CLAY WORKING INDUSTRIES. 151 



The processes of preparation have now been described. They are 

 common to all industries using hard or rocky clays for vitrifying pur- 

 poses, and are used for the preparation of clay for many other purposes 

 beside. At this stage the clay passes to the special machinery required 

 in making the kind of ware under discussion. 



Brick Making Machinery. The manufacture of bricks by machinery 

 is accomplished in several ways, and with a great variety of machines. 

 As paving brick are liable to be made in any one of the processes it is 

 necessary to give, an outline of all the different means employed. The 

 bulk of the paving brick manufacture — all that is important — falls' under 

 one of two plans which will receive careful consideration. Bricks are 

 made at present in the following ways: 



1. By hand moulding. 



2. By soft mud machinery. 



3. By stiff mud machinery. 



4. By dry press machinery 



Hand moulding is not employed to any extent in making paving 

 material. It is still used in making fire brick and in making common 

 brick. 



Soft mud machinery is used to a limited extent in paving bricks and 

 to a large extent in making fire brick and building bricks. The process 

 is characterized by using the clay in a very soft and pasty state and by 

 the fact that the soft clay is forced into molds like those used in hand 

 molding, and these molds are then removed, emptied, cleaned, sanded and 

 replaced by hand to be refilled by the machine. This process will thus be 

 seen to be but an imperfect attempt to perform by machinery the same 

 processes originally carried out by hand. There are a number of different 

 machines of this class, but all unite the same essential principles and 

 attain similar results. 



Stiff mud machinery, is that now almost universally used in paving 

 brick plants, and is becoming more and more important in the manufact- 

 ure of all kinds of bricks for building and refactory purposes. The 

 clays in stiff-mud machines, are tempered to a plastic state but are not 

 soft and pasty. They are able to retain their shape under considerable 

 Weight when taken fresh from the machinery, and the process unites the 

 benefits obtained by wetting the clay, with those which accrue from the 

 easier handling of the product. 



The dry press process, as its name indicates, takes the ground and 

 sifted clay, and by the exertion of great pressure forces it into a compact 

 and dense brick, without the use of any moisture. The products of 

 this process are used in a limited extent for making fire brick, but are 

 ordinarily applied to the production of fine building material. Some few 

 dry pressed bricks have been tried as paving material with nearly always 

 unfavorable results. 



The character of the wares made by these four processes may be 

 briefly described as follows: 



