0 On Spontaneous Inflammations . 
the putrefaction of animal substances which have been 
buried. The flames often seen to issue from the earth, 
and which are known under the name of will-with-the- 
wisp, arise only from phosphorized hydrogen gas : as 
these fires generally appear in the open fields in places 
where they are notin contact with dry combustible mat- 
ters, they rarely produce disagreeable accidents ; but it 
is disengaged also in forests, and it may happen in very 
warm summers, when the grass and bushes are entirely 
dry, that the gas in combustion will meet with these com- 
bustible 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 malev- 
olence or to incendiaries those fatal events which some- 
times are the result of causes purely natural. 
9. Sulphuret and Phosphuret of lime and Potash form- 
ed during the Combustion of several Vegetables . 
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 
substances are suffered to remain in water in which they 
are dissolved, so that very often nothing is necessary 
but a little 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 sugar, farina, or any matter which 
becomes reduced to charcoal. 
The inflammation of pyrophorus, which takes fire 
merely by the contact of damp air, arises only from the 
sulphuret of potash, which by attracting the humidity of 
the air becomes heated to such a degree as to set fire to 
