PYR

( 26 8 ) QJJ A

mouth of the vial being clofed with a plug ofpaper, it is to be quickly cooled till the vial canbe fafely handled; the pyrophorus is then to behaftily poured into a warm and perfectly dryground-ftoppered vial, in which it may be keptwithout injury for any length of time providedthe accefs of air is carefully avoided.

Another excellent method of preparing pyro-phorus is the following. b Mix together threeparts of Roman alum and one of flour, andheat the mixture to drvnefs in an iron pot, asdefcribed in the preceding paragraph: the blackcalcined mafs thus produced, is to be put intoounce phials of green glafs, coated without andwithin with clay. The phials thus charged areto be lightly flopped with balls of tempered clay-and then let up to their necks in fand in an ironpot; charcoal powder is then to be ftrewed onto the depth of half an inch, over which is tobe placed an earthen cover, luted to the pot.The whole apparatus is now to be placed in afurnace and kept at a red-heat for an hour anda half-: at the expiration of this period beingtaken out of the furnace and cooled quickly, itis to be unpacked, and the phials containingthe pyrophorus are to be placed with theirmouths inverted in mercury, in which fltuationthe pyrophorus may be kept for many yearswithout injury.

• Pyrophorus is a light dry black powder,which when poured out in a little heap on anyflat furface, and expofed to the air, prefentlygives out an odour of fulphuretted hydrogen,and in about a minute becomes red-hot, andburns with a very light bluilh flame till thewhole of the carbonaceous and other inflamma-ble matter is entirely confumed, nothing beingleft but the white earthy bafe of the alum..Sometimes, either from a defedl in the prepa-ration, or from the air not having been entirelyexcluded from the phial in which it is contained,the pyrophorus when poured out undergoes nofenfible change; when this happens, however,

the comhuflion may often be brought about bybreathing on the powder, and thus fupplying itwith the moiflure which feems to be the pri-mary agent in this phenomenon. Pyrophoruswhen made according to the lafl mentionedmanner is fo very inflammable as to take fireas it is falling from the mouth of the phial.If poured into a jar of pure oxygen gas it formsa brilliant fiery {bower; the oxygen is for themoll part confumed, and there remain in thejar fulphureous acid and carbonic acid gaffes:the pyrophorus alfo being confumed, with theexception of its aluminous bafe.

The chemical changes that take place duringthe formation and decompofition of pyrophorus,appear to be the following. Firft, by beingheated below rednefs in the open air the ingre-dients enter into fufion, and thus mix accuratelywith each other, then the water of cryftallizationis driven off from the alum, and of the fugaror flour little elfe than the charcoal efcapesvolatilization. Secondly, the red-heat to whichit is expofed in the phial, caufes the fulphuricacid of the alum and the charcoal of the fugarto rea£t on each other, by which part of thecharcoal is driven off in the form of carbonicacid, and part of the fulphuric acid efcapes asfulphureous acid: the blue flame that charac-terifes the latter part of this procefs is in alllikelihood caufed by the volatilization and corr-buftion of a portion of fvlphur, more than isrequifite to faturate the potafh of the alum.Thus the pyrophorus when prepared, confiftsof alumine, charcoal, and fulphuret of potafhin intimate mixture. Thirdly, when this pow-der is expofed to the air a rapid decompofitionboth of the air itfelf and of the moiflure that itcontains takes place, the oxygen of each beingabforbed by the fulphuret, while a fufficientquantity of heat is difengaged to bring thecharcoal and remainder of the fuiphur to a ftateof a£lual inflammation.

PYROXENE. See Augite.

Q

QUARTATION.

A method of feparating gold from filver.See Assay of Golds and Gold, p. 528.

QUARTZ. Quartz, Brock. Quarz , Wern.We fhall. fubdivide this mineral into the fivefollowing fubfpecies.

1 Subfp. Cryftallized quartz. Rock cryftal.Rock cryftal often occurs perfectly tranfpa-rent and colourlefs, it is alfo found reddifh,

yellowifh and greenifh white, pearl grey, fmokegrey, greyifh black, honey yellow, clove brown,yellowifh and blackifh brown, wine yellow,ochre yellow, hyacinth red, blood and brick red,reddifh purple, apple green, leek green, andolive green. Its primitive form is a rhomboidapproaching nearly to a cube. But though thisfigure may be obtained by mechanical divifionof the prifmatic cryftals, it has never yet been

k Higgin’s Minutes, p. a;i.