BOOK X.

455

Those ingredients above are peculiar to each cement, but what followsis common to all. Each of the ingredients is first separately crushed topowder ; the bricks are placed on a hard rock or marble, and crushed with aniron implement; the other things are crushed in a mortar with a pestle ;each is separately passed through a sieve. Then they are all mixed together,and are moistened with vinegar in which a little sal-ammoniac has beendissolved, if the cement does not contain any. But some workers, however,prefer to moisten the gold granules or gold-leaf instead.

The cement should be placed, alternately with the gold, in new and cleanpots in which no water has ever been poured. In the bottom the cement islevelled with an iron implement, and afterward the gold granules or leavesare placed one against the other, so that they may touch it on all sides ; then,again, a handful of the cement, or more if the pots are large, is thrown in andlevelled with an iron implement; the granules and leaves are laid over thisin the same manner, and this is repeated until the pot is filled. Then it iscovered with a lid, and the place where they join is smeared over withartificial lute, and when this is dry the pots are placed in the furnace.

The furnace has three chambers, the lowest of which is a foot high ; intothis lowest chamber the air penetrates through an opening, and into it the

A— Furnace. B—Pot. C—Lid. D—Air-holes.

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