JACQUES LOEB 261 



gelatin. We shall see later that the electrical effect in the lower 

 range of concentrations of AI2CI6 is not lacking, but that the low 

 ordinates are due to the action of the trivalent cation. Curves for 

 the diffusion of water into solutions of LaCls (Fig. 4), which are nearly- 

 neutral, show the same difference as those just described for AI2CI6 

 solutions. When LaCls solutions are separated from water by mem- 

 branes not treated with gelatin, the ordinates (lower curve in Fig. 4) 

 are low in the region of the electrical effect, while they rise steeply in 

 the same region when the membranes have been treated with gelatin 

 (upper curve in Fig. 4) . 



The difference in the osmotic behavior of the two kinds of membranes 

 is still rnore striking when we use solutions of acids. When we 

 separate solutions of strong acids {e.g. HCl, HNO3, H2SO4) from 

 distilled water by collodion membranes previously treated with gelatin, 

 we notice no rise but only a drop (Fig. 5) — negative osmosis — which 

 commences for H2SO4 and H3PO4 at a concentration of about m/256. 

 In the experiments represented in Fig. 5, the pressure head of the 

 solution of acids inside the bag was about 70 mm. at the beginning. 

 It dropped in 20 minutes to about 10 mm. at concentrations of about 

 m/8 or m/4 for H2SO4 and H3PO4 (Fig. 5). Owing to the fact that 

 the drop is due to the repelHng action of the anion of the acid upon 

 the negatively charged particles of water, the drop in the curves is 

 greater when the anion of the acid is bivalent or trivalent than when 

 it is monovalent. When we separate various concentrations of the 

 same acids from pure water by membranes not treated with gelatin 

 we get results of an altogether different order (Fig. 6). Instead of 

 negative osmosis we notice a powerful positive osmosis, i.e. a rapid 

 diffusion of water into the solution, and the acids behave almost 

 like the sodium salts with the same anion. By comparing Fig. 1 

 and Fig. 6 the reader will notice the same steep rise of the curves until 

 the concentration is about m/256; this rise is more considerable in 

 the case of Na2S04 and H2SO4 than in the case of NaCl and HCl. In 

 the case of these two salts and acids, the rise is followed by a drop, 

 until for the acids at m/32 and for the salts at m/16 the gas pressure 

 effect of the solution commences. The drop is not noticeable in the 

 case of H3PO4. 



