MANUFACTURE OF PHOSPHORIC ACID. 5 
plants as acid and hauled away again as gypsum in acid phosphate. 
The chief function of this sulphuric acid is that of a reagent for 
converting the phosphate rock into a form which is quickly available 
to crops. " In the manufacture of ordinary acid phosphate it dilutes 
by 50 per cent every ton of phosphate rock thus treated, forcino- the 
ultimate comsumer to pay freight and handling charges on relatively 
valueless material. While it adds sulphur in the form of gypsum, 
which is recognized as a soil constituent essential for plant growth, it 
is sold strictly on the basis of its content of available P 2 5 . Even 
where sulphuric acid is used to produce phosphoric acid and this 
latter product subsequently employed to make double acid phos- 
phate, the separation of the gypsum by filtration and the subsequent 
evaporation of large quantities of water tend to offset any advantage 
gained in the manufacture of a concentrated product. 
(4) By the use of electric or fuel furnaces located near the phosphate 
mines it would be possible to produce (at the source of the raw 
material) a relatively concentrated product which would stand heavy 
handling charges and the cost of long freight hauls. This concen- 
I 
60000 Uj. Capacity * '/ I 
Fig. 3.— A car loaded to capacity (60,000 pounds) with 16 per cent acid phospate (the standard phos- 
phate fertilizer of to-day)* contains only 9,600 pounds of actual phosphoric acid (P2O5). Yet trans- 
portation and handling charges must also be paid on 84 per cent of gypsum and various impurities 
contained in this product. Our annual freight bill for transporting acid phosphate is fully S12,000,000. 
trated product may be either strong phosphoric acid in liquid or 
crystallized form which can be shipped as such in lead-lined tank 
ears or wooden containers, double acid phosphate (containing from 
40 to 50 per cent of soluble P 2 5 ) made by treating phosphate rock 
with this strong phosphoric acid, ammonium phosphate which is 
produced by passing ammonia gas into phosphoric acid, or potassium 
phosphate which is formed by decomposing a potash salt such as 
muriate with phosphoric acid. In any event a product of the highest 
fertilizer value occupying but little storage or car space would be 
obtained which could be readily shipped and distributed at the least 
possible cost. 
Figures 1 and 2 show graphically the saving in raw materials (and 
in the bulk of finished product) which may be effected by treating 
run-of-mine phosphate by the pyrolytic, or furnace, process instead 
of putting the material through a washing process and subsequently 
treating the washed rock with sulphuric acid. In Figures 3, 4, and 
5 the economies which may be brought about by shipping these more 
concentrated products are illustrated. 
