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wiuriats than of the fulphats, fo that if in anywater where a barytic folution gives but a faintindication of fulphuric acid, an immediate pre-cipitate is produced by nitrat of filver, we maybe certain that it is the muriat of filver, andnot the fulphat which falls down.

Acetite of fdver has a particular ufe in de-compofing the fixed alkaline muriats,. as we areenabled thereby to diftinguifh the alkali moreeafily in the fupernatant liquor; for by evapo-rating the latter to drynefs, rediffolving the re-maining fait in alcohol, and gently evaporatingthe alcoholic folution to drynefs, if it be acetiteof potafh, it will deliquefce, but if acetite offoda it will remain dry and effiorefice.

All the falts of filver aifo give a black or darkbrown precipitate with the fulphuretted waters,which is as delicate a teft of fulphuretted hy-drogen as any that we poiTefs.

18. Salts of Lead. Tlie nitrat and acetite oflead are the falts of this metal employed astells. They will indicate the fulphuric, muri-atic, and boracic acids, and fulphuretted hydro-gen or fulphuretted alkali. The water beingfirft freed from any excefs of alkali by fatura-tion with nitric acid, the addition of either ofthefe falts of lead will decompofe, and form awhite precipitate with the acid of all the con-tained fulphats or muriats. But as fulphat oflead cannot by the eye be diftinguifhed fromthe muriat, the precipitate fhould be digeftedin acetous or very dilute nitric acid or merelyboiled in a good deal of dsftilled water, by any ofwhich means the muriat will be difloJved, butthe fulphat will be untouched. In thefe preci-pitates the acetite of lead is a more fenfible tellthan the nitrat, but as the former when longkept will be partly decompofcd by pure water,it fhould be allayed with water, and a little moreacetous acid added if neceftary.

Acetited lead is alfo decompofed by the car-bonated earths and iron, fo that the water fhouldbe boiled before this tell is applied. This faitalfo produces an infoluble borat of lead whenboracic acid is prefent iu the water, whichtakes place in one or two rare inftances. Theborat of lead is diftinguifhed from the fulphatof this metal by being foluble in nitric acid of1.3. fp. gr. and from the muriat by being info-luble in water, or in weaker acids. But whereboracic acid is fuipedted, Mr. Kirwan advifesfirft. to feparare the fulphuric acid (if any) byacettted ftrontian,. and the muriatic acid by ace-tited filver, neither of thefe acctites being decom-pofed by pure boracic acid.

Acetite of lead is alfo a very delicate teft for

the fulphurets, which it fhews by turning to adeep brown or black. It is often applied bytracing characters on paper with acetite oflead, and immerfing it in the fulphuretted water.

19. Soap. A folution of foap in diftilledwater, or in alcohol, is curdled by water con-taining any earthy fait. It is therefore a teft offome ufe but not diicriminative. The metallicfalts produce the fame effect, but the curd isthen coloured.

20. Tartaredus Acid. This acid is of ufe indiftinguilhing the falts with potafh (with whichit forms a precipitate of cream of tartar) fromthofe of foda which it does not precipitate. Itis necefiary however that the folution of faitwith the bafis of potafh (the fulphat or muriatfor example) be much ftronger than occurs inany mineral water in its natural ftate, fo that itmuft be concentrated by evaporation.

21. Nitro-Muriat of Platina. This fait isftill more diferiminative between potafh andthe other alkalies than acid of tartar, and willproduce a precipitate with a very weak folutionof any fait with potafh. It has not yet beenmuch employed, but may often be of ufe.

22. Alcohol. This moft ufefu! reagent isapplicable in a variety of ways in the aua.yfis ofmineral waters. As it diflblves fome of thefubftances found in mineral waters, and leavesothers untouched, it is a means of feparatingthem into two ciaffes, which laves confidcrablstrouble in the further inveftigation. Thofe faltswhich it does not diflblve, it precipitates fromtheir watery folution, but more or iefs com-pletely according to the fait contained, and theftrength of the alcohol, and, as a precipitant, italfo affifts in many decompofitions. 1 he greatutility of alcohol to the analytical chcmift hasbeen already deferibed under that article, andwill be further mentioned in this.

' l’he above are the principal tells or reagentsemployed. Several others might be enumeratedwhich will eafily fuggefl themfelves to thepractical chemift, and the theory of thefe re-fpeftive operations will be better underftood byconfulting the articles themfelves, to which we{hall refer the reader to avoid repetition.

Before we deferibe the mode of analyfis wemay fhortly recapitulate thofe foreign fubftancescontained in mineral waters, for which thereexifts any appropriate tefl or chemical reagentby which its nature may be readily detefted,and which therefore is to dircdl the operatorin his further analyfis. Where the precautionto be ufed in applying them has been mentioned,we ihaU net repeat it.