Count Rutnford's Experiments on heated Fluids, 533 



Count Rumford has proved, by a fct of very ingenious and happily-contrived experi- 

 ments, that when heat is applied to a fluid, the fluid is heated in oonfequence of every 

 individual particle going in its turn to the fource of heat, combining with caloric, and then 

 giving place to other particles, which combine with caloric in their turn. It is evident, 

 then, that folid and fluid bodies are not heated in the fame manner. The firft fet of bodies 

 can only be heated by their conducing power, in the fccond fet every individual particle 

 goes direftly to the fource of heat» Though fluids, then, when placed upon the fire, acquire 

 heat very fpeedily, we are not entitled to conclude, from this circumftance, that they are 

 condudlors of caloric. This point can only be determined by dire£l experiments. 



The experiments which Count Rumford * made for this purpofe may be divided into 

 two fets. The firft fet was made in order to Ihow that when the internal motions of fluids 

 are impeded, they are not heated fo foon as when their internal motions are unimpeded. 

 This, I think, he has very completely eftabliflied. But as fluids are not heated by their 

 conducing power, it does not follow, from thefc experiments, that fluids are non-conduc- 

 tors.. They demonftrate merely that, if fluids be conduftors, their conducing power is 

 much inferior to the power by which they are heated. Count Rumford appears to have 

 feen this himfelf, and to have looked upon thefe experiments rather as auxiliaries then as. 

 fatisfa£lory proofs.. 



The fecond fet of experiments was made in order to prove that caloric cannot pafs down' ■ 

 ■wards through fluids. Now, as caloric can pafs downwards through all conducing, 

 bodies, and muft indeed, from the very nature of the thing, pafs in every direction through . 

 them, it follows that, if it cannot move downwards through fluids, they are, in faft, tion- 

 conduSors, Thefe. experiments,, then, are perfectly in point. Let us confider. them a» 

 little. 



To fee whether caloric moves downwards, through water,, he fixed a cake of ice in the 

 bottom of a glafs jar, covered ^ inch thick with cold water. Over this was poured gently 

 a confiderable quantity of boiling water. Now, if water were a non-condudtor, no caloric 

 wrould pafs through the cold water, and confequently none of the ice would be melted.. 

 The melting of the ice, then, was to determine whether water be a condu£tor or not. In 

 two hours about half of the ice was melted. This, one would think, at firft fight, a de- 

 cifive proof that water is a conduflor. But the Count has fallen upon a very ingenious 

 method of accounting for the melting of the ice, " without being under the neceflity," as , 

 he tells us, " of renouncing his theory that fluids are non-condu6lors." 



It is well known that the fpecific gravity of water at 40° is a maximum: if it be either 

 heated above 40°, or, cooled down below 40°, its denfity diminiflies. Therefore, when- 

 ever a particle of water arrives at the temperature of 40°, it will fink to the bottom of the 

 veflTel. Now, as the water next the ice was at 32°, it is evident that whenever any part of 

 the hot water. was cooled down to 40°, it would fmk, difplace the water at 32°, come into * 



*. Count Rumford's experiments are detailed in our Journal; for which fee the Indexes, — N.. . 



contaftl 



