In the manufacture of the explosive known as dynamite, an infusorial
earth is used, which is filled with or made to absorb nitroglycerin.
As compared with certain kinds of charcoal, however, the absorptive
and retentive power of infusorial earth in small changes of
temperature unfavorably affect the common dynamite, and cause a
separation of the nitrogylcerin from the infusorial earth. The
improvement we now refer to is the invention of G. Fahnehjelm, of
Stockholm, Sweden, and consists in the substitution of a highly
porous and absorptive species of wood charcoal, in place of the
earth heretofore employed. The author designates his production as
"sebastin," and gives a number of interesting particulars as follow:
In order to produce a charcoal having the required quantities, the
carbonization or coking must be done in such a manner as to completely
destroy the organic substances, and to produce as porous a charcoal as
possible. For this he selects by preference young trees or striplings
or branches of poplar, hazelwood, or alder tree, and he burns them in
an open fire. When the wood has been consumed he does not put out the
fire by means of water, but leaves it to go out of itself. In this
way he obtains a very inflammable and very porous charcoal, which can
absorb more than five, and approaching six times its weight of
nitroglycerin without any risk of the separation of the oil. The
charcoal is pulverized in a wooden mortar, but it should not be
reduced to too fine a powder, else it will not so completely absorb
the nitroglycerin. The charcoal produced in the ordinary way, or by
closed fire, is quite different as regards absorbing power. Charcoal
of fir trees may, however, be used, and may acquire nearly the same
qualities, that is, if charred a second time in a special oven.
By mixing the different kinds of charcoal, a material may be obtained
possessing the required absorbing qualities, and an explosive compound
may then be obtained of the required power without loss of the
necessary consistency--that is, without being too dry, which is not
desirable. The charcoal not only serves as the best absorbent for the
nitroglycerin, but it plays also an important part in the combustion.
The nitroglycerin in exploding decomposes into steam, carbonic acid,
nitrogen, and oxygen. In the explosion of dynamite with inert base the
oxygen goes away without being utilized, but in the explosion of this
new compound (the new sebastin as he calls it) a part of the absorbent
charcoal is burnt by means of the liberated oxygen. The quantity of
gas is thus augmented, and also the development of heat, whereby again
the tension of this gas is augmented. As, however, the quantity of
charcoal necessary for the complete absorption of the nitroglycerin
is in all cases much larger than that which can reduce the excess of
oxygen produced at the explosion into carbonic acid, he adds to the
compound a salt, which also by the combustion gives an excess amount
of oxygen which may contribute to burn the rest of the charcoal. For
this purpose he uses by preference nitrate of potassa, which may be
added without any risk, and which gives the explosive compound a very
much greater rapidity or vehemence, and consequent force of explosion.
The composition of the new sebastin depends upon the objects for which
it is to be used, and the effects intended to be produced. The
strongest compound, and even in this there is stated to be no risk of
the separation of the nitroglycerin, is composed of 78 parts by
weight of nitroglycerin, 14 of the wood charcoal, and 8 of nitrate of
potassa; and when less power is required the proportions are
varied, the second quality consisting of 68 per cent. by weight of
nitroglycerin, 20 of the charcoal, and 12 of nitrate of potassa.
To show the relative strength of the compounds, the inventor says: Let
the dynamic force of pure nitroglycerin be represented by the number
2,884,043.6, then the dynamic force of the sebastin No. 1, as
above, will be indicated by 2,416,575, and of the sebastin No. 2 by
1,933,079.4, while that of dynamite No. 1 (consisting of 75 per
cent. of nitroglycerin and 25 per cent. of infusorial earth) will be
represented by 674,694.
For the above qualities of sebastin the increased effect produced by
the greater rapidity of the explosion must be taken into account also.
The increase has not yet been measured, but is estimated at 10 per
cent. The sebastin may also be compounded in other proportions of the
constituent parts, but the object being to produce explosive compounds
of the greatest force which it is possible to employ without danger,
he merely mentions that the proportion by weight may vary from 50
to 80 per cent. of nitroglycerin, 15 to 35 per cent. of the prepared
charcoal, and 5 to 20 per cent. of the nitrate of potassa; the parts
being taken by weight, as above stated.
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