178 ALFALFA FARMING IN AMERICA. 
give phosphoric acid. This acid then unites with lime thrown 
into the molten metal for the purpose. A phosphate of lime is 
formed. This rises to the surfuce of the metal as a fusible slag, 
and is subsequently poured off and cooled. A dark, brittle, hard 
mass is obtained, which is capable of extremely fine grinding in 
roller mills. 
In 1886, Dr. Hilgenstock showed that basic slag phosphate ex- 
ists as a hitherto unknown compound of phosphoric acid and 
lime, viz., a tetra-basic phosphate (CaO),P.0;. Later investiga- 
tions showed that this phosphate, if only sufficiently ground, 
passes easily into solution even in very dilute acids. In a sample 
shaken up with peat and water, 78.8 per cent of its phosphate 
was dissolved in 14 days. The suitability of basic slag phos- 
phate for direct absorption by plants was thereby demonstrated. 
The special characteristics of basic slag as a manure are (1) 
the easy solubility of its phosphate in dilute acid, (2) the pres- 
ence of free lime giving what is chemically called an alkaline re- 
action. In both these respects basic slag is superior to bones. 
Super-phosphate, the other principal source of phosphoric acid, is 
superior in solubility, being water soluble, but inferior in its 
general effect upon soils, being deficient in lime. These differ- 
ences in character of the three manures are seen in their relative 
effects as crop-producers in carefully conducted experiments. 
The capacity of leguminous crops to utilize atmospheric nitro- 
gen rehders nitrogenous manures generally unnecessary. For 
the same reason farm yard manure, which supplies much nitro- 
gen, can in most cases be better utilized upon some other crop. 
The most profitable return will in ordinary practice be obtained 
from a dressing of artificials supplying phosphates, potash and 
lime. 
Beans, vetches and peas are all lime-loving crops, and for this 
reason basic slag is well suited to their requirements. Belonging 
to the same natural order are sainfoin, lucerne and clover, im- 
portant forage crops. For these, 5 cwt. basic slag, and 2% cwt. 
kainit in autumn, is recommended as a suitable application, with 
3 or 4 cwt. superphosphate, and the same quantity of kainit again 
in spring. The quantities stated may require to be increased or 
diminished according to the fertility of the land. 
While the necessity of applying manures to land under crop 
is now almost generally recognized, the claims of pasture 
strangely enough are almost wholly neglected. Recent investiga- 
tions have shown, however, that this is a mistake. More es- 
pecially is this the case with the medium and _ second-class 
pastures, whicn form such a large proportion of our grazing area. 
