12 BULLETIN 143, U. S. DEPARTMENT OF AGRICULTURE. 
Tables VI, VII, VIII, and IX show that in every case applications 
of the slag fertilizer to the soils had a stimulating and beneficial 
effect. 
The increase in growth caused by the citric soluble potash and 
phosphoric acid in the slag was, as a rule, less than that caused by 
the application of the equivalent quantities of these two fertilizer 
elements in a water-soluble form, but this is to be expected in the case 
of experiments carried on for such a short period of time. The tests, 
of course, are not conclusive, but they indicate that good results may 
be expected from the use of such a fertilizer. 
SUMMARY. 
A method of obtaining both potash and phosphoric acid in citric 
soluble form has been devised. It consists of mixing together phos- 
phate rock and feldspar with the addition of small quantities of the 
oxides of iron and manganese to promote fluidity or lower the melt- 
ing point of the slag, the mass being then heated to about 1,400° C. 
for about 20 minutes. The resulting product is not only soluble in 
a 2 per cent citric acid solution, but is also fairly soluble in water 
saturated with carbon dioxide. Pot tests with typical soils showed 
that the mineral increased the growth of wheat plants, but the bene- 
ficial effect derived from such applications was not, on the whole, as 
marked as it was when more soluble forms of phosphate and potash 
were used. The indications are, however, that the slag product has 
a distinct high fertilizer value. 
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