J 00 Difficulty of tranfmlttingjlrong Heat through Charcoal. 



was 8 decemeters high, 6 in diameter at the mouth : the cylinder of clay was placed la 

 the middle, and the crucible had its cover luted on. 



The other piece, B, was placed in a fimilar crucible, with this difference, that the crucible 

 was filled with powder of charcoal, which had been previoully ignited in a clofe crucible. 



The two crucibles were then placed befide each other on the grate of a large melting 

 furnace, in which the fire was kept up for about three quarters of an hour. 



When the crucibles were cooled, the cylinder A was taken out of the fand, and prefented 

 to tlie pyrometic fcale of Wedgewood ; it had undergone a contraction of 89 degrees. The 

 cylinder B was then taken out of the charcoal, and Hopped in the gage at 60,25 degrees. 

 It had acquired a grey tinge, but without any appearance of glazing. 



Hence it follows, that the tranfmiffion of heat through the fand, is to the tranfmiffion 

 through the charcoal nearly in the proportion of 3 to 2. In proportion as this difference 

 is in itfelf ftriking, the more it becomes neceffary to attend to fuch precautions as are re« 

 quired to prevent deception arifing from foreign circumftances. The crucibles had moft 

 affuredly undergone the fame degree of fire. The flate m which they were found exhibited 

 the traces of its aftion : the conditions were tlierefore as equal as poffible ; but it might, 

 poffibly, be fufpe£ted that fome defe£t:, or want of uniformity in the pyrometic piece, or 

 fome imperfedtion in its compofition, or fabrication, might have altered its difpofition to 

 contraci: equally, and proportionally to the heat it might undergo. There was a very fnnple 

 method of removing thefe doubts ; namely, to afcertain whether the fame piece put into 

 the fand, and expofed to a much ftronger heat, would refume the common courfe of con- 

 traction, and agree with the former. This, in fa£t, was performed ; the fame two pieces, 

 A and B, were inclofed in one and the fame crucible filled with fand, fo that they were not 

 more diflant from each other than about 7 or 8 millimetres, and the crucible was expofed 

 for half an hour to the moft violent heat of a forge, urged by three twyers. 



The crucible, when cold, was found to have loft fome of its thicknefs by vitrification, fo 

 that there was a crack in one of its fides. The fand, however, was not deranged within. 



The piece A marked 163,5 "pon the pyrometic fcale, it weighed no more than 1,491 

 grammes ; its fpeclfic gravity was 2,232. 



The piece B exhibited 160 degrees on the pyrometer, it weighed 1,53 grammes, and its 

 fpeclfic gravity was 2,346. It had almoft loft the grey tinge which it had acquired in the 

 charcoal, and was no longer diftingulfliable from the other but by a black vitreous point, 

 produced by the acceflion of fome foreign matter. 



I confefs I did not expe£t to be fo completely fuccefsful in this verification : the fmall 

 difference of 3 ' degrees is nothing, when we confider that the piece firft inclofed in the 

 charcoal, and which had ftopped at 60, was ftill capable of contracting through an additional 

 1 00 degrees. It is, befides, known to be phyfically impoffible, that two bodies placed in 

 the fame crucible, and in contaCt with the fame fubftance, fhould be ftriCtly in the fame 

 fituation as to the reception of heat, particularly when the blaft is directed from three differ- 

 ent nozzles, which are neceffarily unequal. The advanced ftate of one of the fides of the 

 crucible, with refpeCt to the fufion, is a proof that this was in fa£t the cafe. 



We may therefore conclude from thefe effays, that the body included in the charcoal in 



the 



