WAT
WAT
theater, taken from the furface of the Gulf at Lyons, to contain only ^ of fait, while thut of the fame place, taken ■at a greater depth, contained ™.. From this that author argues for the leas being falter at greater depths than near the furface-, but this might be owing to the falling in of the frefh-uwter rivers near that place ; for Mr. Boyle found the fea-water of our own feas to be of the fame faltnefs at all ■depths : and indeed there is great reafon for fuppofing, that in many places, where there falls in little .frefh water, and where the fun daily raifes a great deal of water in vapour, it may remain much more fait near the furface than at great depths, juft contrary to the foregoing fuppofition. Hales, Exper. on diftilled Sea-water.
From late experiments it appears,- that fea-water is heavieft and falteft at great depths, and that it is of a temperate heat there ; that is, 53 degrees of Fahrenheit's thermometer. See Phil. Tranf. Vol.47, p-213, 214.
It is to be obferved, that all the authors who have made ex- periments of this kind have evaporated fea-water, and given the weight of the dry remainder as the quantity of fait con- tained in it; but this is not the true ftate of the cafe, for this dry refiduum always contains a quantity of the calcari- ous earth, or fcratch, and of the falts of the bittern : befide this, a certain quantity, more or lefs, of aqueous moifture will remain in the fait, and this will alter its weight, as it will be in a greater or lefs proportion, according to the de- gree of fire ufed ; and Mr. Boyle found that his refiduum of the water of the Nore, which, when in the form of what he called a dry fait, was T ' - part of the water, when it had been well dried in a crucible, was but T ' T of the water ufed. Boyle of the Saltnefs of the Sea.
Befide common fait, the fea-water contains other falts, which are found in the bittern, or bitter brine remaining after the fea fait is extracted, Firft it contains a bitter purg- ing fait, known in the (hops under the name of Epfom-falt. This was firft extracted from the Epfom, Dullwich, and other purging waters, but is now made only from the bittern at Newcaftle, and other places ; and it is chiefly to this bit- ter fait that the fea-water owes its bitter tafte, though that has-been fuppofed to proceed from bituminous matter con- tained in it, and often found on its furface, or lodged upon the rocks by its motion. Philof. Tranf. N° 377, 378. Another fait is alfo found in bittern, which is called a mu- riatic calcarious fait, its acid principle being fpirit of fea fait, and its bafis an earth nearly allied to quickfilvcr. This fait remains in the bittern after the purging fait has been extract- ed from it, and though it is a neutral fait, it cannot be made to fhoot in cryftals, but may be procured in' a dry form by fire; but it is very difficultly kept in this form, be- ing, of all other falts, the moft ready to imbibe the watery particles of the air, and run per deliquium. Hoffman, Obf. Chym. de Lixiv. a Sale rclift.
Befide thefe falts, the bittern contains a considerable portion of a fixed mineral alkali. Thefe principles are all found in boiling the fea-water into fait. But befide thefe there muft be many other fubftances, which efcape our fearch in this manner, fuch as the feeds and excrements of innumerable plants and animals, and the tin£tures which thofe plants and animals impart to it in their decay. Thefe, together with divers faline and fulphureous particles, will naturally fall under the obfervation of thofe who fhall attempt a perfect analyfis of fea-water by the nicer methods of chemiftry ; ; a thing yet much wanted in the learned world. Brownrig of Salt, p. 92.
Many ways have been attempted to arrive at the art of mak- ing fea-water frefh and potable ; the advantages of fuch a thing are evident enough, but the difficulties very great. Lifter propofes the doing it by means of fea plants ; thefe ve- getables, like other plants, continually exhaling a large quan- tity of water in form of vapour, and that being all frefh, lie propofes on this bafis a diftillation, without fire, in this manner. The body of a large ftill, or alembic, is to be filled three parts with fea-water, feveral frefh and growing fea plants are to be put into this in their growing pofture, and the head being then fitted on, and a receiver 'adapted to the nofe, there will be a continual afcent of vapours from the plant, which will condenfe into water in the head, and this will be thence conveyed into the receiver fweet, clear, and every way fit for drinking. The quantity thus procured, however, though cohfidcrable in regard to the manner of its being obtained, can be but fmali in proportion to. the wants of a fhip's company.
Mr. Kanton therefore attempted a more general method of doing it in quantities ; to this purpofe a large quantity of fea-tvater is to be taken up in a proper vefiel, and as much oil of tartar per deliquhan is to be added to this, as will ren- der it turbid, and caufe a large precipitation. After this the water is to be diftilled, the furnace of the ftill being (o contrived as to take up very little room, and confu'me but a fmall quantity of fuel ;. the fea itfelf may ferve for a worm- tub, the worm paffing out of the fhip, and in again at an- other place. When the water is thus diftilled, it is to-be
- mixed with an alkaline earth, and after ftirring thoroughly
about., the earth is to be fufered. to fubfidc.ip the bottom, i«pd the water poured off clear; it is then faid by the in-
ventor of this frheme to he perfectly fweet, and no way di- ftinguifhable from the very pureft river water. Phil. Tranf, N° 67.
Another method of fcparating fait from fea-water without fire is propofed in the Philofophical Tranfactions : take a vef- fel of wax, hollow within and every where tight, plunge it into the fea, or other fait water, and there will be made fuch a feparation, that the vefiel fhall be full of fweet water* the fait fraying behind. But though this water have no faltifh tafte, yet a fait will be found in the efiay. Philof. Tranf. N D 7. p. 128.
To obtain frefh wholefome water from fea-water, Dr. Hales's method is to keep the fea-water clofe fhut up till it has putrefied, and has again become fweet, then to diftjll, three fourths of the fea-zuater will be free both of the bittern and acid. Mr. Hales enters into a particular detail of the circumftanccs which may make the practice of this fupply of frefh water eafy. Philof. Experim.
Drinking fea-zuater with fome wine, is faid to prevent peo- ple from being fick at fea. Act. Phyf, Medic, Acad. Nat. Curiof. Vol. V. Obi. 84.
Sea-water, drank to the quantity of a pint, is a moderate purgative to moft people. It has been of late much in fa- fhion, and is faid to be very beneficial in many cafes, par- ticularly in glandular diforders.
Simp/e-W at ers. In the diftillation of f.mpk '-waters, a good general rule is this : take as much of the dried herb, as when cut fmall will fill two thirds of the ftill to be ufed ; pour upon this as much rain water as will make the plant float com- modioufly, leaving however a fourth of the ftill empty; di- geft this a while in a gentle heat, and then give fire enough to work the ftill, and draw oft" fo long as the water appears thick or milky, and taftes of the herb. Shaw's Lect. p. 198. It is a principal caution in this operation to remove the re- ceiver before the more pellucid, acid, faint, and dead water comes over, as it will at length do, and by mixing with the reft will fpoil the whole, by giving it a vapid or faint tafte, and fometimes a degree of acidity or vitriolic ftypticity, or emetic quality ; for part of the eflential fait of the plant now rifing, corrodes the head of the ftill, and carries over with it fome particles of the metal ; for which reafon, fuch waters fhould be either diftilled with a glafshead, or a pewter one, or elfe the laft running carefully watched, and not fuf- fered to come over and mix with the firft; for want of this caution, children, and perfons of tender habits, have been often vomited, purged, &c. contrary to the intention of tha prefiriber, by a ftmple-water.
The ftmple-waters diftilled by this method may often be too ftrong to give alone, but then it is eafy to let theni down, to a proper ftrength with common zvater; which is beyond all comparifon better than to mix them with their own faints, or the liquor of their fecond running. There are yet however two methods of improving the com- mon fmple -waters, which might eafily be put in practice: the firft is the cohobating, and carefully digefting'the plant; the fecond the fermenting it. With regard to the firft, if the liquor remaining in the ftill be exprefTed from the herb, and returned, along with all the water that came over, upon a frefh quantity of the fame fubject, and they be digeffed to- gether in a gentle heat for two days, and then diftilled as before, the water thus obtained will- be much richer, and more efficacious than before; and if the fame operation be repeated two or three times, thofe who have not tried it can- not eafily conceive how very rich a fimple-water may by that means be made : and this is' moft necefTary in diftilfing the fimple-waters of rofes, elder-flowers, balm, and the like iubjects, which afford but little oil, and otherwife make but weak waters. - <
The other method recommended, viz. by fermentation, is performed by adding to the plant and water, put together as:.for diftillation, a tenth or twelfth part of fugar or honey, or elfe a fortieth part of yeaft ; then fetting the whole in a warm place to ferment for three or four days only, fo that the herb may not fall to the bottom, nor the fermentation , bei above half finifhed ; then the whole being committed to the ftill, a water may be procured at one operation, ex- tremely, rich, or impregnated with the whole virtue of the
' plant; and thus mzy fmpk-watersht made .fit for long keep- ing without fpoiling, the fmall quantity of inflammable fpirit generated in the fermentation ferving excellently to prefcrve them. Shaw's Lectures, p. 199.
Di/lii/ed^W at ers. To procure the dljiilkd-waters of vegeta- bles, or other fubjedts, pure and free from all mixture of the other principles of the body it was extracted from, let the water, as diftilled, be put into a funnel lined with paper to be filtred,. and the funnel being kept continually filled up, that the lighter oil may not come in contact: with the paper, the ivatcr will be tranfmitted through, in a great meafure, without the oil ; but there ftill remains fome proportion of oily, and commonly of faline matter alfo in it. If the faline
- matter be acid, the 'way to deftroy it is by mtxinc chalk,
. or any alkaline fait with the water, which being afterwards diftilled again, will then rife pure. If the: plant were alka- line, and an alkaline fait he. fuf; ended inthe water, let it ■ ■-■■ > ■■' & : be
