72 Dr. WoLLASTON oji a Method 



as to the quantities of heat, that become latent in the conver- 

 sion of ice into water, and of water into steam, being 140' and 

 ;96o' respectively, we should find the following statement to 

 be not far from the truth. 



If 32 grains of water were taken at the temperature of 62% 

 and if one grain of this were converted into vapour by absorb- 

 ing 960', then the whole quantity would lose ^-^ = 30% and 

 thus be reduced to the temperature of 32". 



If from the 31 grains, which still remain in the state of 

 water, 4 grains more were converted into vapour by absorb- 

 ing 960°; then the remaining 27 grains must have lost -^ of 

 960**= 142*, which is rather more than sufficient to convert 

 the whole into ice. In an experiment, conducted upon a small 

 scale, the porportional quantity evaporated did not much differ 

 from this estimate. 



If it be also true, that water in assuming the gaseous state, 

 even at a low temperature, expands to 1800 times its former 

 bulk ; then in attempting to freeze the small quantity of water 

 abovementioned, it would be requisite to have a dry vacuum 

 with the capacity of 5 x 1800, or equal to that of 9000 grains 

 of water. 



As a means of avoiding the necessity of so large a vacuum, 

 Mr. Leslie had recourse to the ingenious expedient of em- 

 ploying an extensive surface of sulphuric acid, for the purpose 

 of absorbing the vapour generated in the course of the expe- 

 riment, and by that means contrived to freeze much larger 

 quantities of water, than could otherwise have been done, and 

 by a far less laborious process. 



But even in this method the labour is not inconsiderable. 



