442 



BOOK X. 



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 the 

 ingredients placed in the ampulla, they are gradually heated over burning 

 charcoal until they begin to exhale vapour and the ampulla is seen to trickle 

 with moisture. But when this, on account of the rising of the vapour, turns 

 red, and the aqua distils through the spout of the operculum, then one must 

 work with the utmost care, lest the drops should fall at a quicker rate than 

 one for every five movements of the clock or the striking of its bell, and 

 not slower than one for every ten ; for if it falls faster the glasses will be 

 broken, and if it drops more slowly the work begun cannot be completed 

 within the definite time, that is within the space of twenty-four hours. To 

 prevent the first accident, part of the coals are extracted by means of an iron 

 implement 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 the 

 ampulla are heated with a sharper fire, and the air-holes on the furnace 

 are 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 



