2iO 



Sulphuret and 

 phofphuret of 

 lime or potaih. 



Pyrophorus. 



A pyrophoric 

 matter may be 

 formed in ordi- 

 nary combuf- 

 tion. 



ON SPONTANEOUS INFLAMMATIONS. 



This gas, which in chemical experiments offers the beautiful 

 fpedacle of a fountain of fire over water, is produced natu- 

 rally by the putrefadion of animal fubltances which are buried. 

 The lights which are frequently feen to come out of the earth, 

 and which are known by the name of Jack o' Lanterns are 

 only owing to the difengagement of this phofphorated hidrogen 

 gas: as thefe lights generally appear moving about in places 

 where they do not touch dry combuftibles, they feldom occa- 

 fion difag^ee^ble accidents; but they are alfo difengaged in 

 forells, and it may happen that in hot fummers, when the grafs 

 and brurti-wood are thoroughly dry, the gas in combuftion may 

 meet with thefe combuflible materials, and fet fire to them, 

 and thus produce the conflagration of a whole foreft : we 

 (hould not therefore, too lightly, and without fufficient proofs, 

 attribute to the malevolence or to the connivance of mankind, 

 thofe dreadful events which are fomelimes only the refult of 

 caufes purely natural. 



9. Sulphuret and Phofphuret of Lime and of Potajh formed in 

 the Combvfiion of feveral Vegetables. 



Sulphur is always formed when gypfum (fulphate of lime) or 

 any other fulphate, whether earthy or alkaline, is ftrongly 

 heated with charcoal, wood, or, generally, with any com- 

 buflible which is reduced to charcoal by heat. The fame falts 

 form fulphureous waters if the remains of animal or vegetable 

 fubftances are left in a water in which it is difTolved ; fo that 

 it frequently requires only a little fulphate of lime, or fome 

 other fulphuric fait, to communicate the odour and lafte of 

 fulphur to water which is ftagnant, 



Pyrophorus is obtained by calcining the alum of commerce, 

 or fulphate of potalh with fugar, meal, or any other fubftance 

 which is reducible to charcoal. 



The inflammation of pyrophorus which takes fire by the 

 fole contact of humid air, is only owing to the fulphuret of 

 potafli, which by attrading the humidity of the air, heats to 

 that point that it kindles the carbonaceous matter which fur- 

 rounds it, and which being in a ftatc of greater tenuity, is {o 

 much the more difpofed to burn. 



But fince many of our common combuftibles contain fulphu- 

 ric falts, it may happen that, in their combuftion, a pyrophoric 

 matter is fometimes formed by chance, which remains in the 



reljdue 



