OF ARTS AND SCIENCES : MARCH 28, 1865. 491 



ordinarily forms at or near the margin of the red-hot portion of the 

 glass, the tendency seemingly being to aggregate away from the point 

 of greatest heat, and in a matrix which has not assumed the fluid con- 

 dition. In consequence of this tendency, if the heat be too long con- 

 tinued — which may be known by the reddening of the whole or greater 

 part of the surface of the bead — the precipitate, especially when 

 scanty, is driven completely off the glass and thrown upon the wire 

 loop, where it is often invisible, besides exercising, if in the metallic 

 state, a damaging influence on the wire itself. Frequently the precipi- 

 tate is in the form of a narrow, crescent-shaped band, at the edge of the 

 heated portion of the glass ; and repeated cautious applications of the 

 flame will generally produce a repetition of these bands ; thus render- 

 ing quite distinct what otherwise might scarcely have been visible. 



Where the precipitate is metallic, translucency of the glass is not 

 important, and, unless microscopic study is intended, rotundity of the 

 bead is not objectionable ; on the contrary, within certain limits, is pref- 

 erable, on account of its being more slowly heated, and thus allowing 

 a moi'e prolonged action of the flame. 



In reference to the mixtures experimented on, where the proportions 

 are given, bulk, not weight, is to be understood. Many and carefully 

 conducted experiments are needed to determine the constancy and deli- 

 cacy of the reactions I have described, to say nothing of the multitude 

 of combinations which remain untried. The subject of combinations 

 suggests the possibility of finding certain substances which, when 

 brought together under the influence of the fluxes, and of the different 

 blowpipe flames, shall give decisive evidence of the presence of one or 

 both of them, when, perhaps, alone they would wholly have escaped 

 detection in this method of chemical investigation, and as bearing on 

 this point, the reactions of antimony and arsenic with oxide of copper, 

 that of the former with iron and of alumina with lime, are especially 

 worthy of attention. 



The following extracts from Muspratt's " Chemistry, as applied to 

 Arts and Manufactures," pages 194 and 197, Art. " Devitrified or 

 Semi-crystallized Glass," cannot fail to be of interest in connection with 

 the subject of crystals in blowpipe beads : — 



" As excessive brittleness results from the sudden cooling of glass, 

 so, on the other hand, when the fused metal is cooled too slowly, the 

 amorphous state entirely disappears, the mass assumes a crystalline 

 structure, and other changes occur which are termed devitrijication. 



