1916] SHULL—SOILS 9 
tested were suspended in shallow paper baskets a few millimeters 
above the surface of the acid, the baskets being hung on cotton 
threads fastened to the corks with carna-uba wax. All metallic 
condensers were thus avoided. After the seeds were carefully 
weighed and arranged, the bottles were sunk in a trough of running 
water to prevent any considerable changes in temperature. Con- 
densation effects due to change of temperature could not occur 
except over water, for MiTscHERLICH (21) has shown that even 
ro per cent sulphuric acid will prevent deposition of dew in deter- 
mining hygroscopic coefficients of soils. It may be questioned 
whether the inclosed space actually reaches the vapor pressure of 
the solution, for, as H1Lcarp (17) points out, it is most difficult 
to secure complete saturation in the case of water vapor. How- 
ever, the space of air to be brought into equilibrium with the 
solution vapor pressure in these experiments is very small, and it 
seems probable that the whole system of liquid, air, and seed 
comes to an equilibrium pressure in the time of the experiment, 
except possibly in the case of water. After allowing 15 days for 
reestablishment of equilibrium by the seeds, the point of no change 
was determined by weighing. 
The osmotic pressure of the sulphuric acid is roughly deter- 
. J~f*: SRT 
mined by the use of the vapor pressure formula P 7 9 3 ae 
in which f is the vapor pressure of pure water at the temperature 
of the experiment, J* the vapor pressure of the acid, M the molec- 
ular weight of the solvent’s vapor, T the absolute temperature, 
S the density of the sulphuric acid, and R the gas constant. The 
osmotic pressure (P) is given in grams per square centimeter, and 
must be reduced to atmospheres. This formula has been developed 
. for dilute solutions and does not hold accurately for high concen- 
trations, but there are at present no data on which to base more 
accurate estimations. The boiling-point method yields a result 
close to that given by this formula for sulphuric acid, as will be 
shown later. 
The earliest soil measurements were made with no. 2/o sand. 
Seeds of known weight were packed firmly in sand of known 
water content in paraffined wire baskets, and allowed to come to 
