512 Mr. D. M c Intosh on the Conductivity of 



The mixtures in all cases consisted of equal volumes of the 

 constituent solutions. In preparing them the same pipette 

 was used for both solutions in exactly the same way, having 

 been washed out before use in each case with a portion of the 

 solution with which it was to be filled. In all cases solutions 

 were prepared and analysed at 18° C. 



The method employed in the observations of conductivity 

 was that of Kohlrausch with alternating current and telephone, 

 the apparatus consisting of a bridge-wire of german-silver 

 about 3 metres long, wound on a marble drum, a set of resist- 

 ance-coils (of which I needed to use but one) , a small induction- 

 coil with a very rapid vibrator, and an ordinary Bell telephone. 

 I calibrated the bridge-wire by the method of Strouhal and 

 Barus, and was able to determine resistances to within from 

 0'2 to 0*3 per cent. 



The electrolytic cell was of a U-shape, and was placed in a 

 water-bath kept at or near 18° 0. by a thermostat and stirred 

 by a current of air. Its temperature was read by a ther- 

 mometer graduated to 0*1 degree Centigrade, and capable of 

 being read easily to 0*05 degree. Its errors had recently 

 been determined at the Physikalisch-technische Reichsanstalt, 

 Berlin. When the bath could not be kept at 18° C, the 

 temperature coefficient was determined. In the platinizing 

 of the electrodes, and in the whole procedure of the deter- 

 mination of the conductivity, 1 followed carefully the recom- 

 mendations of Kohlrausch's recent papers. 



As I was to employ Kohlrausch's observations as data in 

 the calculations, I reduced all my observations of conductivity 

 to his standard (the conductivity of mercury at 0° C.) . The 

 factor requisite for this purpose was determined by comparing 

 my own observations for certain solutions with the values 

 given by him for the same solutions. This factor I found (as 

 Bender had also) to vary somewhat with the conductivity of 

 the solution used in finding it, but not with the nature of the 

 solution. I therefore found its values as given by using a 

 series of solutions of different conductivities ; and in reducing 

 the observed conductivity of a mixture to Kohlrausch's 

 standard I used the value of the factor corresponding to the 

 conductivity of the mixture. All observations given below 

 are expressed in terms of Kohlrausch's standard. 



Results of Observations on Mixtures. 



The following tables give the concentrations of the con- 

 stituent solutions of the mixtures examined and the observed 

 conductivities of the mixtures : — 



