358 Experiments on Charcoal, &c. 



a temperature frequently beyond that of boiling water, the 

 crucible was cut acrofs, and found to contain 18 grains. It 

 appeared, therefore, neceflary to the volatilization of the char- 

 coal that a greater heat be urged. 



Exp- IX. The fame quantity of charcoal was employed, 

 and hibjccted to the fame treatment. The crucible was then 

 placed in the annealing furnace, and broken, as it came from 

 thence, after cooling. The charcoal had disappeared, and, in 

 place of the vitrid matter formerly obtained, a few flakes of 

 alkaline fait were found on the bottom. The heat of the 

 annealing fire did not exceed 30 of Wedgewood. The cru- 

 cible was weighed before put in and when taken from the 

 annealing fire, and was found to have loft ^th part of its 

 weight, which was fuppofed to be water. 



It appears pretty conclufive, from the two laft experiments, 

 that a high heat is neceflary to expel the laft portions of 

 water ; and that, as in Exp. VIII., the charcoal nearly re- 

 mained entire where a temperature confiderably beyond that 

 of boiling water was applied : it was in confequence of the 

 expulfion of this water that the charcoal had difappeared. 



This conclufion will eafily explain the evaporation of dia- 

 monds in balls of moift clay, wherein the fame circumfiances 

 would take place as at prefent. It will particularly explain 

 an experiment of Macquer's, wherein he inclofed charcoal in 

 baked and unbaked crucibles of clay. In the former, where 

 no moifture was prefent, the charcoal remained unchanged; 

 but in the latter it difappeared, and the allies were found 

 vitrid, as in thefe experiments. This was attributed to cer- 

 tain fhrinkages or cracks, which might take place with green 

 clay, and which afterwards became inviflble in cooling. 



It is probable, however, that charcoal of wood may furnifh 

 part of the means of its own difappearance by a confiderable 

 deoxidation at a high temperature, and leave its refiduum in 

 a much purer ftate than formerly. The following experi- 

 ment will prove this. 



Exp. X. I took 30 grains of beautiful black charcoal col- 

 lected from experiments where it had been expofed to heats 

 of 1 65° Wedgewood. Thefe were inclofed in an unbaked 

 pot, which was fet afide to dry. In three months the cruci- 

 ble was found to weigh - - grs. 83 13 



It was then placed in the annealing fire, and weighed 

 3t a bright red heat - - - 7403 



Loft equal to — th part 910 



The 



