44 IOWA ACADEMY OF SCIENCES. 



These three samples of fire brick clays are selected from a 

 list of about 100 analyses of clays taken from various parts of 

 the United States and Europe, and, I think, represent a fair 

 average as to composition. From these it may be seen that in 

 general a large amount of Al^Og and Si 0.„ with small amounts 

 of alkali, or alkali earths, or iron oxide, is characteristic of these 

 highly refractible clays. Further, it seems that a large per 

 cent, of AIj O3 over Si O3 increases the inf asibility. However, 

 there seem to be two varieties of fire clay, varying considerably 

 in composition, which make equally good fire brick. One is 

 where the silica is nearly all combined with a percentage of 

 about 40 to 50 per cent, and a large amount of aluminum oxide — 

 probably 25 to 35 per cent. — and water making up the greater 

 amount of the remaining 100 per cent. This clay, of course, as 

 the per cent, of the alumina over the silica, and these two over 

 other metallic oxides increases, finally rans into kaolin. The 

 other kind is one where the combined silica is small and the 

 alumina less than in the first case, the combined silica prob- 

 ably not having a much higher percentage than the alumina, 

 the remaining part being made up almost entirely of free silica 

 (quartz sand) and water. No. 2 above illustrates the first and 

 No. 3 the second class. 



By comparing the Indianola clays with these it will be seen 

 that the average is essentially the same as No. 1. This being 

 an average of several samples of each of the two classes 

 referred to above, i. e. , No. 2 and No. 3. But in the Indianola 

 clays there is but small amount of free silica. This being the 

 case, and from the fact that it is so free from magnesia, lime, 

 potash, and iron oxide, it would seem that this clay would be 

 well adapted to be used as the clay basis of fire brick, and then 

 the necessary amount of free silica (either powdered quartz, 

 glass, or silicious brick dust) be added. By a very careful com- 

 parison of all the clays the analyses of which I have, and the 

 qualities of brick made from these, theoretically it seems to me 

 by this means very superior fire brick could be made. The 

 fusibility of bricks made by this method with this clay as far 

 as I know has not been determined. Yet it seems it would be 

 an experiment worth trying, and one which we may attempt at 

 a later date. 



I am informed that the pottery made at this plant is not made 

 from the clay at Indianola, but is made from clay taken just 

 above the upper vein of coal at Carlisle, Iowa. I have not 

 analyzed this clay and cannot at present make a comparison. 



