330 CLAYS AND CLAY INDUSTRY. 



ioo-mesh it fuses at cone 26, whereas the brick fused at cone 31, 

 due to> the presence of the silica in coarse quartz grains. 



In No. 20, the actual fusion point of the brick was cone 31-32, 

 but when ground to ioo-mesh its fusion point was cone 28, while 

 the theoretic fusion point of the silica-kaolinite ratio in the an- 

 alysis of this brick would be cone 29 according to the curve in 

 Fig. 41. The ferric oxide and titanium oxide aided in lower- 

 ing it. 



Again in No. 23, a calculation of the silica-kaolinite ratio would 

 lead us to expect a fusion point of cone 28, if the brick were 

 fine grained and free from iron oxide or titanic oxide. The 

 fusion point of the brick when ground to ioo-mesh is cone 26, 

 owing to over 3 per cent, of iron and titanic oxide. The actual 

 fusing point with the silica present in coarse grains is cone 31. 



For the sake of clearness it may be well to tabulate the facts 

 given above. 











Fusion 



Actual 



No. of 



Silica 



Kaolinite 



Theoretic 



point 



fusion 



brick. 



percentage. 



percentage. 



fusion point. 



ground. 



point. 



1 



53-6i 



46.39 



28 



28 



33 



2 



63-59 



36.41 



26-27 



26 



32 



14 



63-52 



36.48 



27 



26 



3i 



20 



50.65 



49-35 



29 



28 



31-32 



23 



55-22 



44.78 



28 



26 



3i 



The first column refers to the number in the table of tests. The 

 second and third gives the percentage of silica and kaolinite recal- 

 culated to 100. The fourth gives the theoretic fusion point of such 

 a mixture according to the curve in Fig. 41, the fifth the fusion 

 point when ground to ioo-mesh, and the sixth one the fusion point 

 of the brick. 



We see here that those mixtures, such as numbers 2 and 14, 

 having the highest percentage of free silica, show the lowest 

 fusion point theoretically, and that this was true practically when 

 the material was finely ground, the fact that ground bricks in such 

 cases fused lower than the silica-kaolinite mixture being due to 

 the presence of fluxes, such as ferric and titanium oxide, as well 

 as to a small total quantity of lime, magnesia and alkalies, repre- 



