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Dr. Kopp on the Specific Heat of Solid Bodies, [May 12, 



The author gives for all compounds, whose specific heat has been inves- 

 tigated in a trustworthy manner, a comparison of the specific heats found 

 experimentally with those calculated on the above assumption. The 

 atomic heat of a compound is obtained by adding the atomic heats of the 

 elements in it, and the specific heat by dividing this atomic heat by the 

 atomic weight. The calculated specific heat of chloride of potassium, 



KCl,is-^^i±|^ = 0-172 ; of sulphide of lead,Pb S,^^l±^= 0*0494 ; of 

 borate of potass, K B O^, it is ^ ^"^^ ^^^^^^^ =0-209 ; of tartaric acid, 

 H, 0„ it is (1^118)±(gM±i2il=0-.SOO. 



The Table, embracing 200 compounds, shows, on the whole, a sufficient 

 agreement between the calculated and the observed specific heats. The 

 author remarks that a closer agreement between calculation and observation 

 cannot be hoped for than that between the observed atomic heats of those 

 compounds for which, from all we know at present, the same'atomic heat is 

 to be expected in conformity with Neumann's law, to which in such cases, 

 of course, calculation corresponds. In only a few cases are differences be- 

 tween calculation and observation met with which exceed these limits or 

 exceed the deviation between the results of different observers for the same 

 substance. The author states that he is far from considering the agree- 

 ment between his calculations and the experimental results as a measure of 

 the accuracy of the latter, since the bases of calculation are too far from 

 being trustworthy. But he hopes that his Table of atomic heats will soon 

 acquire such corrections, and therewith greater trustworthiness, as was 

 the case with the first Table of atomic weights. Here, the data for 

 the Table were at first but little certain, and the differences between the 

 calculated and observed composition of chemical compounds very con- 

 siderable ; but the Table was the means of corrections being introduced 

 by which these differences were diminished. 



If calculation of the specific heat does not supersede the necessity of 

 experimental determination in the solid state, and does not give a trust- 

 worthy measure for the accuracy of such determinations, it gives a rough 

 control for the experimental determinations, and it indicates sources of 

 error in the experiments which without it would not have been noticed. 

 An instance may be adduced. The author found for sesquichloride of 

 carbon, Clg, which, according to Faraday, melts at 160°, the specific 

 heat between 20° and 50° to be 0*276 in one series of experiments, and 

 0*265 in another. Hence the number 0*27 might from this be taken 

 to express the specific heat of the compound. But calculation gives 

 (2xl'8)-}-(6x6'4)^Q..^>^^^ ^ ^^^^ different number. A. third series of 

 237 



experiments with substance once more recrystallized, gave for the specific 

 heat between 21° and 49° 0*278, confirming the previous determinations. 



