CAPACITY FOR HEAT OF METALS AT DIFFERENT TEMPERATURES. 



121 



If we consider the endeavours to ascertain the mean capacity over the range C. 

 to 100 C., the same lack of agreement is evident. For copper we have 



Temperature range. 



0. 



15-100 



0-100 



At 50 



17-100 



23-100 



15 100 



At 50 



Specific heat. 



G'09331 



G'09332 



0-09169 



G'09333 



0-0940 



0-09232 



0-09261 



Observer. 



I '.U.K. 



TMMI.INSMV. 



LORENZ. 



NAOCARI. 

 TROWBRIDGE. 

 TILDEN. 

 GAEDE. 



The methods described in this paper, although they doubtless present their own 

 peculiar difficulties, are, we believe, free from many, if not all, of the sources of error 

 above referred to. The method is briefly indicated in the following numbered 

 paragraphs : 



1. The energy was supplied electrically and the conclusions are not dependent 

 upon any assumption concerning the capacity for heat of other bodies than those 

 under consideration. 



2. The substances were raised across a given temperature through very small ranges 

 of temperature (extreme limit of range, about 1'4 C.). 



3. These temperature changes were measured by means of' differential platinum 

 thermometers, for which purpose these instruments are admirably adapted. 



4. Large masses of the substances were used, ranging from 1 to 4 kgr. 



5. The apparatus was constructed with all its parts duplicated. The metals 

 examined were suspended by quartz tubes in similar air-tight brass cases whicli were 

 placed side by side in a large tank containing rapidly stirred water or oil. This tank 

 was electrically controlled with great constancy at any given temperature, . 



One of the metal blocks remained at the tank temperature throughout an experi- 

 ment while the other, having been previously cooled below , was raised to a 

 somewhat similar temperature above it by a supply of heat electrically developed in 

 the centre of the block, the difference in temperature between the two blocks being 

 determined at regular intervals by means of the differential platinum thermometers. 



All changes in the surrounding conditions would therefore affect both blocks equally ; 

 hence, by measuring the difference of temperature only, many possible causes of error 

 were eliminated. 



6. The equation connecting the various quantities is 



where M = total mass, S its specific heat ; 0, the initial temperature, and 3 the 

 final temperature ; E, the potential difference at the extremities of the resistance 

 VOL. ccxin. A. R 



