Chemical-Apparatus. 107 



of glass, serve for most distillations by the heat 

 of the lamp. 



3. Earthen vessels of the best kind resist the 

 strongest heat without melting, and are not easily 

 corroded. Vessels made of clay alone are very 

 close and compact, but are liable to break from 

 their inflexibility, as well as to melt. To re- 

 medy these, sand is added, which endures vio- 

 lent heat without melting, and at the same time 

 lessens the expansion of the clay, and consequent- 

 ly renders it less apt to break. If the vessel is 

 required to be very compact, more clay and less 

 sand must be used: they must be heated and 

 cooled slowly. If vessels are necessary that will 

 bear to be heated sooner, more sand must be 

 employed. Mr. Pott, of Berlin, recommends 

 powder of clay, burnt till it is quite hard, instead 

 of sand, which has all the advantages without 

 the inconveniences of that material. Chemists 

 have long wished to discover a vessel in which 

 lead may be vitrified without loss. This metal 

 dissolves common vessels, as water dissolves salt. 

 Mr. Pott's method answers this purpose extreme- 

 ly well. Dr. Lewis recommends a porcelain of 

 bottle glass baked in sand * . Black lead vessels 

 endure heat best. 



The forms of the vessels vary according to 

 their uses. 



1 . VESSELS for FUSION. The most common 



* See his Commerce of Arts. 





