230 



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



number of the author's experiments are on substances whose specific heat 

 had not been previously determined ; they extend to all the more important 

 classes of inorganic compounds, and to a great number of organic com- 

 pounds. 



In the fourth part the author gives a synopsis of the materials at pre- 

 sent available and trustworthy for considering the relations between specific 

 lieat and atomic weight or composition. That is, he gives for solid bodies 

 of known composition the atomic formula, the atomic weight, the more 

 trustworthy determinations of specific heat, and (corresponding to these) 

 the atomic heats, or products of the specific heats and the atomic weights. 



The relations between the atomic heat and the atomic weight or the 

 composition are discussed in the fifth part. 



A discussion whether the specific heat of a body varies materially with 

 its difi'erent physical conditions forms an introduction to this part. The 

 influence which change of temperature of solid bodies exerts on the specific 

 heat is considered. This difference is inconsiderable, as is also the differ- 

 ence of specific heats found for the same substance, according as it is ham- 

 mered or annealed, hard or soft. With dimorphous varieties of the same 

 substance, even where the specific gravity is different, the same specific 

 heat is found in most cases. Great difference had been supposed to exist 

 in the specific heat of a substance, according as it was crystalline or amor- 

 phous. The author shows that, for a great number of substances, there is 

 no such difference, and that in other cases the apparent differences depend 

 on inaccurate determinations of the specific heat. He shows that three 

 sources of error more especially may give too great a specific heat for a 

 substance, or for one of its various modifications : — 



1 . "When the substance is heated to a temperature at which it begins to 

 soften, and thus to absorb part of its latent heat of fusion. 



2. If the substance is heated to a temperature at which it begins to pass 

 into another modification, and this change, with its accompanying deve- 

 lopment of heat, is continued in the calorimeter. 



3. If the substance investigated is porous, and (as was the case in the 

 earlier methods) is directly immersed in the liquid of the calorimeter, in 

 which case the development of heat which accompanies the moistening of 

 porous substances comes into play. 



The author arrives at the following result : — From what is at present 

 known with certainty, one and the same body may exhibit small differ- 

 ences with certain physical conditions (temperature, or different degrees of 

 density or porosity) ; but these differences are never so great as to furnish 

 an explanation of cases in which a body markedly deviates from a regu- 

 larity which might perhaps have been expected for it — always assuming 

 that the determination of the specific heat, according to which the body in 

 question forms an exception to the regularity, is trustworthy and free from 

 foreign elements. 



The author then discusses the applicability of Dalong and Petit's law. 



