AGRICULTURAL MACHINERY AND IMPLEMENTS 1655 



The damage to the machines varied from slight derangement to total 

 destruction. The total damage for all machines was $ 60 000. 



In almost all cases the flame from the explosion was blown into the 

 straw pile and sometimes spread to the grain in sacks. Several hundred 

 acres of grain were thus destroyed, the loss amounting to about $ 50 000. 

 Seventy-five pei cent of the machines were provided with some form of 

 fire-fighting equipment. 



Static electricity as a cause of explosions. — It was evident from the 

 beginning of the investigation that a large quantity of static electricity was 

 generated during the opeiation of the threshing machine. The writer quotes 

 a case in Idaho where a machine was completely destroyed as the result 

 of an explosion. It was situated more than 15 miles from the railway and 

 more than 4 miles from the main road. On the other hand the xvorkmen 

 were neighbours or men known to be reliable. The enquiry made it quite 

 clear that the fire was due to static electricity (the weather was hot and dry). 

 The wheat contained 31 % of smut. 



In another case the owner of a threshing machine had his attention 

 turned to the cylinder at the time of the explosion. He observed a long 

 blue spark coincident with the explosion. 



In one case the owner stated that his machine was very heavily 

 charged with electricity- on the morning of the explosion, to such an extent 

 that that it was not possible to touch an}' metal part without shock, a 

 condition which had never been noticed on this machine before. The 

 explosion was violent and totally destroyed the machine. 



Mill explosions. — The theory of dust explosions is not exactly new, 

 and yet it is not generally believed that an explosion can occur in the absence ■ 

 of imflammable gas. But experiment has shown that dust produced by 

 handling wheat can be ignited and cause serious explosions. The extremely 

 fine state of division of the dust, combined with a siifficienth' high tempera- 

 ture bring about the phenomenon. It has been shown in the laboratory 

 of the Universit\' of Idaho that an electric spark can explode dust. Experi- 

 ments made in the " Pittsburgh Testing Station of U. S. Bureau of Mines " 

 indicate that to produce complete combustion of 0.12 oz. of coal dust requires 

 all the ox3'gen in i cubic foot of air. Cereal smut dusts are very inflamma- 

 ble, more so than ordinary cereal dust. The explosions observed were of 

 two different kinds : one quick and sharp and the other resembling a loud roar, 

 lasting longer than the first and accompanied by more flame. The concus- 

 sion produced by the original ignition shook the dust settled in the machine 

 and gave rise to the explosion flame. The mixture of snuit-dust and air 

 may have limits of exj)losibility, and it is quite possible to have too much or 

 too little dust present for an ignition. For this reason explosions ma}' occur 

 at a given time and under certain conditions and not occur at other times or 

 under different conditions. These conclusions are drawn from the Pittsburg 

 experiments mentioned above. 



Methods developed lor preventing explosions or extingitisliing fires. — The 

 writer described the investigations made on this point. 'Jlie first method con- 

 sisted of an arrangement of conducting wires connected to all the moving 



