340 BABCOCK. 



3. Ratio of Volt Box Coils. 



The ratio of the volt box coils, as determined, included the resistance 

 of the lead wires. The average of ten readings was taken to allow 

 for a slightly varying current. 



4. Laboratory Equation for the Calorimeter Temperature 

 Change: Cooling Correction. 



The temperature change occurring in the calorimeter and measured 

 by the observing thermometer, is not the temperature change actually 

 produced by the introduction of the heat bH\ or 5//o, but is compli- 

 cated by several circumstances which must be allowed for in com- 

 puting the true W. These circumstances are as follows: 



1. The temperature of the mercury in the calorimeter rises more 

 rapidly than that of the container and ammonia, so that the tempera- 

 ture recorded on the thermometer at an}' instant, while very closely 

 the temperature of the mercury, is not the equalized temperature of 

 the calorimeter. 



2. A heat transfer to the surroundings takes place due to the 

 difference of temperature between the mercury and these surroundings. 



3. Heat is added to the mercury and the calorimeter by the friction 

 of stirring. 



The method of procedure in correcting for these effects was as fol- 

 lows: 



The oil bath was set to regulate at the temperature at which it was 

 desired to make a measurement, and the calorimeter temperature 

 brought to within a degree or so of this bath temperature. No 

 attempt was made to have the calorimeter temperature always bear 

 the same relation to the bath temperature, as it was desired to see how 

 closely the method of computing these temperature data eliminated 

 such variables. The theory takes account of these differences of 

 calorimeter and bath temperature and if the conditions are always 

 the same, the agreement between results is rather a check on the 

 reproducibility of the apparatus than a true indication of the experi- 

 mental error. A half hour was allowed to elapse before measurements 

 were begun, to permit time for the parts of the calorimeter to equalize 

 their temperature differences. Figure 7 is a typical time-temperature 

 calorimetric curve, and shows the effects described below. Stirring 

 was started and readings made of the temperature at intervals of 

 one minute. ^^ It was assumed that the small amount of heat intro- 



12 The readings were made almost exactly on the even minute. To accom- 

 plish this, the galvanometer telescope was focused on a watch hung on the 



