PNEUMATO CHEMICAL APPARATUS. 17 



the middle, directed to the side of the outer cy- 

 linder, and coming upwards by the side to the top, 

 where there is another cock attached. 



For solution, and dissolutions, and for crystal* 

 lizing salts, vessels of glass or earthenware are 

 used. 



The melting, or causing any body to pass from 

 the solid to the liquid state, by the action of fire, 

 is c'dlledfusion. The fusion of metallic substances 

 requires vessels sufficiently strong to resist the fire. 

 Those vessels are mostly, if not always, made of 

 earthen-ware, or porcelain, or a mixture of clay 

 and powder of black-lead. They are called cru- 

 cibles, and are generally of the forms represented 

 Fig. 3. Sometimes these vessels have covers made 

 of earthen-ware ; but sometimes the fused metal 

 must be exposed to a current of air : in that case, 

 the crucibles are broad and shallow, as at Fig. 4. 

 these are called cupels, and they are formed of 

 calcined bones, mixed with a small quantity of 

 clay, or of a mixture of clay and black-lead pow- 

 der. But the cupels must not be placed in a 

 closed furnace, or be surrounded by coals ; for, in 

 that case, the required current of air could not 

 have access to the fused metal. They are, there- 

 fore, placed under a sort of oven of earthen-ware, 

 which is called a muffle, as represented, Fig. 5, which, 

 with the included cupel, is exposed to the heat of 

 a furnace. 



The various degrees of heat which are required 

 for the performance of chemical operations render 

 a variety of fire-places, or furnaces, necessary for a 

 chemist. Those furnaces are either open at top, 

 or they are covered with what is called a dome, 

 and have a chimney, or tube, to carry off the heated 



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