326 ON THE CALCULATION OF THE CONDUCTIVITY OF 



not quite to that accuracy. In using them for making analyses 

 volumes of 30 c. c. or over were delivered. 



Analyses. 



The strength of NaCl solutions was found by volumetric 

 determination of the chlorine according to Mohr's method. 

 Many of them also, particularly the stronger ones, were made 

 up by weighing dry NaCl, which had been kept in a desiccator, 

 in calibrated flasks, and filling up with water. 



The Bad 2 solutions were analyzed by precipitating the 

 barium with Na 2 SO 4 . The barium sulphate was collected on 

 filters and its amount determined in the ordinary way. In 

 many cases also the amount of chlorine in the filtrate was 

 determined volumetrically. 



The volumetric analyses were not so reliable as the gravi- 

 metric, the error of the former sometimes reaching five-tenths 

 of one per cent, though generally in the direct analyses of the 

 chlorine, one or two tenths. 



Conductivity Measurements. 



The conductivity of the solutions whose strength had been 

 determined in these various ways was measured by Kohlrausch's 

 telephone method. The bridge wire, made of German silver, 

 was divided into thousandths, which again admitted of easy 

 subdivision by the eye into tenths. Of a set of four platinum 

 resistances in the instrument, viz., 1000 ohms, 100, 10, and 1, 

 the first two only were used. These were certified by Queen 

 &; Co., of Philadelphia, to be correct to one-fiftieth of one per 

 cent. A number of solutions were compared with both of these 

 resistances, and the difference between the conductivities thus 

 measured lay within the limits of error. 



To contain the solutions during the measurement of conduc- 

 tivity, two cells of different type were used. One was in the 

 shape of all-tube, the middle part being about f inch in diameter 

 and 5 inches long, while the two arms had each a diameter of If 



