TO) \ ANNUAL REPORT 
These clays may be white or yellowish in color when burnt; a clay 
burning almost a red color may be a fire clay, but the chances are against 
it. The value of a fire clay can, however, be determined definitely only 
by a refractory test. 
The high fire-resisting quality of a clay is due, first, to the absence of 
fluxes which either were never present in the material or which have been 
leached out and removed, and, secondly, the fact that it corresponds 
more or less closely to the composition of the ideal clay substance, 
Al,O,2Si0,2H,O, containing, as we know, 
46.3 per cent. silica. 
39.8 per cent. alumina, 
13.9 per cent. chemically combined water. 
The highest refractoriness is represented by a material of this compositon, 
as many tests have shown. We can readily see, however, that any fluxes 
present will deterioriate the refractoriness. But it has also been proven by 
most extensive experiments that silica above that entering into the com- 
position of clay substance will act similarly to a flux and reduce the re- 
fractoriness. A clay high in silica cannot, therefore, be a high-grade fire 
clay. On the market a fire clay is occasionally offered as being high in 
Silica, a fact which the dealer supposes to be advantageous, but which 
really classifies the clay at once as of low grade. 
This important law has been put to the test both theoretically and 
practically, but we must keep in mind distinctly that it applies only to clays 
already possessing a certain degree of refractoriness. Clays high in fluxes 
having a low fusibility intrinsically do not come under this law; clays of 
this kind are raised in the refractory scale by large additions of silica. 
For cement making purposes the fire clays do not come into practical 
consideration excepting as furnishing the material for the kiln lining. 
This is due to the fact that, first, these clays are very high in alumina and 
consequently would produce dangerous quick setting cements unfit for 
use; secondly, the initial refractoriness of these materials is so high that 
it would increase the cost of manufacture unnecessarily. Though the- 
oretically it is possible to manufacture a cement from limestone, fire clay 
and sandstone, practically it is not a feasible proposition. For this rea- 
son we shall not consider the highly refractory materials in detail. 
In speaking of fire clays we must distinguish principally two kinds, 
the plastic and the hard, slightly plastic variety. 
We have in Ohio no plastic fire clays of very high quality, but we 
have a number of them which are of sufficiently high grade to be used for 
good fire brick and other refractory wares. An example of this kind of 
clay is the Ballou fire clay from: Muskingum county, which shows the 
following analysis :* 
*Vol. VII, Part I, Ohio Geological Survey, p. 222. 
