CLAY WORKING INDUSTRIES. 163 



The claims of the value of repressing have been very much over- 

 stated at times and the prices of paving materials have been raised and 

 kept up, on the strength of the improved quality and additional cost of 

 manufacture of repressed bricks. 



Recently however, a distinct counter current of opinion has set in. 

 Opposition to repressing has heretofore been confined to those who had 

 not provided themselves with the necessary plant for doing the work; 

 the recent movement is coming from those who make both plain and 

 repressed brick and are therefore in a position to know the facts in the 

 case. 



The claims of this faction are that the structure of the bar of clay 

 is determined in the auger machine and die and that to take the bricks 

 fresh from the machine, and inclose them in a fixed space, and there 

 subject them to heavy pressure causes a breaking up of the original 

 structure, and that the new arrangement of the brick, particles is not 

 as good as the old. They allege that the new material is not denser 

 than the old and that it will not wear as well, and chips easier. Some 

 few even say that the pressure in the repress die does not permeate the 

 entire brick, but only affects it to a slight depth and that the change in 

 shape which the brick undergoes in the repress die is effected by a sur- 

 face flow of the clay and not by a rearrangement of the whole structure 

 of the brick, and that this surface flow of the clay produces laminations 

 between the unaffected interior and the exterior. 



This last claim is an absurd one, and one which ought not to find 

 credence with any intelligent man. The clay in the brick machine acts 

 like a fluid; it is still able to respond to the same influences when it is 

 put into the repress die. One of the laws controlling fluids is that pres- 

 sure applied anywhere on it, is transmitted throughout the mass equally. 



The repress die must be larger than the brick in two dimensions, in 

 order to admit of the brick being easily and automatically dropped into 

 the die before pressure; hence the dimensions of the plain brick are 

 appreciably changed in all directions and the theory of surface flow 

 being sufficient to account for this readjustment of the mass is absurd. 

 The mass is altered by just such a flow and response to pressure as 

 occurred when it was made in the auger machine die. 



The question as to the benefits of repressing hinges on this point. 

 No one can doubt that the appearance of the brick is improved by 

 repressing and that new and desirable shapes can be imparted which 

 could not be obtained in any other way. Also, it is apparent that the 

 ragged surfaces of a side-cut or end-cut brick offer facilities for absorption 

 of water, which a smooth surface does not. But whether the new struct- 

 ure obtained in the repress die is as good as the one first obtained in the 

 machine die, is a matter still open for debate. 



In the paving brick tests, conducted by the Survey on Ohio 

 material, ('and of which extended notice will be given further on) the 



