for Chemical Purpose's, 189 



(Plate V.) which may be made from a piece of tin the size 

 of (he arch, being bent so as to form such a concavity as 

 may best suit the purpose to which it is to he applied ; this 

 being done, two square pieces of tin, a a, must have an 

 arch cut out of them, of such a size that the diameter thereof 

 may be about three-fourths of an inch less than the diame- 

 ter of the concave piece before stated 3 these being soldered 

 to each end of the first-mentioned piece, will form a stand 

 for the hollow part of the mould, and the thickness of the 

 muffle moulded in this will be exactly determined by the 

 edge at each end. A piece of hollow tin, b l>, may be iol- 

 dered along the top edge of the mould, to form a better re- 

 sistance to the great pressure within. The next part of this 

 mould is a flat piece of tin. Fig. 2, cut exactly to fit the 

 inside of the mould, the u^e of which is, to form a solid 

 back to the muffles used for chemical purposes. 



The second tool for this purpose is a piece of sheet brass. 

 Fig. 3, about six inches long and one broad, which being 

 bent in a semicircular form, and screwed to a piece of wood 

 extending beyond its breadth about an inch, is used for cut- 

 ting the small air holes c (Fig. 11), in the aforesaid muffles. 



The third is the tool or frame. Fig. 4, for preventino- the 

 contraction of the muffles in drying, which is made of four 

 pieces of beech, about three quarters of an inch broad, and 

 half an inch thick; the length must be adjusted to the 

 mould of the muffle; two of these being laid parallel within 

 the inside of the mould, and being joined across by the 

 other two, the ends of which should extend so far beyond 

 the outer edges of the other two, that they may rest upon 

 the edges of the muffle mould, and thereby prevent its fall- 

 ing into the mould. 



The fourth is the tool for spreading the composition into 

 the mould*, which is formed of iron or steel, (Fig. 5), 

 about thirteen inches in length, one inch and a half broad, 

 and about one-eighth thick j its face under k being rounded 

 in such a manner that its curve may exactly fit the inner 

 curve of the muffle mould (Fig. 6, is a section of it) ; this 

 should likewise have a point orlongue, extending from each 



end. 



