38B 
Brick‘Making, 
ounce and three quarters. I did the same by that at 
Walworth, and during the same time it lost nearly two 
ounces \ that at Camberwell lost in the same time three 
ounces four pennyweights ; that at Battersea, two ounces 
six pennyweights. In the solution of these earths^ after 
having exposed them to the muriatic and the acetous acid, 
it was evident that, besides a large portion of pure argil 
which the earth at Camberwell contained, there were not 
less than eighteen parts in one hundred of iron, a small 
portion of silex, and about six parts in one hundred of 
calcareous earth : and it will be seen, that the quantity of 
water which the clay and the calcareous earth held was 
considerable ; from this I infer, that although the colour 
of the bricks, and the difficulty and consequent expence 
in moulding the latter was greatly against the manufae^- 
tiirer, yet, as to the materials, they were far superior to 
the others in an essential property, I mean durability^ 
Those at Kennington and Walworth were nearly similar 
in their products, the latter possessing the most argil ; 
and those at Battersea still more ; the earth therefore im- 
bibing more moisture, consequently loses more in burn- 
ing. 
The moulds used in making every sort of brick for 
building purposes are ten inches in length, and five in 
breadth ; and the bricks when burned usually measure 
nine inches in length and four and one-half in breadth, so 
that the clamp shrinks about one inch in ten. But the 
degree of contraction (as we have before seen) which clay 
undergoes in being burned, docs not absolutely depend 
upon the purity of the clay ; for as some clay imbibes 
more moisture than others, if that which imbibes the 
most is not exposed a much longer time to the frost to 
divide and separate its particles, and to the heat of the sun 
to exhale its moisture, than that which imbibes less and 
is a. shorter time exposed, it follows, that while the one 
