C 2I 7 ] 
to one another. I took feveral pieces from the fame 
plank, and having carefully weighed and meafured 
them, converted them into coals very (lowly, and by 
a gradual increafe of heat, on an iron plate, held on 
the fire, turning them conftantly, to prevent their 
catching fire. The following were the refults. 
A piece of very old dry oak, weighing 12 grains, 
and which conducted in the imperfed manner that 
wood generally does, from the moifture it contains, 
was, after the lofs of about one grain, no condudor 
at all ; and it continued the fame as baked wood, till 
it was reduced to 4 grains, when it was black quite 
through j and even then, no part of it conduced, 
except one corner, where it had catched fire. 
Another piece I carefully weighed and meafured 
feveral times, in the courfe of the procefs. At firfi: 
it weighed 12 grains, when its dimenfions were 
2 inches and .45. At 8 grains they were 2 and .4; 
at 5 *5 g r - 1 - 9 1 and -4 ; at 3 -5 g r * 1 - 8 and - 35 * 
It was now become an imperfed condudor. I then 
urged it with a ftrong heat, in a crucible, and taking 
it out, it weighed 1 .75 gr. and meafured 1 .6, and 
.3. It was now a perfed condudor ; and though I 
afterwards kept it in a very intenfe heat feveral 
hours, by which it was reduced to 1 gr. and mea- 
fured 1 .6, and .3, its conduding power was net 
fenfibly increafed ; but it was become very brittle 
or friable. 
It appears from thefe experiments, that thefe pieces 
of wood were reduced to about | of their weight 
before they would condud at all ; though, at the fame 
time, they were diminifhed in length (/. s. along the 
fibres) only The breadth and thicknefs could 
Vol. LX. F f not 
