46 MINERALS AND GEOLOGY 



tion 7). If gold and silver be present together, the bead is generally 

 more or less white. By fusing it in a small platinum spoon with 

 bisulphate of potash, the silver dissolves, and the surface of the 

 globule becomes yellow. If the globule be flattened out into a disc 

 on the anvil, before treatment with bisulphate of potash, the silver 

 is more rapidly extracted. The sulphate of silver must be removed 

 by treating the spoon, in a porcelain or platinum capsule, with a small 

 quantity of water, over the spirit lamp. By evaporation, and fusion 

 of the residuum with carb. soda on charcoal, metallic silver can be 

 again obtained. 



Group 2. Yielding infusible metallic grains, without deposit on the 

 charcoal : 



Platinum. Iron. Nickel. Cobalt. 



Platinum is not attacked by the blowpipe fluxes. Iron, Nickel, 

 and Cobalt, are readily dissolved by fusion with borax or phosphor- 

 salt, producing a coloured glass (see under Borax, page 34, above.) 

 These metals are also magnetic. As a general rule, if a substance 

 become attractable by the magnet after exposure to the blowpipe, the 

 presence of iron may be inferred, cobalt and nickel compounds being 

 comparatively rare. The presence of cobalt is readily detected by the 

 rich blue colour of the borax and phosphor-salt glasses, in both an 

 oxidating and reducing flame ; but if much iron be present also, the 

 glass is blueish-green. With borax in the R. F., nickel compounds 

 give reduced metal, and the glass becomes grey and troubled. It is 

 also attracted by the magnet. 



Group 3. Yielding metallic globules, with white or yellow deposit 

 on the charcoal. 



Tin. Lead. Bismuth. Antimony. 



Tin and Lead give malleable globules. The sublimate formed by 

 tin, is white, small in quantity, and deposited on, and immediately 

 around, the globule. The lead sublimate is yellow, and more or less 

 copious. Bismuth and Antimony give brittle globules. The bismuth 

 sublimate is dark yellow ; the antimony sublimate, white, and very 

 abundant. Lead imparts a clear blue colour to the flame-border ; 

 Antimony, a greenish tint. As a general rule, a yellow deposit on 

 the charcoal may be regarded as indicative of the presence of lead ;* 



* Some lead compounds per se give a white or greyish sublimate ; but if the test-substance 

 be mixed with carb. soda, the sublimate is always yellow. 



