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twenty four hours ; but if it be to be made into the ftrong fait, they flacken the fire to fuch a degree, that the opera- tion takes up three days. In both cafes they let the fait re- main in the pan till the whole is finifhed j they then rake it out with wooden rakes, and after it has drained a while in wooden drabs, it is fit for ufe. The mother brine , of which there always remains a large quantity m the pan after the ftrong/*// is made, as alfo the draining* of the drabs where the fait is put, is referved to be boiled up mto table fait i but the mother brine of the table fait becomes more fliarp and bitter after every procefs, and is finally thrown away. Brownrtg of Salt, p. 142.
Sea Salt. The common fea fait is deftructive to almoit all plants except thofe which naturally grow in the fea water, or on 'the fhores. Mr. Tull has invented a method of deter- mining how far the horizontal roots of plants run, by bury- ing fait at a diftance from them. See the article Root. It has been thought by fome that this was an uncertain trial, becaufe, though the roots reaching the fait were deftroyed by it, yet the plant would continue to be fupplied by others, and would not perifh ; but this is' erroneous, for the roots of plants coming where fait is, are not killed by it, but they draw juices from the earth where it is buried, and carry it with thofe juices to the plant, and by this means they fail not to kill it. One root, thus coming in the way of fait, is able to kill the whole plant, though it have ten thou- sand roots, taking good nourifhment from other places. This is finally exemplified in the growing of mint in water. If a ftrong and vigorous fhoot of mint, growing in fimple water, be placed near a glafs at fait water, and one fibre of its roots be raifed out of the glafs in which it ftands, and plunged into the fait water, the whole plant will be killed in a few days by this fait, taken in by this fingle fibre, though all the reft are taking in proper nourifhment from the frefh water all the time. The fame thing happens, if one of thefe roots be taken up and tied in a bag, containing a fpoonful of dry fait; the fait will foon grow moift, and the plant will be killed. On tailing of the leaves of the plants thus killed, they are found to have imbibed a larger quantity of fait than could be conceived from fuch a fmall and fingle root, the whole ftalk, leaves, and every other part of the plant, tafting ftrong of fea fait. Tulfs Horfe- hoeing Hufbandry. See Marine Salt, fupr.
Egra Salt. See the article EgraNUM ^a/.
Effential Salts. See Salts a/Plants.
Fixt Salts. Mr. Romberg has given, in the Memoirs of the Paris Academy, a very curious paper of the fubjedf. of vola- tilizing the fixt falts of plants. He obferves, that the fixt fait of any plant is a faline matter, which has already loft in the fire all, or the greater part at leaft, of the volatile matter contained in the plant it is obtained from, as its phlegm, acid fpirit, urinous fpirit, its effential oil and urinous fait ; and that its figure is in fome degree that of a fpunge, the pores of which being always open, are ever ready to re- ceive again fuch forts of volatile fubftances, as the fire has before driven off" from them; and that art may in fuch a manner add thefe its deprived parts to it again, that the concrete fhall lofe its fixity, and become volatile, as the whole was in a great meafure before. The whole of this operation conftfts in the adding to the lixivial fait one or more of thofe volatile fubftances, the lofs of which gave ic its prefent form. Thefe arc to be introduced into the fait by repeated cohobations, which are to be continued till fo much volatile matter is added to the fixt, that the whole becomes volatile together; the naturally volatile particles being mixed in fuch proportion, as to be able to carry up the fixed in vapour with them. The feveral volatile fubftances of plants are of different kinds, and coniequently require different ope- rations, to make them mix with the fait. Tartar may very well ferve as a general inftance in this cafe, and the man- ner of introducing into its fixt fait thofe principles, of which the fire before diverted it, and by this means rendring it vo- latile, may ferve as a fpecimen of the manner of doing it in all the reft : but as fait of tartar, and all other fixt vege- table alkaline falts, however well purified, always contain a great deal of earth, the feveral volatiles employed act diffe- rently on this, according to their feveral natures ; fome car- rying it all up in vapour, others carrying only a part of it, and leaving at the bottom of the vcffel more or lefs of an earthy matter, infipid to the tafte, and wholly diverted of its alkaline fait ; every particle of which, even in this cafe, has been volatilized, and raifed by the fire. The alkaline fait, thus volatilized, appears alfo, according to the different fubftances employed, in very different forms ; fometimes in that of a faline liquor, fometimes in an acid, and fometimes in an urinous fpirit : fometimes alfo it be- comes changed into a volatile fal faljus, fometimes into an acrid and foetid fait, and finally, fometimes into a volatile aromatic one. The firft matter which fire drives out of tar- tar, or any other vegetable fubftance, is its phlegm ; this being mere water, one would think at fu(\: fhould be little able to change fo fixed a fubftance as fait of tartar into a volatile one ; but when we farther conj'ider the great power of water, when put in action by the fire, and that this agent Suppl. Vol. XL
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is the caufe of fome of the greateft changes that happen in animal and vegetable bodies, and perhaps of every thing of this kind that partes in our earth, we lhall not wonder that it may be made, by the help of fire, one of the agents ca- pable of raifing, or yolatilifcing a part at leaft cf fait of tar- tar ; hut as phlegm Is the leait active of all the principles which chemiftry feparates from bodies, or at leaft acts upon the others the moft flowly, and with the leaft violence, the method of volatilizing part of fait of tartar by means of this, mufl naturally be more tedious than by any of the otber principles ; yet it is to be done with time by this, as well as by the other.
The thing that put Mr. Romberg upon this courfe of expe- riments was, as he candidly acknowledges, an accident. He was difpleafed with the Venice foap, with which he ftiaved himfelf ; and endeavouring to mend it, he cut it into thin flices, and after drying it three months in the fhadc, he powdered it in a mortar, and wetted it in to' a parte again with oi! of lavender and fpirit of wine ; and in continuing his trials to this purpofe, he at length found part of the fait of the foap become volatile.
It is very well known that foap is made of the fait of kali, or pot allies and oil. On the event of this experiment, Mr. Romberg proceeded to jud^e, according to the known rules of chemiftry, that oil, of which the volatile falts are gene- rally fuppofed to borrow their volatility, being intimately mixed with the fixed alkaline falts, as here with that of the kali, might render them all volatile, as in this inftance; for that in this ftate they were no longer alkalis, their pores be- ing now not open, but filled to the utmoft wi.h the particles of oil. All oils contain alfo an acid, and that acid being mixed with the alkali fait, the whole on this muft ceafe to be an alkali, and become a middle, or neutral fait, fuch as common fea fait; but then as the acid is not, in this cafe, joined to the alkali, but by the means of oil, and accompa- nied with oil, this new found neutral fait muft neceffaiily be of an oily, or a fulphureous nature.
In carrying on this idea, and trying by chemical experiments all the objects it offered, Mr. Romberg, in fine, found, that in order to volatilize the fixt falts of vegetables, it was ne- ceffary to begin, by converting them into foap ; then to wait for the mooting of certain cryftals, or bright points, which would appear upon the furface, and that thefe cryftals were a ncutrzi fait, volatilized of itfdf by the mere operation of nature : after this the matter is to be moiftened with a new liquor, and then fet upon the fire, and that thus there would be a new appearance of volatilized fixed fait ; and the repeat- ing this procefs feveral times, affords always, at length, a very large proportion of the fixed fait, no longer fuch, but truly volatilized. The choice of a proper liquor, for the wetting the matter, is a thing of no fmall confequence. Water is, of all others, the leaft proper, and oil appears the moft fo ; and of the different oils, thofe drawn by diflillation are much more effectual than the common expreffed ones. The great reafon of this is, that the liquor ought not only to be the moft volatile that may be, but it muft be alfo fuch, as will moft intimately unite -with fait. Spirit of wine is very- excellent for the purpofe, but would be much more fo, did it not want this laft quality.
Mr. Homberg, by various trials, carried at length this at- tempt to fo great a height, that he was able to volatilize nearly one half of fait of tartar, or of any other volatile fait. The new fait often appears in a dry form, the oil, which is employed in the making it, preferving it from the effect of humid vapours, which would othervvife have re- folved it into a liquor. Mem. de 1' Acad. Far. 17 14. Fojfile Salt. The ifiand of Tfongming, in the Eaft-Indies, affords the moft remarkable kind of foflile, or native dry fait in the world. The country is there, in general, very fruitful, but in certain parts of the ifland there are fpots of ground, of feveral acres, which appear wholly barren, yield- ing not the leaft appearance of any thing vegetable upon them.
Thefe fpots of ground tafte very fait, and abound in fait in fuch a manner, that they fupply not only the whole ifland, but a great part of the neighbouring continent. When the people fee the earth become dry, and covered with white fpangles, which are pieces of fait, they dig it up about a foot deep, and carry it away to the work places, where they put it into large wooden veffels of four or five inches deep, and many feet broad, fet a little flanting. They pour water upon it in thefe. When it has flood a proper time they let it out, and add more, till all the fait is diflblved ; then they boil this water in the common way, and extract the fait from it. It is very remarkable, that the fame pieces of land, which produce vegetables one year, will produce this fait another; and, on the contrary, the fait parts will fome fea- fons produce vegetables. The fait work there is a thing of great advantage to the Inhabitants, and all the poor are, in the fcafon, employed in it; the men in collecting and wet- ting the earth, and the women in boiling up the water, which they attend as carefully as the men. Qbferv. fur les Cout. dc 1'Afie.
Ri
Glauber
