The Owosso times. (Owosso, Mich.) 1897-1926, 1913-01-10
Raw Rock Phosphate
By A. J. PORTER. Experiment Station Chemist Michigan
Agricultural College
Agricultural College

II VINEL1 ground raw ROCK pHoS
- plate. such us is being sold as u
source of phosphoric acid, for
fertilizing purposes Is found
quite extensively throughout the south
ern, middle western and western states
II has been conservatively estimated
that II the present rate OF consumption
should be increased three times there
Is now In sight an amount of rock
phosphate sufficient to supply the de.
mand for 100 years. The principal
source OF supply for this section at the
presen time is Tennessee, and a good
grade Of rock should be laid down III
car lots along the lines of the trunk
railroads In the southern part Of the
state for $3.50 to 50 per ton.
The grade Of rock phosphate general
ly found upon the markets contains
about 81 per cent bone phosphate OF
lime. which is equivalent to % per
cent phosphoric acid and 33 per cent
lime. Fineness is large factor In de-
termining the availability Of rock phos-
plate. The finer the material the more
readily It will become available; con
sequently this point should be taken
into consideration when purchasing.
To obtain the best results II should
be ground to such fineness that 30 per
cent will pass through q 100 mesh
screen. By far the greater part Of the
rock phosphate used for fertilizing pur-
poses Is In the form of acid phosphate
dissolved phosphate or superphos-
phate). This is prepared by treating
the rock phosphate with an equal
weight Of sulphuric acid (oil of vitrloD.
This treatment changes the phosphoric
acid from an insoluble TO soluble
form and makes it readily available
to the growing plant. The cost of the
phosphoric acid to the consumer is In
creased by this process to nearly four
times, since the acid phosphate sells ut
retail for nearly double what the ra W
phosphate costs, and 1t contains only
half as much phosphoric acid.
In view of this situation the cues
ton naturally arises, would it not be
more economical to use the slowly
available raw phosphate than to pay
the igher price for the acid phos-
pnate? Many of the state expert
ment stations have conducted expert
ments to compare these two forms OF
phosphoric acid, but the results have
been conflicting. In fact, the results
obtained at some stations over q Pc
riod of several years have been so
contradictory as to be Of little value.
The most widely advertised expert
ments with rock phosphate a.e those
conducted by DR.. Hopkins in Illinois.
These experiments have been in prog
ress during a period Of twelve or four
teen years and have been conducted
on the so called prairie soils rich in
organic matter. The crops most -orn-
monty employed have been corn, oats.
wheat and clover. The rock phos-
connection with liberal amounts OF
manure or with clover turned under.
The conclusions drawn from the re-
suits of these experiments are that
rock phosphate is a more economical
source Of phoslhoric acid than the
treated phosphate.
In Ohio the experiments by Director
Thorne have been conducted in much
the SINE manner as the Illinois cX-
perrin nts, but the results here justify
the conclusion that the acid phosphate
is the more &c ,nomical source of phos
phoric acid.
A few experiments have been con
Quoted ty the Michigan experiment
station, md in no case have the re-
suits favored the rock phosphate.
though it should be stated that tie en-