[ 382 J 
XIV. Experiments to determine how far Charcoal is a Non- 
» Conduétor of Heat. By Cit. Guyton. Read in the 
Nat. Injt. Germinal 6, An. 6. From the Annales de 
Chimie, Vol. XXVI. 
From the refearches of chemifts refpecting the matter 
of heat, the different ftates in which it is found, and the 
various ways in which it affeéts bodies, it is well known 
that charcoal is one of the weakeft conductors of it. This 
obfervation has given rife to the idea of forming furnaces 
with a double wall, in order that the intermediate fpace may 
be filled with charcoal; and lately a very happy application 
has been made of this property to veffels deftined for form- 
ing and preferving warm infufions *. 
I, however, do not know that any one has endeavoured to 
fix, at leaft by comparative experiments, the limits of this 
kind of infulation +. They have remained fo vague that the 
ableft chemifts have not thought proper to pay any attention 
to them in judging of the refult of their operations; and 
thus the celebrated Klaproth, in a feries of experiments on 
the alteration which ftones experience in the ftrongeft fire, 
feems to think that the heat was almoft equal for thofe con- 
tained in crucibles of porcelain and thofe enclofed on all 
fides by charcoal. It is in a crucible of charcoal that 
chemifts attempt the reduction of the oxyds of tungften, 
titanium and uranium, though it is well known that what 
is fought is a degree of heat fufficient for their fufion, and 
that every means poffible are fought for, in other refpeéts, to 
expofe them to a greater heat. 
Thefe reflections induced me to think that it might be of 
fome importance to give a more exact flandard of this in- 
** It has been alfo propofed, and certainly would be found to anfwer in 
practice, to furround bodies, intended to be kept cool, with charcoal—ices 
houfes above ground for inftance. Epir. 
+ Some of the ingenious experiments of Count Rumford have been, 
direéted to this very object. See Effay viii, Eprr. 
haa i fulating 
