CLAY MANUFACTURES. 687 
former are usually silicious rocks, but sometimes talcose slates or soap- 
stones are used, which stand heat well in presence of basic slags. All 
firestones are used in the native state, and no other preparation than the 
necessary shaping. Fire-clay is the main refractory material, and is 
used only in the manufactured state. Its products are, Ist, brick ; 2nd, 
retorts ; 3rd, glass-pots; 4th, linings and tile; all of these are made in 
Ohio in large quantity and of unsurpassed quality. 
& FIReE-BRIckK. 
The fire-brick of Ohio are not as widely known or as highly 
esteemed as the Mt. Savage brick, for example, but they can do as good 
work and endure as severe tests as any made in America. 
The processes by which fire-bricks are made are all quite similar, 
though there are several ways of accomplishing the same result, which 
are worthy of notice. As the grinding of the clay, to get the necessary 
uniformity and fineness, is the most important step in any clay process, 
it is in accomplishing this point that the differences in process are found. 
The necessary steps in making fire-brick are as follows: Ist, mixing 
clays; 2nd, washing; 3rd, grinding and tempering ; 4th, molding; 5th, 
drying and pressing; 6, burning; 7, sorting the product. 
The first step, that of mixing the proportions of the clays set 
the part in which the skill of one operator over another is races: 
The discussion of the proper mixtures to produce certain effects will be 
taken up to greater profit after the process has been described, but the 
mechanical part of the work may here be spoken of. The proportions 
of flint, calcined and plastic clays which shall compose the brick, having 
been determined, it is the duty of certain men to prepare these charges 
for grinding. The piles of clay from which the selection of clays is 
made, usually adjoins the works as closely as possible, on the side next 
to the grinding machinery. In many places the amount kept on hand 
is large, amounting to 7,000 or 8,000 tons. There is no object in thus 
storing clay, unless it be either to insure a supply for some time in ad- 
vance and guard against transient interruptions, or to allow the clay to 
_ slack and break up fine, thus omitting part of the mechanical prepara- 
tions otherwise needed. ‘There is a belief largely current, that allowing 
a clay to weather acts advantageously in ridding it of impurities. 
Though it cannot be denied that under. certain conditions this would be 
so, yet it is equally certain that these influences are much overrated. 
