134 Experimental Investigations 



from time to time, in order to keep the frigorific mix- 

 ture constantly at the precise temperature of melting ice. 



As the specific gravity of water at the temperature of 

 three or four degrees of the thermometer of Reaumur 

 is greater than that of melting ice, the water which lies 

 at the bottom of a vessel containing a mixture of water 

 and pounded ice is usually warmer than the fluid which 

 occupies the upper part of the vessel. To remedy this 

 inconvenience, my refrigeratory for the frigorific mixture 

 was a tin vessel, supported on 'three feet of one inch in 

 length; and I placed this first vessel in a larger one of 

 wood, containing a certain quantity of ice surrounding 

 the bottom and part of the sides of the metallic vessel. 



As in the first moments of the experiment the ther- 

 mometers descended too quickly to be observed with 

 precision, I waited till each of them had arrived at the 

 55th degree of Reaumur ; after which I carefully ob- 

 served the number of minutes and seconds employed in 

 passing through each interval of five degrees of the lower 

 part of the scale of the thermometer to the fifth degree 

 above zero. 



Degrees of the Time employed in cooling 



thermometer. By the instrument A. By the instrument B 



Time employed in cooling | g 

 from 55 to 5, j 47 



254 5 



