THE PHYSICAL ACTION OF LIME ON CLAY SOILS 11 



plicity of certain other procedures, the histological method has never 

 come into general use. 



15. Expansion methods are nearly as old as soil physics itself. In 

 1838, Schiibler began work on the subject, and his investigations have 

 been continued by Haberlandt, von Schwarz, Puchner, and Wollny. The 

 lime studies of Thaer and Engels resulted in the conclusion that there 

 was a slight increase in volume on liming. In all the above cases the 

 soils were allowed to come to dryness before making final measurements. 

 Tempany (1917) finds that in drying down, internal friction between 

 the soil particles becomes very great. This raises the question whether 

 measurements after drying are particularly significant. Brown and 

 Montgomery, in a study of the dehydration of clays, finds- that shrinkage 

 is no criterion of plasticity. Furthermore, it appears just as objection- 

 able to make measurements from a dry to a moist condition, as vice versa. 

 R. O. E. Davis cites data from Wollny in which the latter found that a 

 dry soil moistened with water expanded six times as much as the same 

 soil moistened with calcium hydrate solution! 



Wolff, and more recently Tadokoro, have studied the swelling exhibited 

 by soils after being immersed in various reagents. This work is open 

 not only to the objections already mentioned, but is also subject to the 

 further criticism that swelling may be specific for the reagent employed. 

 If expansion readings are made at a constant moisture content, we 

 largely eliminate imbibitional factors, and may more correctly attribute 

 differences to changes in soil structure. 



16. The cohesion method for the investigation of soil properties was 

 first used by Rchtibler, who added a gradually increasing weight to a 

 scale pan suspended from the middle of the dry brickette to be tested. 

 This procedure has been used by Fippin in his investigation of the effect 

 of lime on granulation. The Schiibler method has been modified by 

 Puchner, who suspends the scale pan above the knife edge entering the 

 soil. The Atterberg procedure is essentially the same as that of Puchner, 

 except that the scale pan is supported by a superstructure. The penetra- 

 tion method has been used by Cameron and Gallagher, and by R. O. E. 

 Davis for measuring coherence. The greater portion of their work is 

 unconvincing because they failed to calculate the^ probable error of their 

 determinations. Thaer and Engels have made penetration measurements 

 in their work, but unfortunately the amounts of lime used were excessive. 



It would seem that penetration determinations should be made at a 

 constant moisture content for essentially the same reasons as in the case 

 of shrinkage. On bringing to air dryness, certain cementing materials 

 undoubtedly con>e into play which are not operative under ordinary con- 

 ditions. 



17. The Dynamometer Method consists in measuring 1 the resistance 

 offered to the passage of a plow through the soil. A spring is connected 



