60 WORK OF J. N. PEARCE. 



The wire was calibrated according to the method of Strouhal and Barus. 1 The resist- 

 ance coils were made by Leeds, of Philadelphia, and had been carefully calibrated. 

 Conductivity cells of two types were used. For the more dilute solutions cells of 

 the type devised by Jones and Bingham 2 were employed. For the more concentrated 

 solutions U-shaped cells, similar to those used by Jones and Getman, 3 were found to 

 be very convenient. 



All conductivity measurements were made at C. For this purpose a small pail 

 was filled with finety crushed ice, moistened with distilled water, and the cells packed 

 into the ice as tightly as possible. The small pail was then placed in a spacious pan 

 and the space between the pail and the pan filled with finely crushed ice. 



SPECIFIC GRAVITY. 



Since the solutions were made up at 20, we thought it best to determine their spe- 

 cific gravities at the same temperature. The 20 bath was a large galvanized-iron 

 tub. By means of a very small flame below, and a stirrer within, driven by a hot-air 

 motor, the temperature could easily be kept to within 0.1 of the desired temperature. 

 Throughout this work six pyenometers of the Ostwald type were employed. They 

 were carefully calibrated with pure, redistilled water. 



The flasks and burettes used in this work were carefully calibrated at 20 by the 

 method of Morse and Blalock. 4 



SOLUTIONS AND SOLVENT. 



Kahlbaum's "chemically pure " materials were used in every case, and were further 

 purified whenever it was found desirable to do so. The method of preparing the 

 solutions varied according to the solute employed. In general, a solution of slightly 

 greater concentration than 2 normal was first made, and from this, by successive 

 dilutions, the lesser concentrations were obtained. Whenever possible, the mother- 

 solution was made up by direct weighing; when the nature of the solute did not 

 permit it to be weighed, the mother-solution was diluted to convenient strength, and 

 portions of the dilute solution were standardized cither by gravimetric or volumetric 

 methods. 



The water which was used in all the solutions was purified according to the method 

 of Jones and Mackay. 5 Ordinary distilled water was twice redistilled from an acidified 

 solution of potassium dichromate, and the steam from the second distillation passed 

 through a boiling solution of barium hydroxide. It had, at 0, a conductivity of 

 about 1.2 X10" 6 to 1.7 Xl(T 7 . 



CALCULATION OF THE COMPOSITION OF THE HYDRATES. 



The method of calculating the amount of water combined with the dissolved sub- 

 stance is essentially the same as that used by Jones and Bassett. 6 We have given 

 the observed molecular lowering of the freezing-point, the specific gravity of the solu- 

 tions, and the dissociation. The observed molecular lowering is corrected for the 

 difference between 1 ,000 grams and the amount of water actually present in 1 liter 

 of the solution. This gives the true molecular lowering which would be produced by 

 the substance at the dilution in question if there were 1,000 grams of water present. 



Wied. Ann., 10, 326 (1880). 'Zeit. phys. Chem., 46, 244 (1903). /6., 19, 83 (1897). 



J Amer.Chera.Journ.,34,481(1905). Amer.Chem. Journ., 16,479 (1894). 'Ibid., 33, 843 (1905): 34, 298 (1905). 



