MINERALOGY. 



lefs pcrfcftly. The mod intenfe heat is juft at the point 

 of the blue flame. The wliite flame confifts of matter in a 

 ftatc of full combullion, and calcines or oxygenates fub- 

 ftances immerfed in it ; the blue flame confifts of matter in 

 a ftate of imperfeft combullion, and therefore partly 

 deoxygenates metallic oxyds which are placed in contafl 

 with it. 



" The fupports of the various fubftances while undergoing 

 the aftion of the blow-pipe come next to be confidered. 

 Of fupports there are two kinds, combuftible and incom- 

 buftiblc. The combuftible fupport (ufed chiefly for me- 

 tallic ores) is charcoal. The clofeft -grained and foundeft 

 pieces are to be feledted for this purpofe ; and even the 

 beft often fplit and become rifty after being ufed for a fliort 

 time. This will not unfrequently happen in the middle of 

 an experiment, when the melted globule finks into the 

 cracks, is loft, and the experiment muft be begun again. 

 Inftead of fticks of charcoal, fome perfons recommend that 

 the charcoal, after being finely pulverifed, fliould be moif- 

 tened with a folution of gum tragacanth, and moulded into 

 a convenient form ; a plan that well deferves to be fairly- 

 tried. Perhaps fimply moiftening the charcoal-powder, 

 and then fubmitting it to the aftion of a very ftrong fcrew- 

 prefs, might be ftill better. The incombuftible fupports 

 are, metal, glafs, and earth, in the ufe of all which one 

 general caution may be given, — to make them as little bulky 

 as poflible. The fupport always abftrafts more or lefs of 

 the heat, and in many cafes, efpecially when metallic 

 fpoons are employed, entirely prevents the flame from pro- 

 ducing its due effeft. The beft metallic fupport is platina, 

 becaufe it is infufible, and tranfmits heat to a lefs diftance 

 and more flovvly than other metals. A pair of flender forceps 

 of brafs, pointed with platina, is the beft poflible fupport for 

 non-metallic minerals that are not very fufible. For the 

 fufible earthy minerals, and for the infufible ones when fluxes 

 are ufed, leaf-platina will be found the moft convenient ; it 

 may be folded like paper into any defirable form, and 

 the refult of the experiment may be obtained fimply by 

 unfolding the leaf in which it was wrapped up. Glafs 

 fupports are flender tubes or rods of this fubftance. If the 

 mineral to be examined is of a longifli or fibrous fliape, one 

 end may be cemented to the top of the glafs rod by heating it, 

 and in this ftate it may be further examined with great conve- 

 nience. Earthen fupports are ufed only for extemporaneous 

 cupeliation ; they are beft made of bone afli, and muft of 

 neceflity be of a certain bulk, in order to abforb the litharge, 

 and other impurities, which it is the objeft of this procefs 

 to feparate from the Jine metal. With regard to the mag- 

 nitude of the fpecimens required for examination, no very 

 precife rule can be given ; the moft fufible, fuch as fome of 

 the metallic ores, may be as large as a fmall pea, while the 

 more refraftory of the earthy minerals fliould fcarcely 

 exceed the bulk of a pin's head. 



" The heat that is firft applied to inveftigate the properties 

 of mineral fubftances fliould be very flow, not exceeding 

 that which exifts on the outfide, even of the yellow flame ; 

 at this temperature, the phofphorefcence is beft elicited, 

 and decrepitation for the moft part takes place, the fufible 

 inflammables begin to melt, and the metallic and moft other 

 mineral falts lofe their water of cryftallization. The 

 yellow flame will raife a fubftance to a tolerably full 

 red heat, by which the following cffeas are produced. 

 Many changes of colour take place, all the yellow ores of 

 iron become red, and the peach-blofl'om tinge of flowers of 

 cobalt becomes blue ; certain earthy minerals lofe their 

 water of cryftalHzation or of compofition, and exfoliate, as 

 gypfum, or throw up coarfe and irregular ramifications, as 



5 



prehnite and mefotype. At this temperature, alfo, car- 

 bonate of ftrontian begins to tinge the flame witli its pecu- 

 liar crimfon colour, and muriate of copper with its bright 

 green colour. The roafting of all the metallic ores is beft 

 carried on at this heat ; fulphur and arfenic are drawn off, 

 and exhibit their charaftcriftic odours ; grey antimony melts ; 

 native bifmuth runs out from the matrix, through which it 

 is difleminated ; and pearlfpar and fpathofe iron blacken and 

 become magnetic. In the ftill higher degree of heat pro- 

 duced at the point of the interior blue flame, although 

 fome minerals ftill continue perfeflly refradtory, and 

 undergo but little change of any kind, yet the greater part 

 is very fenfibly altered. Some, as pearl-ftone, enlarge 

 vei-y confiderably in bulk at the firft impreffion of the heat, 

 but are with difficulty afterwards brought to a ftate of 

 fufion. Othersbecome covered with a fuperficial glazing, and 

 the fliarp edges and angles become glofly and rounded off. 

 Others, confifting really, though not vifibly, of an intermix- 

 ture of two fubftances differing in fufibility, undergo the 

 procefs oi fritting, in which refraftory grains are difperfed 

 through a vitreous mafs. In others, a complete fufion takes 

 place, and produces a fpongy opaque femivitreous mafs 

 called a flag, or an opaque glafs called an enamel, or a more 

 or lefs tranfparent or true glafs, which latter may vary in 

 texture from compaft to porous and fpongy or intumefcent- 

 " In examining the habitudes of the earthy minerals with 

 the blow-pipe, no fluxes are required ; whereas to moft of 

 the metalhc ores, fluxes will be found at almoft all times a 

 very ufeful and often a necefiary addition. The ores of the 

 difficultly reducible metals, fuch as manganefe, cobalt, 

 chrome, and titanium, are charafterifed by the colour 

 which their oxyds give to glafs ; in allthefe cafes, therefore, 

 vitreous fluxes muft be largely made ufe of, both to diffolve 

 the earthy matter with which the oxyds are generally 

 mixed very intimately, and to furnifli a body with little or 

 no colour of its own, which may receive and fufficiently 

 dilute the inherent colour of the oxyd. I fay fufficiently 

 dilute, becaufe the colour of moft oxyds is exceflively 

 intenfe, and moft perfons in their firft experiments of this 

 kind, are very apt to obtain ambiguous refults in confe- 

 quence of ufing fo large a proportion of oxyd, that the 

 glafs, whether blue, red, or green, appears quite black. With 

 regard to fluxes, the following will, I believe, be found 

 amply fufficient. Where the objeft is not only to diftblve 

 the oxyd, but at the fame time to retain it at a high ftate 

 of oxydation, the flux employed fliould be cither nitre or a 

 mixture of this with a glafs of borax, or, ftill better, nitrous 

 borax formed by diflolving common borax in hot water, 

 neutralizing its excefs of alkah by nitric acid, then evapo- 

 rating the whole to drynefs, and laftly haftily melting it in 

 a platina crucible. For an aftive, and at the fame time 

 non-alkaline flux, boracic acid may be ufed, or neutral 

 borate of foda ; and where a flight excefs of alkali is 

 required, or at leaft does no harm, common borax by itfelf, 

 or mixed with a little cream of tartar, when a ftrong 

 reducing flux is wanted, may be had recourfe to. For 

 coloured glaftes, the proper fupport is leaf-platina ; but for 

 reduftions, charcoal. In the latter cafe, the ore previoufly 

 roafted, if it contain either fulphur or arfenic, is to be pul- 

 verifed and accurately mixed with the flux ; a drop of water 

 being then added to make it cohere, it is to be formed into 

 a ball, and depofited in a fliallow hole in the charcoal, being 

 alfo covered by a piece of charcoal, if a high degree of heat 

 is wanted. The eafily reducible metals, however, may be 

 treated with lefs ceremony ; a bit of the ore being placed on 

 the charcoal, and covered with glafs of borax, will, in the 

 fpace of a few feconds, be melted by the blow-pipe, and 



converted 



