304 S. F. Peckham—Mill Explosion at Minneapolis. 
The object for which the air is drawn through is to cool the 
stones and to carry off the vapor produced from the wheat by 
the rise of temperature due to friction. In this case the effects 
of fire were traced back from the outside of the building to one 
of the sets of stones on the north side of the mill used for 
grinding middlings. The effects of flame however did not ex- 
tend beyond the blower which produced the exhaust. This 
led to the conclusion that the fire did not enter the dust-house, 
although the smoke must have passed through it. It is sup- 
posed that the fire was caused by friction between the stones, 
they having run dry from one of the causes that may produce 
dry stones. 
In answer to enquiries made of several millers in the Min- 
neapolis mills, I found them uniformly of the opinion that the 
meal or flour as it left the stones had a temperature of about 
100° F. or less. A number of careful experiments, made with 
an ordinary chemical thermometer, showed that the wheat 
_enters the stones from the dryers at a temperature of fully 
100° F. and that it leaves the stones at 120°-180° F. The 
temperature of the ground middlings as it left the stones 
averaged about ten degrees higher. : 
It was also the concurrent testimony of millers and mill 
owners that dry stones are of comparatively frequent occur- 
rence, and that they are practically unavoidable. I am con- 
vinced that in the Washburn A Mill the frequency of danger 
from dry stones was considerably increased in consequence of 
the large number of stones in the mill, and especially from the 
fact that so few men were employed having the immediate 
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the usual signals employed ary stones should be detected as 
which would readily ignite from a spark produ 
stones striking together. Another source of danger arises from 
nails or gravel passing between the stones with the grist and 
increasing the friction, producing either a rise of temperature 
or a train of sparks; per th. 
m aware that numerous instances of dry stones can be 
cited that have proved perfectly harmless. An instance is 00 
