Charles Everitt

“ A common type of condenser consists of a copper worm placed in a water bath; but more generally straight tubes of copper or cast iron which cross and recross a rectangular tank are employed, since this form is more readily repaired and cleansed. Wood-spirit, petroleum and coal-tar distillates are condensed in plant of the latter type. In cases where the condenser is likely to become plugged there is a pipe by means of which live steam can be injected into the condenser. The supply of water to the condenser is regulated according to the volatility of the condensate. ”

“ The still is usually fed continuously by the heated water from the condenser. The first portion of the distillate brings over the gases dissolved in the water, ammonia and other volatile impurities, and is consequently rejected; scarcely two-fifths of the entire quantity of water can be safely used as pure distilled water.
Apparatus for the economic production of a potable water from sea-water is of vital importance in the equipment of ships. The simple distillation of sea-water, and the production thereby of a certain proportion of chemically fresh water, is a very simple problem ”

“ Several modes of heating are adopted. In some cases, especially in dry distillations, the furnace flames play directly on the retorts, in others, such as in the case of nitric acid, the whole still comes under the action of the furnace gases to prevent condensation on the upper part of the still, while in others the furnace gases do not play directly on the base or upper portion of the still but are conducted around it by a system of flues (see Coal-Tar) . ”

“ The vaporization of a substance below its normal boiling-point can also be effected by blowing in steam or some other vapour; this operation is termed “distillation with steam.” “Dry distillation” is the term used when solid substances which do not liquefy on heating are operated upon; “sublimation” is the term used when a solid distils without the intervention of a liquid phase. ”

“ Steam heating, dry or live, is employed alone and also as an auxiliary to direct firing.
The condensing plant varies with the volatility of the distillate. Air cooling is adopted whenever possible. For example, in the less modern methods for manufacturing nitric acid the vapours were conducted directly into double-necked bottles (bombonnes) immersed in water. A more efficient arrangement consists of a stack of vertical pipes standing up from a main or collecting trough and connected at the top in consecutive pairs by a cross tube. ”

“ Dry distillation is extremely wasteful even when definite substances or mixtures, such as calcium acetate which yields acetone, are dealt with, valueless by-products being obtained and the condensate usually requiring much purification. ”

“ The technology of distillation is best studied in relation to the several industries in which it is employed; reference should be made to the articles Coal-Tar, Gas, Petroleum, Spirits, Nitric Acid, &c. ”

“ Operating in a current of carbon dioxide facilitates the process by preventing overheating.
7. Distillation in Chemical Technology.—In laboratory practice use is made of a fairly constant type of apparatus, only trifling modifications being generally necessary to adapt the apparatus for any distillation or fractionation; in technology, on the other hand, many questions have to be considered which generally demand the adoption of special constructions for the economic distillation of different substances. The modes of distillation enumerated above all occur in manufacturing practice. ”

“ The condensing apparatus must also be conditioned by the volatility. With difficulty volatile substances, e.g. nitrobenzene, air cooling of the retort neck or of a straight tube connected with the distilling flask will suffice; or wet blotting-paper placed on the tube and the receiver immersed in water may be used. For less volatile liquids the Liebig condenser is most frequently used. ”

“ Distillation under Reduced Pressure.—This method is adopted for substances which decompose at their boiling-points under ordinary pressure, and, generally, when it is desirable to work at a lower temperature. The apparatus differs very slightly from that employed in ordinary distillation. The “receiver” must be connected on the one side to the condenser, and on the other to the exhaust pump. A safety vessel and a manometer are generally interposed between the pump and receiver. ”

“ By rotating the disk the tubes may be successively brought under the end of the condenser. Boiling under reduced pressure has one very serious drawback, viz. the liquid boils irregularly or “bumps.” W. Dittmar showed that this may be avoided by leading a fine, steady stream of dry gas-air, carbon dioxide, hydrogen, &c., according to the substance operated upon—through the liquid by means of a fine capillary tube, the lower end of which reaches to nearly the bottom of the flask. ”

“ In general, when the substance to be distilled has a vapour pressure of only 10 mm. at 100° C., distillation with steam can be adopted, if the product can be subsequently separated from the water.
When distilling a mixture of partially miscible components a distillate of constant composition is obtained so long as two layers are present, i.e. ”

“ Cast iron stills are provided with a hemispherical head or dome, generally attached to the body of the still by bolts, and of sufficient size to allow for any frothing. It is invariably provided with an opening to carry off the vapours produced. ”