PYRITES. 



word OTfilti?, formed of 7rt/;,/«, denotes fire-ftone; a denomi- 

 nation given to this fiibftancc on account of its inflamma- 

 bility. For the mineralogical characters of copper pyrites, 

 and iron pyrites, fee Copper Ore, and Ihon Ore. 



Belides thcfe there are arfenical pyrites, auriferous pyrites, 

 and tin pyrites. Combinations of fulphur with the metals 

 are called by chemifts fulphurets ; and the different kinds of 

 pyrites are properly metallic fulphurets. Sulphur has a great 

 affinity for iron, and in combination with this metal, under 

 the form of pyrites, exifl;s in cxtenfive beds in primary 

 mountains, or is difleminated through the fecondary rocks 

 and ftrata, in veins and maifes, or varioufly cryllallized : it 

 occurs aUo in beds of coal and bituminous clay. Iron pyrites 

 may "be confidered, after the earths, as one of the moft 

 abundant fubftances in the mineral kingdom, forming a con- 

 ftituent part of the globe, and by it's decompofition giving 

 rife to many important fubterranean phenomena. 



The proportions of iron and fulphur in the different fub- 

 fpecies of iron pyrites enumerated by mineralogiits are, 



52 to 54 Sulphur 



48 to 56 Iron. 



Magnetic pyrites differs from common pyrites : its con- 

 ftituent parts, according to Mr. Hatchett, are, 



36.50 Sulphur 

 63.50 Iron. 



By the application of heat common pyrites becomes fuf- 

 ceptible of attraftion by the magnet ; the cxcefs of fulphur 

 being expelled. Iron pyrites is not worked as an ore of 

 iron, but is principally valued for the green vitriol or ful- 

 phate of iron, which it affords when expofed to air and 

 moifture. Sulphur may alfo be obtained from pyrites when 

 heated with chaixoal. 



The decompofition of pyrites is effected fpontaneoudy by 

 the abforption of oxygen from water and the atmofphere, 

 which converts the fulphur into fulphuric acid, and the iron 

 into an oxyd. Thefe fubftances unite durmg the procefs, 

 and form the fulphate of iron, or green viti'iol. 



Some kinds of pyrites are rapidly decompofed, others 

 require to have part of the fulphur expelled by heat. The 

 pyrites, or pyritous fubftance intended to form vitriol, is col- 

 lected in extenfive heaps, fpreading the furface as much as 

 can be conveniently done. The ground on which thefe heaps 

 are fpread fhould be impervious to water, and inclined, in 

 order that the faline matter which efflorefces may be waflied 

 off, and conveyed into refervoirs to cryftallize. As the de- 

 compofition proceeds the mafs becomes heated, and is occa- 

 fionally moiitened, particularly when the air is dry and warm. 

 Thefe beds continue produftive for many years, and if the 

 pyrites be pure, but httle refiduum is left. An excefs of 

 fulphuric acid is formed during the procefs, on which account 

 a quantity of old iron is added to the folution, to faturate 

 it, and obtain the fait in a cryftallized ftate. During the 

 decompofition of pyrites much heat is evolved, and a confi- 

 derable abforption of oxygen from the atmofphere takes place. 

 The faft was firft obferved by Henckel, who affirmed, in his 

 " Pyritologia," that air was neceffary to the procefs of vitri- 

 olization, and that it enters into combination with pyrites 

 and remains fixed in it : " non ut inftrumentum tranfiens fed 

 immanens." This may be confidered as a happy anticipation 

 of one of tfie moft important doctrines of modern chpmiftry. 

 Some geologifts have fuppofed that fubterranean fires, and 

 the temperature of hot fprings, are occafioned by the fpon- 

 taneous decompofition of immenfe beds of pyrites in the in- 

 terior of the earth, and an experiment made by Lemery 

 gives fome plaufibility to tliis opinion. He found that a 



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mixture of iron filings and fulphur, moiitened with a Jmall 

 quantity of water, becomes hot in a few hours, the mafs 

 fwells, and the parts adhere together : it then breaks with a 

 perceptible noife and crackling, and emits aqueous vapour, 

 and a fetid odour like that of fulpurated hydrogen gas. If 

 the mixture be made in a large quantity, it takes fire in 

 twenty-four or thirty hours. As foon as the eraiflion of 

 aqueous vapour has cealed, the heat becomes greater and 

 greater, is fucceeded by inflammation, the fmell is then much 

 itronger, and appears to arife from the hydrogen produced by 

 the decompofition of water. Beaume, who obferved this 

 phenomenon from a mixture of one hundred pounds of iron 

 filings, with an equal quantity of fulphur in powder, ftates 

 that the flames rofe to a foot in height, but did not continue 

 longer than two or three minutes ; the mafs, however, re- 

 mained red-hot for forty hours. Lemery the elder gave to 

 this experiment the name of the artificial volcano. 



Dr. Watfon, in his Chemical Effays, vol. i. p. 187, fays 

 that he has repeated this experiment more than once. When 

 made in the open air the flame is of fhort duration, and the 

 whole mafs, after the extinction of the flame, continues at inter- 

 vals to throw out fparks. A ladle full of the ignited mafs 

 being dropped down from a confiderable height, defcended 

 like a fhower of red-hot afhes. The fuccefs of this expe- 

 riment depends on a due proportion of water. Haifa pound 

 of flower of fulphur, with half a pound of clean iron filings, 

 mixed with fourteen ounces of water, and worked into a 

 pafte, will acquire heat enough to make the mafs take 

 fire. 



Some dark-coloured carbonaceous and bituminous earths 

 contain pyrites in minute grains, and decompofe with great 

 rapidity when expofed to moifture. In the month of Auguft 

 1 75 1, the cliffs near Charmouth, in Dorfetfhire, containing 

 a fimilar kind of pyritous earth, took fire in confequence 

 of a heavy fall of rain after a hot dry feafon, and con- 

 tinued at intervals to emit flame for feveral years. Almoft 

 all kinds of pit -coal in England contain more or lefs py- 

 rites : in fome the quantity is very inconfiderable, in other 

 kinds it abounds fomuch as to render them unfit for domeftic 

 purpofes, and totally inapplicable for forges or iron works, 

 on account of the fulphur which they emit when burned. 

 This pyritous coal may be diltinguifhed by its greater fpe- 

 cific gravity, and the brafs-like metalhc appearance of the 

 pyrites with which it is intermixed. Pyritous coal and 

 coal fhale, or bituminous clay, containing pyrites, frequently 

 take fire fpontaneoufly in coal mines, or when expofed in 

 heaps out of the pits, and continue burning many years. 

 Inftances of this kind now exift in the north of England ; 

 and fo intenfe is the heat produced by the ignition of thefe 

 maffes, that the coal fhale isfometimes fufed. We havefeen 

 fpecimens from thefe heaps which have all the characters of 

 cellular volcanic lava. In the vicinity of Leeds there is a 

 large heap of coal fhale which has been on fire near half a cen- 

 tury ; it is covered in parts with vegetation, and prefents no 

 appearance of ignition during the day ; but if a dry ftick be 

 thruft into it the furface is changed in a few minutes. In 

 fome of the coal mines in Leiceilerfhire, near Afhby de la 

 Zouch, the ftratum of indurated clay over the main bed of 

 coal contains fo much pyritous matter, and is fo fubjedt to 

 fpontaneous inflammation when it falls down and is intermixed 

 with fmall coal and moifture, that the miners are obliged to 

 clofe up the fpace with brick-clay where the coal has 

 been worked, to prevent the accefs of air to the com- 

 buftible m.atter. In this ftate, excluded from the air, the 

 pyritous earth fometimes becomes ignited, as is evident by 

 the heat communicated to the neighbouring parts of the 

 mine ; but the fire is prevented from fpreading among the 



ood, 



