FERMENTS AND MISCELLANEOUS PRODUCTS 91 



oxygen, but several contain also nitrogen. Though very com- 

 plex, a number of the vegetable colours have been syntheti- 

 cally prepared, and their constitution is well understood. 

 Many of them occur in plants as glucosides, and are obtained 

 on hydrolysis of these compounds. Some are acids, and 

 others have not yet been investigated. 



Indigo, the blue colouring matter obtained from the twigs 

 and leaves of several species of plants, occurs in the form of a 

 glucoside called indican. This compound is resolved by the 

 action of ferments, or of dilute acids, into glucose and in- 

 doxyl ; the latter is a colourless body, but on oxidation yields 

 indigotin (indigo blue). 



C 14 H 17 6 N + H 2 O -> C 8 H 7 ON + C 6 H 12 O 6 



(Indican.) (Indoxyl.) (Glucose.) 



2C 8 H 7 ON + O 2 -> 2H 2 O + C 16 H 10 O 2 N 2 



A number of other products of brown and red colours are 

 obtained at the same time, and are separated by solvents. 

 The indigotin, C 16 H 10 O 2 N 2 , is then purified by sublimation. 

 The constitution indicated by the formula below is ascribed 

 to it. 



(Indigotin.) 



It is insoluble in water, alcohol, and dilute acids, but dis- 

 solves readily in strong sulphuric acid and some organic 

 solvents. 



A substance similar to indican sometimes occurs in the 

 urine of herbivora, and gives rise to a blue coloration when 

 the liquid is allowed to stand, or is treated with dilute 

 acids. 



Alizarin, another important vegetable dyestuff, is obtained 

 from the roots of madder. It occurs in the form of a gluco- 

 side called ruberythric acid. The latter is easily resolved by 

 the action of acids, or by certain ferments, into alizarin and 

 glucose. 



C 26 H280i4 + 2H 2 H> C 14 H 8 4 + 2C 6 H 12 6 



