700 GEOLOGY OF OHIO. 
One of the troubles of a clay brick, which a silica brick escapes, is 
its so called ‘dropping’ when placed in the roof. This means either 
of two things—Ist, that a crack has formed across the brick which 
leaves a piece free enough to fall when any change of temperature 
loosens it—this is the peculiar property of a pure clay ; and 2nd, the 
formation of a crust of fused clay and. ashes on the surface which 
eracks off and falls when the brick cools. 
Besides the Alexander silica brick, there are several other styles in 
use: the N. C. (Niles composition), made by the Thomas Brick Works, at 
Niles, is one of the prominent ones. In this a conglomerate sand-rock 
furnishes the silica which is used with a clay bond. No bricks of this 
highly silicious character, approximating in value the celebrated 
“Dinas” brick, are made in the country. 
Nearly every kind of brick in the market comes from some one 
district in excess of any other; the No. | bricks are mainly made in 
the Portsmouth district, with isolated establishments at Logan, Colum- 
* bus, Mineral Point and Cleveland. No. 2 and No. 3 grades come from 
the Ohio Valley Works. 
Besides the manufacture of bricks alone, these same establishments 
also turn out many other kinds of ware, notably furnace blocks, glass- 
house eyes and special pieces made to order. These are made just as 
brick, after once deciding the composition to use, except that some extra 
hand labor is employed to make a nicely-shaped product. 
RETORTS. 
The manufacture of clay retorts for making gas is now carried on 
quite largely, and the product is fast replacing the iron ones which 
were formerly used. These are made in two places in the State, the 
first and largest at the works of the Cincinnati Fire Clay Retort Co., 
and the second at the Dover Fire Brick Co.’s establishment. 
The clay body is compounded to stand considerable heat without 
any tendency to soften, for so large a piece of hollow-ware must be 
refractory to maintain even its own weight at the temperature used. 
The mixture requires more care in compounding than a brick mixture, 
for more is involved in the failure of the retort to do good service than 
a few bricks. Calcine is used in large amount, but crushed rather finer 
than common, and it needs a very good and plastic bond clay. 
The retort is shaped from the tempered clay by filling the space 
