CLAY A S A N AMPHOLYTE
52 1
to the Director of the Ryerson Physical Laboratory of the University of Chicago for the use of indispensable apparatus and instruments; and especially to E$. I. DuPont de Nemours and Co. for the establishment of a research fellowship under the tenancy of which by one of us much of this work was done. CHICAGO, TI,J.INOIS
CLAY AS AN AMPHOLYTE BY OLOFARRHENIUS Received November 28, 1921
Most soil scientists know that alkali soils during filtration cause serious troubles, because the extract is grayish or turbid. Furthermore, i t is a well known fact that alkali stabilizes, whereas acid peptizes the soil suspensions. The rate of settling of soil suspensions plays a great role in mechanical soil analysis, and there has been much discussion on this subject, such as that between Rohland' and MaschhauptJ2in which the divergences were great and both were right. Rohland points out that the same addition of alkali or acid does not cause the same effect in suspensions of different sciils and Maschhaupt finds that alkali first stabilizes and then suddenly peptizes the suspensions. It is very probable that the actual acidity of the suspension, the hydrogen-ion concentration, plays the greatest role, rather than the amount of acid or alkali added. From this point of view i t is not astonishing that the authors mentioned above and several others have not been able to find a satisfactory explanation. The conception of the soil as a bufier is a rather recent ne,^^^ but only when one assumes this buffer action is one able t o understand why some soils change their reaction markedly and others not a t all when the same amount of acid is added to each. I n order to ascertain the influence of the hydrogen-ion concentration and compare i t with that of the amounts of alkali and acid added, the following experiment was carried out. Two clay soils, one used for brick-making, with a Sorensen value (PH) of 7 . 5 and another, a peaty clay with a Sorensen value of 5.0, were used for making up the suspensions. Two hundred and fifty cc. portions of each suspension (100 g. of clay in 5 liters of water) were placed in glass cylinders; alkali or acid was then added and the different lots filled up to the same volume, 350 cc. The suspensions were then shaken and left 1
8
Rohland, Landw. Vers. Sta., 1914, 85. Maschhaupt, ibid., 1914, 83. Bjerrum, Landbo og Veterinaerhoisk. Aarskr., 1917. Arrhenius, Soh! Science, 1922.
,722
OLOF ARRHENIES
to settle. After definite intervals of time, the heights of the clear columns were measured. The data thus obtained are shown in the table below. TABLG
1
Brick Clay C C .d
i‘r. of
ilci
