670 Explosions from Combustible Dust. [October, 
some oatmeal, the finer part of which only burns; and so I 
might continue with all sorts of finely-ground vegetable 
material. 
Let us take up now the products of the manufacture of 
flour from wheat. There were between 300 and 400 tons of 
these materials, upon which I am now to experiment, in the 
Washburn Mill at the time of explosion, and there was a 
corresponding amount in the Diamond and Humboldt Mills, 
which, by their sudden burning, produced the second and 
third shocks heard direCtly following the explosion of the 
larger mill. 
The wheat is first placed in a machine, where it is rattled 
violently and brushed. At the same time a strong draught 
of air passes through it, taking all the fine dust, straw, &c., 
and conveying it through a spout to a room known as the 
wheat-dust room, or perhaps more commonly it is blown 
direCtly out of the mill. 
You see some of this material here ; it looks like the 
wood-dust of the first experiment, and, as you see, burns 
with a quick and sudden flash when subjected to the same 
conditions. 
Here, then, we have the first source of danger in a flour- 
mill. A thick cloud of this dust, when conveyed through a 
spout by air, will burn in an instant if it takes fire ; and if 
there is any considerable amount of dust, as there would be 
if there were a dust-room, an explosion will follow which 
may become general if it stirs up a thick dust-cloud through- 
out the mill. 
The wheat, after it has been cleaned in this way, goes to 
the crushers, which are plain or fluted iron or porcelain 
rollers, working like the rollers in a rolling-mill. The objeCt 
of these rollers is, I believe, to break off the bran in as large 
pieces as possible, and to crush out or flatten the germ so 
that it can be separated with the bran from the rest of the 
meal. 
The crushed wheat goes now to the stones, where so much 
heat is produced (average 135 0 F.) that a large amount of 1 
steam is formed from the moisture in the materials. This 
steam would condense in the meal, and interfere with 
bolting, &c., if it were not removed. To effeCt this another 
draught of air and another spout are employed, and, as 
might be expected, this current takes a large quantity of the 
very finest flour, called flour-dust, with it. To save this a 
room is provided near the end of the spout, called the flour- 
dust house. The spout conveying steam and dust enters 
this room on one side, and another spout opposite leaves it, 
