TO THEIR STATE OF IONIZATION MACGREGGR. 223 



of accuracy. The expansion of water was taken, according to 

 his observations, to be 3 878 for the same interval. 



Bruckner's observations of viscosity were made at 15 C. ; 

 but he gives an interpolation formula, applicable between 15 

 and 20, by means of which at least approximate values for 18 

 were obtained. His values for water at 15 and 20 do not 

 agree well with those given by Landolt and Bornstein. I have 

 therefore taken 0'010613 as the viscosity at 18 of the water 

 used by him, a value which has to his value at 15 the same 

 ratio as Landolt and Bornstein's for the same temperatures. 

 The actual concentrations of Bruckner's solutions differed from 

 those given in the tables below by about O'l per cent. ; but so 

 small a difference could produce no appreciable error in the 

 result. He gives as his "mean probable error of observation," 

 2'4 in the fifth place of decimals for sodium-chloride solutions, 

 and 1'8 for those of potassium chloride. 



Bother's observations of surface-tension were made at 15 

 and are therefore not precisely comparable with calculated 

 values based on the values of ionization -coefficients for 18. 

 From Kohlrausch's data,* how T ever, it would appear that 

 between 15 and 18 in the case of potassium-chloride solutions 

 containing 0'5 and 3 gramme-molecules per litre, the ionization- 

 coefficient changes only by about O'l 3 and 1'3 per cent, respec- 

 tively ; and in the case of sodium-chloride solutions of the same 

 concentrations only by about 0'4 and 0'6 per cent, respectively. 

 For the more dilute solutions, therefore, my calculations will be 

 practically comparable with Rother's observations. He seems to 

 regard his determinations as possibly in error by 5 to 8 in the 

 the third place of decimals. The surface-tension of the water 

 he used he found to be 7'357. 



Bender's observations of refractive index were made at 

 15 C., but were reduced to 18 by means of data provided in 

 his paper, based on observations made by Fouqu^f. The 

 refractive index of the water he used he found to be 1 '333 10 



*Wied. Ann. xxvi. (1885) p. 223. 

 t Compt. Bend. Ixiv. (1867) p. 121. 



