442

BOOK X.

uWVA'^.

A—Furnace. B—-Its round hole. C—Air-holes. D —Mouth of the furnace.

E—Draught opening under it. F —Earthenware crucible. G —Ampulla.

H-— Operculum. I —Its spout. K —Other ampulla. L —Basket in which this is

USUALLY PLACED LEST IT SHOULD BE BROKEN.

All this preparation having been accomplished in order, and theingredients placed in the ampulla, they are gradually heated over burningcharcoal until they begin to exhale vapour and the ampulla is seen to tricklewith moisture. But when this, on account of the rising of the vapour, turnsred, and the aqua distils through the spout of the operculum, then one mustwork with the utmost care, lest the drops should fall at a quicker rate thanone for every five movements of the clock or the striking of its bell, andnot slower than one for every ten; for if it falls faster the glasses will bebroken, and if it drops more slowly the work begun cannot be completedwithin the definite time, that is within the space of twenty-four hours. Toprevent’ the first accident, part of the coals are extracted by means of an ironimplement similar to pincers; and in order to prevent the second happening,small dry pieces of oak are placed upon the coals, and the substances in theampulla are heated with a sharper fire, and the air-holes on the furnaceare re-opened if need arise. As soon as the drops are being distilled,the glass ampulla which receives them is covered with a piece of linen