THE EOYAL ARTILLERY INSTITUTION. 
279 
especially since the introduction of the exhaust arrangements. Those 
gentlemen point out that it appears scarcely possible to guard against 
such accidents altogether, although the frequency of their occurrence 
may probably be much reduced by adopting efficient precautions to 
prevent, as far as possible, a stoppage of the “ feed 33 to the millstones 
or the accidental introduction of nails between them together with the 
grain, and by prohibiting the employment of naked lights in the vicinity 
of the mills and the dust passages. In order to reduce as far as possible 
the damage and risk of sacrifice of life resulting from such explosions, it 
is important that all receptacles into which the dust-laden air is drawn 
from the mills should be fixed outside the buildings, and constructed so 
as to offer as little resistance as possible to the sudden expansion re¬ 
sulting from the ignition of the inflammable mixture. The conduits 
leading from the mills to the exhaust-chambers should, moreover, be of 
small dimensions, and there should be no other communication between 
the interior of the building and the dust receptacles, which must not be 
opened while the mill is at work. By adopting precautions of this 
kind, the mill-owner may succeed, at any rate, in reducing the mischief 
resulting from an accidental ignition of flour-dust at the millstones to 
such limits that the mill itself and the lives of those engaged in it will 
not be endangered. 
The production of explosions by mixtures of air with marsh-gas, - 
coal-gas, petroleum vapours, or a finely divided inflammable solid, such 
as flour, has been shown to be due to the application of sufficient heat 
to some portion of the mixture to cause the atmospheric oxygen to 
combine with the combustible constituents of the gas, vapour, or solid, 
the results being the development of chemical action, the formation of 
gaseous products, and their expansion by the heat developed. It need 
scarcely be said that the same explanation applies to the production of 
explosions by that class of so-called explosive agents which is prepared 
by intimately mixing combustible or inflammable solids with a solid 
oxidising* agent ( i.e ., an oxygen-compound which readily yields up a part 
or the whole of that gas under the influence of heat, and with the co¬ 
operation of chemical force, to carbon, hydrogen, or other readily 
oxidisable elements). Distinct from these explosive mixtures as regards 
their nature, but quite analogous to them in their behaviour and the 
effects they produce when subjected to heat or other disturbing influences, 
are explosive compounds. The majority of these contain carbon, hydrogen, 
and oxygen as the most important components; they are more or less 
susceptible of sudden or extremely rapid transformation into gases or 
vapours, attended by development of great heat, in consequence either 
of their resolution into their elementary constituents, or, generally, of the 
re-arrangement of these into comparatively simple forms of combination. 
Some of these explosive compounds are of such unstable character, that 
they are liable to undergo change from very slight inciting causes—such 
as the existence in them of minute quantities of foreign substances of 
active chemical character; or they may even be prone to absolutely 
spontaneous change. In such substances decomposition may be in the 
first instance established only to a very minute extent; but this decom¬ 
position, by the products to which it gives rise, and by the attendant 
development of heat, however small, may speedily promote further and 
