388 



Mr. H. M. Vernon on the 



containing the freezing-mixture and the beaker itself were 

 well covered up, and the temperature was found to remain 

 constant throughout the experiment. The thermometer used 

 was a standard one, graduated in tenths of a degree ; and as 

 all readings were taken with a cathetometer, it was read 

 to the hundredth of si degree. The water was then warmed 

 to about 30° C. and readings taken of the thermometer at 



intervals of a minute, till it had cooled to about 



C. when 



ice began to form. In the figure will be seen the curve for the 



:32 40 4S 



Time in minutes. 



rate of cooling which was thus obtained. The curve is only 

 given up to lb'° C, as above this it is quite regular. From 

 about 14° C. the cooling begins to take place slightly less 

 rapidly than would be the case if no internal thermal change 

 were taking place, and continues getting less and less rapid 

 till from about 5°'5 C. to 4°-7 C. it almost stops. At 4*7° C. 

 it suddenly begins to sink rapidly again till about 3° C. After 

 this point the curve becomes regular again. The part of the 

 curve from 30° C, if produced on the supposition that the 

 curve is regular, gives the dotted-line curve in the figure. 

 Water has been found to have its maximum density at 



