COMPABATIVE VALUE OF VARIOUS KINDS OF STONE. 



37 



Results of experiments on stone from North Wales and 

 other places. Specimens Nos. 12, 14, 17, 18, 19, 20, 21, 

 22, 23, 24, 25, and 26. 



The Welsh specimen of grauwacke, from Penmaenmawr, 

 exhibits great powers of resistance, nearly double that of some 

 of the Yorkshire sandstones, and about one-third in excess of 

 the granites, excepting only the granite from Mount Sorrel, 

 which is to the Welsh grauwacke, as *757 : 1. Some others, 

 such as the Ingleton grauwacke, supported more than the 

 granites, but are deficient when compared with that from 

 Penmaenmawr. The specimen No. 23 is the stone of which 

 the Houses of Parliament are built. Specimens Nos. 25 and 25 

 were broken to show experimentally the ratio of the powers of 

 resistance as the size is changed. The results are sufficiently 

 near to prove that the crushing weights are as the areas of the 

 surface subjected to pressure. 



The specific gravity and porosity of the different kinds of 

 rock vary greatly, and Mr. Shaw, in his desire to obtain the 

 best quality of Yorkshire paving stone, had those from the 

 neighbourhood of Bradford carefully tested in regard to their 

 powers of absorption ; the experiments, which were conducted 

 with great precision, gave the following results. 



