CLAY WORKING INDUSTRIES. 155 



dropped into the clay cylinder of his machine. This lump is as nearly 

 the diameter of the cylinder as will allow it to be dropped in and the air 

 in the cylinder is on the ends and outside of the lump of clay where it 

 can most easily make its escape when the pressure comes on it. 



An application of this idea to the feeding of other forms of plunger 

 machines will undoubtedly assist in reducing this most troublesome de- 

 fect in their product. Aside from these faults, 1st, those common to the 

 production of a bar of clay by any means and, 2nd, those due to impris- 

 onment of air in the bar, the plunger process affords a result of high 

 excellence. 



By careful attention to keeping the conditions of plasticity, sandi- 

 ness, richness, etc. as favorable as possible and using every means to 

 keep air out of the clay, this process can probably be made to yield better 

 results than any process in which a bar of clay is formed. In the nature 

 of the case, mere pressure on a plastic mass of clay imparts no structure 

 other than that due to flow. 



The plunger process is subject to one peculiarity or limitation, that 

 is, the intermittent character of the flow. This is a feature which can- 

 not be eliminated ; it does not interfere with the production of a good bar 

 while the flow is in motion, but it limits the methods of removing and 

 handling the output to those plans which employ a good deal of hand- 

 ling by men instead of machinery. No automatic devices have as yet 

 been successfully applied to handling the output of plunger machinery, 

 and the intermittent character of the flow threatens to stand in the way 

 of such improvements. The methods of handling a bar of clay for the 

 production of bricks will be discussed under the head of auger machinery. 



There are several types of plunger machines applied to brick making. 



1st. The pipe press, in which sewer pipe and hollow goods are 

 made, is also used to a small extent as a means of making brick. The 

 machine will be described in detail under the head of sewer pipe, for the 

 manufacture of which it was devised. It consists of a vertical clay cylin- 

 der surmounted by a vertical steam cylinder. The piston rod is continu- 

 ous from the clay piston to the steam piston, and the pressure is there- 

 fore, a direct one from the steam to the clay. It is an extravagant machine 

 jn the use of steam, but its simplicity and lack of wearing and breakable 

 parts make it one of the favorite machines in use. 



2nd. The same principle has been used in the horizontal steam 

 press, this is used for brick and small sizes of hollow goods. It is made 

 usually double ended, a steam cylinder in the middle and clay cylinder 

 at each end, so that instead of losing the steam on the return stroke it is 

 used in making ware; also two kind of ware can be produced at once, 

 which is of great importance in some places and in any place it saves the 

 loss of time in changing dies frequently. 



3rd. The Penfield Plunger consists of a pair of press boxes of rec- 

 tangular section, situated on either side of a central vertical shaft. The 



