184 ELECTRIFICATION OF WATER 



Negatively charged particles of water are attracted powerfully by 

 bivalent or polyvalent cations and repelled powerfully by bivalent 

 or polyvalent anions. We may, therefore, expect that when we make 

 a CaCl2 solution sufi&ciently acid through the addition of HNO3 or 

 HCl the curves showing the influence of the concentration of the elec- 

 trolyte on the rate of diffusion of water should be similar to the curves 

 in Figs. 3, 4, and 6, representing the influence of different concen- 

 trations of neutral solutions of Na2S04 upon the rate of diffusion of 

 positively charged particles of water through the same membranes. 

 Fig. 7 shows that this is correct. The two upper curves represent the 

 influence of variations in the concentration of CaCl2 or Ca(N03)2 dis- 

 solved in m/ 1,024 or m/128 HNO3 or HCl. These acid solutions of 

 CaCl2 or Ca(N03)2 cause a negative electrification of the water par- 

 ticles diffusing through the membrane. The attraction of the nega- 

 tively charged water particles by Ca ions increases with an increase 

 in the concentration of the calcium salt up to m/64, when the curve 

 falls until the concentration of the calcium salt is m/4 where a mini- 

 mum is reached. After this the gas pressure effect makes itself felt 

 and the curve rises rapidly with rising concentration. In this case 

 the drop in the two curves for the acid solutions when the concentra- 

 tion of the calcium salt exceeds m/64 is due to the fact that beyond a 

 certain concentration of the calcium salt the repelKng effect of the 

 anion (CI and NO3) upon the negatively charged particles of water 

 increases more rapidly with increasing concentration than the attrac- 

 tive action of the Ca ion. 



The fact that the curve for Ca(N03)2 in m/128 HCl is sKghtly 

 lower than the curve for CaCl2 in m/ 1,024 HNO3 is due to the "nega- 

 tive osmosis" caused by acid solutions of sufficient concentration, as 

 will be shown in the next chapter. 



The three lower curves of Fig. 7 represent the influence of various 

 concentrations of CaCl2 upon positively charged particles of water 

 and these curves are similar to those given for the effect of neutral 

 solutions of CaCl2 in Figs. 5 and 6. When CaClo is dissolved in m/128 

 KOH the rise and drop of the curve become a Httle more marked than 

 when the solution of CaCl2 is neutral. The reason for this will become 

 clear through the discussion in the next chapter of the phenomenon 

 of negative osmosis caused by Ca(0H)2. 



