﻿ATOMIC HEAT TO CRYSTALLINE FORM. 129 



increased capacity for heat is about one-tenth, the increase in expasion amounts to 

 one-hundredth. But we cannot conceive of this expansion taking place without the 

 atoms being moved farther apart, thus increasing the volume. Coincidently with this 

 change, and as a proof of its reality, we find the specific gravity of the metal diminish- 

 ed. Hence it is, that the capacity for heat of any body increases with the temperature; 

 for the arrangement of the atoms at greater distances from each other must necessarily 

 afford more space for the accumulation of caloric around the particles. Thus the 

 specific heat of copper is reduced, by violent hammering, from 0*095 to 0-935 ; but 

 raised again by ignition, to 0.0949. Lead and tin, on the contrary, which do not in- 

 crease in specific gravity under the die, likewise suffer no diminution of specific heat 

 by pressure. The specific heat of soft bell-metal, (Cu 80 Sn 20 ) which has a density 

 of 8-6843 is 0-0862, while the same metal hardened, in which state its density is 

 8-5797, has a specific heat of 0-0858. (Regnault.) The more dense a body is, the 

 greater is its specific gravity and the less its specific heat. A beautiful example is 

 given by Regnault in the case of precipitated silver. The specific heat of this sub- 

 stance varies with the degree of condensation, as shown by the following results de- 

 termined by the method of cooling : — 



Very little pressed, 

 More strongly " ... 



Still more " ... 



Strongly hammered and rubbed, 

 More strongly " " 



Peroxide of iron and peroxide" of nickel when strongly ignited, increase in density 

 and diminish in specific heat. The varieties of carbon present the same result. The 

 interesting experiments of Messrs. Hopkins, Fairbairn and Joule, upon the effects of 

 extreme pressure, demonstrate that the temperature of fusion increases in proportion 

 to the pressure to which the fused mass is subjected. In employing a pressure of 

 about 13,000 lbs. to the square inch, on bleached wax, they found that increase in 

 the temperature of fusion was not less than 30° F., about one-fifth of the whole 

 temperature at which it melts, under the pressure of the atmosphere.* Such facts, I 

 may say in passing, militate strongly against the generally received, though probably 

 erroneous theory of the exalted calorific condition of the centre of our planet. 



But the active agency of caloric in affecting specific gravity, is seen by comparing 

 compound bodies with the elements of which they are composed. Thus hydrogen 

 and chlorine unite, without condensation, to form hydrochloric acid gas. The specific 

 gravity of one volume of hydrogen is 69-26 ; of one volume of chlorine, 2421-6; and 

 of one volume of hydrochloric acid gas, 1247*4 ; the mean of the two former numbers. 

 The specific gravity of hydrogen is about 36 times less than that of chlorine ; its 



* President Hopkins' Address before the 23d Annual meeting of the British Association. 



20° to 15° 



15° to 10° 



10° to 5° 



0-08535 



0-08441 



0-08519 



0-05844 



0-05772 



• 0-05781 



005749 



05713 



0-05749 



0-05634 



0-05671 



005654 



005616 



0-05624 



0-05650 



