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lence,* fo that this dangerous experiment fhouldbe performed with the utmoft caution.

There are various methods of reducingmuriat of filver. The moft frequently ufed isby carbonat of potafh. For this purpofe rub thedry muriat with about twice its weight ofcommon pearl-afh, put it into a crucible, cover itwith a little more pearl-afh, and put it into anyfurnace capable of giving a filver-melting heat.The crucible mull be large enough to hold abouttwice the bulk of the materials employed. Applyheat gradually, and the mafs will firft melt andthen give oft' a great quantity of gas with muchintumefcence, and become quite black. Whilftthis is going on the heat fhould not exceed amoderate rednefs, otherwife part of the con-tents are very liable to fpurt out by the effer-vefcence, after which it may be raifed to a fullwhite red for a few minutes, and the crucibleis then to be taken off, (truck gently on theoutfide with a hammer, to fhake down all thefcattered globules of metal, and cooled verygradually. On breaking it, if the redudtion iswell performed, it will be found to contain aclean faline mafs confuting of muriat and car-bonat of potafh fufed into an uniform fubftance,and at the bottom will be a button of perfectlypure filver, beautifully white and refplendent,without the leaft difcoloration on the furface,and eafily detached from the faline mafs aboveit It requires fome practical fkill to knowhow long to continue the fufion, for as thereis a great excefs of carbonat of potafh, theoperator need not wait till all effervefcence isover, but yet if the heat is urged too brifklyfome of the luna cornea is volatilized along withpart of the alkali. However, where the mereobject is to procure a quantity of pure filverfrom luna cornea, it is not difficult to do itwithout incurring any material lofs; but whenit is required for the purpofe of analyfis toobtain all the filver from a given quantity of themuriat, more precaution is requifite. In exa-mining the crucible and faline mafs afterreduction, minute globules of filver are fome-tlmes found either difperfed through the mafsor more commonly flicking to the lides of thecrucible. In the former cafe they arife eitherfrom not heating the mixture fufficiently, or(what is more probable) from cooling it toofuddeniy, whereby the filver, which becomesfolid much fooner than the fait, in the momentof congealing, fpurts up fome globules, whichpenetrate and arc detained in the fluid above.When the globules flick to the crucible it is

often owing to fome roughnefs in its fides,which may be prevented by giving it a coatingof borax by melting a little of this fait in itbefore the reduction. Small quantities of lunacornea may alfo be reduced in a dry phial fetin fand inftead of a crucible, by which all thefilver may be colledted very accurately. Car-bonat of foda anfwers as well as potafh. Moftof the effervefcence may be prevented by em-ploying the caullic alkalies initead of the carbo-nated, but this is expenfive in the .large way.Whatever care is taken in the reduction, it isfeldom that quite 75 parts of filver can berecovered from 100 of luna cornea, fo that afmall portion is volatilized.

Luna cornea may alfo be reduced by mercury.This method was firft difeovered by Marggrnf,who has alfo given the following intereflingexperiments on the fubje£t. c This excellentchemift firft obferved that fpirit of fal ammoniacmade with fal ammoniac and litharge, (or pureammonia diffolved in alcohol) diffolved lunacornea in the cold; and a folution was equallyeffedted by fpirit of fal ammoniac preparedfrom lalt of tartar and fal ammoniac, (or carbo-nated ammonia diffolved in alcohol) and onadding to the latter folution fix times as muchmercury as it contained of luna cornea, on thenext day a fine Arbor Diana: was found in themixture, which was a perfect amalgam otmercury and filver. This led him to attemptthe reduction of luna cornea more direct I y,which he performed in the following way. Putin a glafs mortar, one part of luna cornea, addto it about twice its weight of dry carbonatedammonia with juft fufficient water to bring it tothe confidence of foup, and rub them togetherfor a quarter of an hour, during which themixture will fwell and eftervefee a little: thenadd fix parts of the pureft mercury revived fromcinnabar, and continue the rubbing for fomehours, during which the mixture will firftbecome of a blackifh grey, and a perfect amal-gam of mercury and filver will be formed.Then add a quantity of wafer, which will be-come milky, and pour it off into a feparateveffel before the white powder impended in ithas fubfided, leaving the amalgam in the mortar.Waih the latter repeatedly with water, andcontinue rubbing, till all ti.e white powder isrinced out, and the water returns clear from offthe pure amalgam. The white powder is fub-muriat of mercury, very fimilar to calomel, andthe filver has paffed into the mercury of theamalgam, whence it may be recovered by di£~

k Preafl. « Hilt. de 1 ’Acad. de Berlin lor 174).

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