CHEMICAL PROPERTIES OF CLAY. 49 



THE CHEMICAL ANALYSIS OE CLAYS. 



There are two methods of quantitatively analyzing clays. One 

 of these is termed the ultimate analysis, the other is known as 

 the rational analysis. 



The ultimate analysis. 1 — In this method of analysis, which is 

 the one usually employed, the various ingredients of a clay are 

 considered to exist as oxides, although they may really be 

 present in much more complex forms. Thus, for example, cal- 

 cium carbonate (CaC0 3 ), if it were present, is not expressed as 

 such, but instead it is considered as broken up into carbon 

 dioxide (C0 2 ) and lime (CaO), with the percentage of each 

 given separately. The sum of these two percentages would, 

 however, be equal to the amount of lime carbonate present. 

 While the ultimate analysis, therefore, fails to indicate definitely 

 what compounds are present in the clay, still there are many 

 facts to be gained from it. 



The ultimate analysis of a clay might be expressed as follows : 



Silica, (Si0 2 ) 



Alumina, ( AUOs) 



Ferric oxide, (Fe 2 O s ) 



Lime, (CaO) 



Magnesia, (MgO) 



( Potash, (KaO) 



" \ Soda, (Na 2 0) 



Titanic oxide, (Ti0 2 ) 



Sulphur trioxide, (SO s ) 



Carbon dioxide, (C0 2 ) 



Water, (H 2 0) 



Fluxing impurities, -< 



Alkalies, 



In most analyses, the first seven of these and the last one are 

 usually determined. The percentage of carbon dioxide is usually 

 small, and commonly remains undetermined, except in very cal- 

 careous clays. Titanic oxide is rarely looked for, except in fire 

 clays, and even here its presence is frequently neglected. Since 

 the sulphur trioxide, carbon dioxide and water are volatile at a 



1 The method followed was in general that given by Hillebrand, in Bulletin 

 176 of the United States Geological Survey. 

 4 CL G 



