16 



THE PHYSICAL ACTION OF LIME ON CLAY SOILS 



readings were made when the moisture percentage of the soil was' between 

 14-15 per cent. Five readings were attempted in each pot, and since the 

 series was in triplicate, fifteen readings per treatment were obtained. 



TABLE III. PENETRATION IN GRAMS OF SOILS LIMED FOR 100 DAYS 

 (Each figure is the average of 15 determinations) 



While the probable error in some cases is rather high, nevertheless, 

 we may draw the general conclusion that calcium hydrate decreases sur- 

 face penetrability more than any of the other salts tried. One thing 

 worthy of note is that calcium carbonate seemed to increase the value 

 when used in small amounts. Unfortunately the question of crust forma- 

 tion enters in, and tends to confuse the results. There is virtually no 

 hardening on the surface of the untreated soil, while those to which has 

 been added a half a ton of lime per acre may form quite a tough crust, 

 as in the case of the gypsum treatments. What our results indicate, 

 then, is that calcium hydrate causes the formation of a less impervious 

 crust than any other lime. If the penetration method is to be used as a 

 measure of the internal and not the surface condition, the crust must be 

 removed. 



Penetration studies on the interior portion of the soil were attempted. 

 Brass pins of various shapes and sizes were advanced into the soil with 

 the ratchet of the micrometer used in connection with the expansion 

 studies. The distance that the ratchet forced the pin into the soil was 

 read directly on the micrometer scale. (The crust had been removed.) 

 The results failed to show significant differences between the different 

 salt treatments. We may therefore conclude that the influence of salt 

 treatment is primarily on crust formation, in so far as the penetration 

 method is a proper criterion. It cannot be used for very sensitive meas- 

 urements, because it is subject to a number of uncontrolled factors. 



EXPANSION STUDIES 



It was evident from the preliminary discussion that we would expect 

 flocculation and expansion to go hand in hand. Furthermore, it seemed 

 that expansion studies should be conducted at a constant moisture con- 



