140 



PHILOSOPHICAL TRANSACTIONS. 



[anno 1792. 



Heat lost. 



176 grains 1 1 76 grains 

 of fine pow- of fine pow- 

 der of char- der of char- 



coal. 



Exp. No. 04. 



70° 

 60 



50 

 40 

 30 

 20 

 10 



79' 

 95 

 100 

 139 

 196 

 331 



9+0 



coal. 



IQSgiains of 

 lamp-black. 



307 grainsof 



pure diy 

 wood ashes. 



Exp. No. 25. 



Exp. No. 26. 



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 on the natures 

 of those bodies, considered as chymical substances, or on 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 ex- 

 periment with charcoal, as I had done with various other bodies. Accord- 

 ingly, having filled the globe of the passage-thermometer with 176 grains 

 of that substance in very fine powder, 



the bulb of the thermometer being The bulb of the thermo meter surrounded by 



surrounded by this powder, the instru- 

 ment was heated in boiling water, and 

 being afterwards plunged into a mix- 

 ture of pounded ice and water, the 

 times of cooling were observed as men- 

 tioned in the annexed table. I after- 

 wards repeated the experiment with 

 lamp-black, and with very pure, and 

 very dry wood ashes; the results of 

 which experiments were as there men- 

 tioned : 



The next experiment was with semen lycopodii, commonly called witch-meal, 

 a substance which possesses very extraordinary properties. It is almost impossible 

 to wet it; a quantity of it strewed on the surface of a basin of water, not only 

 swims on the water without being wet, but it prevents other bodies from being 

 wet which are plunged into the water through it; so that a piece of money, or 

 other solid body, may be taken from the bottom of the basin by the naked hand, 

 without wetting the hand; which is one of the tricks commonly shown by the 



91' 



91 

 109 

 133 



19'2 

 321 



9^7 



124 

 118 

 134 

 164 

 237 

 394. 



1171 



96' 

 92 

 107 

 136 

 185 

 311 



927 



