274 IMPROVED MUFFLES. 



tvhen exposed to a great heat ; and it will also be plainly seen, 

 that, in the old mode, a great disadvantage is felt by the sides 

 of the muffle, while in its wet state, hanging from its centre, 

 which also tends to crack it, as there can be nothing applied 

 to assist it in this case, but by employing a greater proportion 

 of cohesive clay in the composition, which, however, produces 

 little if any advantage; whereas in the mode which I have 

 invented, this fault is entirely obviated, and the composition, 

 by its contraction in drying, assists the extrication of the muf- 

 fle from the mould. 

 Farther advan« Fourthly, With respect to simplicity, this new mode will 

 tagesofthe ^^ found to possess a very great advantage, for a boy of 

 new method. ^ u f , . , ., - 



twelve years oi age may be taught to make them m a very 



short time. 



The fifth advantage of this improvement, and of equal con- 

 sideration, is the cheapness of the article; the price of which 

 has been reduced nearly one third to the consumer; and 

 when the superior quality of them is taken into consideration, 

 it may fairly be said to be one half. I mean, when regard is 

 had to their superior quality; and that the muffles may be 

 used over again when broken and ground, with a much less 

 proportion of cohesive clay than in the old mode; and this 

 1 conceive to be no inconsiderable advantage; for it is 

 well known, that when the old muffles or broken crucibles 

 can be used without much fresh clay, they are far superior to 

 jiew materials. 



Sixthly, The muffles made in the old wa"y are seldom of 

 equal thickness ; whereas those made according to the method 

 , Avhich I have the honour to present before the Society, will be 



found to possess that necessary quality in perfection ; for, if 

 a hundred are made from the same mould, they will be all of 

 the same thickness. 



Description of the Moulds and Implements, 



Description of ^^^ ^'^^^ mould for this purpose is a tin one, Plate "VTII, 



the method of flg, j^ vvhich may be made from a piece of tin the size of the 



MHffles. arch, being bent so as to form such a concavity as may best 



suit the purpose to which it is to be applied. This being done 



two square pieces of tin, a a, must have jiu arch cut out of 



them, 



