i54 THE POPULAR SCIENCE MONTHLY, 



more favorable conditions the dust would ignite directly from sparlis, 

 but it seems very improbable. 



Let us continue now with the process through which the ground 

 wheat is made to pass. From the stones it is conveyed to the bolting- 

 reels, where the very finest is sifted out first, and we obtain a grade of 

 flour'; after the finer material is sifted out it goes to a coarser bolt, 

 where the " middlings," as it is called, passes through, leaving the 

 bran which comes out at the end of the reel. The middlings, as it 

 comes from the bolts, has fine bran and dust in it, and, to purify it, it 

 is subjected to an operation similar to that of cleaning the wheat, that 

 is, in the middlings purifiers it is subjected to a draught of air which 

 takes away all the light bran and dust, leaving the heavier material 

 (purified middlings), which goes again to the stones to be ground into 



flour. ' , . „ 



Here is some of the dust from these "middlings-machmes ; you 

 observe it burns as the other materials burned, quickly, and with in- 

 tense heat. 



Here is some of the purified middlings ; each grain is comparatively 

 large and heavy, making it difficult to blow it well into the air, but, as 

 the blaze produced by each particle is quite large, a flash is produced 

 which does not differ materially from the others. 



Here is some of the general dust of the mill, that is, dust swept up 

 from the floors, walls, beams, etc. You will see it acts in all respects 

 like the other substances. 



And, finally, here is some of the flour taken this afternoon from the 

 flour-sai at home ; it burns, you observe, if possible with even more 

 energy than the other kinds of dust. 



I have performed a few experiments, which I will now repeat, which 

 will illustrate to you the immense power that these materials exert 

 when burned in a confined space. 



This box (Fig. 2) has a capacity of two cubic feet ; the cover has a 

 strip three inches deep nailed around it, so that it telescopes into the 

 box; there is in this lower corner an opening for the nozzle of the bel- 

 lows, in this an opening for the tube to the lamp. I place now a little 

 flour in the corner, light the lamp, and my assistant places the cover 

 upon the box and steps upon it. Take notice that upon blowing through 

 the hole, and fiUing the box with a cloud of flour, the cover comes up 

 suddenly, man and all, until the hot gas gets a vent, and a stream ot 

 fire shoots out in all directions. 



Here is a box (Fig. 3) of three cubic feet capacity, includmg this 

 spout, nine inches square and fifteen inches long, coming from the top 

 of it- at the ends doors are arranged closed like steam-boiler man- 

 holes ; openings for light and bellows are arranged as in the previous 



Here is a box, weighing six pounds, that will just slip over the 

 spout; it has a rope lest it should strike the wall after the explosion. 



