THE PHYSICAL ACTION OF LIME ON CLAY SOILS 15 



for magnesium in the limestone (it was nearly pure), and for water of 

 hydration. Applications were made in the equivalents of one-half, 

 one and one-half, four and one-half, and ten tons of calcium oxide per 

 acre, taking two and one-half million pounds as the weight of an acre 

 eight inches of soil. The one and one-half ton treatment exactly corre- 

 sponded with the lime requirement of the soil. Into each pot was 

 weighed the equivalent of 253 grams of oven soil. The container was 

 given a prolonged tamping, two thicknesses of cotton gauze added, and 

 finally a mulch of washed quartz sand placed on top to a thickness of one 

 centimeter. Aerated distilled water was added to bring the pots up to 

 24 or 28 per cent water content, at which they were maintained for the 

 remainder of the experiment. (Note: all references to water content 

 in this treatise are on an oven dry basis.) A portion of the series were 

 set up in triplicate; the rest in quadruplicate. The duration of the 

 experiments was 45, 100, and 225 days. On the expiration of the required 

 time, the mulches were removed, the soil sieved (20 mesh), dried down 

 to 7-10 per cent, and bottled. The soils were never allowed to reach air 

 dryness. 



In the exposition on procedures for estimating internal surface, 

 eighteen methods were examined as to their respective merits. We found 

 that the great majority are for one reason or the other inaccurate. Six 

 of them were used in the present investigation, namely, 



1 . Penetration. 



2. Expansion. 



3. Total retentive power. 



4. Dye adsorption. 



5. Hygro-interstitial water. 



6. Oxidative power. 



EFFECT OF SALTS ON PENETRATION 



The apparatus used for the measurement of penetrability was the 

 Atterberg apparatus as improved by Prof. H. O. Buckman of Cornell 

 University. The feature worthy of particular attention is the device for 

 controlling the distance that the pin enters the soil. With the pin point 

 flush with the surface of the soil, the mercury well may be set so that the 

 metal point on top just makes contact with a similar point on the piston. 

 The distance from this position to the surface of the mercury is constant, 

 and represents the distance which the pin penetrates. Water is used to 

 give the gradually increasing force to the head of the piston. On receiv- 

 ing the signal from the sounder, the water is stopped, and the weight in 

 the container is determined. This value represents the penetrability of 

 the particular soil concerned. 



A series which had run for 100 days was used for the penetration 

 determinations, and in order to avoid the results incidental to air drying, 



