22 



MINERALS AND GEOLOGY 



minerals, when treated with hot nitric acid. The acid gives up part of its 

 oxygen to the dissolving mineral, and the portion of the acid, thus altered, 

 escapes in ruddy fumes. Sulphides and other non-oxidized bodies also cause 

 the evolution of these coloured fumes. Acid cupreous solutions are green or 

 greenish-blue in colour. A piece of polished steel or iron immersed in a 

 diluted solution of this kind, becomes coated with metallic copper. 



(g. ) Solution, or partial solution, and production, with hydrochloric acid, of 

 chlorine fumes. Ex. pyrolusite or black manganese ore, &c. The chlorine is, 

 of course, derived from the decomposition of the acid. Care must be taken 

 not to inhale its fumes. 



(h.) Solution, or partial solution, with production of fluohydric acid in 

 corrosive fumes. Example Fluor spar, in powder, with hot sulphuric acid. 

 The evolved fumes corrode glass. The experiment should be performed in a 

 platinum or lead vessel. If a piece of glass coated on its under side with a 

 thin layer of wax through which a pattern has been traced, be laid over the 

 vessel for a few minutes, and then removed and washed in warm water, the 

 lines of the pattern will be found more or less deeply etched on the surface of 

 the glass. Great care must be taken to prevent the fumes from being inhaled. 



(i.) The substance may remain undissolved and unattacked. Example 

 Quartz, orthoclase, zircon, &c. 



Application of the Blowpipe : The blowpipe in its simplest form 

 is merely a narrow tube of brass or other metal, bent round at one 

 extremity, and terminating, at that end, in a point with a very fine 

 orifice (fig. 26). If we place the pointed end of this instrument just 



within the flame (and a little above 

 the wick) of a lamp or common candle, 

 and then blow gently down the tube, 

 the flame will be deflected to one 

 side in the form of a long narrow 

 cone, and its heating power will be 

 wonderfully increased. Many min- 

 erals, when held in the form of a 

 thin splinter at the point of a flame 

 thus acted upon, melt with the 

 F IG - 26- greatest ease ; and some are either 



wholly or partially volatilized. Other minerals, on the contrary, 

 remain unaltered. Two or more substances, therefore, of similar 

 appearance, may often be separated and distinguished in a moment, 

 by the aid of the blowpipe. 



The blowpipe (in its scientific use) has, strictly, a three-fold appli- 

 cation. It may be employed, as just pointed out, to distinguish 



