CARBONATE OF LIME. 141 
and calcium hydroxide (CaO,H,) are ordinary forms of lime; 
also that magnesium carbonate (MgCO,), magnesium oxide 
(MgO) and magnesium hydroxide (MgO,H,) are the correspond- 
ing magnesium compounds, more or less of which are contained 
in magnesian limes, of which the most common form is calcium 
magnesium carbonate CaMg(CO,),.. Any of these compounds 
may be used for neutralizing acids and thus for correcting the 
acidity of the soil. 
If it can be kept clearly in mind that these are the substances 
properly called lime, and that nothing else is lime, much confu- 
sion can be avoided. However, a compound properly named cal- 
cium chloride (CaCl,) is often called chloride of lime and yet it 
contains no lime whatever and does not possess the property of 
lime. In other words, it is not an alkaline substance and has no 
power to correct the acidity of the soil. It does contain the ele- 
ment calcium which is also contained in the ordinary forms of 
lime, but the element calcium is not lime. 
Now let us turn to the subject of plant food. There are 10 
essential elements of plant food and it is true that calcium is one 
of these elements and that it is required to a greater or less ex- 
tent by all agricultural plants, but it is not at all essential that 
calcium as an element of plant food be applied to the soil in any 
form of lime. It may be applied as calcium sulphate or as calcium 
phosphate, and it even exists in many soils which are absolutely 
devoid of lime which are even strongly acid and markedly in need 
of lime, but which, nevertheless, may contain abundance of cal- 
cium for plant food in the form of acid calcium silicates. Thus 
the acid soils of Illinois which require an application of several 
tons of ground limestone to correct their acidity contain several 
tons of the element calcium in the plowed soil of an acre. In 
some cases soils are found which are not only deficient in lime 
but also deficient in the element calcium and on such soils the 
application of any of the calcium limes would furnish both lime 
for correcting soil acidity and the element calcium for plant food. 
Summary.—Alfalfa is one of the most beautiful, 
most valuable and most profitable crops in the 
world. It makes the most hay. The hay is the rich- 
est and best. It enriches the soil on which it grows. 
It endures for many years with one sowing. It has 
redeemed the arid and semi-arid west. It is coming 
into every state in the Union. 
