PRINCIPLES OF FRACTIONAL DISTILLATION. 



25 



The separation of the several constituents of a mixed liquid is most 

 quickly, economically, and completely effected hi a column still, 

 several common forms of which are shown in figures 1, 2, 3, and 4. 

 This consists essentially of a number of small, simple stills placed one 

 above the other in the same column. The general statements made 

 with reference to the liquid and vapor in a simple still are equally 

 true of the contents of each still or chamber of the column still. 

 The vapors above the liquid in the lowest chamber are richer hi the 

 lighter constituents than is the 

 liquid itself. These vapors 

 pass upward through perfora- 

 ted plates or capped openings 

 (see figs. 3 and 4) and, partially 

 condensing, become the liquid 

 in the second chamber, and the 

 vapors in this chamber are in 

 turn richer in the lighter con- 

 stituents than is the liquid in 

 the same chamber. This re- 

 lation is repeated in each suc- 

 cessive chamber until the va- 

 pors at the top of the column, 

 in the earlier stages of the dis- 

 tillation, are practically pure or 

 constitute a mixture of definite 

 composition. If, when this 

 point is reached, the heavier 

 constituents of the liquid are 

 not removed from the still, but 

 the distillation is continued 

 with rising temperature, these 

 constituents pass upward into 

 each successive chamber, obey- 

 ing the same law as in distilla- 

 tion from the simple still. As 

 there are a number of successive stills, however, the mixed liquid 

 when passed through a column still once is, as a rule, separated more 

 completely into its several constituents than by several distillations in 

 a pot still. 



Several forms of column stills applicable to the refining of wood 

 turpentine will be considered. Figure 1 shows one of the simplest 

 forms. It consists of the still proper, surmounted by a fractionating 

 column. The column consists of one or more chambers, containing 

 broken quartz rock or other inert material, or of a number of cham- 

 bers separated by plates, as shown in figure 2. The former is the 



FIG. 2. A periodic column still, with the chambers 

 separated by hooded plates. 



