NOTES AND COOLTDGE. — ELECTRICAL CONDUCTIVITY. 193 



10. If the vapor above the solution had an appreciable conductivity it 

 would make the conductivity between the upper electrode and the bomb 

 appear too great. But this is not the case, as is shown by the fact that 

 unless the liquid is in contact with the electrode there is no measurable 

 conductivity here, even at 30G° with a 0.1 normal KC1 solution. "We 

 can at present only assign an upper limit to the conductivity of the vapor: 

 but it certainly does not exceed ^ooW^ V av ^ °f ^ na t of the solution. 



Errors Affecting the Conductivity Values. — 1. All the errors in the 

 values of the specific-volume have an effect of the same magnitude upon 

 those of the equivalent conductivity, with Wie important exception of that 

 due to the amount of solvent in the vapor space at the two highest 

 temperatures, 281° and 306°. No error arises from this last source by 

 reason of the fact that, owing to the increase in concentration of the 

 solution, the specific conductivity increases in the same proportion as the 

 volume diminishes; for at 281° and 306° (but not at 140° and 218°) 

 the quantity of liquid in the bomb was the same in the two series of 

 measurements. 



2. The cell-constant might be expected to vary with the height of the 

 liquid level in the bomb ; but direct experiment showed that for the 

 range of the liquid level in our measurements the effect of this was 

 less than the error of observation. The smallest amount of solution 

 employed in any of the experiments was first introduced into the bomb 

 and the conductivity measured at 2G°. Then more of the same solution 

 was introduced until the liquid was in contact with the whole cover ; 

 but the resistance was not measurably changed. 



3. The cell-constant changes with the temperature owing to two 

 causes : first, the expansion of the quartz-crystal cup ; and, secondly, 

 that of the bomb itself. The correction for this is calculated as follows: 

 The resistance inside the bomb may be considered as made up of two 

 parts, that (a) inside the crystal cup, and that (b) between the mouth 

 of the cup and the platinum lining. The ratio of a to b can be roughly 

 determined by putting any solution into the bomb, measuring the resist- 

 ance, and then introducing a third electrode in the form of a platinum 

 disk placed over the mouth of the cup, and measuring the resistance 

 between this new electrode and the electrode at the bottom of the cup. 

 This ratio, so determined, is not strictly identical with the actual one, 

 since the lines of current-flow inside the quartz cup have been some- 

 what changed in direction by the interposition of the new electrode; but 



for the present purpose the approximation sufliees. The ratio r 



a -f o 



vol. xxxix. — 13 



