92 Mr. F. A. Ahel [April 28, 



Attention has again been recently directed to this subject of flour- 

 dust explosions by a fatal and extensive calamity of the kind which 

 occurred at a flour mill at Macclesfield in September 1881, and has 

 been made the subject of an interesting report to the Home Secretary 

 by Mr. T. J. Richards, of the Board of Trade, in which he confirms 

 the conclusions of Messrs, Rankin and Macadam, and repeats the 

 recommendations made by them. 



In this particular case, again, there appears to have been no doubt 

 that the infiammation of the dust-and-air mixture surrounding a 

 particular pair of millstones was due to the stones remaining empty 

 for some time, sufficient heat being consequently developed to ignite 

 some portions of flour dust existing between the bearing surfaces. 

 One of the owners of this mill deposed that he had seen flame pro- 

 duced by stones when remaining empty, and that the appearance of 

 the stones in question convinced him that flame had been thus 

 j)roduced. A very dry grain was, moreover, being ground at the time 

 of the explosion. A strong consensus of opinion appears to exist that 

 it is very difficult, with the best arrangements for feeding the mill- 

 stones with grain, to guard against their running empty occasionally, 

 and there is no doubt that on these occasions portions of flour are 

 exposed to heat sufficiently great to char and sometimes even to ignite 

 them. In connection with this effect of the heat to which portions 

 of flour may be exposed between " dry " stones, the opinion of an 

 " experienced person " (quoted as a regrettable one by Mr. Richards) 

 deserves not to be lost sight of. It is to the effect that a stive room 

 can at all times be safely entered with a naked light " except when 

 there is observed the peculiar odour which is noticed there when one 

 of the millstones has been previously running empty." It is not 

 difficult to demonstrate that fine flour very thickly suspended in air 

 will produce with the latter an inflammable mixture, through which 

 flame will be rapidly transmitted ; there is also no doubt that if, as is 

 frequently the case, the enclosed dust-and-air mixture in the air- 

 passages of a mill is somewhat warm, the propagation of flame 

 through the mixture will be facilitated. But experimental observa- 

 tions which the lecturer has had occasion to make in connection with 

 another branch of the subject of this discourse, lead him to consider 

 it not impossible that the development of even very small quantities 

 of inflammable gas or vapour from flour particles which become 

 heated between " dry " stones to an extent to be charred, may, in 

 some cases, decidedly facilitate the propagation of flame by a parti- 

 cular mixture of dust and air, which might otherwise only be bordering 

 upon an explosive mixture. 



Mr. Richards calls attention, in an appendix to his report, to four 

 very disastrous fires which had occurred in flour mills at Wakefield, 

 York, Liverpool, and Deptford, within two months of the completion 

 of his report, the origin of the fire being in each case unknown. 

 There is no doubt that the number of fires occurring in corn- and 

 rice-mills, the origin of which is wrapped in obscurity, is very great ; 



