102 CLEAYAGE. TJSE OF THE BLOWPIPE. 



instrument on which to rest a mineral which we are desirous 

 of cleaving. Minerals, sometimes, cleave only in one direction, 

 as mica ; sometimes in two, three, or four. As some prac- 

 tice is requisite, it will be expedient to commence with a 

 facile substance, as carbonate of lime, or galena, and proceed 

 to others more complicated and refractory. 



"When the student has gone through this preliminary 

 course of reading, he may enter on the practical examination 

 of his collection. In so doing, he will find it expedient to 

 confine his attention to a few objects at once ; and a single 

 genus, if somewhat extensive, as, for instance, quartz, will 

 afford ample study for the first few lessons. 



USE OF THE BLOWPIPE. Having become acquainted 

 with the laws of crystalline form, and the system of crys- 

 tallography, most generally adopted, as weft as with the 

 general characters of minerals, the student should next 

 examine them by means of the blowpipe. His text-book for 

 this purpose should be a cheap and unpretending little work;* 

 by the guidance of which he will not only acquire the use 

 of that instrument with little trouble, but will soon have 

 no difficulty in satisfying himself of the name and properties 

 of any mineral which may fall in his way. Another work, 

 by the same author, entitled " Chemical Recreations," con- 

 tains some useful tables of the phenomena presented by 

 minerals before the blowpipe, the colour of their beads when 

 fused with the various fluxes, &c., &c. The directions con- 

 tained in these treatises are so simple and judicious, that 

 we shall at once refer to them for farther particulars, and 

 content ourselves with a very few practical observations. 



In the first place, we have ever found the most simple 

 blowpipe to be the best : the common curved brass instru- 

 ment used by jewellers, without a bulb, is what we prefer ; 

 and of these we should recommend two, one with a small 

 orifice for the inner, and one with a larger for the outer 

 flame. With reference to the use of the instrument, our own 

 experience tends to convince us that the difficulty of employ- 

 ing it is much exaggerated. "We add, however, the following 

 directions for those who may require them : 



The great object is to maintain an' equal and steady 



* Griffin's Treatise on the Use of the Blowpipe. 



