622 EXPERIMENT STATION EECOED, 



as they affect suspension and as they are affected by various external condi- 

 tions, sucli as tlie presence or absence of soluble salts, acids, alkalis, and organic 

 colloids. The knowledge of this phase of the subject is summarized as follows: 



" The phenomena of flocculation occur in ' disperse ' systems consisting of 

 fine particles distributed through a medium, and classifiable according to size 

 of particle and to the physical state of the particle and the medium. 



" They are characteristic of these states of matter and not of any particular 

 substance or substances. 



" Flocculation and deflocculation are but relative terms. The more exact 

 concept is that of degree of flocculation. 



" This degree of flocculation is influenced by many factors, of which the main 

 are added substances of the following three classes : (1) Most acids and neutral 

 salts which increase the degree of flocculation; (2) the stronger alkalis, which 

 decrease the degree of flocculation ; (3) most organic (liquid-particle) colloids, 

 which prevent increase in the degree of flocculation. 



"The action of salts, acids, and alkalis is probably at least two-fold: (1) On 

 the mutual Interpeneti'ation (solubility) of particle and medium; (2) on the 

 electric charges on the surface of the particle. 



" The stabilizing action of organic colloids is due to the formation of thin 

 films of the colloid substance about the suspended particles." 



Various applications of flocculation phenomena are noted and flocculation of 

 soils is treated in an appendix based largely upon Bulletin .50 of the Bureau of 

 Soils (E. S. R., 19, p. 818). In this it is shown that flocculation phenomena in 

 soils are very different from those occurring in suspension, the controlling factor 

 in the former being the surface tensions at the gas-liquid surfaces of the soil 

 particles. 



A report on soil temperature in connection with plats differently treated, 

 B. E. Brown (Prniisi/lrcnrKi Sta. Rpt. 1909, pp. 92-103). — This is an account of 

 the continuation of experiments described in an earlier report (E. S. R., 21, p. 

 219). In addition to the detailed temperature records data are given for 

 moisture, nitric nitrogen, and water-soluble potassium and calcium. 



The influence of rnoisture upon yields of hay in 1908 and 1909, B. E. 

 Bkown and W. H. MacIntire {Pennsylvania Sta. Rpt. 1909, pp. 10^-106, pis. 

 2). — Observations of soil moisture and yields are reported in tables and dia- 

 grams. The results indicate that the moisture conditions in 1908 affected the 

 yields in 1909. 



The effects of adding salts to the soil on the amount of nonavailable water, 

 AV. T. BoviE {Bui. Torrcij Bot. Club, 37 {1910), No. 6, pp. 273-292, figs. ^).— This 

 paper reports investigations to determine the effec-t upon the amount of non- 

 available water of adding varying amounts of sodium chlorid or the salts of 

 the full nutrient solution to the soil. 



It was found " that the amount of nonavailable water is not influenced by 

 adding to pure quartz [0.1 to 0.8 per cent] of either sodium chlorid or the salts 

 of a full nutrient solution. 



" Practically all plants of economic value are land plants, and hence, for 

 both their water and food supply, are dependent on water fllms. Therefore, it is 

 important that we understand the conditions of equilibrium between the plant 

 and this form of water. 



" It is apparent that the isotonic values determined for substances dissolved 

 in free water do not necessarily hold for film water. We can not thoroughly 

 understand the acquisition of water and food by land plants, or the results from 

 fertilizer experiments until some of these values are known. Further, the con- 

 ditions of equilibrium iu film water must be determined for both toxic and 



