THE MAKUFACTUBE 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 7 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 which 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. 



