[175] 



©It tbe Si3e of ©uet^-particlee of Mbeat 

 anb CoaL 



By Hahnemann Epps, 

 Associate of King's College, London. 



ATTENTION may with advantage be directed to the general 

 subject of subdivision, when it is remembered what 

 important resuhs are caused by the minute dust of many 

 substances. I" will now refer, however, only to the powerful 

 agency exerted by such inert substances as the minutest motes of 

 wheat and coal. The subject of dangerous dusts has been 

 treated of by such eminent men as Faraday, Lyell, Galloway, 

 Abel, and others. 



It is well known that the greatest risks in a flour-mill arise from 

 the development of as much heat as will ignite the fine particles 

 of flour. This heat is due to the (temporary) arrestment of the 

 supply of grain, or to the use of naked flames when the air is 

 charged with fluur-dust, or " stivings." The conditions under 

 which a consequent liability to explosion arises are scarcely at 

 present fully defined ; indeed, it is unfortunately the conviction of 

 many practical millers, that whatever precautions may be taken, 

 the risk of explosion from such causes can be only minimized. 

 Explosions and fires in flour-mills from this cause do every now 

 and then attract attention, causing lamentable loss of life as well 

 as of property. 



Again, it is pretty well established that coal-dust plays an 

 important part in the serious explosions that unfortunately are of 

 such frequent occurrence in coal-mines. From the time of 

 Faraday (1845) ^^ the present day, this conviction has been 

 gradually strengthening. It had often been noticed that the per- 

 centage of fire-damp requisite to cause the air of a mine to 

 become explosive was by no means constant, and that the same 

 mixture might or might not be liable to explosion according to 

 circumstances. Gradually, an impression which had long been 

 felt, that the explosive property was due to a third factor — coal- 

 dust — became strong, and has now at length been demonstrated 

 by experiment. 



It willj therefore, be a subject of great interest to the micros- 



