3H 



CLAYS AND CLAY INDUSTRY. 



inspection of these curves, shows quite clearly how an increase 

 in the percentage of silica up to a certain point causes a dropping 

 of the fusion point, but that a further increase in the silica con- 

 tents raises it again, although not quite as high as it originally 

 was. 



It will be seen from a comparison of these two curves that 

 the kaolinite-silica mixtures have lower refractoriness than the 

 pure silica-alumina mixtures. This effect of silica will no doubt 

 be at first accepted with doubt by many brick manufacturers, who 

 have considered that silica or sand adds to the refractoriness of 

 clay in burning, but it should be remembered that common bricks 



Seger 

 Co/7e//o.zer 



KAOLIN i dol 9\> 80 



/fao/in and Silica 



' — rtaolin and Silica with 5', 



Titanium Oxide 



2D 



Axm/ 



35 40 50 60 70 80 90 fOo/.S/l tC/? 



fig. 41. Diagram showing the effects of silica and titanium on the fusibility of kaolin 



are burned at a much lower temperature than that at which the 

 alumina and silica unite. 



In testing the New Jersey fire clays in the Deville furnace, the 

 results obtained seemed to bear out Seger s experiments, but did 

 not agree with them very closely, and in fact the fusion points 

 were usually lower than would be expected from his curve. Ac- 

 cordingly a series of mixtures of a white-burning clay 1 and finely- 



1 This clay was practically free from fluxes, and, hence, had very nearly the 

 composition of kaolinite. 



