1916] SHULL—SOILS 23 
” sents relative lowering of the vapor pressure of the solution as com- 
pared with that of water. His formula actually gives the relative 
eT: 
P 
lowering. NERNST, however, uses for this factor in the 
equation, and with concentrated' solutions it is quite a different 
thing. In a concentrated solution, where the relative lowering of 
the vapor pressure is 0.75, NERNST’s formula will give a value for 
the osmotic pressure 4 times as great as that given by WALKER’S - 
formula. 
In the third English edition of NERNsT he gives an. equation 
for this calculation which he claims gives a very exact value for 
the osmotic pressure from vapor pressure. His equation is as 
follows: 
Fa 
: 0.082%. 7). 1000 » ek 
= i In’ 
The physical chemists claim that this formula should hold in so 
far as it includes the factors involved. But even this exact 
formula does not take care of the change in volume occurring on 
dilution of the acid, nor for the heat of dilution, which is very 
considerable in the strong acid solutions over which equilibrium 
of moisture vapor was obtained in these experiments. 
I have chosen to use WALKER’S formula because it actually 
gives the relative lowering of the vapor pressure, as it is supposed 
to do. However, it is perfectly clear from this discussion that the 
osmotic pressure of sulphuric acid of any given concentration, 
especially of high concentration, cannot be measured accurately 
by any single vapor pressure formula suggested to date. 
he measurements made over sulphuric acid give values, there- 
fore, which are merely suggestive. They indicate that the internal 
forces of air-dry seeds of all kinds are very high, and confirm the 
high values obtained by the osmotic solution method. But the lat- 
ter method only, I believe, can be relied upon for the measuring 
of the internal forces of seeds until the vapor pressure relations are 
more perfectly understood. 
The main conclusion in regard to these seed measurements may 
be stated briefly thus: It is possible, with seeds having a perfectly 
semipermeable coat, to measure the water-attracting internal forces 
