PR. K. II. CKIFFITHS AND MR. EZER GRIFFITHS ON THE 



Statement received with Weston normal cells BO-1, BC-2 : 

 " E.M.F. = 1'0183 international volts at 20 C. 

 T.-mperature coefficient: 



E, = E ao -0'0000406(<-20) -0-00000095 (-20) 3 +0'00000001 (/-20) 3 ." 



While an experiment was in progress, the current in the heating coil was 

 continually adjusted to keep the balance exact. This was effected by two rheostats 

 in parallel ; the shunt being of fairly high resistance. After the preliminary 

 adjustment, the potential balance could be maintained by use of the shunt alone. 



The sensibility of the high resistance Thomson galvanometer (7000 ohms) in the 

 standard cell circuit was such that a deflection of 1 mm. on the galvanometer scale 

 corresponded to a change in the potential difference of 1 part in 20,000. 



During the course of an experiment, the potential balance could be maintained 

 with great steadiness, the slight oscillations rarely amounting to more than 1 part 

 in 10,000. 



SECTION VI. 



Minor Collections for the Thermal Capacity of Accessory Substances. 



In order to facilitate transmission of heat from the heating coil to the metal block, 

 the central hole was, as previously stated, filled at low temperatures with boiled 

 paraffin oil, and at higher temperatures with a heavy hydrocarbon. 



The quantity of liquid thus inserted varied slightly with different blocks, the 

 average volume being about 7 c.c. It was therefore necessary to ascertain the 

 thermal capacity of the oils and their approximate variation with temperature. 



In the construction of the apparatus 15 '06 gr. of alloy were used in fixing the 

 quartz tubes to the lid of the copper case first employed, and 8'25 gr. of solder in 

 the second and somewhat heavier lid. 



Again, the thermal capacity of the portions of the glass sheaths of the thermo- 

 meters which entered the block had to be allowed for; the mass .thus inserted 

 amounted, when thermometer CD was in use, to 3'1 gr., and, in the case of AA and 

 AA', to T67 gr. 



Lastly, allowance had to be made for the heat absorbed by the lower ends of the 

 quartz tubes which supported the apparatus. This was a most difficult correction to 

 determine, as it was not possible, (I priori, to specify what mass of the quartz could 

 be regarded as raised through the same temperature as the copper lid. 



1. Specific Heat of Glass and Oil. 



The mean specific heat of the paraffin oil between C. and 100 C. was determined 

 with a Bunsen's calorimeter, by the introduction of about 2'8 c.c. of oil sealed in a thin 

 glass bull). 



