THE MANUFACTURE OF ACID PHOSPHATE. 23 
another shaft having the same axis but revolving in the opposite 
direction. The casing can be readily opened and the cages slid apart 
and cleaned, as shown in Plate V, figure 2. 
The acid phosphate is fed through a hopper into the inner or smallest 
revolving cage and is thrown by centrifugal force against the bars and 
into the second cage, which is revolving in the opposite direction. 
From the second it is thrown into the third and then into the fourth, 
finally being discharged from the machine thoroughly disintegrated 
by the numerous impacts it has received. Two scrapers fitted to the 
outside cage prevent the material from adhering to the casing and 
clogging the machine. 
After disintegration the acid phosphate is ready to be bagged or 
mixed with other ingredients to make a complete fertilizer. 
COST OF PRODUCTION. 
The cost of producing acid phosphate depends on a number of 
factors, which vary widely. These are the size, location, and equip- 
ment of the plant and the cost of the sulphuric acid employed in the 
process. 
The use of rock mills which grind the largest quantity of rock with 
the least expenditure of time and power and the employment of 
mixers having a capacity of 2 tons instead of 1 ton tend to reduce 
the cost of acid phosphate per ton. Plants located at seaports, 
where the cost of manufacturing sulphuric acid is less and the price 
of Florida rock usually lower, can often produce acid phosphate 
cheaper than those located at inland points. On the other hand, 
factories located at inland points winch are within easy access of 
the phosphate fields can obtain their phosphate rock cheaper than 
those more distant from the source of supply. Again, those plants 
which have their own acid factories can manufacture sulphuric acid 
cheaper than it can be bought by companies which do not make 
their own acid. 
The initial cost of producing acid phosphate by the den system is 
greater than by the open-dump method, but since the material can 
be shipped much sooner when made by the former method, the 
greater cost is compensated somewhat by the more active capital. 
At inland points, such as Atlanta, Augusta, and Birmingham, the 
cost of producing acid phosphate (16 per cent citrate soluble), exclu- 
sive of office expenses, varies from $6.75 to $8 per ton. At seaports, 
such as Charleston, Savannah, Baltimore, and Norfolk, the cost 
ranges from $6.20 to $7.50 per ton. In Table VII is given the cost 
of producing acid phosphate at a plant running under good condi- 
tions located at a seaport and using Florida phosphates. 
