124 Oy THE CALCULATION OF THE CONDUCTIVITY OF 



by recrystallization. Solutions of them were found to be neutral 

 and free from sulphates and magnesia. Neither potassium nor 

 other metals could be detected in the sodium chloride with the 

 spectroscope. Sodium, but no other metal, could be detected in 

 a flame coloured by the potassium chloride. The hydrochloric acid 

 was obtained as chemically pure, and gave no residue on evapora- 

 tion. It was free from sulphates. 



The Water Used. 



The water was doubly distilled, with addition of sodium 

 hydrate, in a tin-lined retort, and condensed in a block -tin pipe, 

 the first part of the distillate being rejected. It was stored in 

 bottles which had been used for this purpose for several years. 

 It gave no residue when evaporated, was neutral, and gave no 

 colour with Nessler's reagent. 



Preparation and Analysis of the Simple Solutions. 



The simple solutions were prepared by dissolving about the 

 amount of salt required for the strongest solution, and subsequent 

 diluting. The concentration in each case was determined by 

 volumetric analysis. A solution of silver nitrate was used in 

 estimating the chlorine in the potassium and sodium chlorides, 

 and the amounts of salt present were calculated from the data 

 thus obtained. 



In making an analysis I c. c. (or 5 c. c.) of the solution at 

 18C was drawn off by a pipette, placed in a flask, diluted, and 

 coloured distinctly with neutral potassium chromate. Silver 

 nitrate standardised at 18C was run in from a burette, and a 

 glass bulb filled with potassium chromate of the same shade as 

 the solution being analysed, was held before the eye. The end 

 point by this means could be seen quite sharply. 



A solution of ammonia was employed for estimating the 

 hydrochloric acid, with cochineal as an indicator. 



The pipettes and burettes used were tested by weighing the 

 water which they delivered. They were found to be accurate 

 to 0.1 per cent. 



