OF ARTS AND SCIENCES. 165 



aqueous solution. Accordingly, a series of experiments was made 

 involving this general reaction, 



^i?„,(S0,)„+BaCl,.2H,0. 



All work was done in a constant-temperature room. The calorimeter 

 was the one used by Mr, Richards, and the accessories were in every 

 respect the same as those described by him. 



The materials required were a standard solution of barium chloride, 

 and a solution of each of the sulphates to be acted upon containing a 

 sufficient excess to insure complete precipitation of the barium. Ac- 

 cordingly, a standard solution of barium chloride was made of the 

 strength represented by the expression, 



BaCla . 2 H.O 4- 200 H.p, 



From this standard value the required amount of each sulphate was 

 easily calculated. 



For every experiment, 250 cc. of the baric chloride and 250 cc, of 

 the sulphate solution were used. Hence this amount of water, in- 

 creased by the water equivalent of the calorimeter, stirrer, and ther- 

 mometer, gave the total water equivalent, which was exactly the same 

 for each experiment. 



The mode of experimenting was precisely like that in the preceding 

 paper, and the maximum rise of temperature took place in less than 

 fifteen seconds, which rendered unnecessary any correction for cool- 

 ing. The limit of error did not exceed 0°,02 C, and if any accidental 

 cause of uncertainty arose, a second experiment was made for con- 

 firmation. 



The following example is taken at random from the note-book : — 



Temperature of BaClg sol. in calorimeter . . 16°. 94 

 « « Na^SO^ sol, in beaker . . . 16°.78 



Mean 16°.86 



Final observed temperature 17°. 50 



Rise of temperature 0°,64 



The last column of the following table shows the amount of heat 

 produced by the reaction of one molecule (244 grams) of baric 

 chloride upon one molecule of sulphuric acid in combination with a 

 base, both being in aqueous solution. The next column to the left 

 gives the observed rise of temperature ; and, since the amount of baric 



