126 THE WAREHOUSING OF GRAIN, 



inches diameter and 4 inches pitch, made in lengths of about 

 12 feet from bearing to bearing, the space between the 

 «crew and the fixed casing in which it revolved being J inch. 

 At 60 revolutions per minute, which was found to be the 

 maximum effective speed, the screw discharged the grain 

 at the rate of 6| tons per hour, and required 0-04 horse 

 power for every foot run. The sectional area of the body 

 of grain propelled was 49 per cent, of the whole trans- 

 verse area of the screw. Subsequent experiments were 

 made with screws contained in revolving casings. A 12- 

 inch screw constructed in that way when driven at 36 

 revolutions per minute, delivered 10 tons of wheat per hour. 

 When driven at a high rate of speed, the grain was simply 

 "Carried round and not propelled forward at all. The best 

 results were obtained with a pitch of f ths of the diameter. 

 However, the great power required to drive screws with 

 revolving casings proved an insuperable objection to their 



use. 



Bands made of canvas were then tried, and afterwards 

 bands made of india-rubber and canvas. It was found 

 that for light grain 8 feet per second was the maximum 

 rspeed, and that for heavy grain about 9 feet was the 

 maximum. With 12-inch bands 35 tons per hour could 

 be carried, and with 18-inch bands a maximum of 70 tons 

 per hour was obtained. Comparing the amount of power 

 required to convey a stream of grain at the rate of 50 tons 

 per hour through a distance of 100 feet by means of the 

 common screw in stationary casing, the tubular screw with 

 revolving casing, and the travelling band 18 inches wide, 

 the following results were obtained : — 



"With the common screw .... 18-38 h.p. 

 „ tubular „ . . . . '2o-00 ,, 

 „ 18-inch travelling band . . 1-02 ,, 



