DISTILLATION 



Ketorts, or flasks with bent tubes, which screw in thus (fig. 614), of copper, are 

 employed when it is requisite to produce high temperatures, as for the preparation of 

 benzole from benzoic acid and baryta, or in making marsh gas from an acetate, &c. 



614 



In distilling hydrofluoric acid the whole apparatus- should be constructed in lead ; 

 the receiver consisting of a U-shaped tube of lead, which is fitted with leaden stoppers 

 so as to serve for keeping the acid when prepared ; or a receiver of gutta percha may 

 be- employed with a stopper of the same material. (Fig. 615.) 



For many purposes in the laboratory as, for instance, the preparation of oxygen by 

 heating binoxide of manganese, in the manufacture of potassium, &c. &c. ; where 

 high temperatures are required, the iron bottles in which mercury is imported from 



615 



Spain may be employed, a common gun-barrel being screwed into them to act as a 

 delivery tube or condenser. (Fig. 616.) 



On a largo scale an almost endless variety of stills have been and are still employed, 

 which are constructed of different materials. 



The common ' still ' consists of a retort or still proper, in which the substance is 

 heated; and a condenser commonly called a 'worm* on account of its having fre- 

 quently a spiral shape. The retort or still is generally made in two parts : the pan 

 or copper, which is the part to which heat is applied, and is commonly set in a furnace 

 of brickwork, and the ' head? which is generally removed after each opoiation, and 

 refixed and luted upon the pan when again used. The condenser or w<>rm is com- 

 monly placed in a tube or other vessel of water. (See fig. 619.) 



The still may be either constructed of earthenware, or, as is very commonly ti 

 of copper, either plain or electro-plated with silver, according to circumstances ; less 

 frequently platinum is employed. 



The still is either heated by an open fire, as in Jig. 615, or, as is now very commonly 

 the case, by steam. The still-pan (fig. 617) is surrounded by an on jacket, 



and steam is admitted between them from a fteam-boiler Ulder any required pres- 

 sure. In this way the temperature may be regulated with tl.> iccty. 



Various adaptations for heating by steam have- been aippropriately arranged fi) a 

 very convenient form by Mr. Coffey, of ]>unhill Kow, Kinsl'iiry. in his so-called 

 Esculapian Still. It is, in fact, a veritable multwn in parvo, being intend. -d to afford to 

 the pharmaceutical chemist the means of conducting the processes of ebullition, distilla- 



