400 REPORT OF THE CHEMIST 
amounts of farm-manure or green manures, or both, ground 
rock-phosphate is one of the most economical forms in which 
to supply phosphorus to crops. Its use is not recommended 
on soils deficient in organic matter or where it is desired to 
have the phosphorus at once available for the growing crop; 
in such cases, the use of dissolved rock (acid phosphate) or 
bone-meal is necessary. The effect of floats on crops is least 
marked the first season but becomes more pronounced later. 
Floats can be used to advantage as a mechanical absorbent in 
the stable using about one pound a day for the manure of each 
animal. It can, if preferred, be mixed with the manure after 
removal from the stable or spread on the field with manure, 
about 100 pounds of floats being used for 1,000 pounds of 
manure. The amount of floats to be used on soils may vary 
from 500 to 2,000 pounds an acre. When applied in a regular 
crop rotation, it may be used once in three to six years at the 
rate of 1,000 or 2,000 pounds an acre; it should under these 
conditions be applied to clover-sod or to a green crop, such as 
cow-peas, soy-bean, etc., which is to be plowed under. 
SLAG-PHOSPHATE. 
This material is known under different names, as odorless 
phosphate, basic iron slag, Thomas slag, etc. It is a by-product 
formed in the manufacture of iron and steel from special 
kinds of iron ore that are rich in phosphorus. It contains 
15 to 20 per ct. of phosphoric acid, not all in quickly available 
form, and considerable amounts of lime and oxid of iron. 
Most of this material at present offered for sale is imported 
from Europe. The practical results coming from its use have 
been variable, often being excellent and again indifferent. The 
present price appears to be high. It is certain that the lime in 
it which is available for neutralizing soil acidity can be ob- 
tained much more cheaply. Before purchasing largely of this 
material, farmers are advised to use it in an experimental way 
in comparison with floats, with and without the lime com- 
pounds that neutralize acidity. 
