Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/446

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own hourifliment, and lives and fidurifhes wholly indepen- dent of the reft.

After having gone through this general fyftem, the author defcends to feveral remarkable particulars. He mentions an inftance of a fucus, whole ftalk, when in its growing ftatc, is a quarter of an inch in diameter, yet in drying fhrinks up fo much, as to be not thicker than a fingle thread. An- other fpecies, called by the fiihermen the jea orange., from its refemblance to an orange in fhape, he obferves is pro- perly a fucus ; it has neither ftalk nor branches, but confifts wholly of this globular body ; it is not a folid fubftance, but a membrane of about 9 of an inch in thicknefs, regu- larly diftended into this fhape, by being filled wthjea water. All over the fides of this cavity there are fixed (lender fila- ments, which traverfe the whole, and probably receive nou- rifhment from the water contained in the cavity, and distri- bute it to the feveral parts of the fides where they are inferted. Another jea plant this author mentions, only appears in the fhape of a bark ; it affixes itfelf to the branches of the lytho- phyta, when they have loft their natural bark, and fome times, in the fame manner, coats and emits over the fur- faces of ftones. When it is frefh, it is of a lively red, of the confidence of a mufhroom, and about the thicknefs of the back of a common knife, and its external furface is full of fmall prominences, which contain a glutinous juice round about thefe alfo there ffand feveral yellow tubercles, which, with the red of the ground of the plant, make upon the whole a very beautiful appearance. Its under furface is perfectly fmooth and glofiy. This feems a much more re- markable plant, as to the manner of its vegetation, than thofe which grow on other plants at land. The fame author obferves, that feveral of the fpunges, when taken out of the jea, have a motion of the nature of a fyf- tole and diaftole, which lafts as long as there remains any of the jea water in their cavities. Some of the fea plants, which while growing are as foft as the fucufes, yet when dried are as eafily rubbed to powder between the fingers, as the bark of the lithophytons. There is one of the lithophytons, which carries Co large a quantity of branches, that they make the refemblance of leaves ; but as thefe leaf-like branches are all truly of the fame nature with the reft of the plant, this is no exception to the general rule, that the lithophyta have no leaves. One of the fpecies of lithophyton is na- turally deftitute of a bark, and is covered in the place of one with a glutinous fubftance, of the nature of varnifh ; this is molt abundant at the foot. The whole plant is full of prickles, and thefe appear the moft plainly on the fummits of the branches, where this glutinous varnifh is more thinly fpread. On this part of the plant, alfo, there appear cer- tain globules of a glutinous matter, when it is taken out of the water, which, when it is again plunged into it, fpread themfelves over the whole furface of the branches. The madreporas grow in the fame places with the coral j they often hang pendulous from the hollow rocks, and often grow erect on the flat ones. They ufually change colour when taken out of the water, and are of very different kinds and different degrees of hardnefs ; many of them are as hard as common ftones, and many others are fo brittle, that it is fcarce poilible to touch them without breaking theij branches.

The flowers of the thorny and naked lithophyton appear to be wholly like thofe of coral, and like them they are not found to contain any folid feed. Mem. de l'Acad. Par, 1710.

The many ufes of the numerous jea plants to the fyftem of the world are not yet fufficiently known. Among others, Dr. Lifter has obferved that they ferve to render a great deal of the jea water frefh, and give it in mifts to the clouds, whence it again falls on the earth. This is eafily proved by experiment thus : if a quantity of fea water be put into a long glafs body, and into it there be put a large and vigo- rous jea plant, fuch as the common /« wrack, and the head placed on the glafs, and a receiver fitted for it without cut- ting the joints, there will daily diftil into the receiver, without giving any fire below, a clear and fwect water, frefh and potable, and without any difagreeable or unwhole- fome quality. _ The quantity is but fmall that is obtained this way, but it is evident, that in the fame manner a very immenfe quantity of the jea water is everv hour made frefh andraifed up into the air from the infinite number of plants that grow in it. Dr. Lifter even thinks that the tropic winds, . which blow conftantly one way, may be owing to this fort of caufe. Philof. Tranf. N° 156. See the article Tropic winds. Ska jalt. The chemifts have, for many ages, been acquaint- ed with many of the qualities, and much of the nature of this common fubftance, but not with the whole ; they know what they can feparate from it, and what they can after- wards procure, by admixtures with the refiduum of the di- ftillation, which is its bafis ; but they do" not feem to have thought, of a long time, of enquiring 'into what that bafe was. They have always known how to feparate an acid liquor from this jab, called the fpirit of it, by breaking its [ union with the bafis of the jalt - t and they know, that if a

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vitriolic acid be added to this bafis, it makes what is called Glauber's jalt, if a nitrous one, they procure what is called quadrangular _ nitre : but they never procured, and brought into view this bafis of jea jalt feparate and pure, exempted from its acid, and in a ftate of being known as to what it is ; they have found out that the bafis of alum is a white cal- carious earth, that the bafis of green vitriol is iron, and that the bafis of blue vitriol is copper; but they have been unacquainted with the bafis of this moft common of aWjalts. For want of this knowledge, no body has been able to recompofe jea jalt, or regenerate it after it has been decompounded by fire ; and the judicious chemift never thinks he is mafter of a fubject, till he can both deftroy, and at pleafure reproduce it.

It has been generally agreed, that the bafis of this jalt is either an earth or an alkali ; and it might be very poilible to reconcile thefe opinions, by fuppofing it an alkaline earth, as there are many fuch, and fo blending the two opinions in one. Mr. Du Hamel, however, has been at great pains on this fubject, and has communicated to the Academy of Sciences, as the refult of them, a very accurate and valuable account of this body.

A hafty obferver may fancy to himfelf, that he has found out this bafis at a very eafy rate, by obferving, that on the dif- (ohing jea jalt in oil of tartar by deliquium, there precipi- tates to the bottom a white earth. This was the firft fub- ject of Mr. Du Hamel's enquiries, but he found this could not be the real bafis of the jalt, nor indeed any thing ef- fential to it, fince it was in too fmall quantity to have fuf- ficed for fo great a purpofe ; and after the precipitation of it, there remained much fine and unaltered jalt, on which the menftruum did not operate; and on all the trials he could make, he found it impoffible to reproduce jea jalt from the mixture of this earth with fpirit of fait. It feems therefore moft probable, that this earth was only accidentally mixed with the jalt, at the time of its formation, but having no eflential fhare in its compofition. When an inflammable fubftance is mixed with nitre, its acid diffipates itfelf with a very little heat, and leaves its bafis naked to the eye. In- flammable fubftances, mixed with vitriols, alfo greatly diminifh the force of the union of their acid to their bafe, and confequently facilitate their fcparation ; and on this prin- ciple Mr. Du Hamel had hopes that powder of charcoal, or filings of iron, might prove happy mediums for the fepara- tion of the acid of jea jalt from its bafis, but thefe had no effect. Chemifts had obferved that the jea jalt, which enters the ftomachs of animals with their food, was decompofed in their bodies ; hence this gentleman tried animal and vege- table fubftances for this purpofe, as alfo the inflammable mi- nerals, but all thefe alfo without fuccefs. When thefe trials had all proved fruitlefs, there appeared no way left, but that of the mixture of the vitriolic and nitrous acids, and the producing the Glauber's fait, and quadrangu- lar nitre, for the fubjects of after experiment. Having care- fully made fome Glauber's fait, the bufinefs was to drive off the acid from that mixt by fire; but no fort of diftillation was found able to do this, as no fire is ftrong enough to dif- unite this acid from any mixture with an alkaline fait. It is well known, however, that the vitriolic acid eafily unites itfelf to inflammable fubftances, and in that union confti- tutes common fulphur. The mixture of powder of charcoal with this Glauber's fait, produced readily a fulphur, but the acid, in running into this union, had carried the bafis of the jea jalt along with it, not left it behind as was expected ; but the fcparation was afterwards effected, by pouring vine- gar upon this fulphur ; the confequence of which was, that the bafis of the jea jalt then remained charged only with the vegetable acid of the vinegar, much weaker than the mineral acid of vitriol, and therefore forming a combination much more eafily broken, and from which the acid was to be raifed into vapour, without any great difficulty, as it con- tained a large portion of an oily matter with it. This hav- ing then been wrought over by diftillation, and the refidu- um ftrong! y calcined, the bafis of the jea jalt was at length obtained pure.

A fecond operation of the fame gentleman in this refearch, was the adding a nitrous acid to the refiduum of the diftil- lation of jea jalt inftead of a vitriolic one, and obtaining by that means a quadrangular nitre, inftead of a Glauber's fait; and diifipating this fpirit, by burning in a red hot cru- cible, with powder of charcoal, the bafis of the jalt was alfo prepared pure ; and both this, and that by the former trial, appeared wholly the fame fubftance.

The bafis of jea jalt, when thus found, appeared not to be an earth, as had been by many fufpected, but a true fait it- felf, eafily foluble in water, and proving itfelf to be an al- kali by its effects with acids. It will not run into a liquor in the air, but moulders away into a fine powder, and is very cold upon the tongue, and has a bitterifh tafte. This fait appears much like the natrum, or nitre of the antients, or our common fait of the kali. The firft of thefe is a na- tive fair, found in the eaftern countries, and which always has with it a large quantity of marine fait ; and it is no wonder, when we know this to be what might have made X the