BRISTOL BUILDINCt STONES. 



101 



of this stone, and partly of Carboniferous Limestone, the 

 sandstone compares very unfavourably -witli tlie limestone. 

 A similar sandstone, but of Permian age, may be seen in 

 tlie ruined Abbeys of Caldcr and Fui'ness in tlio North of 

 T<]ngland. 



The roclv, as generally used in construction, is fairly close- 

 grained, but friable. The spooilic gravity is 2-G. The dry 

 stone weighs about 147 pounds to the cubic foot. Subjected 

 to crushing stress, two-inch cubes of a firm, compact stone 

 from Stoke showed signs of yielding to a load of a.bout Tk 

 tons, and broke down with, a load of from 9| to 12 tons. If 

 I may trust the few experiments 1 have been able to make, 

 the rock gives 1| ton (or 16| per cent.) greater resistance 

 when the linos of bedding are laid lun-izontally than when 

 they are placed vertically. The absorptive powei- varies voiy 

 considerably, the more porous varieties taking up as much 

 as ei<'"ht pints to the cubic foot ; a very compact variety not 

 takinn- up more than two pints. The percentage absorption 

 by volume is 4'4 to 17'5. 



I have made some experiments on compact cubes of this 

 rock with the object of ascei'taining the effects of repeated 

 freezin" and thawing. The cubes wore soaked in water, and 

 placed in tin boxes in a freezing mixture of snow and salt, and 

 were allowed to remain there for from three to four hours. 

 On removing them their surface was found to be frosted over ; 

 and, examined under a lens, minute ice-columns were visible, 

 pressed out, I presume, by the expansion of the ice. On 

 allowing the block to thaw and dry, fine sand-dust, loosened 

 by the action of the frost, could be brushed off with a camel's 

 hair pencil. The loss of weight in the case of one two-inch 

 cube was, after twelve alternate freezings and thawings, '89 

 gram. I have no doubt that in stones of looser texture the 

 loss would be much greater. Subjected to crushing stress 



