1916] SHULL—SOILS 13 
abundance seem to have a somewhat lower equilibrium point than 
those with high fat and protein content. 
The osmotic pressure of the sulphuric acid calculated from the 
vapor pressure formula given runs from tooo to 1350 atmospheres. 
The validity of the vapor pressure formulae will 
be discussed later. If colloids absorbed as much ats” 
moisture from a saturated atmosphere as from Ls 
water, it might be safe to assume that the inter- 
nal force of the seeds is equal to the osmotic 40 
force of the solution. But if von ScHRODER’s 
work holds for all colloids, this vapor pressure 35 
method may give abnormal values. If the colloids ; 
always tended to take up more water when in con- 30 
tact with the fluid, above the equilibrium point as 
well as below, the values given here would be too 25 
low, as the equilibrium point would be shifted c 
toward the stronger acids. If, on the other p20 
hand, intake is increased below the equilibrium 
point, and loss is increased correspondingly by 
above the equilibrium point, the shape of the 
curve would be changed, but the 
equilibrium point would remain fixed. + 
a ‘ 2 - eon ae 2 : 
c Ee 
10845 (73 65755450 4=— 3035 285s tCs«CO 
Fic. 2.—Curves of moisture equilibrium of seeds suspended over sulphuric acid: 
a, Pisum satiowm; b, Stowell’s evergreen sweet corn; c, Xanthium pennsylvanicum; 
shai, strength of sulphuric acid; ordinates, moisture intake by seeds in percentage 
of air-dry weight. 
The values run higher with the H,SO, than with the lithium 
chloride solution, as given in table III. There is one source of 
possible discrepancy which needs to be mentioned. The vapor 
pressure tests were all made in Kansas, where the climate averages 
drier than at Chicago, while the osmotic measurements were all 
