714 EXPERIMENT STATION EECORD. 



(5) The humus was found to oocur in soils in forms which varied in ease 

 of oxidation. 



(6) The quantities of plant food constituents dissolved by treatment with 

 steam or by oxidation calculated to a soil depth of 20 cm. and the amoiints 

 taken up by plants show a definite relation only in the case of potash, but is 

 so consistent in case of this constituent that treatment with steam seems to 

 be well adapted for the determination of available potash in soils. Apparently 

 potash is also set free during the grow^th of plants either as a result of decay 

 or of root activity. 



(7) The pot exiieriments showed that the percentage of mineral matter in 

 fertilized plants was usually much smaller tlian in unmanured plants, probably 

 due to the more rapid growth of the plants. The absorbent power of the soil 

 for water, as well as the use of fertilizers, reduces evaporation, and tlius aids 

 the growth of plants by furnishing a more uniform supply of water. 



(8) It was found that soils possess a small but decided osmotic pressure, and 

 this furnishes a means of securing valuable information as to the solubility 

 of the soil constituents. Suggestions are made as to the application of meas- 

 urement of osmotic pressure in the study of soils. 



(9) According to the authors' observations very small amounts of soluble 

 salts (a few milligrams in 100 gm. of soil) may be observed by means of 

 osmotic pressure. The osmotic pressure was also found to stand in direct 

 relation to the amount of dry matter in plants grown on the soil. 



(10) The amount of water entering the osmometer, which in these experiments 

 consisted of clay tubes and also filter cylinders, depended upon the thickness 

 of the tube and the kind of semipermeable membrane used. Clay filter cylin- 

 ders which under a pressure of 1^ atmospheres allowed 900 cc. of water to 

 pass through in 10 minutes were found to be most suitable. Such cylinders, 

 provided with a double semipermeable membrane consisting of one side of glue 

 solution and formaldehyde and on the other of potassium ferrocyanid and 

 copper sulphate, furnish a very durable osmometer, which can be used six times 

 if after each test it is washed out and treated (hardened) with formaldehyde. 



(11) With filter cylinders of lower permeablity (700 cc. of water in 10 

 minutes) a slower exchange of solution occurs, but the relationship remains 

 the same between the various salts and the soil if tubes of the same permea- 

 bility are employed. For comparative purposes it is recommended that sub- 

 stances of known osmotic pressure, as for example, one hundredth-normal 

 ammonium sulphate or one hundredth-normal saccharose, be used. 



(12) The method may also be used for the determination of the molecular 

 weights of certain substances since the amount of water entering the osmometer 

 stands in inverse relation to the molecular weight. 



The water problem in agriculture, E. J. Russfxl (\nture [London], 78 

 (1908), Xo. 2023, vp. 322, 323). — Recent reports on soil moisture and its con- 

 servation, more particularly that of J. W. Leather on the loss of water from 

 soil during dry weather (E. S. R., 20, p. 214), are briefly reviewed in this 

 article. 



Tlie loss of water from soil, C. von Seelhobst (Jour. Landw., 56 (1908), No. 

 2,. pp. 208, 209; abs. in Chrm. ZentN., 1908, II, No. 7, p. 632).— It was found 

 that in cylinders recently filled with soil the percolation was greater and evap- 

 oration less than in case of cylinders which had been filled for some time. 



Studies of soil moisture in the Great Plains reg-ion, F. J. Alway (Jour. A (jr. 

 Sci.. 2 (1908), No. //, pp. 333-3-'i2). — These studies were made in connection 

 with a series of investigations which have been noted from time to time 

 (E. S. R., 19, p. 516). The observations reported were made during July, 1904, 



