174 Dr. H. F. Weber on the Specific Heat of 



two openings in it. Through one passed a thermometer, while 

 the other, the larger of the two, served as the mouth of the 

 calorimeter. The mouths of the two instruments were at such 

 a distance from each other that the middle point between them 

 coincided with the point midway between the two platinum 

 tubes. Each calorimeter was provided with a copper stirrer ; the 

 two stirrers could, by a simple piece of mechanism, be set in 

 motion simultaneously. The water- value of the first instrument, 

 with thermometer and stirrer, was 3*15 grms.; the water-value 

 of the second was 3*35 grms. Nearly the same quantity of water 

 was used in each, in order that, by bringing into each equally 

 heated substances whose heat-values were the same, the same 

 rise of temperature might be obtained in each case. This was 

 actually found to be the case, to within o, l, in all experiments. 

 The thermometers used with these calorimeters were graduated 

 to hundredths of a degree. The stirrers were set in motion 

 15 minutes before each trial, the alteration of temperature being 

 noted every five minutes in each instrument. Both calorimeters 

 showed always the same change of temperature, this change 

 never amounting to more than +0°'006 per minute. The 

 temperature was noted immediately before the heated substances 

 were thrown in ; as the substance touched the water, no deve- 

 lopment of vapour was noticed in any case, nor could even the 

 slightest sound be heard indicative of the escape of gas-bubbles. 



The stirrers were kept in operation until fully ten minutes had 

 elapsed from the time when the heated substances fell into the 

 calorimeters, the temperature of each instrument being read off 

 minute by minute, in order that the fall of temperature per 

 minute might be obtained. The maximum of temperature always 

 occurred before the expiry of the first minute, after which the 

 temperature very steadily sunk. The temperature at the end of 

 the second minute was taken as the definite final temperature ; 

 and to this was added the correction A=J(A© + 3A©'), where 

 A© and A©' represent the temperature-alterations per minute 

 before and after the heated substance was thrown into the calo- 

 rimeter. This correction never reached 2 per cent, of the tem- 

 perature-increase At of the calorimeter. 



If G and G k represent the weights of platinum and of the 

 other substance, K, used, Q and Q^ the water-values, At and 

 At k the rise of temperature, and t and t k the corrected final 

 temperatures in the respective calorimeters, then the common 

 initial temperature of the platinum and of the substance K, and 

 also the average specific heat, C, _ T , of the substance K may 



be obtained by solving the two equations 



