40 On the Blow-pipe. [Jan. 



Article IX. 



On the Blow-pipe : from a Treatise on the Blow-pipe by Assessor 



Gahn, of Fahlun. 



The substance to be submitted to the action of the blow-pipe 

 must be placed on a piece of charcoal, or in a small spoon of 

 platina, gold, or silver; or, according to Saussure, a plate of 

 cyanite may sometimes be used. Charcoal from the pine is to 

 be preferred, which should be well ignited and dried, that it may 

 not crack. The sides, and not the ends, of the fibres must be 

 used ; otherwise the substance to be fused spreads about, and a 

 round bead will not be formed. A small hole is to be made in 

 the charcoal, which is best done by a slip of plate iron bent 

 longitudinally. Into this hole the substance to be examined 

 must be put in very small quantity ; if a very intense heat is to be 

 used, it should not exceed the size of half a peppercorn. 



The metallic spoons are used when the substance to be exa- 

 mined is intended to be exposed to the action of heat only, and 

 might undergo some change by immediate contact with the 

 charcoal. "When the spoon is used, the flame of the blow-pipe 

 should be directed to that part of it which contains the substance 

 under examination, and not be immediately applied to the sub- 

 stance itself. The handle of the spoon may be inserted into a 

 piece of charcoal ; and if a very intense heat is required, the 

 bowl of the spoon may be adapted to a hole in the charcoal. 

 Small portions may be taken up by platina forceps. Salts and 

 volatile substances are to be heated in a glass tube closed at one 

 end, and enlarged according to circumstances, so as to form a 

 small matrass. 



When the alteration which the substance undergoes by the 

 mere action of heat has been observed, it will be necessary to 

 examine what further change takes place when it is melted with 

 various fluxes, and how far it is capable of reduction to the 

 metallic state. 



These fluxes are, 



1 . Microcosmic salt ; a compound of phosphoric acid, soda, 

 and ammonia. 



2. Subcarbonate of soda, which must be free from all impu- 

 rity, and especially from sulphuric acid, as this will be decom- 

 posed, and sulphuret of soda will be formed, which will dissolve 

 the metals we wish to reduce, and produce a bead of coloured 

 glass with substances that would otherwise give a colourless one. 



3. Borax, which should be first freed from its water of crys- 

 tallization. 



These are kept powdered in small flasks ; and when used a 

 sufficient quantity may be taken up by the moistened point of a 



