1 1 Chemistry. [ Lecture 28. 



limation, when the vapour condenses into a so- 

 lid, we use a cucurbit with a blind head, or 

 without a pipe, but more commonly a retort and 

 receiver: the retort must have a short and wide 

 neck. A capital is sometimes necessary to re- 

 ceive the vapours that condense in a fluid, before 

 those that condense in a solid begin to rise. 

 Many sublimates are difficult to be converted 

 into vapour, and, when converted into vapour, 

 soon condense; for these a Florentine or com- 

 mon oil flask answers sufficiently well. 



The alembic or cucurbit (fig. 16.) is used for dis- 

 tillation when the products are very volatile. It 

 consists of a body, A, to which is adapted a head, 

 B. The head is of a figure inclined to conical, 

 and has its circumference or base depressed lower 

 than its neck, so that the vapours which rise, 

 and are condensed against its sides, run down, 

 and are conveyed by the nose or beak, C, into 

 the receiver, D. The principal object of this 

 instrument is, that in distillation, and more par- 

 ticularly sublimation, the head may receive the 

 more dense and dry products, while the more 

 volatile pass into the receiver. 



An aludel is analogous to adopters in distilla- 

 tion : its use is to condense bodies according to 

 different degrees of volatility. What remains 

 after the spirit or sublimate is taken off, is called 

 the residuum or caput mortuum. 



The 3d process is CEMENTATION, when va- 

 pours act upon one another, by laying the ma- 



