1916] SHULL—SOILS ie i 
made at Chicago. The hygroscopic moisture of the seeds was 
uniformly near 5.5 per cent in Kansas,’ while at Chicago the 
hygroscopic moisture was rarely less than 7 per cent, usually above. 
The equilibrium point would naturally run higher, therefore, in a 
drier climate. However, it is not claimed that the discrepancy 
would entirely disappear if repeated with seeds of 
the same moisture content. = 
There seems to be little doubt as to the high : 
osmotic strength of the sulphuric acid, for the 
boiling-point method of measuring osmotic press- 
ure gives a value in close agreement with those 
' just given. The boiling point of 53 per cent H.SO, 
is 128.5° C. If for each rise of o.52° C. we may 
assume an osmotic pressure equal to one mole of 
dissolved substance (H6OBER, Phys. Chem. p. 19), 
this strength of sulphuric acid should have an 
osmotic pressure of 1227 atmospheres. 
At all events, it is safe to’ con- 
clude that air-dry seeds possess a very os 
high internal attraction for water ; 
r ” . BPO — “ “ 0 
< ee : 
4 T T 7 : Sg 7 J A se mee ve 
100 7 84.5 73 66 57.554 50 39 35 26.5 16 H0 
Fic. 3.—Curves of moisture equilibrium of seeds suspended over sulphuric acid: 
a, pa communis; 6, Triticum sativum; c, Oryza sativa; abscissae, strength: of 
sulphuric acid; ordinates, moisture intake by seeds in percentage of air-dry weight. 
which at the initial moment of intake is but little short of 1ooo 
atmospheres. Owing to uncertainty of the figures for sulphuric 
acid, only those obtained by direct contact with osmotically 
active solutions will be used as a standard for the following soil 
experiments: 
«Seeds sent to Washington were dried in the vacuum oven by Mr. A. B. Camp- 
BELL. Upper seeds averaged 5.48 per cent of the absolute dry weight, and lower 
seeds averaged 5.72 per cent of their absolute dry weight. 
