XXVI. Intelligence and Miscellaneous Articles. 



ON THE SPONTANEOUS INFLAMMATION OF POWDERED CHAR- 

 COAL. 



MAUBERT, colonel of artillery, has made numerous experi- 

 ments on the above subject : he states that charcoal when 

 very finely powdered has the appearance of an unctuous liquid, and 

 occupies only one third the space of sticks of charcoal of about 

 six inches long. 



In this state of division, it absorbs air much more rapidly than 

 when it is in sticks ; still however the absorption goes on slowly, 

 requiring several days for completion ; it is accompanied with the 

 disengagement of heat, which is to be regarded as the true cause 

 of the spontaneous combustion of the charcoal ; the heat is equal 

 to about 350 of Fahrenheit. The inflammation occurs towards the 

 centre of the mass, at about five or six inches beneath the surface ; 

 the temperature is constantly higher in this place than in any other ; 

 there must consequently exist towards the edges of the mass a de- 

 scending current of air, which lends towards the centre, and be- 

 becomes vertical, without penetrating towards the lower parts of 

 the mass, where the temperature is but little raised. It is on this 

 account that a portion only of the charcoal appears to produce the 

 phenomena ; the remainder serves as an isolating substance, and 

 preserves the heat in the centre. 



The variations of the barometer, thermometer and hygrometer do 

 not appear to have any sensible influence upon the spontaneous in- 

 flammation of the charcoal ; if such influence exists, the experi- 

 ments have not been sufficiently multiplied to prove it. 



Black charcoal, strongly distilled, heats and inflames more rea- 

 dily than imperfect or slightly distilled charcoal. 



The black distilled charcoal, which is the most inflammable, ought 

 to be in masses of about 60 pounds at least, that spontaneous in- 

 flammation may take place; with less inflammable charcoal the 

 inflammation occurs only in larger masses. In general the inflam- 

 mation occurs more certainly and readily, as the time is short 

 between the carbonization and powdering. Air is not only necessary 

 for the spontaneous inflammation, but there must be free access of it 

 at the surface ; the weight which the charcoal acquires to the mo- 

 ment of its combustion, is derived not merely from the privation of 

 air, but partly to the absorption of water. During trituration the 

 air undergoes no change from the charcoal ; nor does it suffer any 

 up to the moment of its inflammation. 



Sulphur and nitre, added to the charcoal, take away its property 

 of inflaming spontaneously ; still however there is absorption of air 

 and heating ; and although the increase of temperature is not very 

 great, it is prudent not to leave these mixtures in too large masses 

 alter trituration. Ann. de Chim., Sept. 1830. 



ON 



