136 
MINUTES OE PEOCEEDINGS OF 
cotton-twist being ignited by means of a platinum wire, the combustion 
also ceased almost instantaneously. The effects, therefore, can only be 
ascribed to the high cooling-powers, by convection, of the gases in question. 
It was found, by a succession of experiments, that when nitrogen was mixed 
with only one-fifth of its volume of hydrogen the combustion of gun-cotton- 
twist in the mixture was very slow and uncertain (being arrested after a 
short time in some instances), and that a mixture of one volume of hydrogen 
with three of nitrogen prevented its combustion, like coal-gas. 
The slow kind of combustion of gun-cotton, in the form of twist, which 
is determined by its ignition in currents or atmospheres of nitrogen, car¬ 
bonic acid, &c. may also be obtained in a powerful current of atmospheric 
air, the thread of cotton being placed in a somewhat narrow glass tube. 
If, however, the air is at rest, or only passing slowly, the result is uncer¬ 
tain. In employing very narrow tubes into which the gun-cotton fits 
pretty closely, the combustion passes over into the slow form when it 
reaches the opening of the tube, and occasionally it will then continue 
throughout the length of the tube. In that case, while the gun-cotton 
bums slowly along the tube, with a very small sharp tongue of pale flame, 
a jet of flame is obtained at the mouth of the tube, by the burning of 
the gas evolved by the decomposition of the gun-cotton. Sometimes, 
and especially when wider tubes are employed, the slow combustion will 
proceed only for a short distance, and then, in consequence of the ignition of 
a mixture of the combustible gases and air within the tube, the gun-cotton 
will explode with great violence, the tube being completely pulverized, 
and portions of unburnt cotton scattered by the explosion. If still wider 
tubes are employed, the cotton will flash into flame almost instantaneously 
throughout the tube directly the flame reaches the opening : in these cases 
the explosion is not violent; sometimes the tube escapes fracture, and at 
others is broken in a few places, or torn open longitudinally, a slit being 
produced in the tube directly over the gun-cotton. By using narrow tubes 
and gradually shortening the tube through winch the gun-cotton was 
passed, pieces of the twist being allowed to project at both ends, it was 
found, upon inflaming the material which projected on one side, that the 
slow form of combustion, induced in it as soon as it burned into the tube, 
was maintained by that portion wliich burned in the open air on the other 
side, when the combustion had proceeded through the tube. Eventually, 
by the employment of a screen of wood or card-board containing a perfo¬ 
ration of the same diameter as that of the gun-cotton-twist, through which 
the latter was partially drawn, the alteration of the combustion of the 
material from the ordinary to the slow kind was found to be invariably 
effected: On the one side of the screen, the gun-cotton burned with the 
ordinary flame and rapidity, until the combustion extended to the perfo¬ 
ration, when the flame was cut off and the material on the opposite side of 
the screen burned only slowly, emitting the small-pointed tongue of pale 
yellow flame. 
These results indicate that if, even for the briefest space of time, the 
gases resulting from the first action of heat on gun-cotton upon its ignition 
in open air are impeded from completely enveloping the burning extremity 
of the gun-cotton-twist, their ignition is prevented; and as it is the com¬ 
paratively high temperature produced by their combustion which effects 
