310 cox. 
In an extremely finely divided state coal will ignite almost as 
readily as gas derived from coal. Care must, therefore, be 
taken to avoid the ignition of coal dust, as there is no doubt that 
many serious fires and explosions are directly attributable to 
it and the violence of the latter may have been more severe in 
certain cases on account of absorbed oxygen. 
The presence of sulphur in the form of iron pyrites in stored 
coal has often been thought to be a source of heat and the cause 
of spontaneous combustion owing to the reaction between sulphur 
and oxygen.’ It is a fact that with a high content of sulphur 
coals often give trouble from heating; on the other hand, coals 
containing a small amount of sulphur, not more than 1.5 per 
cent, which include practically all of those from the Philippine 
Islands, also sometimes heat badly. This can not entirely be 
explained by the sulphur present. The amount of sulphur is 
far too small to account for the increase in temperature recorded 
in many instances even if it were all oxidized, which has never 
been shown to be the case. Porter and Ovitz™ have shown 
that there is ‘a very minor contribution, if any, on the part of 
sulphur to spontaneous heating in coal.” Bodenstein and Karo,” 
have shown that for liquid sulphur the velocity of the reaction 
with oxygen is proportional to the surface exposed. On the 
same principle, the fineness of division of the sulphide in coal 
would make its oxidation comparatively rapid and favor spon- 
taneous combustion. 
The question of the influence of moisture in coal upon its 
oxidation has not been sufficiently worked upon to enable us to 
decide it. Griswold1* says that when stored, wet coal should 
be spread out to expedite drying, especially when wet with snow 
and ice, and Doane ™ says: 
The amount of moisture in an air-dried sample of coal is an indication 
of its liability to heat, the danger increasing with the percentage of mois- 
ture contained. Coal containing over 4.75% after air drying is said to be 
dangerous. 
The amount of water naturally present in coal is an indication 
of the grade and, as already pointed out, the kind of coal is a 
factor upon which oxidation partly depends. Aside from this, 
it is probable that the amount of moisture has little significance. 
* Cf. Parr and Kressman, Journ. Ind. & Eng. Chem. (1911), 3, 151. 
* Journ. Ind. & Eng. Chem. (1912), 4, 7. 
* Ztschr. f. phys. Chem. (1910), 75, 47. 
* Eng. News (1904), 51, May 5. 
* Toid. (1904), 52, 141. 
Es 
