PYilOPHORUS. 



niinous pyropVionis of Hombfrg two other clafles of fub- 

 ilances of this kind, viz. the nrjtallic, or thofe made wit!i 

 tlic three vitriols of iron, copper, and zinc; and the neu- 

 tral, or thofc compofed of vitriolated tartar and Glauber's 

 fait. 



The aluminous pyrophorus may be made in the following 

 manner. Take four or five parts of alum, and one part of wheat 

 flour, or any animal or vegetable fubltance ; calcine thefe 

 together to a brown or blackilh mafs : powder the mafs, 

 and put it into a phial ; ftop it loofely with paper, and fet it 

 in a fand heat, fo as to make it continue glowing-hot for 

 fome time ; after this remove the whole from the lire, fet 

 it to cool gradually, and finally ftop the bottle very clofe 

 down. 



The following procefs is recommended by Macquer for 

 this preparation. Let three parts of alum and one part of 

 coarfe brown fugar be mixed together. This mixture mull 

 be dried in an iron ladle or (hovel over a moderate fire, till 

 it be almoft reduced to a blackilh powder or coal; during 

 which operation it muft, be ftirred with an iron fpatula. 

 Any large malles muft be bruifed into powder, and then it 

 xnuft be put into a glafs matrafs, the mouth of which is 

 rather ftraight than wide, and its length fevcn or eight inches. 

 This matrafs is to be placed in a crucible, or rather earthen 

 veftel, large enough to contain the belly of the matrafs, with 

 about a fpace equal to the thicknefs of a. finger all round it. 

 The fpace is to be filled with fand, fo that the matrafs 

 (hall not touch the earthen veflel : the apparatus is then to 

 be put in a furnace, and the whole to be made red-hot ; 

 the fire mull be gradually applied, that any oily or full- 

 ginous matter may be expelled. After which, when the 

 matrafs is made red-hot, fulphureoiis vapours exhale : this 

 degree of heat is be continued till a truly fulphureous flame, 

 which appears at the end of the operation, has continued 

 nearly a quarter of an hour : the fire is tiien to be extin- 

 guiflied, and the matrafs to cool without taking it out of 

 the crucible ; and when it ceafes to be red-hot, it muft be 

 ftoppcd with a cork. Before the matrafs is perfedlly cold, 

 it muft be taken out of the crucible ; and the powder it 

 contains muft be poured into a very dry glafs phial, which 

 muft be well clofcd with a glafs ftopper. If we would 

 preferve this pyrophorus a long time, the bottle contain- 

 ing it muft be opened as feldora as poflible. Sometimes 

 it kindles while it is poured into the glafs phial, but it may 

 be then estinguillied by clofing the phial expeditioufly. 



Another excellent method of preparing pyrophorus, cited 

 by Aikin from Higgins's Minutes, is the following. Mix 

 together three parts of Roman alum, and one of flour, and 

 heat the mixture to dryneis in an irun pot, as already de- 

 fcribed : the black calcined mafs thus produced is to be 

 put into ounce phials of green glafs, coated without and 

 within with clay. The phials thus charged are to be lightly 

 ttopped with balls of tempered clay, and then fet up to 

 their necks in fand in an iron pot ; charcoal powder is 

 then to be ftrewed on to the depth of half an inch, over 

 which is to be placed an earthen cover, luted to the pot. 

 The whole apparatus is now to be placed in a furnace, and 

 kept at a red heat for an hour and a half; at the ex- 

 piration of which period, being taken out of the furnace 

 and cooled quickly, it is to be unpacked, and the phials con- 

 taining the pyrophorus are to be placed with their mouths 

 inverted in mercury, in which fituation the pyrophorus may 

 be kept for many years without injury. 



When half a drachm of this pyrophorus is put on a piece 

 of paper and expofed to air, it quickly kindles, becomes 

 red like burning coals, emits a ftrongly fulphureous vapour, 

 and burns the paper or otjier combultible body which fup- 



Vot. XXIX. 



porta it : and nothing n left but the white earthy bafe of the 

 alum. When no fenfiblc change takes place in the pyro- 

 phorus, either from a ttvfedt in the preparation, or from 

 fome air remaining in the phial that contains it, the com- 

 buftion may be effcdted by breathing on the powder, and thus 

 lupplyiiig It with the moilture which Iceins to be the primary 

 agent in this phenomenon. The pyrophorus that is made 

 in the lall method we have recited is fo highly inflammable 

 as to take fire while it is falling from the mouth of tiie phial. 

 If it be poured into a jar of pure oxygen gas, it forms a bril- 

 liant fiery ftiower : the oxygen is for the moft part confumed, 

 and there remain in the jar fulpliureous acid and carbonic 

 acid gafes : the pyrophorus alfo being confumed with the 

 exception of its aluminous bafe. 



The fpontaneous accenfion of the aluminous pyrophorus, 

 on its being expofed to the air, has been a fubjeft of con- 

 fiderable difcuffion among chemifts and philofophers ; feveral 

 of whom have adopted the hypothefis propofed by M. de 

 Suvigny, in tlie Memoires de Mathematique et de Phyfique^ 

 torn. iii. To explain this curious appearance, M. de 

 Suvigny obferves, that the vitriolic acid in the alum, during 

 the calcination in the phial, leaves its earthy bafis, and unites 

 with the phlogifton in the coal. By its union with this in- 

 flammable matter, a part of it is undoubtedly rendered vo- 

 latile, and exhales partly under the form of volatile vitriolic 

 acid, and partly in that of a blue fulphureous flame ; while 

 another part of it combines likewife with the phlogifton 

 forming a real fulphur, or an earthy hepar fulphuris ; in 

 which the fulphur is protefted from the fire by the earth 

 with which it is combined, and the particles of which remain 

 every where intermixed with thofe of the powder. Thus far 

 (fays Mr. Bewly, an excellent chemift and philofopher) 

 M. de Suvigny is fupported by the appearances, and by a 

 juft chemical analyfis of the powder : but he proceeds far- 

 ther, and fuppofes that, at the end of the procefs, a part 

 of the vitriolic acid is left in a difengaged, or uncombined 

 ftate, and highly concentrated. In this itate it is well knawn 

 that this acid attra£ls moillure, and at the fame time gene- 

 rates a confiderable degree of heat. When the pyrophorus, 

 therefore, is expofed to the air, he again fuppofes that thi« 

 difengaged and concentrated acid fuddenly attrafts the 

 watery particles floating in the atmofphere, and by the heat 

 thus generated, fets fire to the fulphur and other inflammable 

 matter contained in the powder. This hypothefis he has 

 endeavoured to eilablifli by the following obfervations ; that 

 the pyrophorus, as he apprehends, can be made only with 

 fubftances fit for praducing fulphur, or with fulphur itfelf : 

 — that no pyrophorus will be produced, if the mixture be 

 calcined by too long or too violent a fire ; becaufe then the 

 whole vitriolic acid can be combined into perfeft fulphur, and 

 confequently is engaged, and not in a proper ftate to attraft 

 the moifture of the air ; or elfe if it does not combine into 

 fulphur, being half difengaged from its bafis, it is driven off 

 by the violence or long continuance of the fire ; and, con. 

 fequently, after this complete calcination, no acid remain* 

 partly difengaged, as it ought to be, that it might unite with 

 the water with fufficient adlivity : — that when the pyrophorus 

 is very flowly moiftened, as when it is kept in a bottle not 

 well clofed, it does not kindle, becaufe fufficient heat is not 

 produced by this flow and gradual attraclion of water ; it if 

 alfo fpoiled and rendered incapable of kindhng, when ex- 

 pofed to tbe open air ; becaufe its acid becomes then fatu. 

 rated, or nearly faturated with moifture, and cannot, there, 

 fore, unite with that of the air with fufficient adlivity :— « 

 that a pyrophorus, thus fpoiled by expofure to moifture, 

 may be reftored to its peculiar properties by making it agaia 

 red-hot in a matrafs ; fince by this calcination its partly, 

 M difengaged 



