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that of Iron becoming black; of antimony,orange; of arfenic, yellow, &c. but either noprecipitate forms, or if formed, it is redifiolvedby any excels of acid. Thus if fulphuvettedhydrogen is added to a folution of the red ful-phat of iron, the metal is immediately broughtto the ftate of the green, or lefs oxygenatedlulphat, but no precipitate is formed unlefs thefulphuretted hydrogen be in great excefs, asthe red lulphat has naturally an excefs of acid.On this principle is founded an ufeful tell todiftinguifli iron from lead in wine or any otherliquor, for by adding hydro-fulphuretted water,and a flight excefs of dilute muriatic, or anyother weak acid, if iron only be prefent, theliquor will afliime a deep red, but will remaintranfparent, whereas lead will give a blackmuddy fediment. Often too this tell is ufefulfor feparating one metal from another in thefame folution, both where a precipitable and a'non-precipitable metal are prefent, and wherethere are metals more or lefs eafily precipitable.Thus if manganefe, zinc, tin, and copper, arein the fame folution, the firll addition of hy-dro-fulphuretted w;*er will feparate the tin, af-ter which the copper will fall, and then thezinc, whilll the manganefe remains in folution.

In all the above circumllances it is the Am-ple hydro-fulphuretted water which is meant,and not the alkaline hydro-fulphurets, forthough the action of the latter is in generalvery fimilar to that of the Ample hydro-ful-phurets there are fome important differences,and in particular, the alkaline hydro-fulphuretsprecipitate all the metallic folutions withoutexception, as will be afterwards noticed.

Alkaline and Earthy Hydro-Sulphur els.

Sulphuretted hydrogen unites readily, and inlarge quantity with the alkalies and alkalineearths, forming tranfparent, colourlels, oftencryftallizable falts, in which the bale is nearlyif not entirely faturated, and from which thefulphuretted hydrogen is expelled in ftrongcftervefcence by the addition of a ftronger acid(as the carbonic is from the carbonnts) withoutany other decompofition or depoAtion of ful-phur, unlefs the acids ufed ate the nitrous oroxymuriatic which are themfclvcs decompofed,and yield oxygen to the fulphuretted hydro-gen.

The hydro-fulphurets are all foluble inwater, and the folution is at firll colourlefs, butby expofure to air it becomes Aril greenilh yel-low and then depoAts fulphur, and in this hatethe ftronger acids caufe a further precipitationof fulphur. After a while alfo fulphureous

acid is formed, and may be expelled byftronger acid, but this does not take place tillall the fulphuretted hydrogen is decompoled,-finally, when the hydro-fulphuret has beenvery long expofed to the air it becomes againentirely colourlefs, and lofes all its fulphureousftnell and tafte, and is converted into a fulphatof the alkali or earth which was originally em-ployed.

Hydro-Sulphuret of Potajh is formed by pafs~-ing fulphuretted hydrogen through a folutionof potalh till no more will be abforbed, andexpelling the excefs of fulphuretted hydrogenby boiling for a few minutes. The lolutionevaporated and cryftallized gives a perfectlytranfparent colourlefs fait in large cryftals, withan alkaline and very bitter tafte. It deliquefeesin'the air, and then has the peculiar fetid ftnellof fulphuretted hydrogen, but when dry it isfcentlefs. It diflolves in water and alcohol,producing cold during folution, which is aproof of the complete iaturation of the alkali.Acids caufe a lively efFervefcence and' expellpure fulphuretted hydrogen, but no fulphur isdepofited.

This fait may be formed by calcining a mix-ture of fulphat of potalh and charcoal, bywhich the fulphat is converted into a fulphurer,and by lixiviating the fulphuret with water, and -faturating this folution with fulphuretted hy-drogen by which the excefs-of fulphur will bedepoftted, and a Ample hydro-fulphuret of pot-afh will remnin in folution.

Hydro-fulphuret of Soda. This fait is preparedin the fame manner as the laft, and refembles itclofely in moll of its chemical properties. Itwas Arft obtained cryftallized by Vauquelin, inthe following way; a mafs of impure carbonatof foda procured by the decompofition of com-mon fait was lixiviated to extract the carbonatof foda, and the mother liquor after Handing,at reft for a conAderable time was found Ailedwith a colourlefs tranfparent fait cryftallized infour-Aded prifms, which had an acrid burningtafte fucceeded by an intenfe bitternefs, and aflight-flavour of fulphuretted hydrogen. This ■fait diflolves copioufly in water,’ producing coldduring folution, and the liquid has a flightlyfulphureous ftnell. Muriatic and fu-lphuricacids expell fulphuretted hydrogen, and do notproduce any turbidnefs, but the nitric and oxy-muriatic acids, (that is, thofe which yield oxy-gen readily) feparate an abundance of fulphur.

The mode of its production in the cafe men-tioned by Vauquelin, mull have been the fol-lowing; muriat of foda was decompofed in thelarge way, (probably by gypfum and pyrites)