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fo far concentrated as to require a much highertemperature for their ebullition, they graduallydecompofe it without however difengaging anyammonia. In the fame manner diluted fulphu-ric acid produces no effect, though when con-centrated it effebts a decompofition, but merelyin confequence of the greater quantity of heatwhich it requires for ebullition. Nitric acideven when moft concentrated boils at a lowertemperature than is required for the decom-pofition of this fait, and therefore produces noeffect on it. Muriatic acid fparingly diffolvesit, but on the addition of a little fixed alkali letsit fall again unaltered.

If aurum fulminans be mixed with four orfive times its weight of chalk, or fulphat of pot-alh, or in fliort with any pulverulent fubftanceneither fufible nor decompofable at a moderatetemperature, and is expofed gradually to a lowheat it will be quietly decompofed, nothing ofthe fait remaining behind but the purple oxydof gold. A fimilar effedt may be produced,only that remarkable caution is required, byheating the' fulminating gold without any ad-dition ; as foon as it changes colour at all it isto be removed from the fire, and when coldagain heated till the colour is a little moredeepened, proceeding in this way till the powderbecomes purple it will be found to have entirelyloft its explofive faculty. A fimilar changetakes place if fome fulphur is melted at theloweft poilible heat and the fulminating gold isdropped in by half a grain at a time and wellmixed : the fulphur may then be burnt off with-out any danger, and minute grains of metallicgold will be left behind.

The true theory of the decompofition offulminating gold was partially difcovered byBergman, and has fince been fully illuftratedby Berthollet . The former of thefe able che-mifts fhowed that this fait when decompofed inclofe veffels was reduced to gold partly in themetallic ftate and partly in that of purple oxyd,and at the fame time a gas was extricated inbulk about a thoufand times as great as that ofthe original fulminating fait, and which ex-tinguilhed flame and animal life, was not ah-forbed by water and gave no precipitate withlime-water. Berthollet , by decompofmg thefame fubftance in a copper tube connected witha jar inverted in mercury, obtained azotic gasand a few drops of water, and the gold wasreduced to the metallic appearance. Nov/ asammonia is compofed of hydrogen and azot,and as the affinity of gold for oxygen is very

flight, it is manifeft that the decompofition andexplofion under the circumftances already men-tioned, are occafioned by the oxygen of thegold and the hydrogen of the ammonia com-bining to form water, and to the liberation ofthe azot and its fudden affumption of the gafeousftate.

Muriat of gold may be decompofed not merelyby the fuperior affinity of certain fubftances forits acid, or of others for the metallic oxyd, butalfo in confequence of yielding a part of itsoxygen to bafes whofe attraction for this fub-ftance is particularly powerful. Thus if a littlemuriat of gold is poured into fulphureous acid,this laft in a ffiort time deprives the metallicfait of part of its oxygen, and in confequencethe furface of the fluid is covered with a film ofreduced gold: the fame takes place if gallicacid is made ufe of. So alfo if ether and muriatof gold are fhaken together, the water firftgives up the metallic fait to the ether and be-comes itfelf colourlefs, while the ether affumesa bright yellow tinge, and after a while thegold is deoxydated by the combined a£tion ofthe water and ether, and is feparated in its me-tallic ftate. In the fame manner a ftick ofphofphorus being immerfed in muriat of goldwill in a few days be covered with a brilliantcoating of this metal: and a fimilar effect isproduced, according to Count Rumford , bycharcoal, provided its ablion is affiftcd by a boil-ing heat or by expofure in a clofed vial to therays of the iun. Hydrogen gas alfo is capableof decompofing muriat of gold as well as othermetallic falts while they are moift with water; nthus if a piece of filk is dipped in muriat ofgold and expofed in a clofe veflel to hydrogengas, it will in a fhort time be covered with apellicle of gold, partly metallic and in part in,the form of purple oxyd.

Certain of the metals and metallic falts de-compofe muriat of gold accompanied by peculiar;phenomena, which we fliall proceed to mention.

If a piece of clean iron is introduced into adilute folution of muriated gold, this lattermetal is precipitated upon the furface of theiron in the reguline ftate, a proportional quan-tity of the iron being diffolved. If the folutionis largely diluted with alcohol i'nftead of water,the gold precipitates upon the iron and a verylittle of this latter is in return taken up by thedulcified acid ; the gold may he made to adherefirmly to the furface of the iron by burnifliing,and this is the moft convenient and economicalmethod of gilding iron. The red fulphat of

* Mrs FuJhame’s Effjys,