G O L

GOL

C 5

oxyd of gold is precipitated, while the fuper-natant liquor holds ill folution the neutral, muriat. The metallic oxyd after being wellwafhed feems to be perfectly pure, and is de-compofable at a low red heat, merely in cOn-fequence of the very weak attraction of gold foroxygen. Ammonia differs in this refpett verymaterially from the fixed alkalies: its affinityfor the oxyd of gold is remarkably powerful,and in confequence, it decompofes the falts ofthis metal, not only by means of its affinity forthe acid, but alfo for the bafe, hence the pre-• cipitate is not a mere oxyd, but an ammoniu-retted oxyd, and it exhibits, as we {hall proceedto fhow, very remarkable properties . 111

Ammoniuret of gold, or fulminating gold, isprepared in the following manner. To a folu-tion of muriated gold, diluted with fix or eighttimes its bulk of diftilled water, add liquid am-monia drop by drop, till it ceafes to occafionany precipitate: feparate by means of the filter,the yellow powder that will be thus produced,wafh it well in two or three parcels of hotwater, and let it dry in the air or in a warmroom. The fulminating gold thus procured, willbe found to exceed the weight of the originalgold by about 33 on the hundred, or in otherwords, out of 100 parts of this compound 75will be gold. If a little of this powder, half agrain for example, is held over a candle, in afpoon or on the blade of a knife, it fhortly ex-plodes with a loud {tunning report, from whichcircumftance it has obtained its common appel-lation.

Although the procefs which we have juftgiven is perhaps the fimpleft method of pre-paring this dangerous fait, yet fo powerful isthe affinity of ammonia for oxyd of gold that ifthe two come into contact with each otherunder a’raoft any circumltances, they will eager-ly combine together. Thus if the gold infteadof being diffolved in pure aqua regia is diffolvedin one made by mixing nitric acid with muriatof ammonia, the precipitate thrown down fromthis even by a fixed alkali will poffefs the pro-perty of fulminating. Again, if oxyd of goldthrown down from pure aqua regia by a fixedalkali be rediffolved in either the fulphuric ornitric acids and precipitated by ammonia, therefult will be fulminating gold. If even thefimple oxyd of gold, previoufly boiled withcauftic fixed alkali in order to feparate any ad-hering acid, be digefted for fome hours in liquidammonia, it will become equally fulminating asby any other mode.

* Bergman’s Eff. 11. p. 135 . Baum

34 )

The effects of this compound when exploded,though not fo violent as t.aofe of fulminatingr filver, are fufficiently dangerous to juftify thegreatelf caution in ufing it. The preciie degreeof temperature requilite for its explofion is notafeertained, and indeed appears to be fubjedt tofome variation ; it may however be ftated asabove 250° of Fahrenheit’s thermometer. Juftbefore it explodes, its colour changes from yel-low to black, and a momentary flafh is obferv-able at the inftant of its decompofition. Althoughit exerts its force in all direftions, yet its prin-cipal energy is in a downward direction ; hencetwo or three grains exploded on a piece ofmoderately thick fheet copper will tear a holein it. An electrical fhock will alfo decompofethis fait, but it cannot be fet fire to by a fparkeither of electricity or from the flint and fteel.By fudden friction it explodes with great ve-hemence, and feveral inftances are recorded offerious accidents from this caufe: hence itfhould never be kept in a ground-ftopperedbottle, as a little may adhere in the neck andwill be infallibly exploded by the infertion ofthe ftopper. The facility with which this pow-der explodes is prodigioufly increafed by highdrying ; if it is heated till it becomes black andis immediately removed from the fire, it willthen go ofF frequently by a mere touch. Thegrains of this fubllance have not like thofe ofgunpowder the property of communicating thedecompofition from one to another; only thofethat are heated to the precife point are exploded,the reft are difperfed unaltered by the violenceof th'e fhock. Its proper explofive force, thoughattended with a loud report, feems however tobe confidsrably inferior to that of gunpowder,hence if heated in a pretty ftrong clofe veffel itis compleatly decompofed but without anyfhock..

There appears to be no fubftance capable offeparating the ammonia from the oxyd of goldafter they are once united, and the only modeof decompofition is the application of fuch aheat as fhall at the fame time deoxydate thegold and reduce the ammonia to its elementaryparts. By a dry heat this decompofition ismoftly rapid and explofive, but by the inter-vention of a hot liquid it is gradual and filent.Thus the fixed alkalies, whether cauftic or car-bonated, if diluted with water fo that theirboiling point is inferior to the heat required forthe decompofition of fulminating gold, may bedigefted upon it without in the flighted degreeimpairing its character!ftic property, but when

e Chim. exp. Lewis comm, techn.