49 



III. THE SOIL. 

 (Chemical and Physical Departments.) 



(a) MECHANICAL ANALYSTS. 



XV. B. A. Keen and W. B. Haines. " On the Effect of 

 Wear on Small Mesh Wire Sieves." Journal of 

 Agricultural Science, 1923. Vol. XIII., pp. 467-482. 



Fine mesh wire sieves play an important part in agricultural 

 science, especially in specifications for certain artificial fertilisers, 

 and in mechanical analysis of soil. 



The uniformity of new and worn sieves was measured with 

 respect to the linear dimensions and area of the holes, and the 

 diameter of the wire. 



Unused sieves woven to the specification of the Institute of 

 Mining- and Metallurgy compared well, on the whole, with the 

 Specification, but in used sieves the variations were much greater : 

 in one instance, 70 per cent, of the apertures were 25 per cent, 

 in excess of standard area, and no less than 36 per cent, were 

 50 per cent, over standard. In some of the sieves the frequency 

 distribution curves of the data showed double peaks, and the 

 actual observation showed that there was a systematic distribu- 

 tion of values corresponding to these two peaks. It would appear 

 that the guides in one of the combs through which the warp 

 wires are led during weaving had become displaced sideways, 

 thus giving alternate strands of wide and narrow holes. 



A calculation of the increase of area of the apertures due to 

 stretch of the sieve in use led to values below those actually 

 observed. This discrepancy is due to the wires becoming dis- 

 placed from their original positions under the rubbing action 

 employed in mechanical analysis. 



Of the two systems of weaving — double and single — the 

 former is stronger, but the latter is more uniform, since the warp 

 and weft grip one another more tightly and more often in a given 

 area. The fact that it is intrinsically neither as strong nor as 

 durable as a double weave is an advantage, as with ordinary 

 use, some of the strands break and the sieve is discarded before 

 any very serious alteration in aperture area has arisen. 



XVI. J. R. H. Coutts, E. M. Crowther, B. A. Keen., 

 and S. Oden. " An Automatic and Continuous 

 Recording Balance. (The O den-Keen Balance.)" Pro- 

 ceedings of the Royal Society. A., 1924. Vol. CVI., 

 pp. 33-51. 



In connection with (a) the newer methods of mechanical 

 analysis which involve only a single sedimentation, and (b) further 

 experiments on the evaporation of water from soil, there arose 

 an urgent necessity for some form of automatic self-recording 

 balance. At the request of Prof. Sven Oden, of Stockholm, the 

 Soil Physics Department has devised an improved form of his 

 original type of recording balance. The control is effected electro- 

 magnetically. The current passing through a solenoid is auto- 

 matically adjusted, so that the force of attraction on a magnet 



