CHEMICAL PROPERTIES OF CLAY. 53 



Clay substance, 45.21% 



Quartz, 20.62% 



Feldspar, 34- 17% 



If, however, it became necessary to substitute for the one in 

 use a new kaolin, which. had a composition of: 



Clay -substance, 66.33% 



Quartz, 15.61% 



Feldspar, 18.91% 



and added the same quantity of it as we did of the old kaolin, 

 it would change the rational analysis of the body to the follow- 

 ing proportions : 



Clay substance 44.22% 



Quartz, 10.41% 



Feldspar, 45.98% 



Such an increase of feldspar, as shown by this formula, would 

 greatly increase the fusibility and shrinkage of the mixture; 

 but, knowing the rational composition of the new clay, it would 

 be easy, by making a simple calculation, to ascertain how much 

 quartz and feldspar should be added to bring the mixture back 

 to its normal composition. 



The rational composition of a clay can be determined from an 

 ultimate analysis, but the process of analysis and calculation be- 

 comes much more complex. The rational analysis is furthermore 

 useful only in connection with mixtures of high-grade clays, in 

 which the variation of the ingredients can only be within com- 

 paratively narrow limits. For ordinary purposes the ultimate 

 analysis is of greater value. 



Clays may agree closely in their ultimate analysis, and still 

 differ widely in their rational composition. 



MINERAL COMPOUNDS IN CLAY AND THEIR CHEMICAL EEEECTS. 



All the constituents of clay influence its behavior in one way or 

 another, their effect being often noticeable when only small 

 amounts are present. Their influence can perhaps be best dis- 

 cussed individually. 



