80 
CHEMICAL HISTORY AND APPLIANCES OF GUN-COTTON. 
and the tube will be shattered by the explosion. If, however, a long piece of thin gun¬ 
cotton yarn be passed through a small narrow glass tube, one or two inches long, intowhich 
it fits so loosely that it may be drawn through very easily, the change in the form of 
combustion is effected with certainty, and without the aid of a current of air. When 
the gun-cotton, thus arranged and placed upon a flat surface, is inflamed at one extre¬ 
mity, it burns as usual until it reaches the one opening of the tube ; the slow form of 
combustion then takes place within the tube, and the gun-cotton will continue to burn 
in the slow manner, emitting only the small tongue of flame, after the combustion has 
reached the portion of yarn on the other side of the tube, which will be entirely burned 
in this peculiar manner. In fact, to change the ordinary into the slow form of com¬ 
bustion of the gun-cotton yarn in open air , it is only necessary to pass a piece of the 
material through a perforation in a diaphragm of wood, cardboard, or paper, and to 
allow it to rest upon a flat surface on both sides of the diaphragm. The gun-cotton 
will burn as usual upon one side of the screen, until its combustion reaches the perfora¬ 
tion, when the large bright flame will vanish, and the gun-cotton upon the other side 
of the screen will burn in the slow manner to the end. 
The two last experiments show that if the combustible mixture of gases, evolved by the 
action of heat upon gun-cotton when it is inflamed in open air, are prevented, even for 
the briefest space of time, from completely enveloping the burning extremity of the 
yarn or twist; or, in other words, if they are forced for an instant to escape only in a 
direct line with the burning surface of gun-cotton from which they are emitted, those 
particles of the latter which are in immediate proximity to the burning portion cannot 
be raised to the temperature necessary for their rapid and more complete combustion, 
and hence the gases themselves are in turn not supplied with sufficient heat for their 
ignition. Now, as the gases which escape unburned convey away a very large portion 
of the heat developed by the metamorphosis cf the gun-cotton, it is impossible for the 
latter to continue to burn otherwise than in the slow and imperfect manner. If, how¬ 
ever, a flame or highly-heated body be held in the path of the gases as they escape, 
they will at once be ignited, and the yarn will burst into the ordinary form of com¬ 
bustion. The correctness of this explanation may readily be demonstrated by two or 
three simple experiments. Thus, if a piece of loose or open gun-cotton yarn is em¬ 
ployed in place of the compact material which furnishes the results just described, it is 
very difficult, or even impossible, to cause the rapid combustion to pass over into the 
slow form, because the escaping gases cannot be diverted all into one direction, and 
cannot, therefore, be prevented from transmitting the heat necessary for perfect com¬ 
bustion from particle to particle of the material. Again, if a piece of the compactly- 
twisted gun-cotton yarn, placed upon a flat surface, is inflamed in the usual manner, 
and a jet of air is then encircled in a line with the gun-cotton so as to 
meet the flame, the latter will appear to be blown out, though the cotton still 
burns; in fact, the burning gases are prevented for an instant from completely enve¬ 
loping the extremity of the gun-cotton, and hence the combustion at once passes from 
the quick to the slow form. Conversely, if when the yarn has been made to burn in 
this slow manner, a very gentle current of air be directed against the burning portion, 
so as to force back upon the latter the gases which are escaping, thus impeding the 
rapid abstraction of heat, the gun-cotton will very speedily burst into the ordinary form 
of combustion, because, under these circumstances, the gases are almost immediately 
raised to the temperature necessary for their combustion. In the same way, if a 
piece of the yam placed upon a board be made to bum in the slow manner, and one 
end of the board be gradually raised, so that the burning extremity of the gun-cotton 
is the lowest, the latter will burst into flame as soon as the board has been raised to a 
position nearly vertical, so that the escaping gases flow back upon the burning surface. 
The slow or imperfect form of combustion may be at once induced in the compact 
gun-cotton yarn, in open air, by applying to any part of the gun-cotton a source of 
heat not sufficiently great to inflame the gases generated. A wire, or metal rod, heated 
to any temperature between 135° C. to just below visible redness, or the spark of a thin 
piece of smouldering string, will invariably produce the result described. Of course 
this effect, like most of the phenomena described, is to a considerable extent dependent 
upon the mechanical condition of the gun-cotton, upon the relation between the quantity 
as well as the degree of heat applied and the amount of surface of the gun-cotton, and 
upon other conditions. While a small spark, or a thin platinum wire heated full to redness, 
