FIRE CLAYS AND FIRE-BRICK INDUSTRY. 317 



shown in this clay should fuse at about cone 30, and the amount 

 of lime, magnesia, alkalies and titanium, oxide given in the an- 

 alysis should lower the fusion point to at least cone 29 or even 28. 

 As it is, the fusion point as determined is cone 30, and there is an 

 apparent disagreement between theory and the facts. This is 

 probably explainable by the fact that the clay is a very sandy one, 

 and, therefore, since much of the silica is in the form of coarse 

 grains, it is not able to enter into active chemical union with the 

 clay base. In any event this sample illustrates the fact that the 

 fusion point of a clay cannot be determined solely from a chemical 

 analysis. No. 7 owes its low refractoriness to a high content of 

 total fluxes, and not to- high-silica contents. Were it not for 

 nearly 4 per cent, of fluxes, its refractoriness would be quite 

 high. These few examples, will, however, serve to- show the 

 practical application of the facts mentioned above. 



Many manufacturers of fire brick consider that ferric oxide is 

 one of the most important fluxing elements, and that an analysis 

 of a No. 2 brick for example should necessarily show a higher 

 content of ferric oxide than a No. 1 brick. From what has been 

 said above, however, it is easily conceivable that two> fire bricks 

 or fire clays may show the same per cent, of ferric oxide and yet 

 differ in their refractoriness by several cones owing to the differ- 

 ence in the amount of free silica, or the No. 2 brick might show 

 even less ferric oxide than the No. 1 although this is not likely. 



Effect of titanium. — It will be noticed that the percentage of 

 titanium oxide has been determined separately in several of the 

 above analyses, and from the quantity present it is believed to- 

 exert some influence. As has been mentioned under Titanium 

 (p. 70), the presence of 2 per cent, of titanium seems to lower the 

 refractoriness a whole cone number, while 0.5 per cent, lowered 

 it half a cone, when it was mixed with kaolin alone. 



If we compare the curve in Fig. 25 with the one in Fig. 41 it 

 will be seen that the fluxing effect of 1 per cent, of titanium is 

 equal to 10 per cent, silica. 1 



In fire clays the titanium oxide and kaolinite are not usually 



1 Compare No. II and VII, Fig. 25, with No. VII and IX, Fig. 41. 



