1882.] on Some of the Dangerous Properties of Dusts. 89 



vicinity of the source of flame, and the fire will not spread to surround- 

 ing i^articles. 



The difficulty of maintaining, if only for a brief period, a 

 sufficiently uniform and highly charged mixtui'e of air with even a 

 very light inflammable powder, to ensure the propagation of flame 

 through it, and the circumstance that, with powders which are not 

 very highly and completely inflammable, only some portion of the 

 combustible matter is actually burned when flame is applied to the 

 mixture of dust and air, necessitate the presence of a proportion of 

 dust more or less considerably exceeding that which is proportionate 

 to the oxygen supply in the volume of air with which it is mixed, if 

 flame is to be transmitted by the mixture. 



This condition is not difficult of fulfilment in practical opera- 

 tions in which inflammable dust is dealt wdth, and flame may con- 

 sequently be transmitted upon a large scale through mixtures of 

 inflammable dusts and air, with a rapidity calculated to produce more 

 or less violently explosive effects, as has been demonstrated by many 

 accidents in works where manufacturing operations have been attended 

 by the production and escape into the air of large quantities of 

 inflammable dust. The accidental inflammation of sulphur dust in 

 chambers in which its pulverisation has been carried on, has given 

 rise to more than one considerable and somewhat violent explosion. 

 Cotton mills have been known to become rapidly fired by the 

 ignition of, and transmission of flame by, mixtures of cotton dust and 

 air, and very quickly spreading conflagrations originating from dust- 

 explosions have occurred in other works dealing with even less 

 inflammable and dust-producing materials ; thus at the Guarancine 

 Mills, at Sorgues, an explosion occurred in 1878, consequent upon the 

 ignition of a mixture of air with the dust of that substance. But 

 the most numerous and extensive calamities connected with the 

 accidental ignition of mixtures of light inflammable dust and air have 

 occurred in flour- and rice-mills. 



The cause of many disastrous explosions and fires which occurred 

 in flour mills at Budapest in Hungary, at Frideat in Germany, in other 

 parts of the Continent, and in England, prior to 1872, appeared 

 enveloped in much mystery, until Dr. Watson Smith directed attention 

 to the fact that an Austrian observer had apparently traced their 

 origin to the ignition, by flame or some incandescent body (such as 

 sparks produced by the millstones), of mixtui'es of air and the dust of 

 meal and husks formed during the grinding of corn or subsequent 

 treatment of flour. The occurrence of a very serious explosion and 

 fire at the Tradeston Flour Mills in Glasgow, in January 1872, caused 

 that gentleman to direct public attention to what appeared the true 

 explanation of these disasters, and on the occasion of that catastrophe, 

 when several persons were killed and a number injui'ed, the subject 

 was carefully investigated by Messrs. Eankin and Macadam. The 

 origin of the explosion was conclusively traced to the striking of fire 

 by a pair of millstones, through the stopping of the feed, and the 



