SOILS FERTILIZERS. 811 



nitrogen to the soil was accompanied by a marked increase in nitrate pro- 

 duction. 



" From the results obtained in this investigation and by other worlsers it 

 would seem that the increase in bacterial activity on drying a soil is not a 

 question of bacterial numbers, but depends upon the relative resistance of the 

 important soil organisms. In a consideration of the effect of drying a soil on 

 the physiological condition of the soil no definite conclusions can be drawn until 

 more knowledge is obtained relating to the effect on the different groups of 

 organisms. . . . 



" The results of these studies show that the drying of soil affects the physical, 

 chemical, and biological factors, resulting in an increased plant growth. The 

 Increased crop growth on a soil that has been previously dried is of importance 

 to the practical question of soil management, more especially in the arid 

 regions where the soil is often air-dried." 



A biblography of related literature is appended. 



A study of the Atterberg- plasticity method, C. S. Kinnison (U. S. Dept. 

 Com., Bur. Standards Technol. Paper 46 {1915), pp. 18, figs. 3). — In this paper 

 Atterberg's method of measuring the plasticity of clays (E. S. R., 32, p. 617) 

 is briefly described, results obtained by him are reviewed and discussed, and 

 experiments with twenty different clays are reported in which this method of 

 measuring plasticity was compared with some of the present methods. 



" Atterberg classifies the condition of a clay with varying amounts of water 

 into five states, as follows: (1) The upper limit of fluidity or the point where 

 the clay slip flows as water; (2) the lower limit of fluidity or flow where two 

 portions of the clay mass can be made to barely flow together, when placed 

 in a shallow dish which is sharply rapped with the hand; (3) the normal con- 

 sistency, or sticky limit, being the condition in which the clay is most workable, 

 is no longer sticky and will not adhere to metal; (4) the rolling limit, or the 

 condition in which the clay can no longer be rolled into so-called threads be- 

 tween the hand and the surface on which it may rest (this is the lower limit 

 of tiie workable condition) ; (5) the condition in which the damp clay will no 

 longer hold together when subjected to pressure." 



The plasticity of 20 different clays was measured by Atterberg's method 

 and their water of plasticity and volume shrinkage determined, together with 

 the amount of water which the dry powdered clay would absorb when allowed 

 to stand over a dilute sulphuric acid solution. Classification according to the 

 Atterberg method and that based on the percentage of water of plasticity were 

 found to agree more closely than those obtained by any two other methods 

 used. The disagreement in the different evaluations was, however, such as to 

 indicate that neither of these methods used alone will suffice, as each produced 

 results which contradict facts observed in every-day experience with the clays. 

 Since Atterberg's rating was nearest the mean, it is considered preferable to 

 either of the ratings based on shrinkage or water of plasticity. It was found 

 further that Atterberg's plasticity number can not be satisfactorily used alone 

 to evaluate clays with reference to their plasticities unless they are all of one 

 type, and will not, therefore, accurately classify a large number of clays of 

 various types. 



From these results it is thought that Atterberg's factor should be coordinated 

 with the water of plasticity, this scheme, it is stated, giving promise of separat- 

 ing the nonsticky and safe working clays from the sticky varieties dlfllcult to 



work. 



Soil analysis, E. J. Russell (Jour. Bd. Agr. [London'], 22 (1915), No. 2, pp. 

 116-119).— It is pointed out in this article that to 'derive the maximum as- 

 sistance from soil analysis the farmer must bear in mind that " the simplest 



