64 BULLETIN 355, U. S. DEPARTMENT OP AGRICULTURE. 
the acidity in order to secure a good growth of these plants. Some 
other legumes, such as yellow lupine, serradella, and cowpeas are 
usually able to grow well on distinctly acid soils, though in some 
cases even these plants seem to be benefited by lime. The beneficial 
effect of lime on alfalfa and the other first-mentioned crops is in 
changing the reaction of the soil from acid to neutral or alkaline, 
while the benefit occasionally reported in the case of serradella and 
lupine is possibly due to the fact that on certain soils these plants 
do not find sufficient calcium for their growth, and the lime supplies 
this element. 
Detection oj acidity (Ref. No. 1, p. 247). — The presence of acidity 
may be detected in various ways. Perhaps the simplest method is 
by the use of litmus paper. This is cheap and can be purchased at 
any drug store. A strip of blue litmus paper is placed in the bottom 
of a drinking glass and covered with white blotting paper or filter 
paper on which the soil to be tested is placed. Clean rain water 
is added slowly until the soil and the litmus paper become damp. 
If the paper turns distinctly pink it shows that the soil is acid. It 
may be well to wait for ten minutes or more before coming to a final 
decision. The degree of acidity is roughly indicated by the rate at 
which the change in color takes place and its final intensity. Red 
litmus paper turns blue in the presence of alkalinity. It will often 
add to the interest and value of the test if strips of both red and 
blue litmus paper are placed in the bottom of the glass. 
A method of determining the presence of limestone and the con- 
sequent absence of acidity is to drop dilute muriatic acid upon moist 
soil. Any perceptible bubbling, or effervescence, indicates the presence 
of lime. The character of this effervescence may easily be learned 
by dropping some of the acid upon a piece of limestone or marble, 
or into a little baking soda dissolved in water. The presence of 
lime in the subsoil may sometimes be shown by this test when the 
surface gives no positive test. A failure to detect the presence of 
limestone by this test should not be interpreted as proof of acidity in 
the soil. 
The best indication of the need for lime is the type of plant growth 
that the soil bears. Where alfalfa, red clover, and sweet clover 
grow vigorously no lime is needed. The predominance of sorrel, 
broom sedge, white daisy, or redtop indicates a need for lime. 
Correction of acidity (Ref. No. 7, pp. 382-390; or No. 6, pp. SOS- 
SIS). — The practical means for correcting the acidity of soils are. 
(1) drainage, where needed, and (2) the application of lime in some 
form. Lime suitable for use in correcting soil acidity may be in any 
one of three forms. The first is the carbonate; second, burned or 
quicklime; and third, water-slaked or hydrated lime. These forms 
