1. To determine the degree of saturation of a soil, data must be secured to show the amount of replaceable bases, replaceable hydrogen and base exchange capacity.
2. Experiments have been conducted to determine the accuracy of various methods for these determinations.
3. A study was first made of the electrodialysis method for replaceable bases, using both the Mattson and the Bradfield cells.
4. When 100 grams of soil were electlodialyzed in the Mattson cell for 45 hours, the results seemed satisfactory when compared with the data secured with other methods.
5. When a smaller amount of soil (10 grams) was electrodialyzed in either the Mattson or the Bradfield cell for a shorter time, the end point was not definite and the results could not be considered accurate. Furthermore, there was a continued extraction of basic materials from the soil after more bases had been removed by electrodialysis than were known to be present in a replaceable form in the soil. Hence, it appears that the error in this method may be greater than that caused by solubility effects in the leaching methods.
6. The Hissink (T - S) method for determining the replaceable hydrogen in the soil was compared with the method developed by Parker.
7. In a number of Iowa soils differing widely in characteristics and in soils which had been treated with various amounts of limestone of different degrees of fineness, the Hissink method gave practically the same amounts of replaceable hydrogen.
8. There seemed to be no correlation between the replaceable hydrogen in the soil, when measured by the Hissink method, and the hydrogen ion concentration. With the Webster silty clay loam which had a pH of 7.48, the Hissink method showed more replaceable hydrogen than was found in the Tama silt loam which had a pH of 4.79.
9. The amount of replaceable hydrogen found by the Hissink method was greater in all the soils tested than the total base exchange capacity of the soils. According to Kelley. when this method is used, not only does the barium hydroxide added to the soil react with the exchangeable hydrogen but other side reactions occur. The results with the method are certainly rather unsatisfactory.
10. According to the accepted theories of base exchange, the Parker method for determining replaceable hydrogen is sound in principle and the data secured in this work show that it will give accurate and reliable results.
11. The Parker method for determining the base exchange capacity of soils was also found to give excellent results. The principle of this method has been well established and the method has been used, with certain modifications in technic, by other investigators.
12. After the replaceable hydrogen and base exchange capacity are determined by the Parker method, the amount of replaceable bases and the degree of saturation with bases may be calculated.
13. This method has been tested on a number of Iowa soils and on soils treated with various amounts of lime of different degrees of fineness. In all cases satisfactory results have been secured.
14. In general it is evident that of all the methods tested. that proposed by Parker seems to give the best picture of the actual condition of the base exchange complex in soils.
15. Certain modifications in the technic of this method have been suggested for future work
