38 On the Relation of the Specific [July 



sulphur and the metals should be reduced to the half of 

 the numbers which represent them at present. The specific 

 heat of carbon would then be, according to this modified 

 law S-^'^ = ^*2^' ^^ exactly the result of experiment. 

 The number deduced by Avagrado is, however, incorrect, 

 because he adopts -764 as the atomic weight of carbon, 

 instead of '75, the number obtained by Dr. Thomson, and 

 which is here substituted. 



In this view of the subject the specific heat of oxygen, in 

 the solid state, ought to be '1875, a number which Avo- 

 grado also finds to be nearly the specific heat of oxygen in 

 the state of gas,^by a calculation founded on the experi- 

 ments of Berard and Delaroche, relating to the specific 

 heat of the oxygen of the air compared to that of water ; 

 and it is probable that the specific heat of a body, which pre- 

 serves the same atomic composition may not differ much in 

 each state. This could not happen, however, if the numbers 

 are preserved to which Dulong and Petit applied their law, 

 because the specific heat of oxygen would then be '375, or 

 the double of that which it possesses in the gaseous state. 



2. Phosphorus. — The specific heat of this substance was 

 determined by Avogrado, by observing how many degrees, 

 phorphorus at several degrees below zero cooled the liquid 

 (which was spirit of wine) in the exterior vessel. The mean 

 of two experiments gave for the specific heat of phosphorus 

 0*385, taking that of water as unity. Now, the atomic 

 weight of phosphorus being 2* we obtain an approximation 

 to thjs number if we take the fourth of it, or '5, and divide 

 the co-efficient -1875 by it. The quotient is -375, or the 

 specific heat of phosphorus in the solid state. Hence, 

 according to the view laid down by Avogrado, the thermic 

 atom of phosphorus will be '5. In the gaseous atom he 

 considers that there would be 8 thermic atoms 



3. Arsenic. — The atom of this substance is 4*75, the half 

 of which is 2-375. To obtain the specific heat we have 

 •i-^TTb =* 79 or '80. The number obtained by the experi- 

 ment was -81. Mitscherlich has found the density of the 

 vapour of arsenic correspond to double the number at 

 present received as the atom of arsenic. There would, 

 therefore, be in the gaseous atom four thermic atoms. 



