Issued September 1, 1909. 



United States Department of Agriculture, 



BUREAU OF CHEMISTRY Circular No. 45. 

 H. W. WILEY, Chief of Bureau. 



A NEW METHOD FOR MEASURING THE ELECTROLYTIC DISSOCIATION 

 I OF WATER. 



By C. S. HUDSON, Assistant Chemist. 



In a recent article a it was shown that the measurements of the veloc- 

 ity-coefficient of the mutarotation of glucose in acid, alkaline, or neutral 

 solutions are accurately expressed over the whole range by the formula 

 k= AH-B(H') + C(OH'), where k is the velocity-coefficient, A, B, and C 

 ape constants, and H' and OH 7 are the concentrations of hydrogen- and 

 hydroxyl-ions, respectively, in the solutions. For neutral solutions or 

 pure water let the velocity-coefficient be written k w , and the hydrogen- 

 ion concentration which is equal for this case to that of the hydroxyl-ion 

 be written HW'; the above formula then takes the form, for pure water 

 or neutral solutions, kw = A + ( B + C ) H w * . Solving this expression gives 



(k A) 



H w ' = -j^ . This relation gives a new method for measuring the 

 (B-f 0; 



hydrogen-ion concentration or, in other words, the electrolytic disso- 

 ciation of water, for the four quantities on the right-hand side of the 

 equation can be determined experimentally by measuring the rate of 

 mutarotation of glucose in ordinary distilled water and in acid and 

 alkaline solutions. The first formula above is based on measurements 

 of the rate of mutarotation of glucose in alkaline solutions by Osaka, b 

 and similar ones in acid solutions by the writer, a and has the form, as 

 was shown in the previous article, k = 0.0096 + 0.258 (H') -f-9750(OH'), 

 k being expressed in minutes and decimal logarithms, H' and OH' 

 in gram-molecules per liter, and the temperature being 25 C. The 

 constants for glucose at 25 are therefore A = 0.0096, B = 0.258, and 

 = 9750. The velocity-coefficient for pure water was found at the same 

 ,time to be k<#= 0.0106, which agrees closely with the value which Osaka 

 found, 0.0104. The substitution of these constants in the formula pre- 

 ceding gives H w ' = 1.0(10)~ 7 , a value which is in close agreement with 

 those that have been found in the past from measurements that are 

 based on entirely different facts and principles. In the following table 

 is recorded a list of the values for the hydrogen-ion concentration of 

 pure water, which have been found by various investigators, together 

 with a statement of the method by which the value was found. Those 

 values which were later shown to be erroneous are inclosed in brackets. 



J. Amer. Chera. Soc., 1907, 23:1571^ 

 b Zts. physik. Chem., 1900, 55:702. " 



