COLORING PRINCIPLES. 145 



CHLOROPHYLLE. 



The green matter which colors the leaves of vegetables is so 

 designated. The attempts which have been made to isolate this 

 matter, render it probable that it is somewhat of the nature of the 

 vegetable waxes. Pelletier and Caventou endeavored to procure it 

 by treating with cold alcohol, the pulp remaining after expressing 

 all the juices from the leaves of various herbaceous plants. By 

 evaporation of the alcoholic liquor, a substance of a deep-green color 

 was obtained, which is chlorophylle, a matter soluble in ether, in al- 

 cohol, the oils, and the alkalies. Heated, it softens and is decom- 

 posed before it melts. Acetic acid dissolves it in very appreciable 

 quantities, so do the sulphuric and hydrochloric acids ; w^ater precipi- 

 tates it from these acid solutions. Berzelius says that chlorophylle 

 exists only in very small quantity in plants, the leaves of a large tree 

 will not perhaps contain more than about 100 grains. 



OF COLORING MATTERS. 



The matters which color the different parts of plants are extreme- 

 ly numerous ; they present great varieties of shade, but are in gen- 

 eral derived from red, yellow, and green. It is seldom that the col- 

 oring matter of a plant exists isolatedly ; it is almost always allied 

 with one or several immediate principles, which are themselves fre- 

 quently colored. Thus red coloring matters are generally combined 

 with yellow principles, which having nearly the same properties, one 

 is with great difficulty separated from another. 



Coloring matters are solid, inodorous, and have little taste. Some 

 are soluble in water, others only dissolve in alcohol or in ether. 

 All combine with the alkalies, and several of them unite intimately 

 with acids ; the greater number are powerfully affected, undergo a 

 true destruction, on exposure to the sun's rays, especially when in 

 contact with moist air. It is familiarly known that vegetable tissues 

 of all kinds, beeswax, &c., are bleached by exposure to the sun and 

 air ; a high temperature acts like light : some vegetable colors are 

 altered, bleached, when they remain exposed for a time to a tem- 

 perature of from 334° to 424° Fahr. The oxygen of the air, which 

 so quickly destroys certain colors, develops others under particular 

 circumstances. 



Alkalies and acids, by uniting with vegetable colors, almost al- 

 ways modify their tints and often change them entirely. Many blues, 

 for instance, become reds, under the agency of acids, greens or 

 yellows under that of alkalies. By neutralizing the acid or the al- 

 kali, the color generally resumes its original tint. 



Several substances, which are colorless in the state in which they 

 are formed in vegetables, become colored by the united action of 

 oxygen and an alkali, such as orceine, which is oxidated and be- 

 comes blue under the simultaneous contact of air and ammonia. 

 The greater number of vegetable coloring matters are destroyed 



13 



