be tested 1 ? How are the common luxes employed, and 

 what is their use 1 



