38 



HEAT. 



supply is made to pass through the 

 syphon tube 6, into the funnel c, and 

 thence into the tube d, which is en- 

 closed in a larger one supplied with 

 steam from the furnace /: the water, 

 passing through the tube g, imparts its 

 temperature to the thermometers placed 

 in it ; it then enters at the bottom of 

 the calorimeter h, and traversing the 

 spiral tube passes out by the tube o, 

 and drops into the graduated tube p. 



The results obtained by Delaroche 

 and Berard are contained in the follow- 

 ing TABLE, the specific heat of atmos- 

 pheric air being considered 1.000 : 



The specific heats of the gases in- 

 cluded in the foregoing table being 

 each compared with that of an equal 

 weight of water, the following numbers 

 are obtained : 



Oxygen 0.236 1 



Azote 0.2754 



Water 1 .0000 



Air 0.2669 



Hydrogen gas 3.2936 



Carbonic acid 0.2210 



Oxide of Azote 0.2369 



Olefiant gas 0.4207 



Carbonic oxide 0.2884 



Aqueous vapour 0.8470 



With the exception of hydrogen, 

 which has a greater degree of specific 

 heat than any other body, all the gases 

 mentioned in the preceding table have 

 less specific heat than water, and more 

 than any of the metals. 



The results of these experiments are 

 hostile to the theory invented by Irvine, 

 adopted by Crawford, Leslie, and others, 

 that the evolution of heat, when bodies 

 combine together, arises from a di- 

 minution of the specific heat of the 

 bodies combined. One of their strong- 

 est arguments against this theory is 

 derived from a comparison of the spe- 

 cific heat of water obtained by experi- 

 ment with that of the constituent parts, 

 deduced by calculation, which they state 

 as follows : 



Water (composed of 0.87 oxygen and 0.13 



hydrogen), 



Its specific heat by calculation". . . 0.6335 

 By experiment 1.0000 



By which it appears, that the specific 

 heat of the constituents of water is 

 increased by their combination. 



The specific heat of oxygen compared 

 with that of water is 0.2361; that of 

 carbonic acid being 0.221 T 5 parts 

 less than that of oxygen. " Let us sup- 

 pose a pound of charcoal consumed. 

 From Lavoisier's experiments, it appears 

 that the heat evolved is sufficient to 

 melt 96|lbs. of ice. Now, this (suppos- 

 ing Mr. Cavendish's estimate correct) 

 is equal to 1.3027J degrees of heat. 

 The oxygen consumed amounts to 

 28lbs. nearly; so that each Ib. of oxygen, 

 when changed into carbonic acid, must 

 have given off 3428 degrees. Here a 

 change in the specific heat amounting 

 only to T f o or not quite & of the whole, 

 occasioned the escape of 3428 degrees. 

 Such a conclusion can only be adopted, 

 if we suppose the absolute quantity of 

 heat in the oxygen gas to amount to 

 147.404 degrees. This supposition ex- 

 ceeds the estimate of Dr. Crawford 

 nearly 100 times; and it is more than 

 ten times greater than that adopted by 

 Dalton. No person can believe that 

 oxygen gas contains so much heat. Of 

 course, the supposition that the^ heat 

 evolved during combustion is owing to 

 a change of capacity merely, cannot be 

 defended. If heat be a fluid, it must 

 enter into chemical combination with 

 certain bodies ; and the decomposition of 

 these bodies must be the cause of heat 

 evolved during combustion." Annals 

 of Philosophy, Dec. 1813. 



Experiments have frequently been 

 made to ascertain specific heats by sus- 

 pending bodies heated to a given degree 

 in a cool and uniform medium, until 

 their temperature descends through a 

 certain part of the thermometric range, 

 marking the times which different sub- 

 stances require to cool the same number 

 of degrees, all of them being exposed 

 under the very same circumstances ; 

 their specific heats are considered to be 

 directly as the times of their cooling. 



The method by which Dulong and 

 Petit ascertained the specific heats of 

 metals was by reducing them to very fine 

 filings, which were close pressed into a 

 thin and small cylindrical vessel of sil- 

 ver, having the bulb of a thermometer 

 in its axis, the vessel containing about 



