176 PROCEEDINGS OF THE AMERICAN ACADEMY. 



ison of the observed rise with water and with the liquid under investi- 

 gation gave a simple means of determining the relative heat capacities 

 A variant of this method consisted in using either water or the studied 

 liquid in the calorifer, the calorimeter always being rilled with the 

 former. This method, with various independent modifications, was 

 used by Schiiller, 3 Person, 4 Pfaundler, 5 Marignac, 6 Hammerl, 7 and a 

 number of other investigators. The simplicity of this procedure, and 

 the elimination of many doubtful factors by using comparative results, 

 are strong arguments for its use ; but the interchange of heat by radi- 

 ation between both the calorifer and the calorimeter and their envi- 

 ronments, coupled with the unavoidable lag of the thermometer, 

 introduces elements of uncertainty fatal to the highest accuracy. 



The ingenious device of Thomsen, 8 whereby measured amounts of 

 hydrogen are burned, under constant pressure, inside the calorimetric 

 system, gave concordant results ; but the values obtained are subject 

 to some of the same corrections as those demanded by the Andrews 

 method. Pfaundler, 9 using electrical energy as his source of heat, 

 attempted automatically to eliminate the radiation-correction by heat- 

 ing simultaneously two calorimeters, one containing water, the other 

 the liquid under investigation. If the rise of temperature were the 

 same, the loss by radiation would cancel. But as varying heat capac- 

 ities involve varying amounts of electrical energy to secure this result, 

 the electrical heat unit enters the computation, and by its uncertainty 

 detracts from the absolute accuracy of the determination. This device 

 has been recently applied in a modified form by Magie 10 with consid- 

 erable success ; but it is by no means easy to find a heat-producing 

 electrical resistance suitable for immersion in electrolytes. 



Several other different methods have been suggested by others, 

 but these also are not wholly free from defect. In one, the radiation 

 method of Dulong and Petit, 11 the hot object was enclosed in an evac- 

 uated and blackened chamber, losing its heat by radiation. The 

 chamber was placed either in an ice bath or in a water bath of suffi- 

 cient size to be unaffected by the heat given up by the cooling object. 

 The relative temperatures of the hot object and its environment, and 



3 Ann. de China, et Ph., 3, 88, 437. 



4 Pogg. Ami., 136. 70, 236 (1869). 



6 Wien. Ber.,62, (2), 879 (1870). 



« Arch. Gen., 2. 89, 217 (1870) ; 2, 65, 113 (1876). 



7 C. K ., 90, 694 (1880). 



8 Thennochem. Untersuch., 1. 24 el Beq. (1882) ; Pogg Ann., 142, 887 (1871). 



9 Wien. Ber., 59, (2), 145 (1809) ; 100, (2a), 862 (1891). 



10 Phys. Rei . 9,66 (1899); 13, 91 (W01)j 14, 198 (1902)j 17, 105 (1903). 



11 Ann. de Chim. et Ph., 2, 10, 395 (1819). 



