WORK OF J. N. PEARCE. 



69 



BARIUM NITRATE. 



Owing to the very small solubility of this salt we did not attempt to make meas- 

 urements beyond 0.15 normal. Barium nitrate has special interest in that it is the 

 first salt thus far studied in this investigation which, under ordinary conditions, 

 crystallizes without water. 



It will be seen that, like strontium nitrate, the molecular lowering of the freezing- 

 point decreases regularly as the concentration increases, without showing a minimum 

 value. The amount of water held in combination decreases rapidly and reaches a 

 minimum at 0.1 normal. The hydration per molecule is very small, as we should 

 expect, since the salt in its solid state is anhydrous. In the more dilute solutions, 

 however, where the ions predominate, the hydration is of the same order as that of 

 the other nitrates of the alkali earths. This is, indeed, convincing proof that the ions 

 themselves have great hydrating power. 



It was pointed out in the introduction that if there were no hydration the corrected 

 molecular lowering of the freezing-point should be equal to the corrected lowering. 

 A glance at table 52 will show how closely the assumption agrees with facts. The 

 values for the corrected freezing-point lowerings for the three most concentrated 

 solutions, in which the hydration is least, are only about 1 per cent higher than the 

 calculated values. Moreover, if there is no hydration, and if we may disregard the 

 effect of viscosity upon the velocity of the ions, we should expect the dissociation as 

 measured by the conductivity and freezing-point methods to be the same. That 

 this is true may be seen by consulting the values of a for 0.075, 0.10, and 0.25 normal 

 in table 52. Owing to slight hydration, the amounts of dissociation, as measured 

 by the freezing-point method, are slightly higher than those measured by the con- 

 ductivity method. The curves for barium nitrate are given in figs. 24 and 25. 



