on Wood and Charcoal. 365 



were reduced at last to 0.27 of a gramme, or about a 

 twentieth of the original weight. 



I am persuaded that I should have diminished it still 

 more, if I had continued the experiment longer ; but it 

 has been tried long enough to establish this remarkable 

 fact, that charcoal can be dissipated by a heat much less than 

 has been considered necessary to burn it. 



It may be supposed that I was very desirous of 

 knowing whether the same thing would occur to charcoal 

 already formed by the usual process. Accordingly I 

 took a piece of charcoal from my kitchen, heated it to a 

 strong red heat, and, while it was still red, put it into a 

 marble mortar, and powdered it. Having passed it 

 through a sieve, I took 4.03 grammes of the powder, 

 placed it in the saucer, heated it in the stove twelve 

 hours, and then left it twelve hours to cool. On taking 

 it out, it weighed but 3.81 grammes. 



As this powdered charcoal was nothing but a collec- 

 tion of small bits of charcoal, which were in contact 

 with the air only by a very small surface compared with 

 that of the shavings, I made another experiment, the re- 

 sult of which was more striking and more satisfactory. 



Having enclosed in a cloth a quantity of powdered 

 charcoal, that had been passed through a sieve, I beat it 

 strongly in a place where the air was still ; and when the 

 air appeared to be well loaded with the fine dust of the 

 charcoal, I placed on the ground a white china saucer, 

 quitted the place, and left the dust to settle. 



The saucer was covered with it, so as to appear of a 

 very dark gray. 



Before all the dust had settled, I wrote some letters 

 on the saucer with the point of my finger, and these let- 

 ters were afterward covered with a still finer dust. 



