166 POROSITY OF ROCKS. [IX. 



TABLE OF THE DENSITY AND POROSITY OF VARIOUS ROCKS. 



reference to the choice of building-stones for the Houses of Parliament. 

 They made use of blocks of an inch cube, which were first soaked in water 

 and then placed under the vacuum of an air-pump, as in my own experi- 

 ments. The following examples are taken from a table in the above re- 

 port, giving the results for thirty-six specimens of building-stones. The 

 value of x in III., or the absorption of water for 100 volumes of rock, as 

 determined by them, is as follows : For three silicious limestones, 5.3, 8.5, 



