X. THE CHEMICAL CONSTITUENTS OF PLANTS 205 



Many aliphatic alcohols, in some cases free, but more commonly 

 as esters, occur in essential oils. 



Many fatty acids also are found, chiefly as esters of organic radicles, 

 e.g., the acetates of linalol, geraniol, borneol, menthol are of common 

 occurrence. Hydrocyanic acid, HCN, occurs in bitter almond oil. 

 Sulphur compounds are characteristic of several essential oils derived 

 from cruciferous plants, e.g., vinyl sulphide, (C 2 H 3 ) 2 S, boiling-point 101, 

 occurs in oil of Allium ursinum ; ally I sulphide, (C 3 H 5 ) 2 S, boiling-point 

 140 , occurs in oil of garlic ; allyl isothiocyanate, C 3 H 5 NCS, boiling- 

 point 201, is the chief constituent cf oil of mustard. They all possess 

 a most disagreeable odour. 



Many of these substances are not present as such in the plant, but 

 in union with glucose and other substances as the compounds known 

 as glucosides ; e.g., almonds do not contain any benzaldehyde, but 

 amygdalin, C^H^NO-^, which in presence of water and under the 

 action of an enzyme, emulsin, splits up into benzaldehyde, hydrocyanic 

 acid and glucose 



C 20 H 27 NO n + 2H 2 = C 6 H 5 CHO + HCN + 2C 6 H 12 O G . 



Similarly, allyl-isothiocyanate is not present as such in mustard 

 seeds, but as a compound, potassium myronate, KC 10 H 18 NS 2 O 10 . This, 

 under the action of an enzyme, myrosin, is split up as follows : 



KC 10 H 18 NS 2 O 10 = C 8 H 5 NCS + KHSO 4 + C 6 H 12 O fl . 



The Resins are now regarded as the products of the oxidation of 

 terpenes rather than the mother substances from which terpenes are 

 derived. They have no uniformity of constitution, as is the case with 

 the fats, but present wide differences in chemical character. They may 

 be divided into 



1. The balsams, which consist of resinous substances associated 

 with terpenes. Canada balsam, obtained from Pinus balsama of 

 South America, and crude turpentine or Venice turpentine, from many 

 pines, are good examples. 



Crude turpentine consists of ordinary rosin or colophony dissolved 

 in turpentine oil. Rosin consists mainly of sylvinic acid, C^H^O^ 1 a 

 monobasic acid, whose sodium salt is used in the manufacture of 

 cheap soaps. 



2. The solid or hard resins. These are amorphous substances 

 of vitreous character, which contain very little terpene. They consist 

 chiefly of esters, alcohols, anhydrides and acids of the aromatic series, 

 generally of very complex character. In addition there are present 

 certain substances which are neither hydrocarbons, esters, alcohols, 

 anhydrides, nor acids, and which are called resenes. Many different 

 bodies of this class have been isolated and analysed, but their con- 

 stitution is not known, e.g., from copal a substance, C 25 H 38 O 4 , from 

 dragon's blood, C 20 H 40 O 4 . Many other substances of complicated 

 character have been obtained from the hard resins. 



To the class of hard resins belong many substances of great im- 



iFahrion, Zeit. filr angew. Chemie,' 1901, 3 Dec. 



