OF ARTS AND SCIENCES. 163 



As the investigation was a question of comparison rather than of 

 absolute measures, great care was taken to render the conditions as 

 uniform as possible. For this purpose, all the solutions and apparatus 

 were left for twenty-four houi's in a room of nearly constant tempera- 

 ture before being used. 



The calorimeter was similar in every respect to that described by 

 Berthelot, and the method of operation was exceedingly simple. In 

 every case 250 cc. of the solution of the metallic chloride were 

 poured into the platinum calorimeter, and at the same time 250 co. 

 of the silver solution (containing 4 grams of AgNO„ as stated above) 

 were poured into a beaker, which had a capacity when filled to the 

 brim of 255 cc. The beaker was rested upon many folds of a non- 

 conducting cloth, and surrounded by a cardboard cylinder with a mov- 

 able cover. 



When the temperatures of the liquids in both the calorimeter and 

 the beaker (which were at first very nearly the same) had become 

 constant after much stirring, they were noted, and the beaker was 

 grasped by a heavily gloved hand and its contents poured rapidly 

 into the calorimeter, the temperature of the resulting mixtures 

 being noted. 



Following is an example taken at random from the note-book. 



Temperature of NH^Cl sol. in calorimeter . 17°.220 

 " AgNOg sol. in beaker . . . 17°.280 



Mean 17°.250 



Final observed temperature 18°. 000 



Rise of temperature 0°.750 



In every case the maximum temperature was attained in 10 to 15 

 seconds, so that no correction for cooling was necessary. 



The water equivalent was always as follows : — 



Solutions, 500 grms. ; platinum calorimeter, 3.5 grms. ; platinum 

 stirrer, 1.5 grms. ; thermometer, 5 grms. Total water equivalent = 

 505.5 grms. 



Below is a table of all the results found. 



The first column contains the number of the experiment, the second 

 the chloride acted upon, the third the observed rise of temperature, 

 and the fourth the amount of heat evolved in calors, and the last 

 column the difference between the amount in each case and the av- 

 erage amount. 



