Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/708

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a few days ; and, as this is effected, the fait will vegetate in feveral places into branches; thefe will furround the whole furface of the water, and will continue to form themfelyes anew as the water evaporates, till it is all gone; after which they will ceafe ; but if more water be added to the fait, they will appear again in all their beauty, as that afterwards eva- porates.

Another example of thefe faline Vegetations is feeii in the branched cryitaHizat'ions of falts, naturally produced on the fhore of the Spanifh and other leas, and which may eafily be imitated by art : This is no other than a natural confequence of the fea plants growing on the fhore, being, when their leaves are decayed, crufted all over their branches with cry- ftals of fea-falt, left by the evaporation of the water, which had been left upon them by the recefs of the fea ; this procefs being very frequently repeated on them, every wetting leaves a frefh coat of fait over them ; 10 that, at length, the whole appears a mere plant of fait. Very beautiful fpedmens of this kind are often met with on the mores ; and may be imitated by art by means of fea-falt diffolved in water, and the folution carefully filtred. But, in doing this, it is necefTary to peel off the bark of the plant which ferves for the mould ; for as the bark is ufually brown or green, or of fome colour different from that of the fait, it difcovers itfelf too plainly, and takes greatly off from the beauty of the whole. A third very ftrtgular inftaflce which Mr. Romberg gives of thefe Vegetations is this : He collected about three pints of rain-water from the bottom of an old wooden trough, in which it had flood about half an hour, after running down from the tiles of an old houfe. This water had fallen in the time of a tempeft, attended with thunder. He had fet this bottle of water, careltfsly flopped with a piece of paper, in a window, which looked toward the fouth, where it flood three months. The water had appeared tolerably clear, when it was firfl faved ; but, by degrees, as it flood, there fubfided to the bottom a grcenifh fediment, of about a quarter of an inch in thicknefs. There was apparently a fermentation in this matter, and it appeared fpongy and cavernous, and had frequently air-bubbles rifingup from it. In the middle of a hot day, in July, Mr. Homberg obferving this bottle, fa w that there, was no muddy fediment at the bottom, but only a clear and beautiful green Vegetation, part of which had alio raifed it- felf to the furface of the water, and part remained fufpended, in form of flender filaments, in the middle. The extremity of every one of thefe filaments was furnifhed with a fmall round globule, which appeared white and bright as filver, and refembled a fort of fruit at the top of the branch.. On fhak- ing the bottle about, the whole Vegetation difappeared, and the matter of it blended itfelf among the water in a loofe irre- gular manner. About ten o'clock the next morning, when the fun began to warm the bottle, the Vegetations appeared again in their former fhape, and were only owing to fmall bladders of air which, in their riling from among the green mud at the bottom, drew up long firings of it along with them, and appearing in form of fmall round pearls at the tops of the branches. This appearance continues fo long as the fun mines upon the bottle ; after which the bubbles, and their pedicles, gradually fink together, and lie confufedly at the bottom, till the morning fun of the fuccecdingday raifes them again in the fame manner from the bottom to the furface. Mem. Acad. Par. 1710.

The molt beautiful of all metallic Vegetations is the arbor Diana, or filver-tree. A great many proceffes for the making this have been publifhed ; but fome of them are not found to fucceed, upon experiment ; and others are too tedious to fol- low. Mr. Homberg gives a fuccin£l account of the method by which he ufed to make it, and this is never known to fail. Make an amalgam in the cold, with four drams of pure filver, and two drams of crude mercury ; diflolve this in four ounces of aqua fortis ; mix this with a pint and half of water, and fet it by in a bottle well flopped. When there is occafion to ufe it, pour about an ounce of it into a little via! ; put into this a piece of the bignefs of a fmall pea of the common amalgama, cither of gold or fdver, made as foftas butter. Leave the vial to reft for two' or three minutes; and in that time there will begin to arife a number of little upright flalks from the ball. Thefe will vifibly increafe in length every moment, and, foon' after, will throw out feveral fide branches. Thus, by degrees, the whole will have the form of a little tree ; the ball of amalgama will be of a dead whitifh colour; but the trees will be Tike the brighteft filver. The whole of this beautiful Vegetation will be performed in a quarter of an hour : But it is to be obferved, that the liquor which has ferved once, will not do again.

The matter which forms the tree is not formed by the amal- gam put into the liquor ; but by the firfl amalgam which was diffolved in it, the water added afterwards having fo much weakened the diflblvent, that it is not able to keep the matter fufpended, when there is offered any opportunity for its preci- pitating; and the mercury, thus diffolved, meeting here with mercury undiffolved, quits the diffolvent, and applies itfelf to it ; but that not in its own form of globules, but in fuch fhapes as the mixture of filver, and of the falts of the nitrous acid in the diflblventj determine it to.

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This procefs may be varied a great many ways, as to the thicK> nefsor thmnefs of the branches, and the flow or fpeedy man- ner in which they are formed, according to the nature of the liquor, and of the amalgama. The weaker the liquor is, the .flower will the branches be formed ; and they will, in this cafe, be longer, and fewer in number, and by that means the more imitate a tree. On the contrary, when the liquor is too flrong, the whole furface of the globule of amalgam thrown into it, will, in a few minutes, be covered with a low and fhort tuft of bufhes ; and that water, which is flrong enough of the folution to produce trees upon a thick amalgam, will not be able to produce any thing upon fimple mercury, and but very little upon a thin amalgam. And, on the con- trary, that liquor which is flrong enough to produce a ramifi- cation upon fimple mercury, will, on a thin amalgam, pro- duce only a few fhort bufhes ; fome yet lower than thefe will be formed by it on a thicker amalgam, and it will, in fine, diflolve the amalgam.

It appears from the whole, that there is in this nothing of true Vegetation, but merely a fimple cryflallization in this form. There is alfo another Vegetation formed by cryflallization, without the afiiftance of mercury ; hut it is more flow, and wants the beautiful metalline colour of the lafl. It is thus performed :

Diflolve one part of fine filver in three parts of aqua fortis, evaporate half the diffolvent, and add to the remainder of it twice its weight ofdiflilled vinegar, well dephlegmated ; fet this mixture by for a month, and atthe end of that time there will he found, in the middle of the vial, a tree, in form of a fir, with its brunches reaching up to the furface of the water. This is no other than a cryflallization of the diffulved filver, whofe parts have been thrown into this form by the mixture of the falts of the vinegar with thofe of the nitre. This there- fore has not the colour of filver, but is white and tranfparent, in the manner of a genuine fait, and makes a very elegant fi- gure in the menflruum.

A third Vegetation of the metallic kind is thus performed : Take a quarter of a pound of common white river pebbles, calcine them two or three times over, quenching them every time In water ; after this, beat them to a .fine powder, and mix them exactly with twelve ounces of fait of tartar. Melt the whole in a flrong fire, and let it cool, it will be a vitrified mafs. Powder it, and lay it on a marble in a cellar, it will diffolve into an oil per deliquium : Keep this in a vial ; then takeany metal you "pleafe; diffolve it in aqua-fortisoraqua-regia; evaporate the diffolvent, and there will remain a grey powder. When you have a mind to fee the Vegetation, put a fmall piece, about the bjgnefs of a pea, of this calx into fome of this liquor. In three or four minutes there will iffue out of it a flalk, which will grow longer and thicker every moment ; and finally will moot out two or three branches from its fides, and each of thefe, as well as the main .trunk, will be termi- nated by a large round air-bubble.

This is a Vegetation extremely different from either of the others. In them the branches were only cryflallizations of the diffolved metal ; and the little mafs of matter, thrown into the liquor, furnifhed nothing to them. In this, the whole is owing to the matter thrown in, and is the mere cffecl of a fermentation. The calx of the metal yet contains fome acids. The alkaline liquor ferments with thefe ; the fermentation indeed is but flow, becaufe the metalline particles envelope the acid falts. But as, in all fermentations, there is air difcharged; fo in this air-bubbles are fent upward from the mafs ; but the metalline particles rifing with them, detain them, and make their afcent very flow, while they are compelled to draw up a long filament of the metallic matter with them. The metal is foftened during the time of the fermentation, otherwife it could not be thus drawn up with the air-bubbles ; but it im- mediately hardens again, when out of the flate of ferment, and becomes able to fupport itfelf in the branched form, even when taken out of the liquor it is formed in. There is another metallic Vegetation, which is formed by merely amalgamating a metal with mercury, without the mixture of any acid liquor. Take three or four parts of mer- cury, purified by five or fix fublimations, and one part of fine gold or filver; make an amalgam without heat; fet this amalgam to digefl for fifteen days in a flow heat, in a matrafs hermetically fealed ; the amalgam will in this time harden, and all its furface will be covered with branches and trees, fome of them rifing to an inch high ; the quantity of mercury muft be nicely adjufled in this experiment, for otherwife there will be no Vegetation, whether the quantity be too much or too little; and if the veffel be not perfectly clofed, the procefs will fail, though the quantities and the degree of fire have been ever fo well obferved. This Vegetation is enly made by the fire heating the mercury, and railing it, in order to its flying off; in which rifing it lifts up parts of the metal with it, and leaves them in that poflure, in the forms of trees and plants. Mem. Acad. Par. 1692. Vegetation of Salts, a name given by Mr. Petit, of the academy of Paris, to the concretions which falts form, after folution in water, when fet in the air to evaporate. Thefe concretions always appear'round the furface of the li- quor, affixed to the fides of the veffel, or arifing above its top, 3 and