450 CHEMICAL DISCOVERY AND INVENTION 



to the production of an essential oil which can be distilled off in 

 steam, and is sold as a perfume and flavouring essence. This 

 substance is benzoic aldehyde, C 6 H 5 -CHO, and it is well known 

 that in the crude state it is very poisonous, owing to the presence 

 of prussic acid, which accompanies it. These facts were explained 

 by Liebig and Wohler in 1837. If the cake of bitter almond from 

 which the fixed oil has been squeezed out is exhausted with 

 boiling alcohol a crystalline substance, amygdalin, can be procured 

 from the solution. This is inodorous and almost tasteless, but 

 if mixed with a small quantity of the pulp of sweet almonds and 

 water the essential oil is at once developed : 



C 20 H 27 NO n +2H 2 0=C 7 H 6 0+HCN+2C 6 H 12 6 

 Amygdalin Benz- Hydro- Glucose 



aldehyde cyanic 

 acid 



The bitter and the sweet almond both contain an enzyme, or 

 rather a pair of enzymes (amydalase and prunase) commonly 

 known under the collective term emulsin, which together break 

 up the amygdalin in the manner shown in the equation. It 

 would appear in such a case that the amygdalin, the glucoside, 

 and the enzyme are contained in separate cells within the seed. 

 The seeds of many other fruits of the same natural order as the 

 almond, namely peach, apricot, cherry, etc., as well as the leaves 

 of the common cherry laurel yield essential oil in a similar way. 



Another familiar instance of enzyme action is afforded by 

 common mustard. The domestic mustard flour is destitute of 

 pungency so long as it is dry, but when mixed with water the 

 odour of the essential oil becomes apparent almost immediately. 

 Both black and white mustard seed, like the almond, yield by 

 expression a quantity of a fixed fatty oil which has nothing to do 

 with the pungency. The black mustard seed contains a glucoside 

 called sinigrin or potassium myronate associated with an enzyme 

 called myrosin contained in a separate system of cells. When 

 crushed with water the glucoside is broken up into glucose, 

 mustard oil (allyl isothiocyanate), and potassium hydrogen 

 sulphate : 



CioH 16 NS 2 9 K+H 2 0-C 6 H 12 6 +C 3 H 5 NCS+KHS0 4 

 Potassium myronate Glucose Allyl Potassium 



isothio- hydrogen 

 cyanate sulphate 



