154 



HISTORY OP THE VEGETABLE KINGDOM. 



enrplificd in tlie cinnamon tree and camplior 

 tree. The peacli tree, liowever, furnishes an ex- 

 ception to this rule. Its flowers are purgative, 

 and the whole plant aromatic ; but its juice is 

 without any distinguished virtues. 



Malpighi regarded the proper juice as the prin- 

 ciple of nourishment, and compared it to the 

 blood of animals ; hut this analogy does not hold 

 very closely. The sap is, perhaps, more analo- 

 gous to the blood, from Avhich the proper juice 

 is rather a secretion. In one respect, however, 

 the analogy holds good, that is, with regard to 

 extravasated blood and peculiar juices. If the 

 blood escapes from the vessels, it forms neither 

 flesh nor bones, but tumours ; and if the proper 

 juices escape from the vessels containing them, 

 they form neither wood nor bark, but a lump or 

 deposit of inspissated fluid. To the sap, or to 

 the proper juice, or rather to a mixture of both, 

 we must refer such substances as are obtained 

 from plants under the name of expressed juices, 

 because it is evident that they can come from 

 no other source. In this state tliey are generally 

 obtained in the first instance, whether with a 

 view to their use in medicine, or their applica- 

 tion to the arts. It is the business of the che- 

 mist, or artist, to separate and purify them after- 

 wards, according to the peculiar object he may 

 happen to have in view, and the use to which 

 he purposes to apply them. They contain, like 

 the sap, acetate of potass or of lime, and assume 

 a deeper shade of colour when exposed to the 

 fire or air. The oxymuriatic acid precipitates 

 from them a coloured and flaky substance, as 

 from the sap ; and they yield by evaporation a 

 quantity of extract; but they differ from the 

 sap in exhibiting no traces of tannin or gallic 

 acid, and but rarely of the saccharine principle. 



Ashes. When vegetable matter is submitted 

 to the action of fire, all its volatile parts are 

 dissipated, and there only remains a small pro- 

 portion of incombustible ashes. Tliis ash ex- 

 hibits a flaky whitish appearance, is soft and 

 crumbling to the touch, and is both tasteless and 

 inodorous. Ashes may be obtained from all parts 

 of the plant, but in different quantities from the 

 same weight, not only in different plants, but in 

 dififerent parts of the same plant. Thus, herba- 

 ceous plants, after being dried, yield more ashes 

 than woody plants, the leaves more than the 

 branches, and the branches more than the ti-unk. 

 The alburnum yields also more ashes than the 

 wood ; and putrified vegetables yield more ashes 

 than the same vegetables in a fresh state, if the 

 putrefaction has not taken place in a current of 

 water. The result of Saussure's experiments on 

 this subject was the following: p,ni..k« 



1000 part* of dried leave» of oak pathfri'd in Mav, , 53 



• Rhoaodendrum f('rrii£fineum, 30 



Kftcului hippofastiinus, . 72 

 do. trunk & brandies, 35 

 do. gathered in Sept. 86 

 do. gathered in Oct. 3 1 



dn. 

 do 



do. 



1000 parti dried bark of the oak. 



This ash is a compound of several ingredients, 

 the principal of which are alkalies, earths, and 

 metals. 



Alkalies. Two of the well known alkalies, 

 potass and soda, are obtained from the ashes of 

 plants ; but of late years chemists have discovered 

 upwards of thirty distinct alkaline substances in 

 the vegetable juices. These alkalies have been 

 named generally after the plants from which 

 they are derived, as strj/chnina, atropina, qui- 

 nina, &c. 



Potass. If the ashes ot vegetables, burnt in 

 the open air, are repeatedly washed in water, 

 and this water filtered and evaporated to dry- 

 ness, potass is left behind. The potass of com- 

 merce is manufactured in this manner, though it 

 is not quite pure; but it may be purified by 

 dissolving it in spirits of wine, and evaporating 

 the solution to dryness in a silver vessel. When 

 pure, it is white and semi-transparent, and is 

 extremely caustic and deliquescent. It dissolves 

 all soft animal substances, and changes vegetable 

 blues into green. It dissolves alumina, and also 

 a small quantity of silex, with which it fuses 

 into glass with heat. It had long been suspected 

 by chemists to be a compound substance, which 

 conjecture was put beyond a doubt by the bril- 

 liant experiments of Sir H. Davy, who proved it 

 to consist of a metallic base, in combination with 

 oxygen. 



Soda. This substance is found chiefly in ma. 

 rine plants, and those growing within the influ- 

 ence of salt water. It is obtained from the ashes 

 of burnt fuci, by means of solution in water. 

 Besides the fuci, or sea weed, it is found in great 

 abundance in salsola soda and zostcra maritima. 

 It is generally obtained in the state of a carbon- 

 ate, and is purified in the same manner as potass, 

 to which it is similar in its general properties, 

 but from which it is easily distinguislied by its 

 forming a hard soap with oil, while potass forms 

 a soft soap. It, too, is a combination of a me- 

 tallic base with oxygen. The importance of 

 tliis alkali in the arts is very great. It enters 

 into the formation of glass, soap, and various 

 other materials used in the dyeing and manu- 

 facture of cloths. They are also of essential im- 

 portance in medicine. 



Earths. The earths which are usually found 

 in vegetables are lime, silex^ alumina, and mag- 

 nesia. Of these, lime is by far the most frequent 

 and abundant, and it is generally found com- 

 bined with phosphoric, carbonic, or sulphuric 

 acids. The phosphate of lime is, next to the al- 

 kaline salts, the most abundant ingredient in tlie 

 ashes of green herbaceous plants, whose parts are 

 all in a state of active vegetation. The leaf of 

 a tree bursting from the bud contains in its ashes 

 a greater proportion of earthy pliosphate than 

 at any other period. One hundred parts of the 

 ashes of the leaves of the oak, gathered in May, 



