52 CEMENTS, LIMES, AND PLASTERS. 



cylinders between which the log is pressed. One machine will cut 

 enough fiber in nine or ten hours to make 30 to 40 tons of plaster. The 

 usual mix consists of 75 to 150 Ibs. wood fiber to one ton of calcined 

 plaster. 



Plasters are usually packed in jute sacks containing 100 Ibs. or in 

 paper bags containing 80 Ibs. An extra charge of 10 cents is com- 

 monly made for each jute sack, rebated on the return of the sack. As 

 the sacks may cost the mill 4 to 6 cents each, any sacks not returned 

 furnish a fair profit. A charge of 50 cents per ton of plaster is usually 

 made for packing in paper bags, which are not returnable. 



Costs of plaster-manufacture. An estimate of the cost of plaster- 

 manufacture at Kansas mills, made in 1897 by G. P. Grimsley,* follows. 



COST OF PLASTER-MANUFACTURE PER TON. 



Mining costs $0 . 80 



Fuel at mill . 30 



Labor at mill . 50 



Office force and sales agents 1 . 25 



Total cost of plaster per ton $2 . 85 



Setting aside the question of cost of "office force and sales agents", 

 which varies greatly in different mills, the estimate given above appears 

 to the writer to be very high for mining costs, rather below the average 

 for fuel costs, and about the maximum for labor. The following esti- 

 mates of cost of manufacture by the kettle process have, therefore, 

 been prepared as giving, in the writer's opinion, fairly close limiting 

 values : 



Max. Min. Average. 



Mining or quarrying 2400 Ibs. gypsum $0 . 72 $0.12 $0 . 30 



Power fuel at mill, 75 to 125 Ibs. coal 0.19 . 05 0.10 



Kiln fuel at mill, 225 to 325 Ibs. coal . 49 0.15 . 30 



Labor at mill . 50 . 30 . 40 



Total cost per ton plaster at mill $1 . 90 SO . 62 $1.10 



The rotary process of plaster calcination has not been used at enough 

 plants to give accurate limiting figures of costs, but the following esti- 

 mates are believed to be fairly close: 



Max. Min. 



Mining or quarrying 2400 Ibs. gypsum. ... $0 . 72 $0 . 12 



Power fuel at mill, 50 to 80 Ibs. coal .... . 12 .04 



Kiln fuel at mill, 150 to 200 Ibs. coal . 31 . 10 



Labor at mill. .. 0.30 0.18 



Total $1.45 $0.44 



* Mineral Industry, vol. 7, p. 392. 



