818 
ME. W. HOPKINS’S EXPEEII^IES'TAi EESEAECHES 
maximum value for chalk, the general structure of this clv/ach of the Lower Qialk 
being much more compact, and approaching nearer to the character of rock than the mass 
k 
of the Upper Chalk. I should estimate the value of - for chalk in the general mass at 
about ‘25. 
Similar experiments were made on an Oolitic block from the quarries at Ancaster. It 
gave, when saturated with moisture, 
and when dry. 
In the first case the weight was 
immediately after the experiment, and 
8041 '5 grains 
when dry. The quantity of water contained in it, when satm-ated, may therefore be 
estimated at 
591-5 grains, 
so that the effect on the conductivity in this instance was much less in proportion to the 
quantity of moisture, than in chalk. The result was verified by similar experiments on 
k 
another block. Both blocks had given ~ = '37 when first tried. They had probably 
imbibed considerable moisture, the season being at the time very wet. These experi- 
ments were made at about the lower temperatures above mentioned. 
(2) Arenaceous Rocks . — A block of New Red Sandstone was very much affected in its 
conductivity by being saturated with moisture. When saturated it gave 
-=•30. 
c 
8633 grains 
and when dry. 
In the first case the weight, after the experiment, was 
7442 grains, 
and when dry, its weight was 
6883 grains ; 
and therefore, the weight of the contained water was 
559 grains. 
The effect on the conductivity was much greater than in any other case. The quantity 
of water imbibed in the saturated state was about 350 grains greater than the last-stated 
amount. These 350 grains were lost during the experiment, though made at tempera- 
tures little exceeding 100°. 
