RATIONAL ANALYSIS OF CLAY. 51 



shall fully supplant the ultimate one for eac'h serves 

 its own purpose. 



The ultimate analysis may be used to supply in- 

 formation on the following points. 



1. The purity of the clay, by showing the propor- 

 tions of silica, alumina, combined water and fluxing 

 impurities. 



2. Prom the ultimate analysis Ave can form a gen- 

 eral idea regarding the refractoriness of the clay, for, 

 other things being equal the greater the total sum of 

 the fluxing impurities, the more fusible the clay. 



3. T'he color to which the clay burns may also be 

 judged approximately for the greater the amount of 

 iron in the clay the deeper red will it burn, provided 

 the iron oxide is evenly distributed, and there is 

 not an excess of lime in the clay. If the proportion of 

 iron to lime is as 1; 3, then a buff product results, 

 provided the clay is only heated to incipient fusion or 

 vitrification. The above conditions will be affected 

 by a reducing atmosphere in burning or of sulphur in 

 the fire gases. 



4. Clays with a la'rge amount of combined water 

 sometimes exhibit a tendency to crack in burning. 

 This combined water would be shown in the ultimate 

 analysis. 



5. A large excess of silica would indicate a sandy 

 clay. 



The connection between refractoriness and chemical 

 composition may be illustrated by the following 

 analvsis. 



