Chap. 6.] Comluftion of Iron. 147 



only the pholphorus of K.unkei, but the pyrophori, 

 which are made of three parts of flour, or any vege- 

 table matter convertible into charcoal, and one of alum, 

 will immediately ignite, on being expofed to the air 

 in the ordinary heat of our atmofphere. In this cafe 

 the pyrophorus, which is of a light fpongy texture, 

 prefents a large furface containing a quantity of in- 

 flammable matter to the atmofphere, and the union 

 of the two fubftances immediately fucceeding, the 

 matter of fire is emitted, and ignition takes place. 



Every means, indeed, by which pure air may be 

 attracted and condenfed, will produce flame. It was 

 obferved in the preceding paragraph, that iron was 

 ignited with difficulty ; yet if a very fmall iron wire is 



before the detonation takes place ; and this faft is fufficient to ex- 

 plain the whole appearance. When cryftallized nitre and liver of 

 fulphur are expofed to the adYion of heat, inflammable or hepatic 

 gas is difengaged from the latter, while the fait gives out vital 

 air. Now thefe two, which together are capable of producing a 

 ftrong inflammation, as we have obferved in the hiflory of inflam- 

 mable gas, are fet on fire by a portion of the fulphur. But as the 

 thick fluid they are obliged to pafs through prefents a oonfiderable 

 obftacle, and as the whole takes fire at the fame inftant, they ftrike 

 the air with fuch rapidity, that it refifts in the fame manner as the 

 chamber of a muiquet refills the expanfiort of gunpowder. A 

 proof of this is obfervable in the effecl: the fulminating powder has 

 on the ladle in which it explodes. The bottom of this veflel is 

 bulged outwards, and the fides bent inwards, in the fame manner 

 as if it had been a&ed on by a force directed perpendicularly 

 downwards, and laterally inwards.' Fourcrqy's Chem. v. ii. p. 388. 

 Gold precipitated from its folution in aqua regia by means of 

 rolatile alkali, conftitutes a fubftance called fulminating gold, the 

 effe&s of which are flill more tremendous than thofe of the pre- 

 ceding compofitions. An extremely fmall portion of it is fuf?.- 

 cient to produce alarming, and even fatal effedls ; and what ren- 

 ders it ftill more dangerous is, that a mere blow, or a flight degree 

 of fridion, are furacient to ignite it. With refpeft to the caufe of 

 the explofive power of this fubftance, it will be explained when I 

 treat of gold itfelf. 



L 2 conveyed 



