19-4 PROCEEDINGS OF THE AMERICAN ACADEMY. 



was thus found for Cell II to be f^f. Le Cliatelier * has studied the 

 expansion of quartz both parallel and at right angles to the main axis 

 up to 1000° ; and, with the help of his values, the resistance of one of 

 the cups was calculated to decrease by 0.69 per cent of its value upon 



heating from 26° to 306°. Multiplying this by gives 0.53 per 



cent for tlie decrease in the resistance of the bomb due to the 

 expansion of the cup. On the other hand, h will increase at a rate 

 roughly proportional to the linear expansion of the bomb, or between 

 26° and 306° by O.OOOOlo X (306 — 26), or 0.42 i^er cent. Multiply- 

 ing this by gives 0.10 per cent for the increase in resistance of 



the bomb due to the expansion of the shell. The total decrease in the 

 resistance of the bomb is therefore 0,43 per cent. The change in the 

 cell-constant is similarly calculated for the other temperatures. These 

 corrections are given in Table IV and have always been applied to the 

 results. 



4, The effect of the pressure on the cell-constant is entirely negligible. 

 For at 306° the radius is increased by the pressure 0.01 per cent, and 

 this affects the cell-constant by only 0.002 per cent. 



5, The resistance of the lead-wires has to be deducted from the meas- 

 ured resistance of the bomb ; and since a portion of the leads is subjected 

 to the temperature of the bath, this correction is different for different 

 temperatures. This resistance may be considered as made up of three 

 parts: ^i, the constant resistance of the heavy leads; -So, the resistance 

 of the small leading-in wires, L^ and Lj ; and R^, tliat of the steel 

 electrode rod. i?i and R.^ were measured at room temperature. For 

 the other temperatures R^ was calculated from its value at room tempera- 

 ture, i?3 was calculated from its dimensions and the specific resistance 

 of steel. The maximum value (at 306°) of the total resistance of the 

 lead- wires was 0.061 ohms. 



6, In the case of the more dilute solutions it was necessary to correct 

 for the conductivity of the water used. To do this, some water pre- 

 pared in the same way and of the same conductivity cold as that used 

 for making up the solutions was put into the bomb, and just such a set 

 of experiments was made with it as had been made with the solutions. 

 Then for any temperature the conductivity of the water, measured at 

 that same temperature and under the same conditions, was deducted 



* Compt. rend , 108, 1046 (1889). 



