P Y R 



P Y R 



ooal, by the precautionary meafure of clofing the cavities 

 with clay. 



The great heat evolved during the decompofition of 

 pyrites, may proceed in part from the combination of oxygen 

 with the fulphur and iron, and may be increafed by the 

 different capacity of the new compound for heat. When- 

 ever chemical changes take place rapidly, they produce a 

 change in the temperature of fubihaices, as in the well- 

 known inllances of lime and water, nitric acid and vegeta- 

 ble oils, &c. 



The phenomena accompanying the mud volcanoes in 

 various parts of the world, prefent many appearances which 

 give probability to the opinion, that they proceed from the 

 decompofition of pyritic ftrata. See Volcano. 



Tlie formation ot alum is alfo effcfted naturally, in many 

 fituations, by the decompofition of pyrites, the fulphuric 

 acid combining with the alumine of pyritoiis clay. This is 

 not unfrequently the cafe in excavations of coal mines that 

 have been long worked out. 



At Hartlet, near Glafgow, in the excavations of an old 

 coal mine that has been worked fome centuries, there is a 

 very extenfive formation of alum, from the decompofition of 

 the roof of the pit. It is a pyrilous clay ten inches thick. 

 In the old workings of the mine which are dry the air cir- 

 culates flowly, and the roof gradually decompofes and ex- 

 foliates, and falls upon the floor, in which fituation the decom- 

 pofition proceeds, and the fubltance affumes the appearance 

 of a fpicular efflorefcence. In time the whole fpace to the 

 roof is filled ; it is then removed. The mafs confifts of'Carth 

 richly impregnated with fulphate of alumine, fulphate of 

 iron, and in fome inllances with fulphate of magnefia. Tiie 

 coal in this mine, contrary to the ufual pratlice, is worked 

 to the dip, fo that the old workings are always dry. To this 

 circuraftance may principally be attributed the great accu- 

 mulation of alum in this mine. In many of the mines in Eng- 

 land a fimilar formation of alum would take place, but they 

 contain too much water to permit the faline fubftances to re- 

 main. In general, alum rock or alum fliale require to be 

 expofed in heaps, and burned in the open air, to expel the 

 fulphur, and combine it with the oxygen from the atmofphere. 

 The fulphuric acid thus formed unites with a requifite portion 

 of the clay during the procefs. 



The gypfum, or the fulphate of lime which occurs in beds, 

 among fecondary ftrata of red fand-ftone and beds of marie, 

 probably may owe its prefent ftate to maffes of pyrites, which 

 h.ivc exilled over common lime-flone, and been decompofed 

 naturally. The fulphuric acid thus produced woiJd unite 

 with the lime, and form gypfum. The great quantity of the 

 red oxyd of iron which is in the flone and marie that ac- 

 company this kind of gypfum, gives much probability to 

 this opinion. The cryftals of gypfum or felenite found de- 

 tached in beds of clay had probably a fimilar origin. 



oulphuret of iron may be formed by heating together iron 

 filings and fulphur. From the experiments of Vauquehn it is 

 proved that there are four fulphurets of iron, according to 

 the degree of heat and other circumftances under which the 

 combination may be formed. The firft fulphuret conlifls of 



78 Iron 

 22 Sulphur 

 The fecond fulphuret, of 



I Artificial. 



64 Iron 7 TvT 1 



56 Sulphur \ N^^""^ magnetic pyntes. 



36 Sulphur j 

 The third fulphuret, of 



S;84 Sdphur}^'"*''^'^'- 



The fourth fulphuret, of 



''■' c™i" I J- Natural common pyrites. 

 33 Sulphur J '^•' 



When the quantity of fulphur does not exceed ^opereent. 

 pyrites is foluble in muriatic acid, and may be rendered per- 

 manently magnetic. The fpecific gravity of common pyrites 

 is from 4.60 to 4.83. Of magnetic pyrites 4.51. 



Arfenical pyrites, called marcafite, is dillingui(lied from iron 

 pyrites by its colour, which is a filver white, and by yielding a 

 fmell like garlic when rubbed or expofed to heat. See 

 Arsenic Ores. 



Auriferous pyrites, or iron pyrites, with a fmaU alloy ot 

 gold : the richell fpecimens of this ore in Europe are found 

 in Tranfylvania, containing from 0.02 to 0.03 oi gld. 

 Thefe ores are dilUnguilhed from iron and copper pyrites 

 by their colour, malleability, and fpecific gravity. 



Tin pyrites. See Tin Ore. 



The pyrits, in fubftance, are never ufed medicinally ; 

 neverthelefs, in their produfts they are very important. 

 From thefe common fulphur is extrafted, in Sweden and 

 Saxony ; the native vitriols are produced in caverns of the 

 earth, or on its furface ; the greateft quantities of artificial 

 vitriol are prepared ; and the mineral waters, vitriolic, alu- 

 minous, fulphureous, hot or cold, are fuppofed to receive 

 their impregnation. 



When the matter of the pyrites is mixed with the lead 

 ores, the method of feparating the metal by allaying is this : 

 roalt two centners of the ore, as in the ufual method, and 

 keep a flronger fire than when the ore is pure. The pyrites, 

 efpecially when it is merely iron, hinders ore from eafily 

 growing clammy or turning into large lumps, or entirely 

 melting. When the ore is fufficiently walhed, let it cool, 

 beat it to powder, and repeat the roafling to a third fire, 

 till when it is red-hot in the fire, there is no fmell of fulphur ; 

 then mix the ore with fix centners of the black flux, and two 

 of fandiver, and finifh the work in the common way, only 

 making the fire greater, and continuing it longer, toward 

 the end of the operation. Cramer's Art of AfTaying, p. 292. 

 See Lead Ore. 



Pybites is applied by fome authors to the marcafite ores 

 of all metals ; the names of which are varied according to 

 the metals they partake of. 



Thus chrvftlis is that of gold ; argyrlth that of filver ; 

 ftderitii that of iron ; chakhis that of copper ; and molybditis 

 [hat of lead, &c. 



PYRITICUM LiQUAMEN. See Liquamen Pyriticum. 



PYRITRICHIPHYLLUM, in Natural H'ljiory, the 

 name of a genus of foffils of the clafs of the pyrites, the 

 charadlers of which are thefe : they are compound, inflam- 

 mable, rnetalKc bodies, found in loofe maffes not of any 

 regularly angular figure, and of a ftriated texture, with 

 foliaceous ends to the ftrix, appearing on the furface, or 

 within the mafs. 



Of this genus there are only two known fpecies : one 

 having the foliaceous ends of the ftrix on the outer furface 

 of the mafs ; and the other having a fmooth external furface, 

 and the fohaceous ends of the ftrise covering the fides of in- 

 ternal hollows. 



The firft of thefe is found in many of the Englifh and 

 German mines ; the other lias been yet only found in the 

 mines on Mendip hills in Somerfetfhire, but there in con- 

 fiderable plenty. Hill. 



PYRITRICHUM, the name of a genus of pyrites, the 



charafters of which are thefe : they are compound, inflam- 



mable, metallic foffils, always found in detached maffes of 



K 2 no 



