By maceration in water he alfo found that the former yielded a greater quantity of extractive matter than the latter.

Next to this, Mr. K. relates other experiments made for the purpose of difcovering the laboratory, or place, wherein the matter which gives additional weight to the winter-felled trees, is formed, and how it circulates through the plant. After the defcription of thofe experiments, he concludes with faying,

"It has been proved in the preceding experiments on the af cending fap of the fycamore and birch, that that fluid does not approach the buds and unfolding leaves in the fpring, in the state in which it is abforbed from the earth: and therefore we may conclude that the fluid, which enters into, and circulates through the leaves of plants, as the blood through the lungs of animals, confifts of a mixture of the true fap or blood of the plant with matter more recently abforbed, and lefs perfectly affimilated.

"It appears probable that the true fap undergoes a confidera ble change on its mixture with the afcending aqueous fap; for this fluid in the fycamore has been proved to become more fenfibly fweet in its progrefs from the roots in the fpring, and the liquid which flows from the wounded bark of the fame tree is alfo fweet; but I have never been able to detect the flightest degree of sweetnefs in decoctions of the fycamore wood in winter. I am there. fore inclined to believe that the faccharine matter existing in the afcending fap is not immediately, or wholly, derived from the fluid which had circulated through the leaf in the preceding year; but that it is generated by a procefs fimilar to that of the germination of feeds, and that the fame procefs is always going for. ward during the fpring and fummer, as long as the tree continues to generate new organs. But towards the conclufion of the fum. mer, I conceive that the true fap fimply aceumulates in the albur. num, and thus adds to the fpecific gravity of winter-felled wood, and increases the quantity of its extractive matter.

"I have fome reafons to believe, that the true fap defcends through the alburnum as well as through the bark, and I have been informed, that if the bark be taken from the trunks of trees in the fpring, and fuch trees be fuffered to grow till the following winter, the alburnum acquires a great degree of hardness and durability. If fubfequent experiments prove that the true fap def cends through the alburnum, it will be eafy to point out the cause why trees continue to vegetate after all communication between the leaves and roots, through the bark, has been intercepted and why fome portion of alburnous matter is in all trees generated below incifions through the bark." P. 102.

V. On

* I have in a former paper stated that the perpendicular shoots

L13

of

V. On the Action of Platina and Mercury upon each other. By Richard Chenevix, Efq. F.R.S. &c.

Our readers may recollect to have feen in our accounts of the preceding volumes of the Philofophical Transactions, that about two years ago, a new metal, under the name of Palladium, was made known to the world; but in a manner rather doubtful and myfterious. Mr. Chenevix having undertaken a chemical examination of this metal, was led to conclude, or at leaft ftrongly to fufpect, that this palladium was nothing more than a mixture of mercury and platina; he could not, however, difcover a direct, or effectual method of forming that fuppofed compound; nor have the repeated endeavours of other chemifts, for the fame purpose, proved more fuccessful,

An account of the attempts made by other chemifls in England, in France, and in Germany, with proper remarks, occupies feveral of the first pages of the prefent paper; after which, the author defcribes nine experiments, which he made with platina and mercury in different ftates, and with the addition of other articles,

"From all thefe experiments," he fays, it is evident that mercury can act upon platina, and confer upon it the property of being precipitated in a metallic ftate by green fulphate of iron, By Experiments 1 and 2, it is proved, 1ft, That platina can protect a confiderable quantity of mercury from the action of nitric acid; and 2dly, That mercury car, increase the action of nitromuriatic acid upon platina. From Experiments 3, 4, 5, 6, 7, 8, it appears that mercury can combine with platina in fuch a manner as not to be feparated by the degree of heat neceffary to fufe the compound, fince after the fufion it retains that property, which is effentially characteristic of the prefence of mercury in a solution of platina. The 8th Experiment proves that the action of mercury upon platina is not confined to the metallic ftate; but that thefe metals can combine and form an infoluble triple falt with an acid which produces a very foluble compound with platina alone. The 9th Experiment fhows that platina can retain in folution a certain quantity of mercury, and prevent its reduction by a fubftance which acts most powerfully to that effect, when platina is not prefent. That part of the general pofition, therefore, which

of the vine form an exception. I fpoke on the authority of nume rous experiments; but they had been made late in the fummer; and on repeating the fame experiments at an earlier period, I found the refult in conformity with my experiments on other

trees,

is

is the object of this Paper, is proved, if thefe experiments, upon being repeated by other chemists, fhall be found to be ac

curate.

"One or two of the above experiments feem to be in contra. diction to fome that I have ftated in my Paper upon palladium; for in the prefent examples, platina protects mercury against the action of nitric acid; whereas in palladium the mercury is not only acted upon itself, but it conduces to the folution of platina in the fame acid. I am well aware of this objection; but confining myfelf to my prefent object, I fhall wave all further difcuffion of it till another opportunity. In the mean time, however, it may be laid down as an axiom in chemistry, that the ftrongeft affinities are thofe, which produce in any fubftance the greatest deviation from its ufual properties.

"When a button of the alloy of platina and mercury as prepared by any of the above methods, is diffolved in nitro-muriatic acid, and afterwards precipitated by green fulphate of iron, the entire quantity of the alloy ufed is feldom obtained. A confiderable portion of platina refifts the action of green fulphate of iron, and remains in folution. This may be looked upon as the excefs of platina, and can be recovered by a plate of iron. Hence it appears that lefs mercury is fixed, than can determine the precipitation of the entire quantity of platina; yet in this ftate it can draw down a greater quantity of the latter, than when it is merely poured into a mixed folution of platina, not before so treated. Indeed the whole of thefe experiments tend, not only to show that these two metals exercife a very powerful action upon each other, but that they are capable of great variation in the ftate of their combination; and also that fubftances poffeffing different properties have refulted from my attempts to combine platina with mercury.

This obfervation furnished me with a method of afcertaining, or at least of approaching to the knowledge of, the quantity of mercury thus fixed by platina, and in combination with it. The experiment, however, having been feldom attended with full fuccefs, I mention the refult with the entire consciousness of the uncertainty to which it is fubject. I obferved the increafe of weight, which the original quantity of platina had acquired in fome cafes after it had been treated with mercury, and fufed into a button. I counted that augmentation as the quantity of mercury fixed. I then determined how much was precipitated by green fulphate of iron from a folution of this alloy, and fuppofed it to contain the whole quantity of mercury found as above, But, even if attended with complete fuccefs, there is a chemical reafon which must make us refufe our affent to this estimate. It is poffible, and not unlikely, that a portion of mercury may be retained in folution by the platina, as well as that a portion of the platina may be precipitated by means of the mercury. The mean refult, however, was that the precipitate by green fulphate of iron

114

confifted

confifted of about 17 of mercury, and 83 of platina, when the fpecific gravity was about 16.

"With regard to palladium, left it fhould be fuppofed that either my own obfervations, or those of others, have given me caufe to alter my opinion, I will add that I have as yet feen no arguments of fufficient weight to convince me, in oppofition to experiment, that palladium is a fimple fubftance. Repeated failure in the attempt to form it I am too well accustomed to, not to believe that it may happen in well conducted operations; but four fuccefsful trials, which were not performed in fecret, are in my mind a fufficient anfwer to that objection. By determining the prefent question, we may overcome the prepoffeffion conceived by many against the poffibility of rendering mercury as fixed, at an elevated temperature, as other metals: we may be led to fee no greater miracle in this compound, than in a metallic oxide, or in water, and be compelled to take a middle path between the vifions of alchemy on the one hand, and the equally unphilofophical prejudices on the other, which they are likely to create. In the courfe of experiments juft now related, I have feen nothing but what tends to confirm my former refults, yet the only means which I can, after all, prefcribe for fucceeding, is perfeverance.” P. 126.

VI. An Investigation of all the Changes of the variable Star in Sobieski's Shield, from five Year's Obfervations, exhibiting its proportional illuminated Parts, and its Irregularities of Rotation; with Conjectures refpecting unenlightened heavenly Bodies. By Edward Pigott, Efq.

Mr. Pigott, in the year 1795, difcovered that a star in Sobiefki's fhield regularly varied in brightnefs. He endeavoured to determine the period of its increafe and decrease of brightness, and from the obfervations he made at that time, the period feemed to be about 62 days. But repeated examinations of the fame ftar, made fince that time during five years, having given Mr. P. much better documents for determining the defired period, he now ftates his obfervations in the prefent paper, together with the refult, or a mean, of the fame; whence it appears, that the period of the star's increase and decrease of brightness is 61 days, which differs from Mr. Pigott's former determination by not more than 1 day.

He further obferved, that the time of the decrease of brightness is longer than that of the increase; and confequently, (fuppofing that the phenomenon is owing to the ftars having fpots on its furface, and to its revolving round its axis like the fun,) that the places of the full and the leaft

brightness

brightnefs are not fituated at the diftance of half the circumference from each other, which feems to be the case with all variable flars.

Mr. P. endeavoured to deduce from his obfervations the duration of the brightnefs of the fame ftar, without any perceptible change, while at the maximum and minimum; but the refults are not fatisfactory.

After the statement of all his obfervations, and of the remarks made upon them, this author concludes the first part of the paper with a table, wherein he collects the refuls of all the above-mentioned obfervations, and which we thall fubjoin.

The first column of this table defcribes the nature of the remarks; the fecond exhibits the prefent refults; the third exhibits the former refults; and the laft column, a mean of both computed proportionally according to the number of obfervations of each.