41 



A g-eneral discussion of the methods used for the determination 

 of the acidity and lime requirements of soils, with especial 

 reference to the hydrogen-ion concentration of soil suspensions 

 and the action of neutral salts on acid soils. 



XXX. W. B. Haines. "The Volume-Changes Associated 



with Variations of Water Content in Soil." 

 Journal of Ag^ricultural Science, 1923. Vol. XIII. 

 pp. 296-310. 



A new and simple method of measuring- the shrinkag^e of moist 

 soil on drying- is described, which at the same time g-ives values 

 for the pore space and specific g-ravity of the soil. Diag^rams are 

 g-iven showing- the characteristics of the shrinkag-e for diverse 

 samples, including^ pure clay, heavy loam, sandy and peaty soils. 

 The shrinkag^e is shown to take place in two stages, in both of 

 which there is a linear relationship to the moisture content. The 

 first stage is largely governed by the clay-content of the soil and 

 its limit is fixed by the point at which air begins to replace water 

 in the pores of the soil. The second stage, called the residual 

 shrinkage, is smaller than the first, and seems to depend upon the 

 more highly colloidal material which has been supposed to 

 surround the clay and other particles. Explanation of the 

 shrinkage is developed on these lines with confirmatory 

 experiments. 



The effect of alternate wetting and drying of soil in producing 

 a good tilth is illustrated. 



XXXI. B. A. Keen and H. Raczkowski. "The Relation 



between the Clay Content and Certain Physical 

 Properties of a Soil.*' Journal of Agricultural 

 Science, 1921. Vol. XI. pp. 441-449. 

 A simple experimental method has been described for measur- 

 ing certain physical constants of soil, using small brass boxes into 

 which soil passing a sieve of 100 meshes to the inch has been 

 packed by hand. The quantities determined are : — 



1. The weight of unit volume (1100 ccs.) of air-dry soil, or 



the apparent specific gravity. 



2. Amount of water taken up by unit weight of soil. 



3. Pore space. 



4. Specific gravity of the soil. 



5. The volume expansion of unit volume (100 cc.) of soil 



when saturated. 



The results for one soil only are given, and discussed, to 

 illustrate the method. With the co-operation of the Science 

 Masters' Association it is being applied to a number of soils by 

 various schools. 



The particular soil used was obtained in six depths, as follows : 

 0-6", 6-12", 12-18", 2-3', 3-4', and the constants were determined 

 in each depth. It was shown that 1 and 4 varied inversely with 

 the percentage of clay in the soil, while 2, 3, and 5 varied directly 

 with the clay percentages. The effect on the constants of the 

 larger quantities of organic matter present in the top two layers 

 of soil was, weight for weight, approximately equal to that of the 

 clay, except in the volume expansion results where the effect, if 

 any, was within experimental error. 



