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 ^/arious parts of 
the United States and Europe, and, I think, represent a fair 
average as to composition. Prom these it may be seen that in 
general a large amount of Alg O 3 and Si O^, 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 AI 2 O 3 over Si Og increases the infusibility. 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 runs 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. 
