Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/943

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the ftones lie high, and the waves break upon them; the globules of water are in the fame manner raifed from their Surface, and little rainbows of fiiort duration are formed. Near the fhores the fea-water, inftead of appearing of all this variety of colours, generally looks white : this is ow- ing to the violent motion of the waves, in which they beat one againft another, as alfo againfl the rocks and fands, and by the mere agitation of their parts put on this colour. The water at thefe times feems, in thefe places, really of a milky nature, but as foon as it fettles again into a calm, the clearnefs of the water returns, and no fettlement happens in the whole body of it; which fhews that it was not made white by the addition of any other matter to it, but only by the difturbing of its own particles, Thefe are all the various colours and appearances that the fea-water puts on in different places, and on various occa- sions; and we fee, in the whole, that thefe differences are in general owing not to the alteration in its nature, but only in its change of parts in their directions to the eye, and in their breaking one againft another, or receiving more or lefs light, or that from a clear or from a cloudy iky. Marfigli, Hift. Phyf. de la Mer.

Count Marfigli has gone through a long courfe of experi- ments upon fea-water, and after a thoufand tedious proceffes has obferved, that three liquors alone are of power to fliew the different nature of the fea-water- in various places, and that very readily : thefe only need, therefore, be carried abroad by thofe who intend to make experiments of this kind. Thefe are an infufion of mallow-flowers in water, made fo ftrong, as to be of a violet colour, fpirit of fal ar- moniac, and oil of tartar. The two laft of thefe will al- ways keep as long as there is occafion ; the other may be preferved from decay by fugar diffolved in it in different quantities, according to the time it is to be kept, and the climate it is to be carried to ; for this ingredient, if added in fo large a quantity as twice the weight of the liquor, fo as to make it a true fyrup, does not prevent it from per- forming its office in thefe experiments; and in this ftate it will keep every where, and ever fo long. When intended for lefs fevere trials, it may have a fmaller proportion of the fugar, and its effects will be then more fudden and more manifest. This infufion of mallow-flowers mixed withy?a- water, turns it to a greenifh yellow colour, like that of the chryfojite. The fpirit of fal armoniac mixed with fea- •water, renders it turbid and muddy, and after a time a white fediment is formed, and fubfides by final! pieces at a time to the bottom of the glafs. Oil of tartar occafions the fame change, but it does it with much more violence. By mixing thefe liquors with fea-water, taken up in diffe- rent places, and at various depths, we fee the different quan- tity of fait it contains manifefted, by the more or lefs fud- den productions of thefe changes, and by the deepnefs or palenefs of the colour, and thequantity of matter precipitated. The common attempts of fweetning fea-water are alfo eafily proved by this means, for the more fait it contains, after thefe pretended fweetnings, the more colour or precipitati- on it will occafion in thefe mixtures; and the mixing them with it, if perfectly freed from its fait, will produce no change at all, as is evident by mixing them feverally with fea-water carefully diftilled ; for as this procefs intirely robs it of its fait, there is no fort of alteration made in it by the mixing thefe liquids. Id. ibid.

The fudden and furprifing clearnefs of fea-water, on certain occafions, is a thing not yet accounted for : we have many inftances given of the fact by the writers of voyages and travels, but one of the moft remarkable is recorded in the PhilofophicalTranfacKons, as having happened on the fhores of Iceland. On the 13th of May, in the year 1642, all the fea that beats upon the promontories of that coaft, and which is ufually very thick and turbid, was for two days to- gether fo perfectly pellucid and mining, that the fmalleft ftones and plants, and the fea fhells, where the water was forty fathom deep, were feen in fo diftinct a manner, that they appeared not more than four feet from the furface. The fifhermen who were out in their boats, were fo terri- fied at the unufual appearance, that they left their bufmefs, and the whole country looked on it as a prodigv. Philof. Tranf. N'no.

In the making of common fait from fea-water, it appears that there are. other fubftances befide fait contained in it, as there is a ftony cruft formed on the fides of the pans, and a powder precipitated to the bottom at the corners ; befide thefe, there are fome fubftances feparated from the water be- fore it is let into the pan, during its fubfidence in the ciftern, and there alfo remain fome afterwards mixed in the bittern, after all the fait is extracted from it. Vid. Brozunrig of Salt, p. 74.

The fea-water in its motion gathers up mud, fand, and many other impurities, which foon fubfide in the ciftern ; others, fomewhat more intimately mixed, are feparated with the fcum raifed by the whites of eggs in clarifying the brine. But befide thefe grofs fubftances, fea-water contains a glu- tinous matter of a much finer texture, which is more inti- mately mixed in St: this Count Marfigli fays is fo light, as to rife with the water when diftilled in a fand-heat, and

therefore may eafily be raifed in vapour by the fun, and falling may fecundate the fields, and promote the growth and nourifhment of plants. This vifcous matter feems earthy $ faline, and oleaginous; and this is the fubftance which, in ftormy weather, forms a thick fcum upon the furface of the waves; and to this vifcous part is chiefly owing the putre- faction of fea-water, when fuffered to ftagnate : for it is evident that the whole fea in any place wilt become fetid, when it has been calm for fome time together, fo that in mips becalmed people have often been threatened with fiek- neffes from the flench. Mr. Boyle records two inftances of this, one in the African feas, the other near the Azores i(- Iands. In the putrefaction of fea-water this flimy matter is attenuated, and its texture deftroyed, and part of it flies off in fetid exhalations, while part fubfides to the bottom. Afcr^//,Hift.Phyf. delaMer. Boyle on theSaltnefsoftheSea. Befide this vifcous matter, fea-water probably alfo holds an earthy fubftance, fo very bright and fubtile, that it is ele- vated in the foregoing procefs along with the watery vapours, as well as the flimy matter. The walls of the houfes where fait is boiled are covered with this earth, and it feems of the nature of that earth contained in clear Wme-water, which is known to fubfide from it by proper methods, even after it has been raifed in diftillation.

Befide this light earth, fea-water contains another very coarfe" one ; this the fait-workers call fcratch, and find it on the fides and at the bottom of the corners of their pans. And it is very probable that this would be feparated {mm fea-water by congelation, for if Biidol-water be frozen, and thawed again, there is always an earth of this kind feparated from it ; and the petrifying water at Knarefborough being frozen in the fame manner, depofits its ftony or calcarious fedi- ment. Thefe earthy particles are not feparated from ihe water in the fame ftate in which they were fufpended in it, for when the watery particles are evaporated, then ftony ones get together, and concrete in clufters ; and in this ftate they can no more be diffolved in zuater, unlefs they are again fe- parated into the fame minute malfes which they were in before. It is evident that this powder can rife in vapour from the experiments of diftillation, and accident has proved this yet clearer; for in the boiler of a fire-engine, if water be ufed which is highly impregnated with this ftony matter, as' is ufually the cafe with that which arifes from among ftrata of freeftone, and the like, the cylinder into which the vapours rife will be fo filled with ftony matter, that the pifton cannot rife in it.

This powder is properly a fparry matter, and is in general the fame fubftance which forms incruffations on the vege- tables, &c. in fprings. It has been found, and defcribed by all authors who have analyfed waters of any kind. Dr. Collins, in bis Difcourfe on Salt and Fiftieries, calls it ftone- powder; Dr. Lifter calls it arena alba, and lapis albui ', white land and white ftone ; and Dr. Hoffman puhis Candidas, and in fome other parts of his works fuccus maris fclino-terreus calcifonnis b. a Lijier, de Font. Med. Angl. b Hoffman ^ Oper. Tom. III.

Thefe particles are extremely fmall and minute while fuftain- ed in the water, as appears by their pafling through paper with it in filtration, as has been proved by Dr. Plot in his experiments on it ; and hence it is able to enter the vcffels of plants and animals, particularly the teftaceous fifties, the fhells of which it has great affinity to. It alfo forms the ftalactita? in caverns, and many other of the cruftaceous fof- fils. Plot, Hift. Staffordfhire, cap. 2. p. 109. This earth is capable of being diffolved in water in Very confiderable quantities, fome of our fait fprings affording a water which contains it in the proportion of one thirty - fixth part of its own weight, which is nearly the fame pro- portion In which common fait is found diffolved in feti- water in general. Lijier, deFont. Med. Angl. lib. I. cap. 6. The great folubility of this earth in water, fhews that it very nearly approaches to the nature of falts ; and it is even found to enter into the compofition of perfect falts, for be- ing long expofed to the open air, k imbibes the aerial vitri- olic acid, and with it is converted into a neutral fait, which Lifter ranks among his calcarious nitres. This fait nearly refembles the bitter purging fait of the Epfom-waters. It is of a highly alkaline quality, and turns a mixture of fyrup of violets and water green.

The next ingredient of fea-water^ that offers itfelf in art analyfis of it, is fait : this is the moft obvious of all others,- and is contained in it in very different quantities at different times, and in different places. The Baltic fea is very weakly impregnated with fait; the Englifh and German feas 1 are much more ftrongiy fo, and the Mediterranean much more fo than any other ; and finally, the water on the coaft of Mofambique is fuppofed much falter even than this. Mem. Acad. Par. 171 1.-

Father Feuillee, in paffmg through the Straits of Gibraltar towards America, obferved the fea-water to diminifti in gravity as he approached the line. Dr. Hales found the' wafer of the fea, taken up near the buoy of the Nore, to contain -^ ^ of its whole weight in fait, and that of the Mediterranean contained yj^sl an( ^ Count Marfigli fcund

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