4 Mr. W. Hadfield on the Spontaneous Ignition of Charcoal. 



Exp. 3. — The same quantity of charcoal was taken as in the 

 foregoing experiments : it was quite fresh, and ground into 

 coarse powder. In 36 hours the temperature was 130° ; it then 

 gradually declined to 70°, when the experiment was given up. 



From the preceding experiments I was satisfied that spon- 

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

 tity. I therefore 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 before,in 

 a leaden pipe. Several holes were bored 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 see 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 risen to 90°; the following morning to 150°; and in 

 the afternoon of the second day the thermometer stood at 1 80°. 



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 

 the thermometer, though the temperature, as indicated by the 

 thermometer, was only 180° or 190°. 



It may perhaps be proper to remark, that the combustion 

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

 be laid against a wall, the combustion generally begins either 

 at the surface, or close to the wall. 



On the 13th of October 1831, small charcoal was 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 20th combustion 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. 



The 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 days before it was put together ; and 

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

 posed in the open air. 



I am not aware that any experiment has been made to as- 

 certain the effect of an exposure of the charcoal to pure oxy- 

 gen gas. A bell-glass, of the capacity of two quarts, was filled 

 with oxygen gas previously freed from carbonic acid by wash- 



