THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



MARCH 1875. 



XXI. The Specific Heat of the Elements Carbon, Boron, and 

 Silicon. — Part I. The Relation between the Specific Heat of 

 these Elements in the free state and the Temperature. By Dr. 

 H. Friedrich Weber, Professor of Physics and Mathematics*. 



[With a Plate.] 



DULONG and Petit in 1819 measured the specific heats of 

 thirteen solid elements. In each case there appeared a 

 very simple relation between the specific heat and the atomic 

 weight : the product of the specific heat into the atomic weight 

 was a constant quantity. The atoms of all the elements examined 

 have therefore the same capacity for heat. If the specific heat 

 of water be taken as the unit, and 16 as the atomic weight of 

 oxygen, this constant (the so-called atomic heat) averages 6*0. 

 By numerous researches, extending from 1840 to 1862, M. Reg- 

 nault has shown the general applicability of this law of Dulong 

 and Petit — the general result being that this law seems to hold 

 good for the greater number of the solid elements, provided the 

 specific heat of any element be determined at a temperature suf- 

 ficiently under the melting-point of that element. The average 

 atomic heat for thirty-two solid elements was 6*3, the extremes 

 being 6*7 for sodium and 5*5 for phosphorus and sulphur. For 

 three solid elements, however (viz. silicon, boron, and carbon), 

 considerably smaller atomic heats were obtained — for crystallized 

 silicon 4'8, for crystallized boron 2*7, and for crystallized car- 



* An Experimental Research presented at the fifty-sixth Anniversary of 

 the Royal Wurttemberg Land- and Forest-Management Academy at Ho- 

 henheim. Translated by M. M. Pattison Muir, F.R.S.E. 



Phil. Mag. S. 4. Vol. 49. No. 324. March 1&75. M 



