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Page 21
The effect of the high explosives upon horizontal armor is very great;
but we have yet to learn how to make it shatter vertical armor. No
fact about high explosives is more curious than this, and there is no
theory to account for it satisfactorily. As previously stated, the
French have found that four inches of vertical armor is ample to keep
out the largest melenite shells, and experiments at Annapolis, in
1884, showed that masses of dynamite No. 1, weighing from seventy-five
to 100 pounds, could be detonated with impunity when hung against a
vertical target composed of a dozen one inch iron plates bolted
together.
In conclusion, I may say that in this country we are prone to think
that the perfection of the methods of throwing high explosives in
shell is vastly in favor of an unprotected nation like ourselves,
because we could easily make it very uncomfortable for any vessels
that might attempt to bombard our sea coast cities.
This is true as far as it goes, but unfortunately the use of high
explosives will not stop there. I lately had explained to me the
details of a system which is certainly not impossible for damaging New
York from the sea by means of dynamite balloons. The inventor simply
proposed to take advantage of the sea breeze which blows toward New
York every summer's afternoon and evening. Without ever coming in
sight of land, he could locate his vessel in such a position that his
balloons would float directly over the city and let fall a ton or two
of dynamite by means of a clock work attachment. The inventor had all
the minor details very plausibly worked out, such as locating by means
of pilot balloons the air currents at the proper height for the large
balloons, automatic arrangements for keeping the balloon at the proper
height after it was let go from the vessel, and so on. His scheme is
nothing but the idea of the drifting or current torpedo, which was so
popular during our war, transferred to the upper air. An automatic
flying machine would be one step farther than this inventor's idea,
and would be an exact parallel in the air to the much dreaded
locomotive water torpedo of to-day. There seems to be no limit to the
possibilities of high explosives when intelligently applied to the
warfare of the future, and the advantage will always be on the side of
the nation that is best prepared to use them.
* * * * *
THE MANUFACTURE AND USE OF PLASTER OF PARIS.
It has long been a familiar fact that gypsum yields on baking a
material which possesses the power of setting with water to a firm
mass, this setting being accomplished much more quickly than is the
case with mortar.
The explanation of the setting of plaster was first given by
Lavoisier, who pointed out that gypsum is an hydrated salt, and that
the set plaster is in fact gypsum reformed, the change brought about
by baking being merely loss of water of crystallization. The beds of
gypsum of most importance both formerly and at the present time in the
plaster manufacture occur in the neighborhood of Paris in the lower
tertiary formation. Different beds differ (1) in respect of character
and quantity of admixed materials and (2) in the structure of the
gypsum itself. With regard to the first point, some deposits contain a
notable proportion of carbonate of lime, a fact which under certain
circumstances may considerably influence the character of the plaster.
In the matter of structure two principal varieties occur (1) granular
and (2) fibrous. Further, hardness of the granular kind varies
considerably. These differences of structure in the original material
appear to exercise an influence on the properties of the plaster. Thus
according to Payen the plaster formed from the granular variety sets
more gradually than that derived from the fibrous, and forms a denser
mass. The softer kinds of the granular gypsum are those principally
used in the production of plaster for the moulds of potteries.
In the old fashioned process which is still employed for making the
common kinds of plaster, the material is exposed to the direct action
of flame. Large lumps are placed in the lower part of the furnace,
above them smaller lumps, and, after the heating has been carried on
for some time, finely divided material is filled in at the top. The
outer portion of the larger lumps is always overburnt, and in the
upper part of the furnace the presence of shining crystalline
particles generally indicates the fact that some gypsum has remained
unchanged. Provided that the amount of unburnt and overburnt material
does not exceed about 30 per cent. of the total, the plaster is
suitable for many applications.
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