DISTILLATION 



1809 



DISTILLATION 



and condensing the vapor which it forms is 

 called distillation. In the above example, the 

 water collected in the milk bottle is distilled 

 water. Distillation, it will be noted, embraces 

 the two processes of evaporation and condensa- 

 tion. Water is sometimes distilled to purify it. 

 If the original water contains salt (or any other 

 substance) that does not evaporate at the boil- 

 ing temperature, that substance will remain in 

 the kettle. The distilled water will not be 

 salty. The natural purification of water by dis- 

 tillation is constantly proceeding on a grand 

 scale. Water is evaporated from the sea, from 

 the soil and from the leaves of trees and plants. 

 The water vapor so formed is recondensed into 

 clouds and mists and dew. Rain and dew are 

 forms of naturally-distilled water. 



The apparatus for distilling is called a still. 

 It has three essential parts: (1) the boiler, or 

 receptacle to hold the liquid after distillation; 

 (2) the condenser, in which the vapor is cooled 

 to reconvert it into liquid; (3) the retort, in 



FIG. 1 



In this kind of still is the boiler, b is the re- 

 tort for collecting the distilled liquid, c is the pipe 

 leading from a to b, and d is the condenser, 

 through which the tube c passes, surrounded by 

 running cold water. 



which the distilled liquid (the distillate) is 

 collected. In our experiment the kettle was 

 the boiler, the cooled bottle the condenser, and 

 a glass held under the mouth of the bottle 

 would constitute a retort. The accompany- 

 ing diagram (Fig. 1) shows the parts of a 

 simple still. In large stills the condenser 

 usually consists of a long pipe coiled in a 

 spiral and immersed in a tank through which 

 cold water is constantly running (Fig. 2). 



Fractional Distillation. As a rule it is not 

 possible to separate two liquids by a simple 

 distillation. Although alcohol, for instance, 

 boils at 172 F. (forty degrees below the boil- 

 ing point of water), water will evaporate fairly 

 rapidly at that temperature. If, then, we 

 boil a mixture of alcohol and water and con- 

 dense the vapor, the product obtained will con- 

 114 



Q 



tain water as well as alcohol. But the dis- 

 tillate collected at the first will have a much 

 larger proportion of alcohol than the liquid 

 in the retort. So by collecting the distillate 

 in fractions, we 

 can partially sep- 

 arate the two 

 liquids. By re- 

 distilling each of 

 the fractions we 

 can carry the sep- 

 aration further. 

 Fractional distil- 

 lation is made use 

 of in distilleries, 

 and the propor- 

 tion of alcohol in 

 distilled liquors, 

 such as brandy, 

 whisky and rum, 

 is always much 

 greater than in 

 liquors (such as 

 wines and beers) 



made without T 



In this larger condenser o 



distillation. is the pipe leading from a 



r, , | boiler ; b is a coil of pipe 



Petroleum re- called the worm, and it is sur- 



finini? ij nnnthpr rounded by cold water which 



r flows into the vessel from the 



industry in which tank c; d is the retort for re- 



fractional distil- celving the c 

 lation plays a very important part. Petroleum 

 (which see) is a mixture of a great many sub- 

 stances. By fractional distillation it is sepa- 

 rated into a number of fractions, which are 

 used for different purposes. The first fractions 

 obtained in distilling petroleum are naphtha 

 and benzine. Next comes gasoline, afterwards 

 kerosene, and then heavier oils which are used 

 as fuels or for lubricating machinery. All of 

 these fractions are still mixtures of different 

 substances, but the original, very complex mix- 

 ture has been sufficiently separated to yield 

 a number of useful products. In a similar 

 manner a number of useful products are ob- 

 tained from coal tar. 



Destructive Distillation. In simple distilla- 

 tion and in fractional distillation, no new sub- 

 stances are formed. These present are merely 

 separated, completely or partially. The term 

 destructive distillat\on is applied to processes in 

 which new substances are produced. When 

 wood is heated in closed boilers, charcoal, 

 acetic acid, wood alcohol and acetone arc pro- 

 duced, together with water and some gases. 

 When coal is similarly treated, coal gas, ammo- 

 nia, coal tar and coke are obtained. These 



