86 Prof. A. J. Brown. Selective Permeability of the [Jan. 23, 



of sodium chloride is about 125 atmospheres, the power with which water is 

 absorbed by the seed contents probably corresponds to a pressure somewhat 

 in excess of this value. 



Table I contains the results of a further series of determinations, made 

 with a variety of solutes, in which seeds of H. vulgare were steeped in the 

 liquid until equilibrium was established ; in all cases the solutions were of 

 volume normal strength, i.e., they contained a molecular proportion in grammes 

 of the dissolved substance per litre of solution. 



Table I. 



Solute. 



Percentage of water 

 absorbed. 



NaCl 



37 -4 



NaNO, 



37 -9 



KC1 



37 -1 



KN0 3 



40-5 



CuS0 4 : 



41 -7 



H 2 S0 4 



37 -8 





42-2 





39 -3 



Water (control) 



74 -3 



Although the various solutes appear to regulate the diffusion of water 

 into the seeds in a very similar manner, minor differences are observable ; 

 thus, contrasting sodium chloride with potassium nitrate, there is an excess 

 of 3 per cent, in the amount of water absorbed from the solution of the 

 latter. This small excess was at first regarded as an experimental error, 

 the method being open to suspicion when small differences are concerned ; 

 but as all experiments made subsequently with the same salts have consistently 

 afforded similar results, there can be little doubt that the small departure 

 is real. Small differences are also noticeable between the values for cupric 

 sulphate and tartaric acid in comparison with that afforded by sodium 

 chloride. 



As the amount of water present in a volume normal solution varies from 

 substance to substance, experiments were now made with iveight normal 

 solutions equivalent in strength, prepared by dissolving the solute always in 

 the proportion of 1 gramme molecular proportion to 1000 grammes 

 (55*5 molecular proportions) of water. The results obtained are recorded 

 in Table II, the values in the last column being those observed when 

 equilibrium was established. Although they are in close general agreement 

 with those obtained on using volume normal solutions, small specific 

 differences between the salts become apparent, the potassium salt being less 



