SOILS — FERTILIZERS. 813 



seedling riant « JQ extremely dilute culture s^olution (30 parts per million), the 

 toxicity of wliich was partly or wliolly negatived by tlie addition of a complete 

 nutrient solution containing nitric nitrogen, or by the addition of lime to neu- 

 trality," it was thought to be reasonably clear that the soil's infertility was due 

 in no small })art to the presence of toxic organic compounds which accumulate 

 in acid soils deficient in basic constituents. This conclusion was further con- 

 firme<l by the fact that the application of superphosphate was followed by 

 beneficial effects on crop growth similar to those observe<l in the case of 

 liming, and that the toxicity to sorghum seedlings observed in water cultures 

 with extracts of the soil was diminished by the addition of phosphate, although 

 it is recognized that the results witli the superphosphate may have been due 

 in part to the fact that it supplied a deficiency of phosphoric acid in the soil. 



The colloid chemistry of humus, S. Odkn (KoUoid ZtscJir., IJf (1914), No. S, 

 pp. 123-130; (lbs. in Ztschr. Angcw. Chem., 27 (lOl.'f), No. 88-89, Referatmteil, 

 pp. 613, Gl.'i). — Studies of the humus of sphagnimi peat in which the principles 

 of colloid chemistry were used in an attempt to isolate the individual constit- 

 uents of humus are reported. 



Three substances, two of which were colloidal and one noucolloidal, were 

 obtained from the water extract of the peat. Also substances exhibiting dis- 

 tinctly colloidal properties were obtained from the ammonia extract. Tests of 

 some of these as regards electrical conductivity indicated the presence of active 

 acids which are thought to be the main constituents of humus acids. Further 

 tests of the electrical conductivity of a solution of pui-e humus in very dilute 

 ammonia verified these results. The author considers this to be conclusive 

 evidence as to the existence of humus acids. 



A note referring to similar work by Ehrenberg and Bahr is appended. 



Soil colloids and the soil solution, F. K. Cameron (Jour. Phys. Chem., 19 

 (1915), No. 1, pp. 1-13). — The author comments on the loose use of the term 

 colloid as applied to soil chemistry, reviews the arguments of others advanced 

 to demonstrate the existence of colloids In soils, and attacks the popular 

 theories regarding the supposed relations between soil phenomena and soil 

 colloids on the grounds that they have no definite experimental basis. 



He points out that many of tlie soil phenomena attributed to soil colloids can 

 be accounted for by the mere fact that the soil particles present a large surface 

 for absorbent action. He is of the opinion, however, that soil chemistry can 

 be considered a branch of colloid chemistry provided a colloid is defined as a 

 phase sufficiently divided where surface phenomena are predominant. 



" The relation of the gas-liquid surface tension to the solid-liquid surface 

 tension is a most important problem requiring investigation for a clear purview 

 of the functions of soil colloids. It is a necessary consequence of the colloid 

 constitution of the soil that very small changes in the concentration of the soil 

 solution correspond to relatively large changes in the composition of the solid 

 phases resi)eeting those constituents derived from the minerals of the soil." 



Soil water in relation to plant growth, W. J. Colebatch (Jour. Dept. Agr. 

 So. Aust., 18 (1914), No. 4, pp. 363-374). — The author discusses the functions 

 of soil moisture, with particular reference to plant growth in excessively wet 

 soils. 



Experiments on the effect of varying water and food supplies on the water 

 requirements of oats showed that plants do better in dry seasons when the 

 food supply is plentiful and that in dry years a portion of the manure is lost 

 to the crop. Further experiments with oats on the influence of water supply 

 on the effectiveness of phosphates bore out the conclusion that the water 

 supply exerts an important influence on the effectiveness of fertilizers. 



