338 MR. W. C. D. WIIETHAM ON THE IONIZATION OF 



the amounts being gradually increased, till the whole quantity of stock solution 

 (6) in the cell was about 10 grammes. The liquid had then to be levelled. It 

 was at first intended to add larger quantities of a weaker stock solution and 

 to level the liquid for each observation, but it soon became evident that the errors 

 would be much reduced in all directions if this mode of procedure was abandoned, 

 and a correction for level applied to the measured resistance. This correction was 

 determined by experiment, and, in the final state of the cell, was found to be '31 per 

 cent, for each gramme of liquid in the cell above the normal amount. 



By this means it was only necessary to level when the total quantity added 

 amounted to about 10 grammes, and the consequent change of level in the liquid 

 in the cell was about one quarter of a centimetre. Thus one or two levellings were 

 usually enough for a complete set of observations on any one substance. 



When the quantity of solution (b) added to the liquid in the cell reached about 

 10 grammes, it became possible to use solution (a), for the equivalent quantity of 

 that solution was about '25 gramme, an amount which could be weighed with care 

 to the necessary accuracy of one part in a thousand. By the time that about 

 10 grammes of (a) had been added, the resistance had usually sunk to the value at 

 which accurate measurement became impossible, and the experiments were stopped. 



At intervals throughout the experiments it was necessary to adjust the 

 temperature by means of the ether apparatus. It was generally possible to keep 

 the solutions within the limits of a tenth of a degree above or below zero. While 

 small quantities of solution were being added it was not necessary to cool between 

 each experiment, but when a gramme or more of liquid at the temperature of the room 

 was run in, the liquid in the cell was heated through several tenths of a degree, and 

 had always to be cooled by the ether apparatus. These opportunities were taken to 

 determine temperature coefficients for the small corrections necessary on the observed 

 values of the resistances. 



SECTION 10. On the deduction of the Observations. 



1. Calculation of the Concentration. The weight of the stock solution (6) added 

 for the first experiment is multiplied by its concentration in terms of gramme-equiva- 

 lents of solute per gramme of solution. This gives the number of gramme-equiva- 

 lents of solute present in the cell. The weight of solution in the cell is equal to the 

 weight of water left after levelling (which is known from separate and preliminary 

 experiments) plus the weight of stock solution added, and the weight of solvent is 

 equal to the weight of solution minus the weight of solute added. Thus the concen- 

 tration of the solution can be calculated in terms of gramme-equivalents of solute per 

 thousand grammes of solution or per thousand grammes of solvent. These values 

 are sensibly the same while the solutions are dilute, and the difference only becomes 

 appreciable for the two or three strongest solutions of each set. Throughout this 



