690 GEOLOGY OF OHIO. 
clay is tempered to the right consistency by additions of water. The 
pan is usually fitted with a pipe from the engine from which water can 
be had by turning a faucet. Hither hot or cold water may be used ; it 
probably makes no difference which, in the quality of the brick, but the 
former makes the work of the molder much more endurable. 
This machine is found in widest use, where a hard, flinty clay and 
considerable calcine is used. In charges containing considerable 
amounts of both these bodies and only a little plastic clay, such hard 
and intimate mixing is the only way in which the structure of the brick 
can be made sound. This wet pan process is used entirely in the Scioto- 
ville district, Ironton and Logan, and from this part of the State much 
ot the finest brick comes. 
The dry pan and pug mill mixer is the style of grinding least 
adapted to general use of all three ways, but is a cheap and useful 
method in some cases. The pan is very similar to the ordinary wet pan, 
but has this difference: the floor is fitted with plates cast in segments 
fitting on a framework of radii beneath the pan. ‘The plates are thus 
fitted into a level and continous floor; they are full of parallel slots or 
holes, which open immediately into a larger room from the underside, so 
that any particle of matter which passes thé surface will have no chance 
to stick lower down. Beneath the pan is a bin into which the clay, as 
fast as it is reduced fine enough to pass the bottom of the pan, falls; in 
this bin revolve arms, which collect continually the powder and deliver 
it at the foot of an elevating belt which is at one corner of the bin. The 
charge is all introduced together and is run until it has all disappeared 
beneath the surface, or else its proportions of calcine would not be equally 
distributed. All dry pans are subjected to this disadvantage, that the 
softest parts go through first and the harder last, so that the powdered 
clay, as delivered by the elevating belt would not be strictly nomo- 
geneous; also the largest part of the clay goes through at once, and the 
longest part of the grind is devoted to getting the least of the charge 
through, which is a waste of energy. Another disadvantage resulting 
from this pan is the fact that the hard material is never rendered finer 
than is necessary to pass the holes in the floor, which to make the 
machine work at all rapidly are necessarily larger than is good for the 
brick. The powdered clay having been delivered into a bin above, is 
ready to be mixed as needed. The mixing machine is a trough about 18 
inches wide by 8 feet long by 18 inches deep; in it works a horizontal 
