62 Chemistry. [Lecture 26. 



is the lightest body, might be made to assume 

 the density of gold. 



In the second place, I have to notice the dis- 

 tribution of caloric or heat. That substances, 

 when heated above the temperature of those bo- 

 dies which surround them (a bar of iron for in- 

 stance), soon part with their superfluous caloric 

 (in other words cool) is well known : and in like 

 manner a cold body introduced into a warm 

 place soon acquires the temperature of that 

 place. The distribution of heat is more rapid 

 in proportion to the contact of parts ; hence the 

 excessive slowness with which heat is communi- 

 cated to those bodies which are rare and spongy, 

 and hence its celerity in hard bodies. If a rod 

 of iron is put into the fire for a little time, the 

 end which is at a good distance from the fire 

 will almost burn the hand, but a stick will be 

 burnt to ashes before the other end is heated. 

 We find qaloric greatly retarded by cork, and 

 still more by feathers and wool. Hence arises 

 the distinction of good and bad conductors; 

 the iron is a better conductor of caloric than the 

 wood, and the wood is still better than cork or 

 feathers. The difference in the cooling of hot 

 bodies depends much upon their goodness as 

 conductors. When mercury and water, each 

 heated to the same degree, are placed in similar 

 circumstances, the mercury cools twice as fast as 

 the water. Straw, flannel, and feather-beds are 



