NOTES AND ABSTRACTS. 



417 



is added for which the solid material has a great attraction or affinity, the second 

 liquid will be attracted by the solid material with as much force or manifestation of 

 heat as though the first liquid were not present at all. The converse of this is 

 not true. The remarkable phenomenon of the attraction of a solid material 

 being exerted for a liquid through an enveloping solid or highly compressed film 

 of another liquid throws an abundance of light on understanding the possible 

 mechanism in the reaction between soils and soluble salts or their ions. 



As to whether the '* combined water " is chemically or physically combined, 

 it appears that it exists partly as water of hydration and partly as water of 

 solid solution, with probably the former predominating. It may, however, exist 

 all as water of solid solution, but not all as water of hydration. If we accept 

 the recent theory that all interatomic or intermolecular forces should be regarded 

 as strictly chemical, including such forces or phenomena as surface tension, 

 evaporation, cohesion, adsorption, condensation, &c, then all the " combined 

 water " is chemically combined. 



The results obtained seem to necessitate a complete and radical change of 

 many of the present conceptions regarding soil moisture. The present ideas 

 regarding the forms of water in the soil, the movement of moisture, the rate of 

 evaporation, the available and non-available moisture, must all be changed. 



There is also a close relationship between the " unfree water " (that which 

 fails to freeze at — 1-5° C.) and the wilting coefficient of soils. The amounts of 

 the combined water and the unfree water were ascertained by the dilatometer 

 method. — F. G. A. 



Soils, Salt Contents of, Determination by Freezing-point Method of the. By 



G. J. Bouyoucos and M. M. McCool {U.S. A . Jour. Agr. Res. xv. No. 6, Nov. 

 1918, pp. 331-336). — The freezing-point method is held to be an excellent 

 means of determining the absolute salt content of soils with considerable accuracy. 

 Formerly the method was restricted to the determination of the actual concen- 

 tration of soil solution at different moisture contents, but now the method may 

 be used to measure the absolute salt content of soils, and thus affords a means 

 of comparison of the absolute salt contents of soils. The salt contents of soils 

 depend upon the following factors : (1) Season of the year in which the soil is 

 collected ; (2) amount of rainfall and length of period since rainfall ; (3) tem- 

 perature and rate of evaporation ; (4) cultural conditions ; (5) depth. The 

 comparative stud}'' of the absolute salt content may be determined in the fol- 

 lowing manner. The soils are air-dry first; then a 15 grm. sample is taken and 

 placed with 10 c.c. distilled water in a freezing-tube. The soil is stirred, allowed 

 to stand, and its freezing-point depression noted. For this determination the tube 

 is placed in an ice mixture at — 2 5 0 C, and the soil is stirred with a Beckmann 

 thermometer until the temperature falls to about i° above zero point. It is 

 then left undisturbed until temperature falls to -5° below zero, when the soil is 

 again stirred to cause solidification. When this takes place, the tube is taken 

 out of the ice mixture and placed in an air-jacket in same bath, and the freezing- 

 point read by means of a lens. This determination of the freezing-point can 

 be easily completed in about ten minutes. — A . B. 



Soils, Soluble Salt Content of, and Some Factors affecting it. By 



M. M. McCool and C. E. Millar (U.S.A. Exp. Stn. Mich., Tech. Bull. 43, 

 Nov. 1918, pp. 47 ; 34 tables, 4 graphs). — Describes a large number of experiments 

 made by means of the freezing-point method. The chief conclusions are as 

 follows : 



The translocation of salts in the soil is due mainly to water movements. When 

 large quantities of salt are present there is a movement to areas of lower con- 

 centration even when water movements are prevented. Higher water contents 

 of the soil aid this movement. It is probable that plants are supplied with 

 food elements by diffusion from local areas around the roots only. The accumu- 

 lation of soluble salts on the surface of uncropped areas indicates that, when 

 water movements occur in the soil, salts are carried along with them. 



As a result of laboratory studfes, it appears that the constituents of soils 

 which have been cropped for a long period of years go into solution at a some- 

 what slower rate than do those of the corresponding virgin soils. The rate of 

 solution of the soils studied was governed to some extent by temperature, and 

 the moisture content had a marked influence on the rate of solubility. It is 

 probable that biological activities play an important role in these phenomena. 



Usually, under laboratory conditions, the concentration of the soil solutions, 

 at all water contents, was lower after thirty days than after ten days. This may 

 be due to reabsorption of the soluble material by the soil, to the utilization of 

 the salts by organisms, and to the formation of less soluble compounds.. 



