48 DISTILLATION 



used, based upon tho solubility of those, and the insolubility of carbolic ncid, in a 

 small quantity of water. In this case proceed as follows : 2. Put a wine-glassful of 

 the liquid to bo tested in a bottle, and pour on it half a pint of warm water. If tho 

 greater part dissolves, it is an adulterated article. Test the liquid in the bottle with 

 litmus-paper; if strongly acid, it will show the probable presence of sulpho-.-n-iils, 

 whilst if alkaline it will show that caustic soda has boon probably usod as a sohvnt,.' 



DISINTEGRATION. Tho mechanical breaking up of rock under tho action of 

 atmospheric influences. It is distinguished from decomposition, which always refers 

 to some chemical action. 



DISTHENE. A name given to Cyanite, in allusion to the unequal degree of hard- 

 ness which crystals of this mineral exhibit in different directions. See CYANITE. 



DISTILLATION". Distillation consists in the conversion of any substance into 

 vapour, in a vessel so arranged that the vapours are condensed again and collected in 

 a vessel apart. 



The word is derived from the Latin dis and stillo, I drop, meaning originally to 

 drop or fall in drops, and is very applicable to the process, since the condensation 

 generally takes place dropwise. 



It is distinguished from sublimation by the confinement of the latter term to cases 

 of distillation in which the product is solid, or, in fact, where a solid is vaporised and 

 condensed without visible liquefaction. 



Tho operation may simply consist in raising the temperature of a mixture suffi- 

 ciently to evaporate the volatile ingredients ; or it may involve tho decomposition of 

 the substance heated, and the condensation of the products of decomposition, when it 

 is termed destructive distillation ; in most cases of destructive distillation the bodies 

 operated upon are solid, and the products liquid or gaseous ; it is then called dry 

 distillation. 



In consequence of the diversity of temperatures at which various bodies pass into 

 vapour, and also according to the scale on which the operation has to be carried out, 

 an almost endless variety of apparatus may be employed. 



Whatever be the variety of form, it consists essentially of three parts : the retort 

 or still, the condenser, and the receiver. 



On the small scale, in the chemical laboratory, distillation is performed in tho simplest 

 way by means of the common glass retort a, and receiver b, as in fig. 609. The great 



609 



610 



advantages of tho glass retort are that it admits of constant observation of the mate- 

 rials within, that it is acted upon or injured by but a few substances, and may bo 

 cleaned generally with facility. Its great disadvantage is its brittlenoss. 



Tho retort may be either simple, as in fig. 610, or tubulated, as infiff. 611. 



Eetorts should generally bo chosen sufficiently convex in all parts, the degree of 

 curvature of one part passing gradually into that of the neighbouring portions, as is 

 represented in the figure ; tho part to bo heated should, moreover, bo as uniform in 

 point of thickness as possible. Tho tubulated retort is more liable to crack than tho 

 plain one, on account of the necessarily greater thickness of the glass in tho neigh- 

 bourhood of tho tubulaturo ; nevertheless, it is very convenient on account of tho facility 

 which it offers for tho introduction of tho materials. 



In charging retorts if plain, a funnel with a long stem should bo employed, to avoid 

 soiling tho neck with the liquid to bo distilled ; when a solid has to bo introduced, it 



