CLAY MANUFACTURES. 697 
the Akron district and in a few of the river works. There are 
usually 3 fires to each end; a fire-wall is used instead of pockets, and 
the down-draft finds exit through a central row of perforations to the 
flue Sbeneath. The draft has a little tendency to strike straight from 
the fire-wall to the flue in the floor, but by judicious piling the draft can 
be entirely controlled. | 
ene refractory property of clay can be studied to no better 
advantage in any way than in the compounding and burning of fire-brick. 
As the work is done at present, no great knowledge of the theory of 
the subject is required, but there is room for great improvement in its 
scientific treatment. 
The problem of making a refractory brick from native clays is 
based upon the fact, “the purer the clay the more infusible.” Our 
purest clays are our flint clays, which are probably refractory by reason 
of theiristructures, as well as their composition. These then make an 
admirable basis for the brick. As they are non-plastic, their successful 
use compels the addition of a small amount of plastic clay, and on the 
choice of this clay all depends. A fine-grained, sandy clay hard in its 
native state, and plastic when ground up in water, makes the best bond ; 
it is needless to add it should be pure. The more aluminous a clay is 
the more it will shrink on burning, and if the clay which has been used to 
incorporate the non-plastic part should shrink materially on burning, it 
would loosen the bond between the pieces of hard clay and make the 
whole fabric unsound. ‘Therefore the clay fit for a bond is one in which 
the natural shrinkage is at a mininum; this condition is found in a fine- 
grained sandy clay. It is ignorance of this point, which seems so 
_ simple, that has caused the failure of so many patent mixtures for 
_ refractory materials. It has seemed to each man in succession, who has 
approached the subject, that as pure kaolin is infusible, and pure sand 
is infusible, and as these bodies represent respectively our ideal of plas- 
ticity and non-shrinking qualities, a proper mixture of the two should 
produce the most desirable results. But, when such a mixture is heated, 
the enormous shrinkage of the kaolin loosens the bond of the whole 
body and makes it weak and fragile. For the clear statement of this 
point, thanks are due to Hon. J. Park Alexander, of Akron, who has 
experimented widely on the compounding of refractory mixtures. 
If, then, a pure, sandy and plastic clay can be found, the bond is one 
likely to be satisfactory ; but the main trouble is in a lack of purity, for 
