, 1872-12-25
WHY DO FLOuR-El!lLs BURN ?

| To the Editor Of The Chicago Tribune:
sIR: The writer has had occasion to pay some
attention to the origin Of fires, and finds a re-
uaarkable confirmation OF his own conclusions as
to the combustibility OF Touring mills, in the
extract below.
| Some TWO or three years ago, mill Was burned
at Milwaukee by bringing en open light too near
a feed-spout from which middlings we're being
discharged from bins il, III upper story Tbs
blaze ran up, the spout as If it were filed with
coalgas, aud destroyed tho mill.
few weeks later, q mill Nas burned at St.
Louis from similar cause. only, in this case,
fire caught from the flame in globe-lamp and
the result was equally rapid and disastrous.
Various theories we're started and discussed as
to the cause OF these fires, though but little was
definitely known, except that milIs.vere very
apt to burn, and most insurance COMPANIES de-
c1ined to write on those where open lights we're
permitted to be used. The following extract
writer's especially:
On the 25th Of last month, before the Roya1 Scottish
Society Of arts, Dr. Stevenson MacAdam read paper
tending to show that 1oU.-ns arc almost az danrer-
ous neighbors IS gunpowder-mills. The chemical
component8 OF grain are co1nbustiba when burned
rapidity when didused a. cloud throush t6o l. air.
When -four Is showered through sieve p1aced above
gas-a3ne, rapid combustion takes place. Indeed tho
tour burns with explosive Eapidty and the flame ticks
mp the four-shower somewhat in the same way that
1t aaehes through mixture Of gas and air. or that
1t treads along a train Of Runpowder Then
burned, the -four resolves itself into gases, The
carbon, by mixing with tho oxygen of the air becomes
carbonic oxide or car5onc acid aud tie hydrogen and
oxygen become water, vapor, or steam. The volume
Of these gases much increased by the high empera
ture atthe moment Of combustion. The conditions
required to bring about flour explosion are some
Whist similar to those which cause gas-e1plosjon.
Flour agrees with coagas in being simply combusti-
ble when unmixed with air, and equally agrees with
coa1gas in being explosive when mingled with air:
but the fine, impalpab1e dust must be difused through
the air In definite proportions in order to constitute an
explosion when white heat, s11ch as fame or spar,
brought near. In order to bring about an e1p1o.
ton, It is also necessary that the 1our-rni1-
ture be mo1e or less confined within . given
space. The more common way Of the production d
the spark or tame which fires the aonrair explosive
mixture is the feed going of the stone doing work
when the stones set down each other and as they
are Of fnty or other hard sicious rocks and are re-
EolE1ng at from 100 to 160 revolutions in q minute
they quickly strike fire and become very hot The
feed may 60 of for want Of grain in the hopper or
any obstruction in the fecd-ppe. spiders web &C.
tual1y stopped the feed In case and led to VIC
lent explosion in English four-ni11 AIr alacAdam
suggestg various expedients to be adopted for avoiding
dour-1n explosions, such the removal Of exhaust
boxes, snaurooms and other receptacles
Of hour-dust, to tha outside Of the mill,
CHICAGO, Dec 90, 1879. Z.