FIRE CLAYS AND FIRE-BRICK INDUSTRY. 329 



pointed out in discussing the fusibility of clays (p. 99) the size 

 of grain exerts a strong influence on the fusing point. 



The above theory is not new, and is well understood, but in 

 order to make it perfectly clear a portion of the brick was ground 

 sufficiently fine in a mortar to pass through a sieve of 100 meshes 

 to the linear inch so as to< greatly reduce the size of the grains, 

 especially the quartz ones. This ground mixture when tested, in 

 the Deville begins to get viscous at cone 28, which is the point 

 we should expect it to fuse at if the silica and kaolinite were 

 exceedingly fine. Owing to the fact that the quartz grains are 

 only ground so as not to exceed one-hundredth of an inch, it 

 would tend to fuse a little higher, were it not for the fluxing 

 action of the .68 per cent, of ferric oxide and 1.66 per cent, of 

 titanium oxide which the brick contains. 1 



We see from this therefore that much of the silica in the 

 above described brick is bound up in grains and fluxing action 

 can only proceed from the surface of the grain inward, and, 

 therefore, this brick has the ability to resist a higher heat than 

 its chemical composition would indicate. The refractoriness in 

 this case is not determined by the chemical composition of the 

 whole brick, but rather by the composition of the body in which 

 coarse silica grains are held. 



In No. 2 of the list of tests, the silica and kaolinite per- 

 centages recalculated to 100 would be 63.59 an d 3641 respect- 

 ively. Theoretically a mixture of this composition should fuse be- 

 tween cone 26 and 2.7, and a sample of it ground to 100-mesh, 

 and tested in the Deville furnace was thoroughly viscous at cone 

 27, so that viscosity must have begun at least as low as cone 

 26 and probably lower, the ferric oxide and titanium oxide having 

 helped depress the fusion point. The unground brick, however, 

 in which the silica is largely in coarse grains did not fuse lower 

 than cone 32, as shown by the table. The results from this test 

 therefore corroborate the conclusions drawn from No. 1. 



In No. 14 the fusion point of the calculated mixture of kaolinite 

 and silica should lie a little below cone 27, but when ground to 



1 In the case of fine-grained clays, free from fluxes the theoretic and actual 

 fusion points agree very closely. (See p. 315.) 



