BOOK X. 



455 



Those ingredients above are peculiar to each cement, but what follows 

 is common to all. Each of the ingredients is first separately crushed to 

 powder ; the bricks are placed on a hard rock or marble, and crushed with an 

 iron 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 been 

 dissolved, 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 clean 

 pots in which no water has ever been poured. In the bottom the cement is 

 levelled with an iron implement, and afterward the gold granules or leaves 

 are 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 and 

 levelled with an iron implement ; the granules and leaves are laid over this 

 in the same manner, and this is repeated until the pot is filled. Then it is 

 covered with a Ud, and the place where they join is smeared over with 

 artificial 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 ; into 

 this lowest chamber the air penetrates through an opening, and into it the 



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



