k would probably have been thrown for a considerable
distance, and have caused serious damage to surrounding buildings.

It is also a very good plan to surround all danger buildings with mounds
of sand or earth, which should be covered with turf, and of such a height
as to be above the roof of the buildings that they are intended to protect
(see frontispiece).[A] These mounds are of great value in confining the
force of the explosion, and the sides of the buildings being thrown
against them are prevented from travelling any distance. In gunpowder
works it is not unusual to surround the danger buildings with trees or
dense underwood instead of mounds. This would be of no use in checking the
force of explosion of the high explosives, but has been found a very
useful precaution in the case of gunpowder.

[Footnote A: At the Baelen Factory, Belgium, the danger buildings are
erected on a novel plan. They are circular in ground plan and lighted
entirely from the roof by means of a patent glass having wire-netting in
it, and which it is claimed will not let a splinter fall, even if badly
cracked. The mounds are then erected right up against the walls of the
building, exceeding them in height by several metres. For this method of
construction it is claimed that the force exerted by an explosion will
expand itself in a vertical direction ("Report on Visits to Certain
Explosive Factories," H.M. Inspectors, 1905).]

In Great Britain it is necessary that all danger buildings should be a
specified distance apart; a license also must be obtained. The application
for a license must give a plan (drawn to scale) of the proposed factory or
magazine, and the site, its boundaries, and surroundings, and distance the
building will be from any other buildings or works, &c., also the
character, and construction of all the mounds, and nature of the processes
to be carried on in the factory or building.[A]

[Footnote A: Explosives Act, 38 Vict. ch. 17.]

[Illustration: FIG. 1.--SECTION OF NITRO-GLYCERINE CONDUIT. _a_, lid; _b_,
lead lining; _c_, cinders.]

The selection of a site for the danger area requires some attention. The
purpose for which it is required, that is, the kind of explosive that it
is intended to manufacture, must be taken into consideration. A perfectly
level piece of ground might probably be quite suitable for the purpose of
erecting a factory for the manufacture of gun-cotton or gunpowder, and
such materials, but would