120 The Phosphates of America. 



cesses in the pulley -head casting (16). The joint in the pulley is 

 inclosed by means of the cover (13), thus keeping the working parts 

 away from all dust and grit, and lubricating oil is supplied for all 

 parts needing it through the hollow pin (12). 



When the mill is started, the pulley and the roller-shaft revolve 

 together, the roller hanging free in the centre of the ring, when, the 

 shaft being pushed outward, the roll on its lower end comes in con- 

 tact with the ring or die and immediately begins to travel around 

 on the latter's inner surface, pressing against it with a force suffi- 

 cient to effectually pulverize anything that comes in its way. The 

 material to be reduced is fed into the mill in sufficient quantity to 

 fill the pan as high as the shoes or ploughs on the lower side of the 

 roll. The ploughs then stir it up and throw it against the ring, so that 

 it is acted upon by the roll, and when fairly in operation, the whole 

 body of loose material whirls around rapidly within the pan and up 

 against the screens, through which all that is sufficiently fine passes- 

 at once, the coarser portion falling down to be acted upon again. 



The universal joint, by which the roll-shaft is connected with 

 the pulley, allows perfect freedom of movement to the roll so that 

 it can easily pass over obstructions of any kind. Pieces of iron or 

 steel, such as are usually found in all rock to be ground, do no dam- 

 age to the mill. 



In dry grinding the fine material that passes through the screens 

 falls downward through the openings outside of the ring into the 

 receptacle underneath, from which it is carried by a conveyer pro- 

 vided for that purpose. 



The fan attached to the shaft above the roll draws a small 

 quantity of air in at the top of the cone, forcing it through the 

 screens and out into the discharge, thus effectually keeping all 

 dust within the mill. 



It is stated of this mill that four tons of South Carolina phos- 

 phate rock (seventy-five per cent, of which would pass through a 

 70 -mesh screen) may be ground and passed through the screens in 

 an hour. 



Fourth. The Frisbee-Lucop phosphate mill, which is built of 

 steel and weighs about three tons. It is driven by belt, develops 

 a speed of 300 revolutions under full feed, requires 18 horse -power, 

 and is said to be capable of grinding 15 tons of phosphate rock 

 to a fineness of No. 150 mesh, per day of ten hours. 



The pulverization of the material is effected by heavy cylin- 

 drical rollers which are caused to revolve upon the inner surface 



