BOMIi CALORIMETER 



509 



ment useless, ))ut tliey are best avoided. Leave for hall an hour. Place the 

 calorimeter, carefully carried in a cloth, on the cork studs on the thin sheet 

 of ebonite on the bottom of the large double-walled insulating vessel H 

 (Fig. 3), which has been filled with al)out 11 litres of water. Connect the 

 terminals P, and P., by well-insulated flexible leads to a battery (4-6 volts) 

 provided with a simple contact key. Place the ebonite cover, stirring gear 

 and thermometer in position. 



Start the stirring device (best activated by a small electric motor) and after 

 the lapse of a few minutes take readings of the thermometer regularly every 

 half-minute. As the water in the calorimeter is about 1° C. below the tem- 

 perature of the room, the readings will tend to rise, e.g. 



I. Pre-ignit'ION Period. 



Time (minutes) 

 Teni]).' (° C.) 





 14-953 



0-955 



1 



0-957 



U 



0-958 



2 

 0-960 



Time (minutes) 

 Temp. (° C.) 



91 



0-963 



3 



0-964 



3* 



0-966 



4 

 0-969 



i.e. rate of warming at 14-9° C. is 0-002° C. per half minute. 



Ignition. At a known moment, fire the charge by pressing the button at 

 the battery. The temperature rapidly rises. Take readings every half-minute 

 as under. 



II. Ignition Period. 



i.e. the temperature reaches a maximum value six minutes after ignition and 

 then begins to fall. Headings are continued every half-minute till the fall of 

 temperature has become quite regular, e.g. 



III. Cooling Period. 



Time (minutes) 

 Temp °C. (14 omitted) 



1()1 

 2-51 



11 



2-508 



lU 



2-507 



12 



2-505 



121 

 2-5()4 



13 

 2-502 



Time (minutes) 

 Temp. "C. (14 omitted) 



131 

 2-5 



14 



2-498 



141 



2-49"6 



15 

 2-493 



151 

 2-490 



16 



2-488 



i.e. the rate of cooling during this pcrioil is 0-002° C. per half-minute. 



From these two cooling values, e.g. ()-(l02° in the pre-ignition j)eriod and 



