184 Non-conduéting Power of Charcoal. 
pyrometrical piece might have fome fault either in its com- 
pofition or fabrication, which might change its difpofition, 
to contract equally and proportionably to the heat. To ob- 
viate thefe doubts, the two pieces A and B were {hut up in 
one crucible filled with fand ; fo that they were diftant from 
each other only about feven or eight millimetres, and the 
crucible was expofed for half an hour to the moft violent heat 
of a three-blaft wind furnace. When the crucible cooled, 
it was found fo much vitrified that there was a fiffure 
in one of its fides; but the fand had not been deranged 
within it. 
The piece A applied to the pyrometrical {cale gave 163°5 
degrees ; it weighed no more than 1°491 grammes; and its. 
fpecific gravity was 2°232. A ols) 
The piece B gave by the pyrometer 160 degrees; it weigh- 
ed-1°53 grammes; and its fpecific gravity was 2°346. It 
had loft almoft entirely the grey tint it had affumed in the 
charcoal, and diftinguifhed itfelf only by a black vitreous 
point, produced vifibly by the acceffion of fome foreign. 
matter. 
I did not expect, I confefs, fo complete a fuccefs in this 
procefs. The fmall difference of 3! degrees is nothing 
when we confider that the piece firft fhut up in the charcoal,, 
and which ftood at 60, was {till fufceptible of being con- 
tracted a hundred degrees more. It is known, befides, that 
~ it is phyfically impoffible that two bodies placed in the fame 
crucible, in contact with the fame matter, fhould be exaétly” 
in the fame condition to receive the heat, efpecially when 
the wind is conduéted in three directions neceffarily un- 
equal. A proof of this is furnifhed us by the vitrified fufion 
being more advanced on one of the fides of the crucible*. 
* This way of accounting for the difference of 33. degrees might per=. 
haps be admitted, if it could be fhown that a longer expofure to.the heat 
would not have removed it. Eprr- ! 
ase 
