Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/328

 PVR

fulted fome other of the Greeks betides Diofcorides and Theo- phraflus, from whom he principally furnifhcs himfelf with thefe accounts; but he makes no mention of the ruft-coloured or ferrugineous pyrites, which is as common as any of the others, even in the country where he wrote : and thence it is evident, that he did not write from his own obfervation, tho' in fome places we are not able to trace him up to his ori- ginals, which may be loft. Avifenna tells us, that cadmia was made of the pyrites that is, the cadmia fornacum, or tUtty. Pliny and Diofcorides do not in all refpects agree as to the feveral kinds of factitious cadmia ; and tho' Pliny does not mention this particular kind of it, Diofcorides tells us of fuch a fort made in fome places by burning the ftone called pyrites.

The principal contents of pyrites may be in general gueffcd at from their colour. The white pyrites ufually contains arfenic, the yellowifh contains fulphur and iron, and the fully yellow fulphur and copper. The colours, therefore, make a very eflential mark for the diftinclion of the feveral kinds of this foflil The yellowifh pyrites, that is, fuch as contains iron and fulphur, is found in the ftrata of feveral kinds of ftone, in clay, and in the earth lying over the mines of feveral me- tals. The white, or arfenical pyrites, and the fully yellow, are lefs common, but are ufually met with about mines. Jgricola de Metall.

It is a matter of great difficulty to afcertain the time of the formation of foffils. Many of them feem to have remained in their prefent ftate, unaltered, from the beginning of the world; but many have alfo been formed in later times, and continue to be formed to this day. Of the number of thefe laft the ftalaclitje, or ftony icicles, hanging down from the roofs of grottos are known to be ; and it is equally certain, that the pyrites alfo are fo formed, for many of the ftalactitEe in the caveis dug by the German miners are found to be coated over in feveral parts with pyrites a ; and even in our own king- dom, pieces of wood buried in clay that contains pyrites, fuch as is commonly dug to make tiles, if taken up again after a number of years, is always found impregnated with this Jub- ilance, forming veins in it, and fometimes nodules on its furface. [ a A£t. Erudit. Ann. 1726. p. 273.] The pyrita affixed to ftalactita; are finer than the other kinds, and it appears very evident to fuch as have thoroughly con - fidered the procefs of nature in them, that they are not formed of particles brought together by water, in the manner of the Pyrites, in wood buried under clay, or in the manner of thefe ftalactitas themfelves ; but are compofed of infinitely minute particles, brought together by their mutual attractions on a proper bafis, and which had been before floating in the air. The antients in general fuppofed, that copper was contained in the pyrites; but they had no opinion that iron was a part of it, tho' it is certain that iron is the bafis of almoft all of them, and copper has a part only in a very few : but this was the effect of judging from appearances, inftead of having re- courfe to experiments. Our own Lifter has the honour of being the firft author who has treated properly of them, and found out their true and general bafis to be iron ; but he carries it too far when he fuppofes them to be all properly iron ores; for this is not the cafe, many of them, which contain no other metal befide iron, yet holding it in fmall quantity, and in fuch a combination of other principle?, that it is fcarce extricahlc from them, and fome kinds contain no iron at all, Lifter de Font. Medic. Angliae.

Berger, who has written on the Caroline baths, has taken up the fubject, and improving upon Lifter's plan, has given a much more juft account of them. He allows that iron feems the bafis of great numbers of the pyrites, and that this is evi- dent from the obfervation, that the remaining matter of many, of them, after burning away the fulphur, is found to be at- tracted by the magnet ; but he obferves alfo, that in many copper is mixed with the iron, and that tho' iron is in general found in even thofe kinds which give the molt obvious proofs of copper, yet there are fome in which there can no iron be found.

This author obferves alfo, that befides the metalline particles, whether iron or copper, there is alfo contained in the pyrites an unmetallic earth, which is in the compofition of* this ftone moft equally mixed and perfectly blended with the par- ticles of thefe metals, and with thofe of the fiilts and fulphurs contained alfo in the mafs. Sulphur alfo he acknowledges to make a great part of many of the pyt ita, particularly of all the yellowifh and full yellow kinds. The white or filvery pyrites contains lefs fulphur than any of the others, and the yellow or venereal pyrites, tho' it contain much arfenic, yet does not fail to contain fulphur alfo in confiderable quantity. Berger de Font Carolin.

The mention of gold and filver in the pyrites is very common among authors, but the colour of thefe ftones feems princi- pally to have given ground for that opinion. In reality thefe metals are very (eldom found naturally making parts of the pyrites, and when they are, it is only in a very inconfiderable quantity. But in thofe fpecimens found about the mines of gold and filver, the particles of thofe metals affembled into vifible mafles are fometimes found unbedded in lumps of the pyrites; and fuch pieces of this ftone may then well be faid

PYR

to contain thofe precious metals. The occafion of this acci- dent, however, is no more than this, that the pyrites is form- ed in mines and other places at this day ; which is plain from its being in fome places found adhering to the fides of fta- haita?, as has already been mentioned : and in like manner it might adhere to particles of gold and filver, and thereby give ground to the fuppofition of their being parts of it. The common firit* of our clay-pits and fea coafts are ufed in the making of coperas or vitriol ; but among thefe there is found a very great difference, fome of them turning them- felves very eafily to vitriol, when only expofed to moift air ; others doing it with more difficulty; and fome not at all, tho' expofed many years. Some alfo yield all their vitriol at once on pouring warm water on them ; while others muft. lie ex- pofed to the air at feveral different times, and roafted in the mean while in order to obtain it. The fettled obfervations on this fubjea, as collefled from experiments, are thefe ■ No pnta which contains any copper, or any arfenic, will of ltfelf turn into vituol, but requires a previous roafting. i he fulphureous iron pyrites, void of copper or arfenic, all turn to vitriol on being only expofed to the air ; and that the iooner or later, as they are of a more or lefs compaft Jub- ilance. 1 he fibrous or radiated tyritx are ufually of this kind ; but this is no general rule, for there are fome radiated ones which remain whole years unaltered in the air. Copper and arfenic always refift the Mooting of the falts of the pyrites, or its turning to vitriol; but thefe are not the only agents that refift this change, for in fome merely fir. reous and fulphureous pyrites the change is not made but with much time and difficulty. Henielt, Pyritol. It is remarkable alfo, that vitriol is found in fome pyrit/r, if water be poured upon them immediately after the roafting - while others will not yield any till they have been afterwards expofed to the air. It even feems, that we are to look into the air for the caufe of the appearance of vitriol in the cop- peras ftones. This it may greatly affift in effeffing, as it carries a quantity of moift vapours in it : for it is well known, that the acid of fulphur has not the power to refolve iron into the form of a fait without the addition of water; nay, oil of vitriol, or of fulphur, being moderately concentrated' tho it be then diluted with much more water than it is united with while yet in fulphur, does not even diffolve filings of iron unlefs there be four times or fix times as much water poured to it. Water alone, however, tho" a great and ne- cefiary agent, cannot be fuppofed to effect the whole change - for tho' there are fome of the pyrites that yield their vitriol by means of it, yet there are others that do not; and fome pyrites are prefently turned into vitriol, when expofed to the air, which had before remained for many years under water unaltered. Of this kind there are many on the Chores of the fea in moft parts of Europe. In England particularly we have them in great plenty in Sheppey Hand in Kent. Thefe pyrites will long refift the change into vitriol, when in the air and yet they evidently contain no copper nor arfenic. 'I here is alfo a kind very common on the fhores, which re- fembles wood in texture and appearance ; and has probably once been wood, but has now its pores filled with the pyrites- of thefe many lie buried a foot or more deep in the fand un- der the fea water ; and in that ftate they never fhoot into vitriol, but are of a firm texture and confiderable hardnefs and when broken look very bright within, and have no tafte of vitriol, nor give any mark that they contain any • yet thefe, if they are taken up and expofed to the air for a fort- night, lofe all their brightnefs and their hardnefs, and moulder- ing to pieces, become fo rich in vitriol, that it forms itfelf into regular cryftals on their furfaces. Now if moifture alone was fufficient to produce this effect, there is no reafon why they fhould not have been refolved into vitriol under a very moift fand. The great caufe we are able to affign, appears to be the vague acid, fo common in the foffile world, and filling alfo the region of air; but an ingenious reafoner will ftill own, that tho' this may do much, yet there muft be fome other caufe, yet undifcovered, for the produaion of vitriol in thefe foffils ; fince this, as well as the moifture of the air, ought to aa more equally than we find by experience it does on thefe ftones, if all were owing to it. Henkeil, Pyritol. In the expofing thefe copperas ftones to the air, if it be a moift fcafon, no farther care need be taken of them than the piling them up in a heap ; but moiftening them now and then is a neceffary circumftance in dry feafons, and in this cafe the water fhould be fprinkled on them in fmall quantities at a time, and the heaps now and then turned and new made: Much depends on this management, the fame quantity of ftones yielding twice as much copperas, with proper care, as they would without it

When the matter of the pyrites is mixed with the lead ores, the method of feparating the metal by affaying is this : roaft two centners of the ore, as in the ufua! method, and keep a flronger fire than when the ore is pure. The pyrites, efpecially when it is merely iron, hinders an ore from eafily growing clammy, or turning into large lumps, or entirely melting" When the ore is fufficiently wafted, let it cool, beat it to powder, and repeat the roafting to a third fire, till when it is red hot in the fire, there is no fmell of fulphur : then mix the

ore