VOLATILE OILS AND RESINS SI J 



to which the odor is due, and many other compounds such 

 as terpenes, alcohols, aldehydes, and esters. It is obtained 

 from the rind of lemons either by rupturing the oil cells over 

 a sponge, or rolling in a vessel lined with spikes, or by dis- 

 tillation, or expression. The two latter methods do not 

 yield as good an oil as the sponge method. It is a pale 

 yellow oil, lighter than water, and its uses are the same as 

 for clove and cinnamon oils. 



(e) Oil of Mustard.- -This oil is chiefly ally] isothio- 

 cyanate, CH 2 :CH.CH 2 .N:C:S, with some carbon disulphide 

 and allyl cyanide. In nature it occurs in the seeds of black 

 mustard as a glucoside of potassium acid sulphate and allyl 

 isothiocyanate, called potassium myronate which is hydro- 

 lyzed by a naturally occurring enzyme when water is present. 

 The seeds are first expressed for the fixed oil, then treated 

 with water, and digested in the cold when the enzyme 

 myrosin converts the glucoside into glucose, potassium 

 acid sulphate, and allyl isothiocyanate. The latter is then 

 distilled off. It is a colorless or a pale yellow oil, heavier than 

 water, with pungent odor and burning taste. It is used in 

 medicine largely. 



(/) Oil of Onion consists principally of allyl-propyl- 



disulphide, 



CH>:CH.CH2.S 



I 

 CH3 . CH2 . CH2 . s 



and some other sulphides. It is obtained by distillation 

 from onions. It is not of much value commercially, but 

 is the compound which gives to onions and garlic their 

 characteristic odor and taste. 



(g) Oil of Peppermint contains a great number of differ- 

 ent compounds in small amounts — terpenes, alcohols, esters, 

 acids, and aldehydes, but principally menthol, a closed-chain 

 compound but not a binzine compound : 



CH2.CH2 (H3 



/ \ / 



CH3.CH CH.CH 



\ / \ 



CH2.CH CH 3 



I 

 OH 



