CLAYS OF HEW YORK 857 



operation are weighed, tliiis the percentage of loss is determined. 

 The bricks themselves are also to he examined for cracks after 

 this treatment. 



Resistance to acids 



Certain structural clay products, such as bricks for sewer works, 

 pavements and walls, as well as those used in acid works, which 

 ar3 more or less subjected to the action of acids, are to be tested 

 for their resistance to the latter. The best way to do this is to 

 pulverize the product to be tested, separating the fine powder, 

 then subjecting the coarser material to the action of acids of dif- 

 ferent degrees of concentration for 24 hours. The acid is then 

 filtered off, and the powder is washed, dried and weighed to 

 determine the loss. 



Abrasion test 



This is described under " Paving brick ", p. Y45. 



