120
EXPOSITION AT VIENNA.
interior and exterior surfaces of walls, so as to exclude
dampness and secure greater warmth. This is of great
importance, and especially where "furring off” the wall
is avoided, as it should be for many good reasons. But
the great cause of dampness, and consequent great cou-
ducting power of walls, is not likely to be avoided by even
hollow brick of the best construction, unless access of
water to the outside and the foundations is prevented by
imporvious materials. The capillary power of raising
water in walls is well known, particularly in Paris, where
dampness has been observed to rise thirty-two feet above
the foundations. Long, driving rains fully saturate brick
walls and chimneys, and exudations of water are found
inside of dwellings about chimneys where no leak can be
discovered. The capacity of absorption of water by bricks
is probably not less than a pint to each one. Mr. Chad
wick, in Ins " Report on Dwellings for the Poor,” says that
in England common bricks absorb as much as a pint or
pound of water; and supposes a case of a cottage wall
consisting of twelve thousand bricks, which would be capa-
ble of holding fifteen hundred gallons, or six and a half
tons of water when saturated. To evaporate this would
require a ton of coal. Sandstone and granite also hold
quantities of water in their pores. Prof. Ansted states
that granite, in a dry state, is rarely without a pint and a
half of water in each cubic foot. Sandstone may contain
half a gallon, and loose sand two gallons.
The absorptive capacity of bricks varies with their dens-
ity, depending upon the process of manufacture. This has
been shown by Cyrus Chambers, in experiments upon
bricks made by the machine of his invention and on hand-
made bricks, the results of which are given in the annexed
table :—