854: NEW TOBK STATE MUSEUM 



TESTIE'G OF CLAY WARES 



The tests applied to determine the qualities of a clay product 

 depend on the use to which it is to be put. Some wares such as 

 paving bricks are subjected to sudden shocks and abrasion, others, 

 which are placed in exposed positions, must withstand the influ- 

 ence of weather, still others must resist sudden changes of tem- 

 perature, etc. 



Porosity or permeability 



The denser a building brick the better it will be able to with- 

 stand weathering influences. Soft mud bricks are perhaps an ex- 

 ception to this rule, for they may often exhibit 15/^ or 20^ porosity 

 and still resist frost action. The porosity of course depends on 

 the density, and is determined by the increase of weight which a 

 brick shows when immersed in water. It may also be of interest 

 or importance at times to determine the porosity of the different 

 parts of a brick, in which case the brick is broken up and frag- 

 ments taken from the center. 



The absorption of common building brick may be as much as 

 20^ of their weight, while in the case of hard brick it should not 

 exceed 5^ ; in paving bricks and bricks' for sewers not over 2^, and 

 in sewer pipe and canal brick it should never get above Ifo. 



According to Dlimmler (Ziegel Fabrikation, p. Yl) it is import- 

 ant in the case of vitrified roofing tile and sewer pipe to determine 

 not only the porosity but also the permeability. With roofing tile, 

 which simply serve to drain off water, this is done by heating the 

 tile first to 100° C, then placing on it a tube whose cross-section is 

 10 square centimeters, and whose hight is 20 cm. This is 

 fastened to the tile by means of wax, and then filled with lOca 

 of water. The time is then noted which this water takes to soak 

 in, and additional quantities of 10 to 15 cc are added at a time 

 till drops begin to appear on the under side of the tile. Roofing 



