188 An improved Method of making Muffles 



cracks and flaws, which can be but imperfectly closed in 

 smoothing the surface of the muffle, whilst upon the block; 

 the evil consequence attending which is, its being subject 

 to fly or crack when 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 mufBe, whilst in its wet state, 

 hanging from its centre, and 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 advan- 

 tage; whereas in the mode which I have invented, this fault 

 is entirely obviated, and the composition, by its contrac- 

 tion in drying, assists the extrication of the muffle from the 

 mould. 



Fourthly, With respect to simplicity, this new mode 

 will be found to possess a very great advantage, for a boy of 

 twelve years of age may be taught to make them in a very 

 short time. 



The fifth advantage in this improvement, and of equal 

 consideration, is the cheapness of the article ; the price of 

 which has been reduced nearly one-third to the consumer j 

 and when the superior quality of them is taken into consi- 

 deration, it may fairly be said to be full one-half. I mean, 

 when regard is had to their superior quality; and that the 

 mufiles may be used over again when broken and ground, 

 with a much less proportion of cohesive clay than in the old 

 mode; and this I conceive to be no inconsiderable advan- 

 tage ; 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 new materials. 



Sixthly, The muffles made in the old way are seldom of 

 equal thickness ; whereas those made according to the me- 

 thod which I have the honour to present before the Society, 

 will be found to possess that necessary quality in perfection; 

 for, if an hundred are made from the same mould, they 

 will be all of the same thickness. 



Description of the Moulds and Implements. 

 The first mould for this purpose is a tin one. Fig. 1, 



(Plate 



