1019] SOILS — FERTILIZERS. 213 



The conclusions reached are that " (1) there is a real and constant relation 

 between absorption and coagulation. (2) The action of the electrolytes de- 

 termines a single procesa in the unstable bydrosols consisting of coagulation by 



absorption. When atoms and ions of opposite sign conn; into contact they at- 

 tract each other reciprocally, causing the neutralization of their respective 

 charges and the formation of insoluble absorption combinations. This causes a 

 lowering of the concentration either in the colloidal solution or in the electrolyte 

 solution. (3) Considered separately, the two processes proceed in parallel, 

 as the (unction of identical factors and in function one of the other; that is, 

 they advance as the opposed signs of charge between the atoms and ions drop, 

 and are seen to be connected by the relation of cause and effect. (4) The 

 existence of this relation is of great importance as regards the physical- 

 chemical properties of the soil, which are always influenced by it in a manner 

 advantageous to fertility." 



Soil acidity methods, R. E. Stephenson (Soil Sci., 6 (1918), A T o." 1, pp. 

 83-52). — In this paper, a contribution froin the Iowa College, the author reviews 

 preliminary tests of various methods for determining soil acidity, including 

 those proposed by Tacke (E. S. It., 9, p. 32), Veitch (E. S. R., 14, p. 418), 

 Hopkins (E. S. R., 24, p. 397), Jones (E. S. R., 32, p. 610), Truog (E. S. R., 35, 

 p. 503), and Maclntire (E. S. R., 35, p. 715). He concludes that a modification 

 of the Tacke procedure is alone reliable for research work. It is stated that 

 methods depending upon the liberation of an acid from its salt do not give 

 total acidity and indicate a lime requirement depending both upon the soil and 

 the salt used. Methods employing heat or a strong base are likewise deemed 

 unreliable, since their indications are thought to be both excessive and incon- 

 sistent. The nature of the soil acids is also regarded as a very important 

 factor to be considered in studies of lime requirement. 



Experiments testing various modifications of the method proposed by Tacke 

 are described and the following conclusions reached : Pure water was a reliable 

 medium for bringing about the reaction between the acid soil and the carbonate. 

 The use of dilute solutions of calcium or sodium chlorid hastened the reaction 

 to only a limited extent, while a concentrated solution of these salts may have 

 prevented fermentative reactions, altthough such a provision proved unneces- 

 sary. The rate of reaction was somewhat depressed by concentrated chlorids. 

 Toluene proved to be of no value to the method, an antiseptic evidently being 

 unnecessary. The use of normal sodium nitrate hastened the reaction, but its 

 value has not yet been established. The length of time of running, the rate 

 of aeration, and the vigor of shaking are said to be the most important factors 

 in the Tacke method. The rate of aeration should be maintained at a maxi- 

 mum. The effects of temperature and the partial pressure of carbon dioxid 

 can not be determined. A run of from 5 to 10 hours added to the reliability 

 of the method, tending to overcome many momentary influences. The activity 

 of soil acids varied greatly as measured by the rate of evolution of carbon 

 dioxid. The more reactive acids reacted at once, the less reactive only after 

 long contact and thorough mixing of soil and carbonate and after more com- 

 plete removal of the dioxid liberated. The method is believed to be not only 

 consistent in indicating total acidity but also in a limited way is thought to 

 measure the toxicity of the soil acids. 



The decomposition of org'anic matter in soils, F. G. Merkle (Jour. Amcr. 

 Soc. Agron., 10 (1918), No. 7-8, pp. 281S02, figs. 6).— This paper, a contribution 

 from the Massachusetts College, describes experimental work in which obser- 

 vations were made upon the relative rate of decomposition of different oven- 

 dried materials in a fine sandy loam soil as measured by the amount of carbon 



