BLOWPIPE APPARATUS. 27 



made use of. The substance should be very finely powdered 

 and mixed with slightly moistened carbonate of soda, then 

 placed in the cavity of the charcoal, and a gentle heat applied 

 to it in order to drive off moisture ; afterwards the tempera- 

 ture should be considerably increased. Not only must the 

 colour of the incrustation be noticed, but also the fused 

 substance along with some of the charcoal ought to be 

 removed, and ground up with a little water in an agate or 

 porcelain mortar. More water should be added, and the 

 whole mixed up ; the water, together with the lighter matter, 

 should be poured off very carefully, which may be done 

 with the help of a small glass rod or pencil placed at the 

 side of the tilted-up mortar, so as to allow the water to run 

 gradually down the side. The residue at the bottom of the 

 mortar is thus ready for examination, and the metallic frag- 

 ments, if any, will be seen by the naked eye or a magnifying- 

 glass as glistening spangles or as powder. 



When there is no incrustation, the metals gold, silver, 

 and copper if present, yield glistening beads, and iron, 

 nickel, cobalt, leave a magnetic grey powder. 



Should there be an incrustation, the General Table C 

 must be consulted, though each of the metals silver, tin, 

 lead, antimony may be recognised in the residue by its 

 characteristic appearance. As a rule, one ought not to rely 

 upon the treatment with carbonate of soda, rather confirm 

 by that with borax and microcosmic salt. 



The usual fluxes, borax and microcosmic salt, readily dis- 

 solve metallic oxides at a high temperature. In order to 

 make sure that the substance is in the state of oxide, it 

 should be exposed to a gentle heat and roasted, in order to 

 drive off sulphur or arsenic associated with metals in the 

 mineral. 



To treat with either of these fluxes, bend the end of a 

 small platinum wire round the point of a pencil into a loop 

 of this shape, but smaller in size 



D 



Fio, 23. 



