278 
MINUTES OP PROCEEDINGS OP 
faces against each other, the result being the ignition of the mixture of 
air and fine flour-dust surrounding the millstones. 
This ignition alone would not suffice to develop any violent explosive 
effects ; such ignitions, though occasionally observed in small mills, being 
caused either by the striking of fire by the stones, or by the incautious 
application of a light near the millstones, or the meal-spout attached 
thereto, have not in these instances been attended by any serious results. 
But in an extensive mill, where many pairs of stones may be at work at 
one time, each pair has a couduit attached to it, which leads to a com¬ 
mon receptacle called an exhaust-box; into this the mixture of air and 
very fine flour-dust which surrounds the millstones is drawn by means 
of an exhaust-fan, sometimes aided by a system of air-blowers. The 
fine flour is allowed to deposit partially in this chamber or exhaust-box, 
and the air then passes into a second chamber, called a stive room, 
where a further quantity of dust is deposited. It follows that when the 
mill is at work, these chambers and the channels or spouts connecting 
them with the atmosphere immediately surrounding each millstone, are 
all filled with an inflammable mixture of the finest flour-dust and air, 
and that consequently the application of a light to any one of those 
channels, or the striking of fire by any one of the millstones, by igniting 
some portion of the inflammable mixture, will result in the exceedingly 
rapid spread of flame throughout the confined spaces which are charged 
with it, and will thus develop an explosion. The violence of such 
explosions depends much upon details of construction of the exhaust-boxes 
and stive rooms, and upon the dimensions of the channels of communi¬ 
cation ; it must obviously be regulated by the volume of inflammable 
mixture through which fire rapidly spreads, and upon the extent of 
its confinement. In the case of the catastrophe at Glasgow, the 
production of a blaze at a pair of millstones was observed to be followed 
by a crackling noise as the flame rapidly spread through the conduits 
leading to the exhaust-box upon an upper floor, and a loud report from 
that direction was almost immediately heard. Professors ftankine and 
Macadam, who carefully investigated the cause of this accident, report 
that other flour-mill explosions which they have enquired into had been 
observed to be attended by a similar succession of phenomena to those 
noticed upon this occasion. The bursting open of the exhaust-box by a 
similar though less violent explosion, attended by injury of workmen, 
the blowing out of windows and loosening of tiles, appears to have taken 
place on a previous occasion at these particular mills. In the last acci¬ 
dent, however, the more violent explosion appears to have been followed 
by others, the flame having spread with great rapidity to distant parts 
of the mills through the many channels of communication in which the 
air was charged with inflammable dust, resulting from the cleansing and 
sifting operations carried on in different parts of the building, and 
rapidly diffused through the air by the shock and blast of the first 
explosion. 
The subject of flour-mill explosions, though it has attracted little if 
any attention in this country previous to the Tradeston explosion, -is 
discussed in Continental treatises on flour-mills, and the results of 
Messrs. Rankine and Macadands enquiries have demonstrated that 
accidents of this kind are actually of ordinary occurrence in mills, 
