401 
JBrick’ Making, 
had imbibed, which was, as near as could be expected, 
the very same quantity which had been spread over its 
surface j for it was the quantity which had been imbibed 
by the slate, the surface of which was equal to that of the 
tile ; the tile was left to dry in a room heated to sixty de- 
grees, and it did not lose all the water it had imbibed in 
less than six days.” 
The finest sort of blue slate is sold at Kendal, for 3s. 
6d, per load, which comes to 1/. 15^. per ton, the load 
weighing two hundred weight. The coarsest may be had 
for 2^. 4d, a load, or 1/. 3^. 4d. per ton. Thirteen loads 
of the finest sort will cover forty-two square yards of roof, 
and eighteen loads of the coarsest will cover the same 
space ; so that there is half a ton less weight put upon 
forty -two square yards of roof when the finest slate is used 
than if it was covered with the coarsest kind, and the dif- 
ference of the expense of the material is only 3s. 6d. To 
balance in some measure the advantage arising from the 
lightness of the finest slate, it must be remarked that it 
owes its lightness, not so much to any diversity in the 
component parts of the stone from which it is split, as to 
the thinness to which the workmen reduce it ; and it is not 
able to resist violent winds so well as that which is hea- 
vier. 
A common Cambridge tile weighed thirty-seven oun- 
ces : they use at a medium seven hundred tiles for cover- 
ing one hundred square feet, or about two and a half tons 
of tile to forty-two square yards. Hence, without includ- 
ing the weight of what is used in lapping over, See. when 
a building is covered with copper or lead, it will be seen 
that forty -two square yards of building will be covered by 
Zinc about .... 1 cwt. 
Copper .... 4 
Fine slate * = - 26 
Lead ^ ® « 27 
