RATIONAL ANALYSIS OF CLAY. 53 



better opinion of the probable behavior of the clay in 

 burning. 



When mica is present, it ^s dissolved out with the 

 kaolinite and reckoned in as clay-substance, but it is 

 rarely present in large amounts, and may perhaps 

 alter the character of the clay-substance but little, for 

 finely ground white mica possesses plasticity, and can 

 be formed and dried without cracking. It is more re- 

 fractory than feldspar, and holds its form up to 

 1400 C.* 



In the following table are given the ultimate and 

 rational analyses of a number of kaolins, which show 

 how a constancy of ultimate composition may be ac- 

 companied by variations in the rational analysis: 



* G. Vogi, Chem. News, 1890, p. 315. 



