120 EXPERIMENT STATION RECORD. 



The estimation of certain physical properties of soil, G. Auchinleck 

 {West Indian BuL, 12 {1912), No. 1, pp. 50-68).— In this article an attempt 

 is made to coordinate the work of a number of investigators in the West 

 Indies in estimating the shrinkage and friability of soils and the relation be- 

 tween these properties of the soil and its crop-bearing power. 



In determining the shrinkage the soil sample was first kneaded to a proper 

 degree of plasticity. "A brick is then made by pressing the kneaded sample 

 into the space between 2 small cleats nailed on a length of board, the cleats 

 being 1 in. high, 1 in. apart, and 3 in. long. The ends and top of the brick are 

 then trimmed level with the edges of the cleats, and the brick removed. Two 

 fine pins are inserted to their heads into the brick, at as nearly as possible 

 50 mm. apart, and the interval between them accurately measured with a pair 

 of dividers or directly by means of a scale. The brick is then laid on its side 

 and left to dry gradually, and the interval between the pins is measured daily 

 until shrinkage ceases." 



Trials with this method on the surface and subsoil of several cacao fields 

 showed that cacao did not grow well in surface soils with a shrinkage of over 

 10 per cent, whereas in soils under 10 per cent good growth was made. In 

 subsoils with a shrinkage of over 12 per cent the plant did poorly, and under 

 12 per cent good growth was made. It is believed " that the estimation of 

 shrinkage is capable of a considerable degree of accuracy. Future efforts 

 should be along the lines of erecting standards of shrinkage for various crops, 

 and of investigating further the accuracy of the standard temporarily adopted 

 for cacao. The subsoil should be looked on as of perhaps greater importance 

 than the top soil when dealing with deep rooting and permanent crops. Much 

 good work remains to be carried out in determining the limits of shrinkage to 

 be assigned to soils for various crops, and citrus fmits, cotton, rubber, sugar 

 cane, and siiices should eventually be brought under the similar standards and 

 have their respective suitable areas assigned to them." 



The determinations of friability were carried out by molding cylinders of 

 soil of definite diameter and length and subjecting them to end-pressure until 

 they broke, the weight necessary being recorded. The method was found to be 

 accurate enough to classify soils on broad lines. As with the determination of 

 shrinkage, it is believed that the method can be much improved and that 

 standards of friability fbr soils and for special crops should be erected. The 

 ratio of shrinkage to clay content in samples of a given soil may " afford a 

 ready means of determining the approximate percentage of agricultural clay 

 in a sample of soil, without having recourse to elaborate and tedious methods 

 of physical soil analysis; if so, it should serve as a valuable aid to the soil 

 analyst, inasmuch as it would enable a considerable amount of useful infor- 

 mation to be obtained with a small expenditure of labor. Once a physical type 

 for a soil has been established, it should be possible to study by means of it, 

 in considerable detail, local variations from the type." 



The determination of hygroscopicity and the value of physical analyses 

 of soils, E. A. MiTSCHERLiCH aud R. Floess {Intcruat. Mitt. Bodciil-., 1 {1912), 

 No. 5, pp. Jj63-.'i80). — In comparative tests of the Rodewald-Mitscherlich method 

 of determining the hygroscopicity (E. S. R., 15, p. 847) and of the Ehrenberg- 

 Pick modification of it (E. S. R.. 24. p. 521), and studies of the relation of 

 hygroscopicity and physical constitution of soils to plant growth, the Ehrenberg- 

 Pick modification proved unreliable because of the condensation of water and 

 the growth of molds in the soil as a result of the length of time required to 

 bring about vapor equilibrium. The hygroscopicity, as determined by this 

 method, varietl with the water content of the original soil, and changes in 

 the surface area of the soil could not be estimated. The importance of hygro- 



