No. 3 (I921) MANUFACTURE OF FISH OIL AND GUANO I59 



cooker by a conveyor and fed into the press by a hopper; there is 

 no waste of time or material, and the intermediate draining tanks 

 are not needed. 



On the other hand the pressure is so great that a good deal of 

 material is forced through the interstices, and it is calculated that 

 about 3 per cent more of dry guano (scrap) is obtained by 

 hydraulic than by the continuous method ; moreover this material 

 passes into the oil and water and adds to the difiiculty of cleansing 

 the oil from impurities. But these particles of fish, known as 

 " gurry," are to a great extent eventually recovered and separately 

 pressed for oil and fertilizer. 



24. Drying the scrap (solid material ; press cakes). — The old method 

 still used on the southern coasts is that of sun-drying by spreading 

 the broken up " scrap " on platforms (barbecues) where they remain 

 for two or three days. But, especially in the more northern coasts 

 where the weather is less certain, the hot air rotary drier is now 

 almost universal- This is a huge cylinder of iron, some 30' to 40' 

 long with a diameter of 5' or more; at one end is a large furnace 

 and fan, at the other a receiving chamber, which may be double 

 so as to save the dry dust which is blown out by the fan draught. 

 The inside surface of the cylinder is provided with several sets oi 

 plates or shelves (" flights ") set perpendicularly to the surface and 

 slightly spiral, forming a sort of hollow Archimedean screw of 

 small pitch ; consequently, as the cylinder slowly revolves, these 

 plates catch up the scrap and shower it among the hot gases within 

 the cylinder. The spiral setting of the shelves coupled with the 

 fact that the cylinder is set a few inches higher at the hopper end 

 than at the discharge end and aided by the action of the hot gas 

 currents, gradually works the scrap from the hopper to the exit. 



The whole cylinder revolves ; it has no central shaft, but is 

 provided externally with two encircling steel tires which run on 

 rollers ; these rollers being driven by a 25 I.H.P. engine, rotate the 

 cylinder by friction against the tires, or, conversely, they serve as 

 mere bearings, the cylinder being then rotated by separate toothed 

 gearing encircling the cylinder. 



25. The wet scrap is fed in by a conveyor direct from the 

 cooker ; it enters by a hopper at the furnace end so that the wettest 

 material meets the hottest f-irnace gases, and travels in parallel 

 with them. These gases coming direct from the furnace are at a 

 very high heat, and since the wet scrap is brought in thin showers 



