12 THE PHYSICAL ACTION OF LIME ON CLAY SOILS 



with a revolving drum in such a manner as to record the traction at any 

 particular moment. We would expect that the summations of the values 

 ob'tained from various lime plats, for instance, would indicate the effect 

 of the lime on the physical condition of the soil. Work along this line 

 has been undertaken by Alausberg and by Noll. Unfortunately the prob- 

 able error involved is so high that experiments must be carried through a 

 long series of years before significant results are obtainable. 



18. The Oxidative Power of the soil has never been used as a method 

 for the estimation of internal surface. There seems no reason to doubt, 

 however, that oxidation is in large part a surface phenomenon. The 

 great ability of colloidal humus and hydrous ferric oxide to cause oxida- 

 tion, as indicated by the work, of Schreiner and his co-workers, would 

 suggest that oxidation may be a specific and not a general phenomenon. 



Aloin is not suited for measurements of internal surface, owing to the 

 fact that it is catalyzed by alkalies. An aloin solution will "keep" for 

 only a few hours because of the presence of alkali dissolved from the con- 

 tainer. An aloin solution will keep indefinitely if a small amount of 

 acid is added when the solution is first made. The question arises in 

 this connection whether Schreinor and Sullivan's study of the oxidizing 

 power of soil extracts is particularly significant. 



Phenolphthalin is more satisfactory for estimating internal surface. Tt 

 is convenient to read, and, unlike aloin, is very stab'le towards the atmos- 

 phere. One precaution to be observed, is to avoid the use of a strong 

 alkali in bringing out the full color of the phenolphthalein before reading. 

 In a strongly alkaline solution the phenolphthalein is converted into the 

 colorless leuco-basc. Ammonia is a very satisfactory alkali to use in 

 this connection. 



It is frequently desirable to clarify the solution with a precipitant, 

 just prior to rendering the solution alkaline. If a soil has been rendered 

 strongly basic by a salt treatment, the humus brought into suspension 

 may modify the pink color to such a degree as to make a previous precipi- 

 tation imperative. 



DISCUSSION 



In the preceding exposition we noted that the analogy between the 

 suspension method and conditions as they actually exist in the soil, was 

 not very close. There is no reason to doubt, however, that the funda- 

 mental phenomena involved are essentially the same, the differences 

 being simply a matter of degree. Cameron takes the point of view that 

 there is no basis for attributing surface action to colloids, ami Oedroits 

 holds a similar opinion, on account of the small colloidal content of any 

 soil. On taking into consideration the large internal surface involved 

 on even a slight subdivision of any material, however, it is found nnneces- 



