390 SOILS: PROPEBTIES AND MANAGEMENT 



301. Limewater method. — A measured quantity of 

 a standard solution of limewater is brought into contact 

 with the soil and absorption is accomplished by evapora- 

 tion, after which water is added and the filtrate is tested 

 .vith phenolphthalein. Failure to produce a pink color 

 shows that the lime requirement of the soil has not been 

 reached; an alkaline reaction shows that an excess of 

 lime has been added. A number of tests must be made 

 in order to reach a point below which the indicator shows 

 no color and above which it does. The lime requirement 

 may thus be indicated. This determination was devised 

 by Veitch, 1 and is a useful method since it indicates to 

 within a few hundred pounds the quantity of lime re- 

 quired to satisfy the absorptive power of a soil. 



302. Resume. — In conclusion, a few facts regarding 

 so-called acid soils may be restated : (1) acidity is not 

 always due to free acids, but often to the lack of an abun- 

 dance of bases ; (2) it is not injurious to all plants, but is 

 likely to depress the yields of the majority of agricultu- 

 rally important crops, while some valuable ones are bene- 

 fited by it; (3) it may be overcome sometimes by aera- 

 tion of the soil, and always by the application of lime or 

 wood ashes. The correction of acidity by means of lime 

 will be discussed in a later chapter, as will also the rela- 

 tion of certain bacteria to acidity. 



1 Veitch, F. P. The Estimation of Soil Acidity and the Lime 

 Requirements of Soils. Jour. Am. Chem. Soc, Vol. 24, pp. 

 1120-1128. 1902. 



