WORK OF J. N. PEARCE. 59 



The object of the conductivity measurements was to determine the dissociation of 

 the solution in question, as accurately as possible, in order that the theoretical lower- 

 ing produced by the substance, if there was no hydration, might be calculated. 



The freezing-point measurements give us, on the other hand, an exact proportion 

 between the number of dissolved particles, molecules, ions, or the hydrates of these, 

 and the number of molecules of the solvent acting as such. 



EXPERIMENTAL. 



Freezing-point Apparatus. For all concentrations, from the most dilute up to 

 those which could not be frozen by mixtures of salt and ice, a bath of rather large 

 dimensions was used. The outer cylindrical vessel was made of heavy galvanized 

 iron diameter 31 cm., depth 26 cm. covered on the outside by a heavy coat of 

 felt to prevent radiation. Within this was a much smaller vessel of the same mate- 

 rial with a tightly fitting cover. Soldered around the large hole in the center of the 

 cover is a conical-shaped collar, which holds firmly the cork through which the ther- 

 mometer is inserted. By this means the thermometer always reaches to the same 

 depth in the solution. A second smaller hole in the side is provided for the passage 

 of the stirrer. To the bottom and on the outside was soldered a short bolt, which, 

 in turn, was screwed into a nut soldered to the center of the outer vessel. In this 

 way firm support was given the inner vessel and danger of floating was avoided. 

 The freezing-tube proper was a large glass tube length 17 cm., diameter 5 5 cm., 

 of 250 c.c. capacity. It was supported within the smaller vessel at the bottom by 

 a cork, and at the top by a cork ring which rested upon an iron ledge soldered to the 

 inside of the small vessel. These dimensions allowed for an air-space of about 2 cm. 

 all around. 



The stirrer consisted of a gold-plated brass disk, with one large hole in the center to 

 permit the passage of the thermometer, and around this smaller holes about 0.7 cm. 

 in diameter. 



Near the top of the large outer cylinder was soldered a small tube which served to 

 keep the water in the bath at constant level. 



By means of a bath of these dimensions the temperature of the freezing-mixture 

 could be kept constant for five or six hours. No attempt was made to control exactly 

 the temperature of the bath, but experience taught us that only those freezing-mix- 

 tures which required from forty seconds to one minute to cool the solution 0.1 C. 

 could be depended upon for reliable results. 



For solutions requiring freezing-mixtures of calcium chloride, and in the ordinary 

 cryoscopic apparatus consisting of a battery jar, two test-tubes were used. 



For this work four thermometers of the Beckmann type were employed, whose 

 temperature ranges were 1.1, 5.6, 12.2, and 25 C. These were graduated into 

 0.002, 0.01, 0.02, and 0.05, respectively (whole scale) . By means of a lens it was 

 easy to read to a tenth of the above graduations. 



CONDUCTIVITY. 



The conductivity measurements were made by means of the well-known Kohl- 

 rausch method, using the Wheatstone bridge, induction coil, and telephone receiver. 



