OSMOTIC PRESSURES OF AQUEOUS SOLUTIONS OF CALCIUM FERROCYANIDE. 197 



atmospheres at C. AMAGAT'S value for the true coefficient is 0'0 4 0392 ; hence that 

 of the glass is 0'0 4 0223 at C. 



The agreement between this result and STRAUBEL'S value seems to prove that no 

 serious experimental error has been incurred. 



(2) Corrections to be Applied to the Volume Reading. The method used is based 

 on the assumption that the pressure inside and outside the compressibility tube is the 

 same, but it must be remembered that this can only be the, case at the be<riiminir 



/ O O 



of the experiment (i.e., when the level of the mercury is the same inside and outside 

 of the compressibility tube), for when the mercury has been caused to rise in the stem, 

 there is an excess of pressure on the outside of the compressibility tube due to the 

 amount of the rise of the mercury above the level outside. The change in volume of 

 the compressibility tube due to this was determined by special experiments, and a 

 correction has been applied to both the volume and the pressure. The latter 

 correction, in view of the nature of the results required in this paper, is of no 

 importance. 



Results. 



The following tables give the corrected results obtained : 



EXPERIMENTS on the Compressibility of Water at C. 



The 1st column gives the range of pressure in atmospheres ; the 2nd column gives 

 the coefficient of compression per atmosphere in that range ; the 3rd column gives 



AMAGAT'S results for the same range. 



The compressibility of the calcium ferrocyanide solution is only required for the 

 purpose of calculating the osmotic equilibrium pressure from vapour-pressure measure- 

 ments, and as the latter were only made on solutions whose weight concentration 

 varied from 50 to 31 gr. of anhydrous salt per 100 gr. of Aq, the compressibility 

 measurements recorded here were restricted to this range. 



The following table gives the results obtained for the solutions at C. Column 1 

 gives the weight concentration in grammes of anhydrous salt per 100 grammes of 

 water of the solution ; column 2 gives the range of pressure ; column 3 gives the 

 corresponding coefficient per atmosphere : 



