s 
JANUARY 18, 1884.] 
Let the case be the simplest one, such as an 
explosion caused by the fall of a weight from a 
certain height. At first one would suppose the 
effects observed to be due to the heat developed 
by the pressure of the suddenly arrested weight. 
But calculatton shows that the arresting of a 
weight of several kilograms, falling .25 to .50 
of a metre, would not be capable of raising 
the temperature of the explosive mass more 
than a fraction of a degree, if the resulting 
heat were dispersed uniformly throughout the 
entire mass: while for a body such as nitro- 
elycerine, for instance, it is necessary to heat it 
to 190° to induce explosion. 
It is by another process that the mechanical 
energy of the weight, which is transformed 
into heat, becomes the originator of the 
observed effects. It is sufficient to assume, 
that, as the pressures which arise from the 
shock exerted on the surface of the nitro- 
glycerine are too rapid to become uniformly 
dispersed throughout the entire mass, the trans- 
formation takes place locally among the layers 
first reached by the shock. If it is sufficiently 
violent, they may thus be rapidly heated to 
the necessary temperature; and they will be 
immediately decomposed, and produce a large 
quantity of gas. This production of gas is in 
its turn so violent that the shocking body has 
not time to displace itself; and the sudden 
expansion of the gases of explosion produces 
a new shock, probably more violent than the 
~ first, on the layer situated below. ‘The mechani- 
Aq 
cal energy of this shock is changed into heat in 
the layers which it reaches, and produces an 
explosion ; and this alternation between a shock 
developing mechanical energy which changes 
into heat, and a production of heat which ele- 
vates the temperature of the layers up to the 
degree necessary for a new explosion capable 
of reproducing the shock, propagates the reac- 
tion, molecule by molecule, through the entire 
mass. The propagation of the deflagration 
takes place in this way in consequence of phe- 
nomena comparable to those which produce 
a sonorous wave; that is to say, by producing 
a real explosion which advances with a rapidity 
incomparably greater than that of a simple 
burning provoked by the contact of a body in 
ignition, and operating under conditions where 
the gases expand freely in proportion to their 
production. 
The reaction started by the first shock in a 
given explosive material is propagated with 
a rapidity which depends upon the intensity 
of the first shock; and this intensity may 
vary considerably, according to the method 
by which it is produced. Marcel Duprez has 
SCIENCE. T7 
shown that the effect of a blow from a hammer 
may vary in duration from the hundredth to 
the ten-thousandth of a second, according as 
one strikes with a hammer having a flexible 
handle or with a block of steel. From this it 
follows that the explosion of a solid or liquid 
mass may develop itself according to an infi- 
nite number of different laws, each one of 
which is determined, all other things being 
equal, by the original impulse. The more vio- 
lent the initial shock, the greater will the result- 
ing violence of the decomposition be, and the 
greater will be the pressures which are exerted 
during the entire course of this decomposition. 
One and the same explosive substance may 
hence produce very different effects, according 
to the method of ignition. 
Among these methods of ignition, by far the 
most curious and inexplicable is the determin- 
ing of the explosion of one mass by the ex- 
plosion of another mass near by, but not in 
contact with it, which is termed by Berthelot 
‘explosion by influence.’ Abel has offered his 
theory of synchronous vibrations to explain this 
phenomenon, and the theory seemed to be con- 
firmed by the interesting experiments of Cham- 
pion and Pellet ; but Berthelot regards them as 
inconclusive, or else directly opposed to Abel’s 
theory, and he offers a theory of his own, which 
is but an expansion of that of shocks explained 
above. . | 
Working, as Berthelot is, under the direct 
auspices of the French government, he has had 
the best of facilities for the study of explosive 
substances and the phenomena of explosions ; 
and no one has. probably engaged in a more 
critical or extended physical and chemical ex- 
amination of these bodies, and hence he speaks 
with authority. Yet some of his theories have 
failed to find general acceptance, especially 
that concerning the influence of dissociation 
upon the force of explosives; and it is notice- 
able that this theory finds no place in these 
lectures. 
Karl Braun’s sketch is bright and entertain- 
ing but iconoclastic, and, while wresting the 
honor of the discovery of gunpowder from Ber- 
thold Schwartz, intimates that the. knowledge 
of its manufacture was brought from the orient 
to Augsburg in 1353 by a Greek Jew named 
' Typsiles. 
Of the ‘ Bibliography of explosives ’ the best 
that can be said is, that it is an unsystematized 
collection of titles, that it is filled with errors 
of the grossest kind, and that it is unworthy of 
both compiler and publisher. In fact, it must 
be said the book throughout is marred by 
printers’ errors. 
