912 NEUTRAL COLOURING MATTERS. 



and ether. Nitric acid converts it into oxalic acid. It is con- 

 sidered by Gmelin and Baer as a body analogous to as- 

 paragin. 



VEGETABLE ALBUMEN AND LEGUMIN. 



When fresh gluten from wheaten flower is digested in hot 

 alcohol, till everything soluble is taken up, vegetable albumen 

 is left, of a greyish colour. It is soluble in water, and is coagu- 

 lated by heat, insoluble in alcohol and ether, and agrees per- 

 fectly in properties with animal albumen. 



Braconnot observed a peculiar principle in the fleshy cotyle- 

 dons of the seeds of papilionaceous plants, to which he gave 

 the name legumin. Ripe peas, softened with water and reduced 

 to a pulp, gave, when mixed with pure water, a milky liquid, 

 from which starch precipitated, and which retained legumin in 

 solution, seemingly combined with a vegetable acid. When 

 evaporated by heat, the solution does not coagulate, but depo- 

 sits the legumin by little and little, under the form of diapha- 

 nous pellicles. It is purified by washing it, while still moist, 

 with boiling alcohol. It then has a fine white colour, and 

 does not affect litmus paper. Legumin is soluble in water, 

 but insoluble in alcohol. It dissolves very readily in acetic, 

 oxalic, citric and other vegetable acids, but is precipitated from 

 solution, on the contrary, by the mineral acids, which last, form 

 sparingly soluble compounds with legumin. Alkaline hydrates 

 and carbonates also dissolve it with facility, and the solutions 

 froth like a soap. 



M. Liebig has lately made the interesting observation that 

 legumin is identical in properties with the animal principle 

 casein, and has the same composition. It is also accompanied 

 by the same salts, namely potash, phosphate of potash, mag- 

 nesia, lime and oxide of iron, as the casein of milk. 



NEUTRAL COLOURING MATTERS. 





 INDIGO. 



Formula of blue indigo, C 16 H 5 NO 2 . (Crum, Dumas). 



This important colouring matter exists in the leaves of all the 

 species of the Indigofera. It is obtained also from Nerium tine- 

 torium, and in small quantity from Isatis tinctoria (pastel or 

 woad), and various other plants. In India, the indigofera plants 



