326 Analysis of Scientific Books. 



being heated in a species of inflammable gas. If in this opera- 

 tion the assay become covered with soot, it is a proof that the 

 flame is too smoky, which considerably diminishes the effect of 

 the blast. Formerly, the blue flame was considered as the pro- 

 per one for the reduction of oxides, but this idea is erroneous ; 

 it is in reality the brilliant part of the flame which produces de- 

 oxidation; it must be directed on the assay so as to surround 

 it equally on all sides, and defend it from the contact of the 

 air. 



" A very advantageous mode of practice, in order to acquire 

 the art of making a good reducing flame, is to fuse a small grain 

 of tin, and raise it to a reddish white heat on a piece of charcoal, 

 so that its surface may always retain its metallic brilliancy. 

 Tin has so great a tendency to oxidation, that the moment the 

 flame begins to become an oxidating one, it is converted into an 

 oxide of tin, which covers the metal with an infusible crust. We 

 must begin by operating on a very small grain, and gradually 

 proceed to larger and larger. The greater the quantity of tin 

 that he can thus keep in a metallic state, at a high temperature, 

 the more expert is the operator in his art." 



The supports are charcoal, platinum foil, platinum wire, plates 

 of mica, glass tubes, open at both ends, and glass matrasses. 



The best of these, except in particular cases, is the platinum 

 wire ; and we can confirm, by our own experience, its superior 

 convenience. " The diameter of the platina wire is arbitrary ; 

 the finest is the best, provided it be thick enough not to bend 

 with the blast ; if too thick, it absorbs too much heat." We 

 find a wire of 1 — 100th of an inch in diameter, answer the pur- 

 pose excellently. The mode of using it is thus described : It is 

 to be " bent at one end into a hook, which serves as the sup- 

 port in the following manner. Having moistened the hook with 

 the tongue, it is to be dipped into the flux, a portion of which 

 will adhere to it ; this is to be fused by the lamp into a globule, 

 which congeals and adheres to the curvature ; the assay must 

 then be moistened, to make it adhere to the flux, which is now 

 solid, and the whole heated together. We thus obtain an in- 

 sulated mass, which may be conveniently examined without 

 danger of our being deceived by the appearances which some- 

 times ensue on charcoal from the play of colour, when the 

 assay globule is detached on a black ground. This method is 

 much superior to either of the preceding, and so completely 

 answers the purpose, that, in most cases, the platina wire is 

 preferable to charcoal, especially when the reduction of a me- 

 tallic oxide is to be avoided. Generally speaking, all oxida- 

 tions should be performed with the platina wire, as well as 

 tho&e reductions in which change of colour is the only object in 

 view." 



" Plates oj' mica may be used in roasting ores, when the dc- 



