﻿974 Mr. J. Kendall on the Solubility of 



Conductivity of Bicarbonate Solutions. 



The importance of measurements of electrical conductivity 

 in the determination of the purity of a sample of water, and 

 especially in the discovery of any sudden change in the 

 degree of hardness or in the salt content of a town supply, 

 has only recently been recognized. An apparatus for the 

 above purpose (the Dionic Water Tester) is already in the 

 market. 



The introduction of the measurement of electrical con- 

 ductivities into water analysis has rendered necessary the 

 accurate determination of the conductivities of bicarbonate 

 solutions. The values for calcium bicarbonate are clearly of 

 special importance. 



The conductivity of solutions of sodium bicarbonate has 

 been investigated by Walker and Cormack (J. C. S. lxxvii. 

 p. 10 (1900)) for the purpose of determining the velocity of 

 the HCCV ion. Experiments were carried out at 18° C. 

 between dilutions of 32 and 512. Within this range no 

 difference was observed between solutions diluted with pure 

 water and with water saturated with carbon dioxide. 



In the following experiments the dilution was carried 

 further, solutions being used from v = 10 to v = 10,000, at a 

 temperature of 25° C. The conductivities were determined 

 in a Cantor cell, with the use of a rotating commutator and 

 a galvanometer. Much more .accurate values can be obtained 

 by this method for dilute solutions than with the usual 

 induction-coil and telephone. 



Sodium bicarbonate solution was made up by bubbling excess 

 of carbon dioxide through sodium hydroxide solution, freshly 

 prepared from metallic sodium. The solution was standardized 

 both volumetrically by neutralization with a known solution 

 of hydrochloric acid, and gravimetrically, by neutralizing 

 100 c.c. with hydrochloric acid in a platinum basin, evapo- 

 rating carefully to dryness, and weighing the residue. 



Two series Gf dilutions were made, one with pure water, 

 the other with water containing excess of carbon dioxide. 

 The pure water was prepared by distillation, in the open 

 air, of water to which a little Nessler's solution had been 

 added, as described before ; its specific conductivity was 

 1'lOxlO" 6 . The correction for the water conductivity is 

 made as follows. The part due to carbonic acid is, at most, 

 •70 X 10" € (Walker and Cormack, J. C. S. lxxvii.p. 11 (1900)). 

 The influence of this on the bicarbonate solutions is negli- 

 gible up to very high dilutions. The remaining conductivity, 

 •40 x 10~ 6 , is directly subtracted from the observed values, as 

 below. The values given are -the equivalent conductivities of 

 the solutions, expressed in reciprocal ohms. 



