530 PROCEEDINGS OF THE AMERICAN ACADEMY. 



with as great care as at first. After dismounting the apparatus the 

 condensing coil was dried outside and weighed ; and the experiment 

 was thus brought to a close. 



The increasing temperature and the increasing heat capacity of the 

 calorimetric system during an experiment cause complications in the 

 calculation which have usually received insufiicient attention. At 

 the beginning, the heat capacity of the calorimeter is that of the solid 

 apparatus and the water in which the coil is immersed. As the ex- 

 periment proceeds, this heat capacity is augmented by the liquid which 

 collects within the condenser. At the end of the distillation the heat 

 capacity of the calorimetric system reaches its maximum. Evidently 

 the value used in the calculation must be taken as the initial heat ca- 

 pacity plus the heat capacity of half the condensed liquid. 



Heat is radiated and conducted from the hot vaporizer into the calo- 

 rimetric system, and correction for this unavoidable complication must 

 be applied. The correction is primarily based upon the measurement 

 of the heat gained during the preliminary minutes before the experi- 

 ment has been begun, in the usual fashion ; but it must be remembered 

 that this value does not apply exactly to the end of the experiment, 

 because the calorimeter has then risen in temperature, and therefore 

 cannot take so much heat from the vaporizer as before. For example, 

 if the temperature of the calorimeter is 20° at first and 24° at the con- 

 clusion of the experiment, and if the vaporizer has a temperature of 

 100°, it is evident that the difference of temperature between the vap- 

 orizer and the calorimeter is 80° at first and only 76° at the end. 

 Hence, if the calorimeter gains 0.009° during each preliminary minute, 

 it will be expected to gain only 76/80 X 0.009° = 0.0085 during each 

 final minute, and intermediate values during the intervening period. 

 The method of correction for this changing effect is obvious and was 

 easily applied. This practice was justified by the actual results, for 

 the warming effects of the hot vaporizer was always found to be less 

 after the experiment than before. The diminution was manifest even 

 before the vaporizer itself had cooled considerably. 



The changing condition of the calorimeter involved a similar detail 

 in the calculation of the heat given out by cooling the condensed liquid 

 from its boiling point to the temperature of the condenser. The heat 

 actually measured in the calorimeter was due of course not only to the 

 heat given out by condensation, but also to that given out by the con- 

 densed liquid in falling from the temperature of the vaporizer to that 

 of the calorimeter. The first portion of condensed liquid is cooled to 

 the initial temperature of the calorimeter, the last portion only to the 

 somewhat higher final temperature. Obviously here again the mean 



