55 



In each case the variation of properties for different soil types 

 is considered, as well as the variation in the same soil for different 

 moisture contents. 



(a) Cohesion. Atterberg's method was used, the apparatus 

 being- specially designed to give the cutting or breaking strain 

 of prepared soil specimens. A comparison of the author's results 

 with Atterberg's shows a difference in character of theoretical 

 importance. 



(b) Plasticity. A simple statement of the constants involved 

 in measurements of plasticity is first made, in order to clear a 

 certain confusion hitherto shown in applying the subject to soils. 

 One of these constants, which may be called " the pressure of 

 fluidity," was measured by a new method which has proved a 

 sensitive means of classifying the behaviour of clays. 



(c) Surface Friction. The apparatus used for friction 

 measurements is described in another communication (see paper 

 No. XXVI.). The results show very marked differences accord- 

 ing to soil type, and throw an interesting light upon the theory 

 of soil moisture relationships. The subject is a new one in soil 

 measurements, and the method promises to be very effective 

 in the physical examination of soils. 



Although much remains to be done to fill in gaps in the 

 data, the grouping together in this way has thrown into clearer 

 relief many of the outstanding problems of soil physics. 



(c) SOIL CULTIVATION. 



XXVI. E. M. Crowther and W. B. Haines. " An 



Electrical Method for the Reduction of Draught in 

 Ploughing." Journal of Agricultural Science, 1924. 

 Vol. XIV., pp. 221-231. 



The frictional force between mouldboard and the soil con- 

 stitutes an appreciable fraction of the total draught in ploughing. 

 In this paper a simple electrical method is suggested and invest- 

 igated for the reduction of friction on moist substances. In its 

 application to ploughing, a current is passed through the soil 

 having the mouldboard as the negative electrode. As moist 

 soil exhibits the phenomenon of electro-endosmosis, and as the 

 soil colloids have a negative charge, water moves through the 

 moist soil towards the negative electrode under the action of the 

 electric current. The mouldboard thus becomes covered with a 

 water film, which should act as a lubricant and reduce the plough- 

 ing draught. Under laboratory conditions, striking reductions 

 in friction were obtained. A number of field experiments showed 

 that the device reduced the effort required in ploughing. The 

 reduction was, however, much smaller than in the laboratory 

 experiments, but there is considerable possibility of improvement 

 in the method of applying the current, and thus obtaining greater 

 reduction in draught. The method promises to have useful 

 extensions to certain other cultivation processes such as mole 

 drainage and deep ploughing. (See paper LXI.) 



