On Spontaneous lujlammations. 353 



dry combustible matters, they rarely produce disagreeable 

 accidents J but it is disengaged also in forests, and it may 

 happen in very warm sumniers, when the grass and bushes 

 are entirely dry, that the gas in combustion will meet with 

 these combustible matters, set fire to them, and in this 

 manner burn the whole forest. We ought not therefore, 

 on too slight grounds, or without sufficient'reason, to ascribe 

 to malevolence or to mcendiaries those fatal events which 

 sometimes are the result of causes purely naturah 



9- Sulphiiret and Phosplwret of Lime and Potash formed 



daring the Combustioji of several Fegctaldes. 

 _ When gypsum (sulphate of lime) or any other sulphate, 

 either earthy or alkaline, is strongly heated with charcoal 

 of wood, or in general with any combustible matter which 

 by heat is reduced to charcoal,' sulphur is formed. These 

 salts produce sulphureous waters, if animal or vegetable sub- 

 stances are suffered to remain in water in which they arc 

 dissolved, so that very often nothing is necessary but a'iittlc 

 sulphate of lime to communicate to stagnant water the odour 

 and taste of sulphur. 



Pyrophorus is obtained by calcining common alum or 

 sulphate of potash with suo-ar, farina, or any matter which 

 becomes reduced to charcoal. 



The indammation of pyrophorus, which takes fire merely 

 by the contact of damp air, arises only from the snlphurct 

 of potash, which by attracting the humidity of the air be- 

 comes heated to such a degree as to set fire to tlie carbona- 

 ceous matter around it, and which being in a state of o-icat 

 tenuity is the more disposed to burn. "^ 



But as many of our common combustible matters con- 

 tain sulphuric salts, it may happen that in their combustion 

 there is sometimes accidentally formed some pvrophoric 

 matier. which remains in the residuum of the combustion • 

 especially if the combustible matter is not entirely co!i- 

 sumed, and if a part of it only is reduced to charcoal ; 

 which sometimes happens in fire-places where the com- 

 bustibles are not burnt in grates, and where the ashes are 

 not separated from the charcoal. There have been instances 

 ol houses being set on fire bv ashes intermixed with char- 

 coa. taken too soon i'rom the hearth and deposited in places 

 where they were surrounded by combustibles, which they 

 set fire to by spontaneous inllammation. Happily these 

 causes of fires rarely occur; for pyrophorus does not long 

 retam its property of iuflaming, and it is often decomposed 

 soon att6r it haslx-en formed, without beinir able to produce 



-No. 7'J. .Vwy ISCil. Z ' that 



