WAT

WAT

( 474 )

wire was converted into a black brittle oxydweighing 8$ grs. more than at firft.. In thisprocefs, lays Lavoifier, the water is decompofed,its oxygen biting abforbed by the iron, and itshydrogen, the other compsnent part, beingliberated in the form of gas. Dr. Prieftley,however, though he admits the faff, explains itin the following manner. The water, accord-ing to him, in part unites with the phlogiftonof the metal forming hydrogen gas, while thereft of the water combines with the calx of theiron. That this black calx really contains waterhe endeavours to fnOw by the following com-parative experiment.* A quantity of feales ofiron and of red oxyd of mercury were mode-rately heated, in order to render them as dry aspoffible, they were then each put into glafsreceivers of the fame fize and form, invertedin dry mercury, and afterwards filled with hy-drogen gas from the fame veflel. The focus of aburning lens was then thrown upon the metal-lic oxyds, and it was found that by the time 4ounce meafures of the inflammable gas wereabforbed by the iron, the water was runningdown the fide of the receiver in drops, whereasalthough the mercurial oxyd was heated till 8ounce meafures of gas were abforbed, there washardly any fenfible quantity of water produced.If this experiment is accurately reported (andthere feems no reafonable ground for fufpicion)it follows not that the phlogillic theory is true,but that the theory of the decompofition ofwater can derive no confirmation from it. It isindeed not improbable that there is a real differ-ence between finery cinder or feales of iron,and the black ethiops of the fame metal, thelatter being a fimple oxyd, and the formera hydrat, that is to fay, a combination of oxydwith water.

Upon the whole it appears that the only per-fectly unequivocal evidence for the compofitionof water is derived from thofe experiments inwhich it is adually produced by the coinbuftionof determinate proportions of oxygen and hy-drogen, and from thofe in which it is firftdecompofed and afterwards recompofed by theagency of the eleCtric fluid. Thefe experimentshowever have been performed with fuch parti-cular care by the molt accurate and intelligentchemifts of the age, that no faCt in the wholecircle of chemical fciepce is more fatisfaCtorilydemonftrated.

WATERS. Mineral.

Every natural water which flows on the earth,

• Boflriiie ef I'lilo;

or is found beneath its furface, holds feme fa-reign matter in folution, which, if it does notfenfibly impart fonre peculiarity in tafte, fmell,and phyfical properties, may at k-aft be deteCledby chemical means •, and when the quantity ornature of this foreign ingredient is fuch as togive obvious fenfible or medicinal properties, itis ufually called a mineral waiter. The faitwaters of the ocean and of fome large inlandlakes, are however excluded from this definition,though in every other point of view they arefull as interefting as the fmaller and compara-tively rare fprings, which have the appellation ofmineral.

The high importance attached to mineralwaters has firft arifen from the extenfive cele-brity which they have acquired in the cure ofdifeafes 5 a celebrity which many of them main-tain to the prefent moment: and they are equallyinterefting to the chemift on account of the va-riety of fubftances contained in them, and themode of their chemical union, and as oftenilluftrating the difficult fcience of geology.

The analyfis of mineral waters has (as mightbe expected ) been benefited by all the improve-ments which have been progreffively made ingeneral chemiftry, and the fubjett has been inparticular elucidated by the labours of manyexcellent chemifts cfpeciafy diredted to thisobjeft. It is ftill however in many cafes com-plicated and difficult, and requires confiderableikill and minuterefs in manipulation, as thefubftances operated on are always in fmall quan-tity and often numerous.

The fubftances hitherto found in naturalwaters are the following :

r. Oxygen Gas , in fmall quantify, was firftdetected by Scheele . It is contained in almoftevery fpriug water, but never exceeds about■j-g-o- of its bulk, and generally is lefs. It exiltsin very loofe combination, and gives no fenfibleproperties to the water. It is incompatiblewith fulphuretted hydrogen and with luiphat ofiron, and therefore cannot be prefent whenthefe are.

2. Azotic Gas, in fmall quantity and in loof*combination exifts in fome waters, fuch as thatof Buxton, and at the fame time a large quantityof it ufually riles in its galeous form alongwith the water, and pailes through it in i largebubbles. This alio gives no obvious fenfibleproperties.

3. Common Air is contained in fmall quantityin ail natural waters, from which the iaft per-son, &c p. J7.

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