igi6] 



SHU LL— SOILS 



507. 



•40 



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 iooo to 1350 atmospheres. 

 The validity of the vapor pressure formulae will 

 be discussed later. If colloids absorbed as much 

 moisture from a saturated atmosphere as from 

 water, it might be safe to assume that the inter- 

 nal force of the seeds is equal to the osmotic 

 force of the solution. But if von Schroder's 

 work holds for all colloids, this vapor pressure 

 method may give abnormal values. If the colloids 

 always tended to take up more water when in con- 

 tact with the fluid, above the equilibrium point as 

 well as below, the values given here would be too 

 low, as the equilibrium point would be shifted 

 toward the stronger acids. If, on the other 

 hand, intake is increased below the equilibrium 

 point, and loss is increased correspondingly 

 above the equilibrium point, the shape of the 

 curve would be changed, but the 

 equilibrium point would remain Axed. 



15 



1-5 



100% 



84-5 



73 66 57.5 54 50 



39 35 26-5 



16 



H2O 



Fig. 2. — Curves of moisture equilibrium of seeds suspended over sulphuric acid: 

 a, Pisum sativum; b, -Stowell's evergreen sweet corn; c, Xanthium pcnnsylvanicum; 

 abscissae, strength of sulphuric acid; ordinates, moisture intake by seeds in percentage 

 of air-dry weight. 



The values run higher with the H 2 S0 4 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 



