686 EXPERIMENT STATION RECORD. [Vol.36 



space. It was further found that with a large grate and open setting, together 

 with a bagasse feeder that excluded air poorly, it was easy to have too much 

 stack vacuum. On the other hand, it was found that a relatively small grate, 

 in connection with a close setting and a hopper that excludes air, not only 

 can be operated efficiently with high draft, but actually requix'es it. 



With reference to flue gas analysis, it was found that the loss due to in- 

 complete combustion of carbon was in most cases small as compared with 

 the loss due to excess air. In practice it was found that if the damper is so 

 set as to obtain a very high percentage of carbon dioxid by reducing the air 

 there is danger of incomplete combustion due to lack of air in portions of 

 the fuel bed. 



The horsepower actually developed per ton of cane ground per 24 hours 

 varied from a minimum of 1.16 where the fiber in the cane and the efficiency 

 were low to a maximum of 1.44 where both the fiber and efficiency were high. 

 In practically all cases the tests showed that boilers operated at overload gave 

 efficiencies equal to or greater than when operated at rated or underload. 



Cereal dust explosions, B. W. Dedbick (Oper. Miller, 21 (1916), No. 12, pp. 

 452, 453; Miller's Rev., 35 (1911), No. 12, p. 332). — Conclusions drawn from in- 

 vestigations conducted at the Pennsylvania State College, in cooperation with 

 the Bureau of Chemistry of the U. S. Department of Agriculture and the Bureau 

 of Mines of the U. S. Department of the Interior, are as follows : 



" Hard substances, such as pieces of iron, nails, and stones, while producing 

 sparks in passing between the grinding disks of attrition mills or other forms 

 of disk mills along with material being ground produce no explosions, as the 

 spark does not seem to possess sufficient intensity of heat or surface to cause 

 ignition, and are almost instantly out as soon as emitted. . . . 



" Matches are not more dangerous than the metal or stone substances in the 

 case of disk mills or millstones, because they are fired almost instantly when 

 coming in contact with the plates at the eye and smothered out before issuing 

 from the mill. None of the matches were ignited when issuing from the mill. 

 With rolls it is possible for the match to become ignited while passing between 

 the rolls and cause a fire or possible explosion, the match stick lodging and 

 burning, furnishing sufficient flame and heat surface. 



" The spark or arc produced by static electricity does not seem to possess 

 sufficient heat to ignite or cause an explosion of material or cereal dust as 

 ordinarily produced in flour or cereal mills. . . . Only an electric arc, a naked 

 flame, as a torch or lamp or burning match, apparently gives sufficient surface 

 contact and heat to cause ignition of dust and cause an explosion which may 

 produce merely a flash or an explosion more or less violent. 



"An Initial explosion may propagate and cause a flame to travel quite a long 

 distance through conveyors and spouts. A conveyor does not seem to offer 

 any obstruction to the flash or flame traveling through it or along its length. 

 A damper in the spout below the mill is quite effective in preventing the flame 

 from passing into the spout or conveyor below, so far as it relates to the 

 ordinary light explosion, but it is possible for the flame in some instances to 

 pass by the damper with a heavier explosion, though the force of the explosion 

 or flash is checked or confined to the immediate vicinity of the damper. Another 

 damper following the first would undoubtedly prevent any fiame from reaching 

 the spout or conveyor. 



" When a secondary explosion follows It Is generally more violent or possesses 

 more force than the first explosion and is of wider extent. 



"Dust in motion, as agitated by the blowing fan or caused by the jarring 

 down or the sudden fall or cave in of. flour or feed sticking around the side of 



