322 



MR. W. S. TUCKER ON HEATS OF 



1 



The Choice of a Calorimeter. 



Kadiation is another factor which becomes important when very small temperature 

 changes are produced. A very well made Dewar cylinder was employed. (Diagram 

 I, A A.) Its walls were well silvered, and during the experiments its contents, 

 together with stirrer thermometer and other adjuncts, were shut in by a well-fitting 

 cork stopper, which again Was covered with a layer of cotton wool. 



Curves were plotted when the contents had 

 varying thermal capacities, and these were found to 

 be perfectly smooth and enabled one to estimate 

 with certainty the rate of cooling at any tempera- 

 ture. The cubical capacity of the vessel was about 

 400 c.c., and in no case did it contain more than 

 300 c.c. of solution. For 20 degrees excess of 

 temperature in the contents over that of the room, 

 a rate of cooling of about 0'038 C. occurred per 

 minute. 



Each series of observations was accompanied by 

 its own radiation experiment and complete consis- 

 tency was given throughout. 



The Mixing Pipette. 



It is highly important that the water added 

 should have the same temperature as the solution. 

 A thin walled glass pipette was employed of the 

 form shown in the diagram. (I., P.) Its bulb 

 passes throughout the length of the cylindrical 

 mass of solution, and parallel to the bulb of the 

 thermometer. Two such pipettes were employed 

 one with a capacity of about 25 c.c., the other about 

 45 c.c. The water was weighed out in these, the 

 former being used when the solutions were strong, 

 the latter when weak. The walls were of thin glass, and the syphon tube was of such 

 length as to introduce the water at the bottom of the vessel containing the solution. 

 The water, being of course less dense than the solution, would rise, and the process of 

 mixing would be assisted in consequence. 



Before mixing, the glass bulb with its contents was left immersed in the solution 

 for some hours, and the stirrer was worked continuously. In this way error due to 

 temperature difference was brought to a minimum. The upper end of the pipette is 

 then connected by a thin rubber tube with the rubber ball, such as is used for a scent 



Diagram I. 



