334 Mr. W. C. D. Whetham. Meclric Conductivity of [Feb. 14, 



room by standing the cell for a few minutes in slightly warmed 

 water. 



The water used as solvent was first boiled, then distilled in glass 

 from alkaline permanganate, and finally redistilled in a platinum still 

 with a trace of acid potassium sulphate. It was kept in a large stop- 

 pered flask of Jena glass till required for the experiments. 



The samples of salt used to make the stock solutions of potassium 

 chloride and copper sulphate were the same as those prepared for the 

 earlier experiments ; details will be found in the account of those 

 experiments to which reference has already been made. In the cases 

 of barium chloride, potassium bichromate, and magnesium sulphate, 

 the best salt, sold as chemically pure, was obtained, the two salts first 

 mentioned being recrystallised before use. Any probable impurities 

 would not affect the results to an amount equal to the other errors of 

 experiment. 



The measurement of the electrical resistance was performed exactly 

 as in the earlier set of experiments. The current from one or two dry 

 cells was alternated by means of a revolving commutator, which was 

 driven by a hand wheel and cord, the connections of a D'Arsonval 

 galvanometer being simultaneously alternated by the same instrument. 

 The alternating currents were passed through a Wheatstone's bridge, 

 in one of the arms of which was inserted the electrolytic cell. This 

 apparatus worked with perfect success ; its sensitiveness was enough 

 to enable readings to be taken to an accuracy varying from one part 

 in one thousand to one part in thirty thousand, according to the 

 resistance in the circuit. 



The results which were obtained are collected below. In the table 

 headed Potassium Chloride I, and in the tables for all the other salts, 

 the concentrations, given in the first column under m, are calculated 

 in terms of the number of gram-equivalents of salt per thousand 

 grams of solution, while, for the sake of comparison, under Potassium 

 Chloride II, the conductivities are reckoned per thousand grams of 

 water. In the second column under m*, for convenience in plotting 

 curves, are tabulated the cube roots of the concentrations ; the third 

 column, E, shows the measured resistances of the solutions; next 

 comes hjm = /x, the equivalent conductivities ; and finally, in the last 

 column, are placed the ratios of fx to its value at infinite dilution, 

 which was estimated from the former set of experiments. It was 

 thought advisable, in view of the freezing point observations now 

 being conducted in Dr. Griffiths' apparatus by Mr. T. G. Bedford, to 

 include magnesium sulphate in the investigation. This substance was 

 not examined in the platinum cell, so that it was necessary to extend 

 the experiments to very dilute solutions. This was done in cell No. 1, 

 which is made of Jena glass, and therefore is not likely to react appre- 

 ciably with a solution of the nature of magnesium sulphate. 



