116 



Mr. G. F. Rodwell on some Effects 



within 20 millims. of the surface, and the colour was observed 

 to gradually shade off till at a depth of 55 millims. it disap- 

 peared; so that the 50 cub. centims. of added alcohol were entirely 

 in the uppermost 55 millims. of liquid. The entire quantity of 

 liquid now exceeded 1000 cub. centims., and its depth was 140 

 millims. The following results were obtained : — 



Time of taking 

 the tempera- 

 ture from the 

 commence- 

 ment of heat- 

 ing. 



Alcohol-and-water mixture 

 at 7° C. 



Alcohol-and-water mixture 



at 7° C, with 50 cubic 

 centims. of alcohol added. 



Upper ther- 

 mometer. 



Lower ther- 

 mometer. 



Upper ther- 

 mometer. 



Lower ther- 

 mometer. 



minutes. 

 10 

 20 

 30 

 40 

 50 

 60 



1500 C. 



20-50 



25-75 



3000 



33-75 



3600 



15-75 C. 



21-25 



2650 



31 00 



34-50 



36-75 



9 25 C. 

 1200 

 20-00 

 26-00 

 30-25 

 34-50 



19-50 C. 



26-75 



3200 



35-00 



39-00 



41 00 



It will be observed that the alcohol-and-water mixture acquired 

 a uniform temperature as rapidly as either of its components 

 heated alone, the greatest difference between the uppermost and 

 lowermost layers of liquid amounting to only 1°C. But after 

 the addition of the alcohol (although its quantity was less than 

 one -twentieth of the total amount of liquid heated) a very dif- 

 ferent result is observed; for we find no less than 14°*75 C. dif- 

 ference of temperature 'between the uppermost and lowermost 

 layers of liquid. The amount of heat, however, associated with 

 the entire mass of each liquid at any given time during the heat- 

 ing is nearly the same, but it is differently distributed. If we 

 take mean temperatures, we find that the greatest difference 

 amounts to 1°*5 C. ; but the approach is often much nearer, and 

 in one case we have coincidence. Thus at the end of forty mi- 

 nutes' heating, the temperatures of the uppermost and lowermost 

 layers of the alcohol-and-water mixture were respectively 30° C. 

 and 31° C. ; and of the same mixture after the addition of the 

 alcohol, 26° C. and 35° C. : we thus obtain the following means . 



30 + 31 



30°-50 C, 



26 + 35 



= 30°-50 C. 



The following Table shows the means for each time of obser- 

 vation : — 



