140 



HISTORY OF THE VEGETABLE KINGDOM. 



tlie juice of the sugar cane. Almonda also, 

 and other kernels, from which emulsions are 

 made, have heen found to contain a substance 

 possessing the properties of curd, which resem- 

 bles albnmen very closely. 



Fihrine. A substance somewhat like the 

 fibi-ine of the animal flesh, or muscular parts, 

 WHS detected in the juice of the papau tree, by 

 Vauquelin. When the inspissated juice of this 

 tree was subjected to maceration in water, the 

 greater part of it was dissolved; but there re- 

 mained a portion that was insoluble. It liad a 

 greasy appearance, and became soft and viscid 

 upon exposure to air, assuming a brown colour, 

 with a slight degree of transparency. When 

 thrown upon ignited charcoal it melted, exuding 

 drops of grease, accompanied with a noise like 

 that of meat roasting, and producing smoke 

 which had the odour of volatilized fat. It left 

 no residuum. This substance was vegetable 

 fibrine, possessing the properties of the fibrine 

 of animals. 



Extract. Vegetable substances, when macer- 

 ated in water, dissolve; and if the water is eva- 

 porated, a residuum remains, which is called 

 vegetable extract. As vegetables differ consider- 

 ably, however, according to the families to which 

 they belong, and to the nature of the soil and 

 climate in which they have grown, it is obvious 

 that this extract must also vary according to the 

 plants which have been employed in its produc- 

 tion. It was necessary, therefore, for the pur- 

 poses of chemical accuracy, to endeavour to as- 

 certain whether there existed in extracts any 

 peculiar and definite principle, independent of 

 such accidental ingi'edients as have been now al- 

 luded to; and which might itself be regarded as 

 the true extractive principle. With this view, 

 Vauquelin commenced a series of experiments 

 chiefly upon the sap and expressed juices of 

 plants, dui-ing the process of which he remarked 

 that they always began to acquire a darker shade 

 of colour from the moment they were exposed 

 to the air; and that during the evaporation a 

 brown or reddish pellicle was formed on the 

 surface, which afterwards broke into flakes and 

 remained insoluble. Similar appearances were 

 observed in medicinal extracts, and the longer the 

 evaporation was continued the more of the in- 

 soluble flakes were formed. This was accord- 

 ingly regarded as a detection of the true extrac- 

 tive principle; and the formation of the peUicIe 

 and flakes was found to be the result of its ab- 

 sorption of a portion of the atmosphere, to which 

 it was thus found to have a strong afiinity. This 

 extract, then, is thus distinguished. It is solu- 

 ble in water when directly obtained from the 

 vegetable, but becomes afterwards insoluble in 

 consequence of the absorption of oxygen from 

 the atmosphere. It is soluble in alcohol, and 

 unites with alkalies, forming compounds which 



are soluble in water. When distilled it yields 

 an acid fluid, impregnated witli ammonia, and 

 seems to be composed chiefly of hydrogen, oxy- 

 gen, carbon, and a little nitrogen. This extrac- 

 tive matter is found in greater or less quantity 

 in all plants, and is very generally an ingredient 

 of the sap and bark, particularly in barks of an 

 astringent taste; but yet it is not exactly the 

 same in all plants, even when separated from all 

 impurities. Several different kinds of extract, 

 then, are distinguishable. 



Extract of catechu is obtained from an infusion 

 of the interior wood of the mimosa catechu. It is 

 of a brown colour, and very astringent, and hence 

 used as an astringent and tonic in medicine. 



Extract of senna is got from an infusion of 

 the dried leaves of cassia senna in alcohol; it 

 is of a brown colour, bitter, and slightly aro- 

 matic. 



Extract of Quinquina was obtained by Four- 

 croy, by evaporating an alcoholic solution of the 

 bark of the quinquina tree. It is of a brown 

 colour and bitter taste; soluble in boiling water, 

 though insoluble in cold. 



Extract of saffron is obtained from the sum- 

 mits of the pistils of the crocus satimis. 



Many other extracts might be enumerated 

 which were formerly much used in medicine, 

 though now their efficacy is not so much de- 

 pended upon as preparations of the substances 

 from whence they were derived. Vegetable ex- 

 tracts are, however, extensively used in the arts, 

 especially for the purpose of dyeing cloths and 

 silks. 



Colouring Matter. Nothing can exceed the 

 beauty and delicacy of the tints of flowers ; and 

 though these have been the admiration of all 

 ages, yet the nature of the colouring principle is 

 not yet by any means well understood. Chemists, 

 however, have endeavoured to isolate this colour- 

 ing matter, and to investigate its nature. It 

 seems to have a great affinity for oxygen, the 

 earthy alkalies, and metallic oxides, as also for 

 cloths made of vegetable fibre or animal wools. 

 This affinity seems stronger for the latter than 

 the former, and hence wool and silk assume a 

 deeper dye, and retain it longer than cotton or 

 linen. Colouring matter exhibits a great variety 

 of tints, as it occurs in different species of plants, 

 and as it is combined with the oxygen of the at- 

 mosphere it assumes a deeper shade ; but it 

 loses, at the same time, a portion of its hydrogen, 

 and becomes insoluble in water, thus indicating 

 its relation to extract. 



The fundamental colotirs used in the art of 

 dyeing are blue, red, yellow, and brown. The 

 finest of all vegetable blues is that which is known 

 by the name of indigo. It is procured from a 

 shrub which is cultivated in Mexico and in the 

 West Indies, the /«(7yro/era tinctoria of Linnaeus. 

 Tlie plant arrives at maturity in about six 



