6$ ' Sir Benjamin Thompson's 
lead to further discoveries relative to the causes of the warmth 
of coverings, or the manner in which heat makes its passage 
through them. But I forbear to enlarge upon this subject, till 
I shall have given an account of several other experiments, 
which I think throw more light upon it, and which will con- 
sequently render the investigation easier and more satis- 
factory. 
With a view to determine how far the power which certain 
bodies appear to possess of confining heat, when made use of as 
covering, depends upon the natures of those bodies, considered 
as chymical substances, or upon the chymical principles of 
which they are composed, I made the following experiments. 
As charcoal is supposed to be composed almost entirely of 
phlogiston, I thought that, if that principle was the cause 
either of the conducting power, or the non-conducting power 
of the bodies which contain it, I should discover it by making 
the experiment with charcoal, as I had done with various other 
bodies. Accordingly, having filled the globe of the passage- 
thermometer with 176 grains of that substance in very fine 
powder (it having been pounded in a mortar, and sifted through 
a fine sieve), the bulb of the thermometer being surrounded by 
this powder, the instrument was heated in boiling water, and 
being afterwards plunged into a mixture of pounded ice and 
water, the times of cooling were observed as mentioned in the 
following table. I afterwards repeated the experiment with 
lampblack, and with very pure, and very dry wood ashes ; 
the results of which experiments were as under mentioned: 
