Book I. COMPOUND PRODUCTS OF PLANTS. 155 



alburnum ; though sometimes it does not flow freely till the bore is carried to the centre. A small branch 

 of a vine lias been known to yield from twelve to sixteen ounces, in the space of twenty-four hours. A 

 maple-tree of moderate size yields about 200 pints in a season, as has been already stated ; and a birch- 

 tree has been known to yield in the course of the bleeding-season, a quantity equal to its own weight. In 

 the sap of fagus sylvatica, Vauquelin found the following ingredients : —Water, acetate of lime, with excess 

 of acid, acetate of potass, gallic acid, tannin, mucous and extractive matter, and acetate of alumia. In 

 1039 parts of the sap of the ulmus campestris, he found 1027 parts of water and volatile matter, 9-240 of ace- 

 tate or' potass, 1.060 of vegetable matter, 0.79b" of carbonate of lime, besides some slight indications of the 

 presence of sulphuric and muriatic acids; and at a later period of the season he found the vegetable mat- 

 ter increased, and the carbonate of lime and acetate of potass diminished. From the above experiments, 

 therefore, as well as from those of other chemists, it is plain that the sap consists of a great variety of ingre- 

 dients, differing in different species of plants ; though there is too little known concerning it to warrant 

 the deduction of any general conclusions, as the number of plants whose sap has been hitherto analysed is 

 yet but very limited. It is the grand and principal source of vegetable aliment, and may be regarded as 

 being somewhat analogous to the blood of animals. It is not made use of by man, at least in its natural 

 state. But there are trees, such as the birch, whose sap may be manufactured into a very pleasant wine ; 

 and it is well known that the sap of the American maple-tree yields a considerable quantity of sugar. 



701. The proper juice. When the sap has received its last degree of elaboration from the different or- 

 gans through which it has to pass, it is converted into a peculiar fluid, called the proper juice. This fluid 

 may tie distinguished from the sap by means of its color, which is generally green, as in periwinkle ; or red, 

 as in logwood; or white, as in spurge; or yellow, as in celandine; from the two last of which it may rea- 

 dily be obtained by breaking the stem asunder, as it will then exude from the fracture. Its principal s : eat is 

 in the bark, where it occupies the simple tubes ; but sometimes it is situated between the bark and wood, 

 as in the juniper-tree ; or in the leaf, as in the greater part of herbs ; or it is diffused throughout the whole 

 plant, as in the fir and hemlock; in which case, either the proper juice mixes with the sap, or the vessels 

 containing it have ramifications so fine as to be altogether imperceptible. It is not, however, the same in 

 all plants, nor even in the different parts of the same plant. In the cherry-tree it is mucilaginous ; in the 

 pine it is resinous ; in spurge -and celandine it is caustic, though resembling in appearance an emulsion. 

 In many plants the proper juice of the bark is different from that of the flower; and the proper juice of 

 the fruit different from both. Its appearance under the microscope, according to Senebier, is that of an 

 assemblage of small globules connected by small and prism-shaped substances placed between them. If 

 this juice could be obtained in a state of purity, its analysis would throw a considerable degree of light 

 upon the subject of vegetation. But it seems impracticable to extract it without a mixture of sap. Sene- 

 bier analysed the milky juice of euphorbia cyparissias, of which he had procured a small quantity consi- 

 derably pure, though its pungency was so great as to occasion an inflammation of the eyes to the person 

 employed to procure it. It mixed readily with water, to which it communicated its color. When left ex- 

 posed to the air a slight precipitation ensued ; and when allowed to evaporate a thin and opaque crust 

 remained behind. Alcohol coagulated it into small globules. Ether dissolved it entirely, as did also oil of 

 turpentine. Sulphuric acid changed its color to black ; nitric acid to green. The most accurate experi- 

 ments on the subject are those of Chaptal. When oxymuriatic acid was poured into the peculiar juice of 

 euphorbia, a very copious white precipitate fell down, which, when washed and dried, had the appear- 

 ance of starch, and was not altered by keepiilg. Alcohol, aided by heat, dissolved two thirds of it, which 

 the addition of water again precipitated. They had all the properties of resin. The remaining third part 

 possessed the properties of woody fibre. The same experiment was tried on the juice of a variety of other 

 plants, and the result uniformly was that oxymuriatic acid precipitated from them woody fibre. 



702. The virtues of plants have generally been thought to reside in their proper juices, and the opinion 

 seems indeed to be well founded. It is at least proved by experiment in the poppy, spurge, and fig. The 

 juice of the first is narcotic, of the two last corrosive. The diuretic and balsamic virtues of the fir reside 

 in its turpentine, and the purgative property of jalap in its resin. If sugar is obtained from the sap of the 

 sugar-cane and maple, it is only because it has been mixed with a quantity of proper juice. The bark 

 certainly contains it in greatest abundance, as may be exemplified in cinnamon and quinquina. But 

 the peach-tree furnishes an exception to this rule : its flowers are purgative, and the whole plant aro- 

 matic ; but its gum is without any distinguished virtues. Malpighi regarded the proper juice as the prin- 

 ciple of nourishment, and compared it to the blood of animals ; but this analogy does not hold very closely. 

 The sap is, perhaps, more analogous to the blood, from which 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 tumors ; and if the pro- 

 per juices escape from the vessels containing them, they form neither wood nor bark, but a lump or depo- 

 sit 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 urder the name of expressed juices, because it is evident that 

 they can come from no other source. In this state they are generally obtained in the first instance whe- 

 ther with a view to their use in medicine or their application to the arts. It is the business of the chemist 

 or artist to separate and purify them afterwards 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 color when exposed to the fire or air. The oxymuriatic acid precipi- 

 tates from them a colored 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. 



7<).'5. Ashes. When vegetables are burnt in the open air the greatest part of their substance is evapo- 

 rated during the process of combustion ; but ultimately there remains behind, a portion which is altogether 

 incombustible, and incapable of being volatilised by the action of fire. This residuum is known by the 

 name of ashes. Herbaceous plants, after being dried, yield more ashes than woody plants ; the leaves more 

 than the branches ; and the branches more than the trunk. The alburnum yields also more ashes than 

 the wood ; and putrefied vegetables yield more ashes than the same vegetables in a fresh state, if the putre- 

 faction has not taken place in a current of water. The result of Saussure's experiments on 1000 parts of 

 different plants was as follows : — 



Gathered in Max), dried leaves of the oak - 53 parts of ushes. 



snreen leaves of the oak • - - 13 



dried leaves of the rhododendron - 30 



dried leaves of the Rsculns himiocastanum 7'2 



trunk and branches of BBKUlUS hinpocastamim 35 



Gathered in September, dried leaves of the eescullU hi)i]iocastanum 86 



dried leaves of the oak - - 55 



green leaves of the oak ... SJ4 



Gathered rrhen injtotver, leaves of nisum sativum 95 



Gathered when in fruit, leaves of uisum sativum - HI 



leaves of Tidajuba • 20 



Gathered before coming intofiower, the leaves of the vicia faba 16 



Oak, the dried bark CO, the alburnum 4, wood - 2 



704. The analysis of the ashes of plants, with a view to the discovery of the ingredients of which they arc 

 composed, produces alkalies, earths, and metals, which must therefore be considered as ingredients in the 

 composition of the vegetable. But vegetable ashes contain also a variety of other principles, occurring, 

 however, in such small proportions as generally to escape observation. Perhaps they contain all substances 

 not capable of being volatilised by the action of fire. 



