FIRE CLAYS AND FIRE-BRICK INDUSTRY. 33 1 



sented by the difference between the sum of the substances de- 

 termined and 100. 



As can be seen, however, from the difference in the fusing- points 

 between the fire brick in a ground and unground condition, the 

 presence of quartz in coarse grains can offset to some extent at 

 least the presence of a high percentage of free silica. This is seen 

 in the case of all five bricks tested. In No. 1, for instance, there 

 was a difference of 5 cones, that is, the fire brick in its normal 

 condition fused at cone 33, while if ground it fused at cone 28. 



Both ferric oxide and titanium oxide will lower the fusing 

 point in proportion to the quantity present. 



No. 8 is perhaps a good example of this. This brick contains so 

 little free silica that its condition, whether -coarse or fine, would 

 affect the fusion point but little. Even assuming that the silica 

 was all finely divided, the fusing point of the silica-kaolinite mix- 

 ture contained in the brick would be as high as cpne 34, as shown 

 "by the upper curve, Fig. 41, but the brick fuses at cone 32, evi- 

 dently because of nearly 5 per cent, of ferric oxide and titanium 

 -combined. 



From what has gone before the following conclusions seem 

 warranted : 



Chemical analyses alone can not be entirely relied on for judg- 

 ing the refractoriness of a fire brick, although it is true that they 

 indicate in a general way whether the brick is likely to be of low 

 or high refractoriness. Large percentages of ferric oxide, or 

 titanium oxide, indicate low refractoriness. So, too, a large per- 

 centage of free silica suggests a low refractoriness under certain 

 conditions. The chemical analyses, however, give no clue regard- 

 ing the texture of the brick, and, as seen in the case of the several 

 numbers of the above table, which were discussed in detail, this 

 may be a very important factor. 



It follows, therefore, that if silica in excess must be added to a 

 fire brick it is more desirable to add it in the form of coarse grains 

 rather than fine sand. It is not, however, a desirable ingredient 

 of fire clay at all, and the most refractory brick made in this coun- 

 try and also in Europe contain a lower percentage of it than those 

 from New Jersey. 



