82 Conductivity of Aqueous Solutions. Part IV. 



37. THE SPECIFIC-VOLUME DATA. 



The results of the specific-volume measurements are given in table 17. 

 The first four columns need no further explanation. The fifth column 

 gives the number of grams of solution which were weighed into the 

 dry bomb at the start. The sixth column gives the volume expressed in 

 cubic centimeters which, at the temperature of 100 (at which the volume 

 of the bomb was determined) corresponds to the observed ratio of the 

 conductances at the upper and lower electrodes. This volume was obtained 

 by interpolation from a plot made as described in section 8, Part II. 

 The actual volume occupied by the solution at the higher temperature is 

 greater than this by an amount equal to the expansion of the bomb upon 

 heating from 100 to that temperature. The temperature-coefficient of 

 volume expansion of the steel shell of the bomb is assumed to be 0.000038 

 per degree, upon the basis of determinations made by R. B. Sosman in 

 this laboratory. The seventh column gives the specific volume of the solu- 

 tion at the temperature of observation. It is obtained by dividing the 

 values of the preceding column, after correcting them for the expansion 

 of the bomb as just described, by the weight of solution given in the fifth 

 column. The eighth column gives the values of the specific volumes at 

 4 of the various solutions used. The last column gives the ratio of the 

 specific volume at the round temperatures 218, 281, and 306, to that of 

 the same solution at 4. Thus, this ratio shows the volume occupied by 

 that quantity of solution which at 4 has a volume of 1 c.cm. The values 

 are obtained from those of the preceding column by reducing them to 

 these temperatures by means of the temperature-coefficient obtained from 

 our specific-volume values, and then dividing the results by the specific 

 volumes of the solutions at 4. 



38. SUMMARY OF THE SPECIFIC-VOLUME VALUES. 



The final values of the ratio of the specific volume at various tempera- 

 tures to that at 4 are summarized in table 18. For comparison the values 

 obtained by Noyes and Coolidge (section 12, Part II) for a 2 milli-normal 

 solution of sodium chloride, which are substantially identical with those 

 of pure water, are given in the table within parentheses. For the 100 

 milli-normal solution of this substance they found 1.187 at 218 in fair 

 agreement with our value and 1.423 at 306 in complete agreement with 

 our value. A comparison of values for the different 50 milli-normal solu- 

 tions shows that these all expand considerably less than water itself, the 

 ratio being 1.425 - 1.429 instead of 1.437 at 306. Up to 218 the expan- 

 sions of even the 100 milli-normal solutions of all the different salts are 

 substantially equal (ratio 1.180-1.182) ; but at 306 the ratios for silver 

 nitrate and barium nitrate, the salts of the metals with high atomic 

 weights, are somewhat smaller than those for the other three salts, being 

 1.426 instead of 1.429 at 50 milli-normal. 



