NEW JERSEY BRICKMAKING INDUSTRY. 259 



do not seem to stand in direct relation to the crushing resistance, 

 "bricks of high crushing strength in some cases showing a low 

 strength on the transverse test, and vice versa. This is notably 

 true of the stiff-mud bricks tested. 



4. In testing the individual bricks it will be noticed that there 

 is sometimes a great difference between the maximum and min- 

 imum, figures, as in tests Nos. 5 and 19. The lower breaks are in 

 many cases due to carelessness in the manufacture, and wherever 

 a low break occurred, it was found in the majority of instances 

 to be due to pebbles in the brick three-fourths of an inch or an 

 inch in diameter. These come from the loam that is mixed with 

 the clay, and could be removed by a proper preliminary screening. 



5. The hardness of the brick and porosity as shown by the 

 absorption test are not necessarily an index to> its crushing 

 strength, except within very wide limits. Thus No. 1 is of low 

 porosity and great hardness, but its crushing strength is very high, 

 whereas No. 19, which is also' of low porosity and great hardness, 

 lias a crushing strength of only about one-half that of No. 1, due 

 perhaps to the fact that it is made of a much more plastic clay, 

 which tends to warp and split somewhat in burning. Again, No. 

 12 is extremely porous, and hard burned, but has a crushing 

 strength almost equal to No. 1. On the other hand, examples of 

 high porosity and low crushing strength are shown in Nos. 2, 3, 

 7, 8, 13, 15, so that, while it is perhaps safe to say that high 

 porosity is more frequently accompanied by low crushing strength, 

 and vice versa, nevertheless, these tests prove that there are many 

 striking exceptions to this generalization. 



If we compare the transverse strengths with the porosity, we 

 find the same lack of any close accord, although generally speak- 

 ing the least porous brick shows the higher transverse strength, 

 and vice versa. Thus, No. 21 has the least strength and the great- 

 est porosity, and No. 19 has the least porosity and next to^ the 

 greatest transverse strength, which accords well with our gen- 

 eralization. A striking excqDtion is to be noted in the case of 

 No. 12, which stands first in point of strength and is, also, one of 

 the most porous, standing eighth in a list of 26, instead of last, 

 as the generalization demands. So, too, No. 4 stands low in 



