680 PROCEEDINaS OF THE AMERICAN ACADEMY. 



a little below that of the room, and the bomb was placed in the silver 

 calorimeter. Connections were prepared for the later use of an electric 

 current by joining a copper wire to the bomb itself, and another, care- 

 fully insulated, to the tip of that one of the two stout platinum wires 

 which was insulated from the bomb. The water for the calorimeter, 3302 

 grams at 20° C, was now measured in a marked flask, and poured into 

 the silver vessel, submerging the bomb, at nearly the temperature desired. 

 The cover containing dilute alkali was put in position, and its tempera- 

 ture roughly adjusted to that of the calorimeter. The stirrers were set 

 in motion, and the thermometers and burettes clamped in position. The 

 temperatures of the two systems were taken with a 0.01° thermometer ; 

 if, after all was ready, a slight difference existed between the tempera- 

 tures of the calorimeter and the other jackets, the latter were easily 

 adjusted by a little ice, or a little hot water or acid, until the whole ap- 

 paratus was very nearly the same temperature throughout, that is to 

 say, within a few hundredths of a degree. All measurements were made 

 between 20° and 25° C. Readings every one or two minutes were now 

 taken on the accurate Fuess thermometer, which was always jarred by an 

 electric vibrator before reading, in order to prevent errors due to friction 

 of the mercury thread. As soon as the readings assured constancy of 

 the temperature of the calorimeter, the switch, completing the electric 

 circuit through iron wire in the bomb, was lowered, and the sugar 

 ignited by the combustion of the wire.^ In a few seconds the tempera- 

 ture of the calorimeter began to rise, and the change in temperature 

 was equalled in the outer system by adding concentrated sulphuric 

 acid from the burettes. For about the first minute the temperature 

 of the outer system, as indicated by the quantity of sulphuric acid 

 used from the burettes, was kept about 0.1° to 0.05° above that in- 

 dicated by the thermometer in the calorimeter, so as to allow for 

 thermometric lag and give time for the equal distribution of the heat 

 in the jacket. In from four to five minutes the calorimeter reached its 

 maximum temperature, and the thermometer gave constant readings. 



The great advantage of this adiabatic method of calorimetry is 

 shown at this point by the constancy of the thermometer at the com- 

 pletion of the combustion. The thermometer usually gave constant 

 readings for a long time after it had reached its maximum, showing 

 indubitably that there was no appreciable heat exchange between the 

 calorimeter and its surroundings. Moreover, there was plenty of time 

 in which to read the thermometer accurately, while the mercury thread 

 was stationary, and no thermometric lag was possible. 



^ The electrical heat thus intrmluccd is very small in amount, and is wholly 

 eliminated by the coraparative method finally used for calculating the results. 



