84 ESSAYS BIOGRAPHICAL AND CHEMICAL 



order to melfc it. He hung up two globes side by side, 

 about 18 inches apart, in a large empty hall, in which the 

 temperature remained practically constant ; each globe 

 contained 5 ounces ; one of ice at 32 F., the other water 

 at 33. The latter had a delicate thermometer suspended 

 in it. The temperature of the hall was 47 F. In half an 

 hour, the water had attained the temperature 40 F. ; 

 and the ice took ten hours and a half to attain the same 

 temperature, that is, twenty-one times as long as the 

 water. The heat, which the ice absorbed during melting 

 was (40 33) x 21 or 147 units; that is, had it been 

 absorbed by the five ounces of water it would have made 

 it warmer by 147. The temperature of the ice, however, 

 was 8 warmer than its melting-point, after the 21 half- 

 hours ; hence 139 or 140 ' degrees had been absorbed 

 by the melting ice, and were concealed in the water into 

 which it had changed.' 



The method of experiment was next varied. Black 

 weighed a lump of ice, and added it to a weighed quantity 

 of warm water of which the temperature was known. 

 The warm water was cooled to a much lower degree by 

 the melting of the ice, than if it had been mixed with a 

 quantity of water of 32 F., equal in weight to the ice. 

 The quantity of heat absorbed by the ice in melting ap- 

 peared from this second experiment to have been capable 

 of heating an equal quantity of water through 143 F. 



A third experiment was made, in which it was proved 

 that a lump of ice, placed in an equal weight of water at 

 176, lowered the temperature of the water to 32. Now 

 176 32=144 again a similar result. The latent heat 

 of water is therefore about 142 or 143, in Fahrenheit 

 units. The result of the most careful measurements give 

 79*5 centigrade units, which corresponds with 143 units 

 of Fahrenheit's scale. Curiously enough, this fundamental 

 datum has not yet been determined with the accuracy 



