74 On Ignition in Charcoal in Atnwqiheric Temperatures. 



From the yireceding experiments I was satisfied that spon- 

 taneous combustiou would not take place in so small a quan- 

 tity. I thcrefoie determined to make the experiment upon a 

 larger scale. 



Exp. 4. — 10 cwt. of new charcoal was finely ground, and 

 put into a hogshead, with a thermometer placed, as hefore, in 

 a leaden pipe. Several holes were hored in the sides of the 

 hogshead to admit the air. The charcoal when ground was 

 65" ; and particular care was taken in examining the charcoal, 

 to sec that it was free from ignition. It was put into the hogs- 

 head at about 10 o'clock in the morning, at night its tempera- 

 ture had rised to 90^ ; the following morning to loO"" ; and in 

 the afternoon of the second day the thermometer stood at 180°. 



I was surprised to find at this time that combustion had 

 taken place at about five or six inches from the surface, and 

 about the same distance from the leaden pipe which contained 

 tlie thermometer, though the temperature, as indicated by the 

 tJierraometer, M'as only 180° or 190°. 



It may perhaps be proper to remark, that the combustion 

 always takes place vear to the surface ; or, if small charcoal 

 he laid against a wall, the combustiou generally begins either 

 at the surface, or close to the wall. 



On the 13th of October 1831, small charcoal Avas thrown 

 into a heap, which covered about 10 feet square, was about 

 4 feet deep, and contained from two to three tons in weight. 

 In three days the temperature had increased to 90°, though it 

 was at first only 57°, being the same as that of the air. On 

 the 19th it was 150° ; and on the '20lh combusiion had occur- 

 red in several places. "Water was thrown upon it ; and the 

 fire was, to all appearance, effectually extinguished ; yet on the 

 21st it was again observed to be burning in different parts; 

 and it continued to burn until it was removed and formed into 

 smaller heaps. 



Tlie last experiment was the most satisfactory one which 

 has ever come under my notice. The charcoal had been made 

 for at least ten or twelve dajs before it was put together ; and 

 had been lying, during the interval, in small heaps freely ex- 

 posed in the open air. 



