PYROPHORUS. 



difengaged acid is again concentrated, and refumea all its 

 force of combining with water ; — and, ladly, that the in- 

 flammation of the pyrophorus is afccelcratcd by placing it 

 upon. a paper a little wetted, or by breathing upon it ; becaufe 

 the acid then attradts the moiilure more hallily, and confe- 

 quently with more heat. 



M. do Suvigny extends the fame reafoning to the fevcral 

 other pyrophori which he difcovercd, fimilar to that of alum ; 

 particularly to thofe which are made by fubftituting vitrio- 

 lated tartar, Glauber's fait, and other vitriolic falts with 

 metallic, earthy, or alkaline bafes, in the room of alum. 

 Mr. Bewly lias examined this hypothefis with his ulual 

 acutenefs and accuracy ; and from numerous well-conduAed 

 experiments he is led to conclude, that pyrophori of all the 

 above-mentioned clafl'es may be prepared, differing from them 

 in no other particular, except that they contain no vitriolic 

 acid, and which neverthelefs kindle asreadily, on beingexpofed 

 to the air, as thofe which have been impregnated witfi that 

 principle. In order to flicw that the pretence of vitriolic 

 acid is not necefl'ary to conilitute the pyrophorus made with 

 vitriolated tartar, he added to a quantity of this tartar 

 more than an equal weight of povv'dered charcoal, and cal- 

 cined the mixture a long time, in a red heat, in an open 

 crucible ; frequently ftirring the powder, in order to expel 

 from it as much of the vitriolic acid as poffible ; the cal- 

 cination was alfo fometimes repeated with freih charcoal : 

 and yet on heating the fait, thus deprived of a confiderable 

 part of its acid, with charcoal, in a crucible or tobacco- 

 pipe, in the manner which we (hall here fubjoin, he obferved 

 no diminution in its quality of producing a pyrophorus. 



Mr. Bewly, in feveral of his experiments, made ufe of 

 the bowl of a tobacco-pipe, in which he combined the ma- 

 terials, which he witbed to examine in fmall quantities, and 

 in an expeditious manner ; preffing them down (lightly, fo 

 as to fill half or three-fourths of the bowl, and filling the 

 remainder of it with fine fand. This is kept in a red heat 

 twenty minutes, or half an hour ; or it may continue there 

 two hours longer, if the operator pleafes, without any in- 

 jury to the pyrophorus. The pipe being taken out of the 

 fire, the matter is knocked out of it as foon as it becomes 

 cool, and generally, pretty foon afterwards, takes fire fpon- 

 taneou(ly. Thus he formed his pyrophorus with a mixture 

 confining of two parts of alum, previoufly calcined in a 

 red heat ; and of powdered charcoal and fait of tartar each 

 one part. 



In another experiment, having added fucceflively various 

 and increafing quantities of fixed alkali to the fait heated 

 as above, till the vitriohc acid contained in the mixture 

 might be confidered nearly as an evanefcent quantity, 

 a pyrophorus was ftill produced on calcining it with 

 charcoal as before. He alfo mixed equal parts of fait of 

 tartar, and vegetable or animal coal, or fometimes three 

 parts of the former with two of the latter, and calcined them 

 in the ufual manner ; and this compofition, on being expofed 

 to the air, generally kindled in half a minute or a minute ; 

 though, as it contained no fulphur, it did not burn with fo 

 much vivacity as the vitriolic pyrophori. This, which Mr. 

 Bewly calls the alkaline pyrophorus, differs in no circnm- 

 ftcince from M. de Suvigny's neutral pyrophori, except 

 in its not containing that principle to which he afcribes their 

 accenfion. However, lelt it might be fufpefted that the 

 fait of tartar which he employed might accidentally contain 

 yitriolated tartar, or vitriolic acid, he repeated the experi- 

 ment with tartar calcined by himfelf, as well as with nitre 

 fixed or alkalifed by deflagration with charcoal, and with 

 iron filings ; and in all thefe cafes with the fame refult. 

 By diverfifying in a like manner M. de Suvigny's experi- 

 Ji 



ments on the metallic pyrophori, Mr. Bewly found that none 

 of the three vitriols, ht-ated with charcoal alone, in his ufual 

 method, could produce a pyrophorus. And thus he found 

 that the addition of an alkaline lalt to the compofition, which 

 was a part of M. de Suvigny's procefs, was eilential to its 

 fuccefs. 



Treating in the ufual manner equal parts of calcined 

 green vitriol and charcoal, the powder which contained no 

 fulphur nor liepar fulphuris, did not acquire any of the pro- 

 perties of a pyrophorus. The vitriolic acid feemed to have 

 been entirely didipated ; having no bafe to detain it, when 

 diflodged from the metallic earth. The charcoal and calx 

 of iron, left in this procefs, were calcined again, togetlier 

 with fome fait of tartar ; and a pyrophorus was produced, 

 which exhibited indications of its containing a fcarcely per- 

 ceptible portion of hcpar fulphuris. Thirty grains of crocus 

 martis aftringens were calcined witli fifteen grains of char- 

 coal, and the fame quantity of fait of tartar ; and the mix- 

 ture burnt fpontaneoufly, though it contained no hepar ful- 

 phuris, or vitriolic acid. Having by thele experiments evinced 

 that metallic pyrophori may be prepared without vitriolic 

 acid, Mr. Bewly proceeded to form an aluminous pyro- 

 phorus of the fame kind. For this purpofe, he procured 

 the earth of alum by a long and violent calcination ; and 

 examming a part of it, he found, by the ufual tefls, 

 that it neither contained any fulphur, hepar fulphuris, nor 

 alum undecompounded. This he confidered as perfe£lly 

 pure, though he afterwards found that it contained a fmall 

 quantity of vitriolated tartar : and yet it repeatedly fur- 

 niihed a pyrophorus as aftive as when alum itfelf is employed. 

 From thele and fimilar experiments he infers, that the feveral 

 kinds of pyrophori are not kindkd by moiilure attradled 

 by the vitriolic acid, as M. de Suvigny has maintained: 

 and his conclufion is farther confirmed by lome experiments of 

 Dr. PrielUey, from which it appears, that they are kindled 

 in dry, nitrous, and deplJogifticated air. 



M. Prouft, cited by Mr. Bewly, defcribes a variety of 

 new pyrophori, which neither contain vitriolic acid, nor 

 feem likely to owe their accenfion to the attraction of hu- 

 midity from the air. Thefe principally confift of a coaly 

 matter fimpl)' divided by metallic or other earths ; fuch are 

 the fediment left on the filter in prtparing Goulard's extraft, 

 various combinations of tartar, or its acid, or the acetous 

 acid, with metals, calcareous earth, &c. 



Mr. Bewly, having evinced the infufficiency of M. de 

 Suvigny's theory, and difcovered that the pyrophori are not 

 kindled by moifture, attradled (merely) by the vitriolic acid, 

 diredled his attention to the nitrous acid, which Dr. Prieft- 

 ley has (hewn to be a conftituent part of atmofpherical air, 

 as the probable agent in the produdlion of this phenomenon. 

 The ftroiig affinity which this acid has with phlogifton, and 

 the heat, and even flame, which it is known to produce with 

 certain inflammable matters, manifefted that it was equal to 

 theeffedl ; and having excluded the vitriolic acid from having 

 any eflential concern in this operation, he fuggells, either 

 that the pyrophorus is kindled by moiilure attradled by fome 

 of the other ingredients which compoft it ; or that it has the 

 power of decompounding atmofpherical air, by fuddenly 

 attradling its nitrous acid, and thereby generating a heat fuf- 

 ficient to kindle the phlogiftic matter contained in it. This 

 idea appeared plaufible, when he farther confidered that Dt. 

 Prieftley produced the pureflref|iirable air with this fame acid 

 combined with other principles ; aid that this as well as 

 common air is diminifhed, and probably in part decom- 

 pounded, in a variety of phlogiftic procefles. This inge- 

 nious writer concludes, upon the whole, from the experiments 

 he hath made, that the pyrophorus feems to owe its fingu- 



lar 



