34 THE PRODUCTION OF VOLATILE OILS AND PERFUMEEY PLANTS. 



Table II. — Yield of oil and percentages of esters and of alcohols ohtaiiuil from 

 fresh and from dry [jlants — Continued. 



These data with respect to the oils from fresh and dry herbs readily 

 illustrate that during the drying of the plants certain factors, assisted 

 by exposure to air and light, undoubtedly bring about chemical 

 changes in the aromatic constituents, which evidence themselves in 

 the final analyses of the oils. 



It will be noted that the yield of oil decreases 63^ per cent in the case 

 of peppermint, while the percentage of decrease of oil from bergamot 

 mint is nearly 43, and from wormwood about 27 per cent. These 

 marked decreases are in part due to the long period of drying, but 

 they at least show that there is a dow^nward tendency, which is very 

 natural considering the volatility of the constituents. 



In all three cases there seems to be an increase in the percentage of 

 esters, w^ith a decrease in the percentage of alcohol, in the dried herb, 

 the chemical changes no doubt being such as to facilitate the produc- 

 tion of esters and to break down the alcohols. Apparently the alco- 

 hols seem to be more unstable, condensing wdth the organic acids in 

 the plant under favorable conditions of heat, light, and moisture to 

 form esters. This latter change is especially noticeable in all the 

 oils, the dry-herb oils being considerably richer in esters than the 

 fresh-herb oils, and correspondingly poorer in alcohols. 



In order to produce the largest yield of oil from a given quantity 

 of herb, distillation should be made immediately after harvesting. 

 There is no noteworthy advantage in drying or even partially drying 

 the plant, since the longer the time between the cutting and the dis- 

 tilling the more volatile oil will be lost by gradual evaporation or 

 volatilization. Although the quantity of oil capable of being carried 

 off into the air by simple drying seems only trifling, nevertheless, on 

 a large scale the loss would be considerable. The increased propor- 

 tion of the odoriferous esters in the oils from dry herbs is insufficient 

 to warrant the drying of the plants before distillation, because of the 

 loss of oil encountered during the drying process. 



VOLATILE OIL PLANTS OF THE UNITED STATES. 



At the present time the number of plants in the United States 

 yielding volatile oils in a commercial way is very small, but the num- 

 ber capable of yielding oils of probable value is correspondingly 



195 



