the moisture under the glass had evaporated. It might perhaps have given a little more in a shorter time, and the hygrometer would have marked a trifle more moisture; but it is forced from the plant, and, so far from giving it naturally, I have every reason to believe, that it acts as heat does, and tears its way through the cuticle, as animals in an air pump will sometimes have the blood forced through the pores of the skin.

finement.

It is certain, that a plant cannot exist without air, and We cannot judge of the that it languishes in a confined air. In this state how im- secretions of a possible to judge of its secretions. I cannot help being plant in conpersuaded, that excellent botanist Mirbel had many doubts Mirbel. of its existence. The clear and simple account he gives of the production of the gasses and juices of plants is such, that but for one line, it would be the most perfect thing I ever saw; I hope I may be excused translating the few lines. "It is certain, that the carbonic acid gas, produced and renewed without ceasing by combustion, is dissolved in water, which the atmosphere holds suspended in vapour; and which passes through the thin cuticle of the leaves, and penetrates the albumen, and gains the nourishing vessels. This absorption takes place when the sap and other fluids (at first dilated by the heat of the day,) become condensed by the cold of the night, and fall towards the lower extremities of the tree; for then the liquids take less room, a sort of vacuum takes place in the higher parts; and the vapours flowing around enter the leaves by the pores, as we see water force itself into the pipe of a pump by the help of the piston, that produces a vacuum. But as soon as the sun appears above the horizon, these same fluids, joined to those the roots have pumped up from the earth, drawn by heat, are carried into the leaves, and escape by the pores, and it is then that the water and carbonic acid gas enforced by light are decomposed, and the torrent of oxigen flows from the leaves."

Now if the water escapes through the pores, how can it be there to be decomposed by the light, and to give out its oxigen? Setting aside therefore this line, it is the clearest account of vegetation, and the most just, I had ever the pleasure of reading. But certain it is, that, if plants perVOL. XXIII.-SUPPLEMENT.

2 A

spired,

Water cannot be decomposed if it escape

through the

pores.

A trifling per spiration.

The vine per

stalk.

spired, they could not give out oxigen. However, though the appearance of perspiration has invariably proved either a cryptogamian plant; the bubbles which hold the perfumed liquor of leaves, and which are to be found in all leaves that are scented; the eggs of insects; the edges of the pores, &c.; I do not deny, that there may be a very trifling degree of insensible perspiration: for I think that sort of scurf, or jelly, found on the leaves, arises from it; but this is trifling, and scarcely worth mentioning.

Of the innumerable quantity of plants I have examined, spires from its there is but one, that in my opinion really does perspire ; and that not on the leaf, but the stalk. This is the vine. When the vine is extremely full of juice, a bubble appears on the stalk, which, magnified, is not a plant; but really issues from the vine as the proper juice of it, for I can see no stalk. With the same truth I should have mentioned it, if I had found hundreds; for to attain truth is my aim, and I am really attached to no system whatever. Mine are merely desultory discoveries, not mine indeed, but those of the solar microscope, to which I transfer all the honour, if there is any. As to the sickness of a plant, any person may perceive, when a plant has been gathered an hour or two, how damp and moist it grows; it is the same when placed under a glass, it droops and grows clammy.

I am, Sir,
Your obliged Servant,

AGNES IBBETSON.

Belleveu 26th June.

Attempts at

numerical tables

of elective at

tractions.

IV.

A numerical Table of elective Attractions; with Remarks on the Sequences of double Decompositions. By THOMAS YOUNG, M. D. For. Sec. R. S.*

ATTEMPTS have been made, by several chemists, to obtain a series of numbers, capable of representing the mu

* Philos. Trans. for 1809, Part I, p. 148. For a Memoria Technica of the double elective attractions, communicated by the learned author, see Journal, Vol. XXII, p. 304.

tual

tual attractive forces of the component parts of different salts; but these attempts have hitherto been confined within narrow limits, and have indeed been so hastily abandoned, that some very important consequences, which necessarily follow from the general principle of a numerical represen tation, appear to have been entirely overlooked. It is not impossible, that there may be some cases, in which the presence of a fourth substance, beside the two ingredients of the salt, and the medium in which they are dissolved, may influence the precise force of their mutual attraction, either by affecting the solubility of the salt, or by some other unknown means, so that the number, naturally appropriate to the combination, may no longer correspond to its affec tions; but there is reason to think, that such cases are rare; and when they occur, they may easily be noticed as exceptions to the general rules. It appears therefore, that nearly all the phenomena of the mutual actions of a hundred different salts may be correctly represented by a hundred numbers, while, in the usual manner of relating every case as a different experiment, above two thousand separate articles would be required.

Having been engaged in the collection of a few of the prin- Aseries of num. cipal facts relating to chemistry and pharmacy, I was induced bers found, answering very to attempt the investigation of a series of these numbers; generally. and I have succeeded, not without some difficulty, in obtaining such as appear to agree sufficiently well with all the cases of double decompositions which are fully established, the exceptions not exceeding twenty, out of about twelve hundred cases enumerated by Fourcroy. The same numbers agree in general with the order of simple elective attractions, as usually laid down by chemical authors; but it was of so much less importance to accommodate them to these, that I have not been very solicitous to avoid a few inconsistencies in this respect; especially as many of the bases of Common tables of simple elec the calculation remain uncertain, and as the common tables tive attractions of simple elective attractions are certainly imperfect, if they imperfect. are considered as indicating the order of the independent attractive forces of the substances concerned. Although it cannot be expected, that these numbers should be accurate measures of the forces which they represent, yet they may

The facts may

be supposed to be tolerable approximations to such meagures; at least if any two of them are nearly in the true proportion, it is probable, that the rest cannot deviate very far from it: thus, if the attractive force of the phosphoric acid for potash is about eight tenths of that of the sulfuric acid for Barita, that of the phosphoric acid for barita must be about nine tenths as great; but they are calculated only to agree with a certain number of phenomena, and will probably require many alterations, as well as additions, when all other similar phenomena shall have been accurately investigated.

There is, however, a method of representing the facts, which be represented have served as the bases of the determination, independently independent of Dypothesis. of any hypothesis, and without being liable to the contingent necessity of any future alteration, in order to make room for the introduction of the affections of other substances; and this method enables us also to compare, upon general principles, a multitude of scattered phenomena, and to reject many which have been mentioned as probable, though doubtful, with the omission of a very few only, which have been stated as ascertained. This arrangement simply depends on the supposition, that the attractive force, which tends to unite any two substances, may always be represented by a certain constant quantity.

There must be a sequence in the simple attractions.

common tables.

From this principle it may be inferred, in the first place, that there must be a sequence in the simple elective attrac tions. For example, there must be an errour in the common Erreurs in the tables of elective attractions, in which magnesia stands above ammonia under the sulfuric acid, and below it under the phosphoric, and the phosphoric acid stands above the sulfuric under magnesia, and below it under ammonia: since such an arrangement implies, that the order of the attractive forces is this; phosphate of magnesia, sulfate of magnesia, sulfate of ammonia, phosphate of ammonia, and again phosphate of magnesia; which forms a circle, and not a sequence. must therefore either place magnesia above ammonia under the phosphoric acid, or the phosphoric acid below the sulfugic under magnesia; or we must abandon the principle of a americal representation in this particular case.

We

double attrac

In the second place, there must be an agreement between The simple and the simple and double elective attractions. Thus, if the fluoric tions must acid stands above the nitric under barita, and below it under agree. lime, the fluate of barita cannot decompose the nitrate of lime, since the previous attractions of these two salts are respectively greater, than the divellent attractions of the nitrate of barita and the fluate of lime. Probably, therefore, we ought to place the fluoric acid below the nitric under barita; and we may suppose, that, when the fluoric acid has appeared to form a precipitate with the nitrate of barita, there has been some fallacy in the experiment.

sequence in the

The third proposition is somewhat less obvious, but per- A continned haps of greater utility: there must be a continued sequence order of double in the order of double elective attractions; that is, between attractions. any two acids, we may place the different bases in such an order, that any two salts, resulting from their union, shall always decompose each other, unless each acid be united to the base nearest to it: for example, sulfuric acid, barita, potass, soda, ammonia, strontia, magnesia, glycina, alumina, zirconia, lime, phosphoric acid. The sulfate of potass decomposes the phosphate of barita, because the difference of the attractions of barita for the sulfuric and phosphoric acids is greater than the difference of the similar attractions of potass; and in the same manner the difference of the attractions of potass is greater than that of the attractions of soda; consequently the difference of the attractions of barita must be much greater than that of the attractions of soda, and the sulfate of soda must decompose the phosphate of barita: and in the same manner it may be shown, that each base must preserve its relations of priority or posteriority to every other in the series. It is also obvious, that, for similar reasons, the acids may be arranged in a continued sequence between the different bases; and when all the decompositions of a certain number of salts have been investigated, we may form two corresponding tables, one of the sequences of the bases with the acids, and another of those of the acids with the different bases; and if either Correction of or both of the tables are imperfect, their deficiencies may often be supplied, and their errours corrected, by a repeated comparison with each other.

errours in ta bles.