ON THE OSMOTIC PRESSURES OF CALCIUM FERROCYANIDE SOLUTIONS. 321 



Results of Density and Equilibrium Pressure Measurements. 



The foregoing table gives the results obtained : Column (l) gives the date ; (2) the 

 weight concentration, i.e. the number of grammes of anhydrous salt to 100 gr. of water ; 

 (3) the density of the solution at C. ; (4) the percentage content of water in the 

 hydrated salt ; (5) the tube employed ; (6) the apparent turning-point, that is, the 

 point at which there was no observable movement of the water-level in the gauge ; 

 (7) the guard-ring leak (see Part I.) ; (8) the time the pressure was on the solution ; 

 (9) the quantity of anhydrous salt passed through the membrane ; (10) the change 

 in the water-level caused by the increment of pressure ; (11) the apparent turning- 

 point corrected for guard-ring leak ; in this case it is the equilibrium pressure. 



The following table gives the mean values derived from Table L, together with the 

 theoretical osmotic pressures calculated on the assumption that BOYLE'S law holds for 

 these solutions. 



Column (1) gives the weight concentration, i.e. the number of grammes of solute to 

 100 gr. of solvent ; (2) gives the corresponding densities ; (3) the number of gram- 

 molecules of anhydrous salt in the litre of solution ; (4) the corresponding equilibrium 

 pressures ; (5) the osmotic pressure calculated from BOYLE'S law, assuming 

 KT = 22-41. 



All molecular weights have been calculated with H = 1. 



TABLE II. 



The agreement at the two lower concentrations between the BOYLE'S law osmotic 

 pressures and those directly observed is remarkable. But as calcium ferrocyanide 

 solutions are conductors of electricity, and therefore presumably ionised to a 

 considerable extent, we should expect the observed osmotic equilibrium pressures to 

 be higher than the calculated. This discrepancy led to similar work being done on 

 solutions of strontium and potassium ferrocyanides, and the following tables give the 

 results. 



VOL. CCIX. A. 2 T 



