186 BOTANICAL GAZETTE |SEPTEMBER 
One of the most difficult problems was to secure adequate data — 
as to the size of the pressures and forces indicated by the results. 
The literature aside from the work of the physical chemists contains © 
serious disagreements, and the physical chemists have done very 
little on the osmotic pressure of concentrated solutions. Moreover, 
there is wide divergence in the interpretation of the little they have 
done. As the writer is not a physical chemist he has been at a 
distinct disadvantage in the attempt to clarify a very confusing 
situation. 
In his work on Hordeum, Brown ascribes to a saturated solution 
of NaCl an osmotic pressure of 125 atmospheres. A few years 
earlier, RActBoRSKI (28), who investigated the upper limits of 
osmotic pressure in living plant cells, cites DreTERICI as authority 
for the statement that saturated NaCl has at 20° C. an osmotic 
pressure of 375 atmospheres. RACIBORSKI gives the pressure as 
349.11 atmospheres at o° C., the saturation concentration being 
35-51 percent. The figures given by BROWN are apparently based 
on the assumption that the law announced by van’T Horr in 1887, 
that osmotic pressure is proportional to concentration, a law based 
on PFEFFER’S work a decade earlier, applies to all concentrations 
whatsoever, without. any allowance for electrolytic dissociation or 
hydration, both of which must play an important réle in the pres- 
sure of these concentrated solutions. On such an assumption the 
pressure should be near 125 atmospheres. 
That this figure is too low can readily be determined from data 
as to the electrical conductivity of NaCl derived from the Landolt- 
Bornstein tables. A 4 M solution would exceed 130 atmospheres, 
so that a saturated solution should run to 160 atmospheres or 
beyond, merely due to ionization. 
Moreover, there is reason for believing that this law of the rela- 
tion of osmotic pressure to concentration holds only for lower 
concentrations, and that still further corrections are necessary in the 
case of highly concentrated solutions; for the actually observed 
pressures depart widely from the theoretical requirements as 
concentration increases. BERKELEY and Hartiey (8) measured 
the osmotic pressure of solutions of sucrose, dextrose, and galactose 
by an igenious method, and have shown that dilute solutions give 



