318 



Mr. H. H. Poole on the Bate of 



by the change of pressure. The following is a typical set of 

 readings : — 



Height of Mercury 



above Standard. 



cm. 



Deflexion 



(on reversal). 



Scale-divisions. 



Means 



(see above). 



Scale-divisions. 



Deflexion caused 

 by change of 



pressure. 

 Scale-divisions. 



o-o 



4-6 







1320 



194 



4-65 



14-75 



00 



47 







1200 



18 2 



4-85 



13-35 



00 



5-0 







1100 



17-05 



5 05 



12-0 



00 



5-15 







1395 



20-8 



5-1 



15-7 



00 



5-1 







1300 



1955 



5-2 



14-35 



00 



53 









It will be seen that the numbers in the last column are 

 sensibly proportional to those in the first. The mean of all 

 the determinations made by this method is a deflexion of 

 11"21 scale-divisions per metre of mercury. 



Taking the density of ice as 0*91674 (Bunsen) and latent 

 heat of water 80*16, we find that the lowering of freezing- 

 point is 0°*00748 C. per atmosphere. Hence 1° C. corre- 

 sponds to r^ — _ A rv-7^> =H38 scale-divisions. The other 

 F 100 x 00-0748 



method gave 1152; so we may take as a mean that 1° C. 

 corresponds to 1145 scale-divisions. 



Experiments with Water in the Calorimeter. 



Three experiments were made with water to determine 

 the thermal conductance of the calorimeter. The straight 

 stem couple was used. As this is slightly shorter than the 

 one whose calibration is referred to above its resistance is 

 less, so that it is rather more sensitive. With this couple 

 1° C. corresponds to about 1220 scale-divisions. In every 

 experiment the water in the calorimeter eventually attained 

 a lower temperature than the junction in the ice outside. 

 This could hardly be due to the conduction of heat down the 

 leads to the external junction considering the precautions 

 taken to prevent this source of error. It is probably due to 

 the ice not being at zero even after all the precautions taken. 

 The ice will accordingly rise in temperature, and the lag of 

 the calorimeter will cause the water to become colder than 



