( 



HANDLING OF VOLATILE OILS. 27 



The spent herb, which on a large scale amounts to no inconsiderable 

 quantity, may be used as fuel and the ash used as fertilizer, or it 

 may be scattered upon a field and plowed under as a mulch. In 

 some cases the spent herb serves as a useful stock food, an example of 

 which is the peppermint grown in Michigan. 



The advantages far outnumber the disadvantages of the distilla- 

 tion method, the only disadvantage being the possibility of slight 

 decomposition of the ester bodies in some of the more delicate per- 

 fumed plants. However, this is only slight and almost negligible 

 in most herbs. 



HANDLING OF VOLATILE OILS. 



PURIFICATION. 



The volatile oil as it comes from the still is in a crude state, being 

 contaminated by volatile substances which are formed during the dis- 

 tilling process by the action of the steam upon the less stable plant 

 constituents, decomposing them into volatile organic substances, 

 which, although trifling in quantity, nevertheless tend to affect the 

 color, odor, and taste of the oil. 



The chemical changes taking place in the still are numerous, the 

 more important being oxidation and reduction of some of the con- 

 stituents of the oil, as well as of the other plant constituents, saponi- 

 fication of the more unstable esters, and resinification brought about 

 by a polymerization of certain plant constituents, all of which aid in 

 forming volatile substances which mingle with the oil. 



Although a process of purification is not always applied to these 

 crude oils, it is important and sometimes highly profitable to subject 

 the crude product to a process of rectification. By rectification is 

 meant a redistillation of the oil with steam, this procedure affecting 

 a moderate separation of the undesirable substances which may have 

 been formed. The substances which detract from the odor of the 

 oil are usually left behind in the apparatus as a heavy, malodorous 

 liquid slightly resinous in character. Rectification usually results 

 in a fine, finished product, free from foreign odors, and leaves an 

 oil much more presentable in color as well as in odor and taste. 



This process may be conducted in a miniature still built on the 

 same general plan as the large commercial still. The loss in the 

 amount of oil is more than compensated for by the better quality 

 and the increased salability of the rectified oil. 



SEPARATION, FILTRATION, AND DRYING. 



To separate the oil from the aqueous distillate in the receiving 

 vessel, the portion which has not been separated by means of the 

 stop cock on the side of the receiver is poured into a separating fun- 

 nel of glass and the heavier liquid drawn off. The oils resulting from 



195 



