IOWA ACADEMY OF SCIENCES. 
41 
about the proportion of the admixture. So that clays con- 
taining more than about 3 per cent of lime can not be made into 
good brick from this fact, and that the calcium carbonate being 
reduced to calcium oxide by heat will slack by moisture and 
the brick then crumble. However, by burning at a higher 
temperature than is usual the injurious effect of lime can be 
greatly overcome unless it is in so great quantity as to lower 
the fusing point too much. The amount of combined water in 
a clay is a very important item in determining its adaptability 
for good brick. In a pure hydrated silicate of aluminum so much 
water will be given off by burning that the brick in going 
through the sweating process become too soft and run 
together, or else crack so as to be made much inferior. So all 
pure clays for brick must be mixed with sand, powdered quartz, 
"powdered brick, gangue, or some such material, in order to 
alleviate this difficulty. In loams a certain per cent, of lime or 
similar material needs to be added to act as a flux, as too much 
sandy material makes the brick brittle. Marls in this country 
have been, it appears, but little used for brick making, as the 
lime is supposed to be detrimental. Yet in Europe a very fine 
malm is made from marls having as high as 40 per cent or more 
of calcium carbonate. They simply heat the brick probably 
200 degrees higher than the ordinary brick. This gives the 
brick a white color instead of red, the iron and calcium being 
united with the aluminum as a ferric- aluminum calcic silicate. 
Of the Indianola brick clays, analyses of two samples will be 
sufficient for our purpose of comparison. The brick are made 
from a certain small deposit of blue clay, taken probably 
twenty feet below the surface, mixed with a much larger pro- 
portion of a darker colored clay immediately above this blue 
layer. 
The lower strata gave the following analysis from the air 
dried samples : 
SiO^ 66.779 
AI 2 O 3 . 19.525 
Fea O 3 72 
CaO- trace 
Loss dried at 100°__„ 8.08 
Loss by ignition 5.48 
Total 100.584 
