762 GUNPOWDER 



if they smouldered. The pressure in the case described must not exceed 8 inches of 

 mercury, but the rarefaction necessary for the result varies with the quantity of gun- 

 cotton, its mechanical condition, its position with reference to the source of heat, the 

 quantity of heat applied, and the direction of its application. 



Gun-cotton, when ignited in small quantities in rarefied atmospheres, may exhibit 

 during its combustion three distinct luminous phenomena. In the most highly rare- 

 fied atmospheres, the only indication of combustion is a beautiful green glow, or phos- 

 phorescence, which surrounds the extremity of the gun-cotton, as it is 



transformed into gases or vapours. When the pressure of the atmosphere is increased 

 to one inch (with the proportion of gun-cotton indicated), a faint yellow flame appears 

 at a short distance from the point of decomposition ; and as the pressure is increased, 

 this pale yellow flame increases in size, and eventually appears quite to obliterate tho 

 green light. Lastly, when the pressure of the atmosphere and consequent proportion 

 of the oxygen in the confined space is considerable, the cotton burns with tho ordinary 

 bright yellow flame. There can be no doubt that this final result is duo to tho almost 

 instantaneous secondary combustion, in the air supplied, of the inflammable gases 

 evolved by the explosion of the gun-cotton. The pale yellow flame will take place in 

 rarefied nitrogen. 



In a series of experiments made under gradually-diminished pressures, oxygen being 

 used, instead of air, it was found that the gun-cotton exploded instantaneously with a 

 bright flash until the pressure was reduced to 1-2 inch; from this pressure to that of 

 0'8 inch, it still burned with a flash, but not instantaneously, and at pressures below 

 0-8 inch, it no longer burned with a bright flash, but exhibited tho comparatively slow 

 combustion, accompanied by the pale yellow flame. In atmospheres of carbonic 

 anhydride, carbonic oxide, hydrogen, and coal-gas, this pale yellow flame is seen as in 

 nitrogen ; but the two latter gases have a great tendency to extinguish the combustion, 

 doubtless on account of their high cooling power by convection. 



The slow kind of combustion of gun-cotton, in the form of twist, may be obtained 

 also in a powerful current of atmospheric air, if the thread of cotton bo placed in a 

 somewhat narrow glass tube. Indeed, it was found 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 the gun-cotton continues to burn in tho 

 slow and imperfect manner, undergoing a transformation similar in character to de- 

 structive distillation. By proper arrangements, these gases may be burnt at the mouth 

 of a tube while the gun-cotton is burning in the interior. There is little doubt that 

 these products of decomposition vary as greatly as tho phenomena themselves ; thus, 

 in the instance of the most imperfect metamorphosis of gun-cotton, the products in- 

 cluded a considerable proportion of a white vapour, slowly dissolved by water, as also 

 small quantities of nitrous acid, and a very large proportion of nitric oxide ; cyanogen, 

 too, is always found. This contrasts strongly with the simpler products of decom- 

 position found by Karolyi when the gun-cotton was exploded under the pressure of a 

 confined space. 



Abel considers that the remarkable facility with which tho combustion of gun- 

 cotton in the air or other gases may be modified, might be taken advantage of to 

 produce a variety of mechanical effects ; and he states, that by enclosing in suitable 

 cases solid cords made up of two or more strands of gun-cotton more or loss com- 

 pactly twisted, ho has succeeded in producing fuses and slow-matches, tho time 

 of burning of which may be accurately regulated. See Watts's ' Dictionary of 

 Chemistry.' 



GUN-MET AI. The Austrians introduced a gun-metal, called, from its in- 

 ventor, Aich metal. It is composed of copper, 600 parts ; zinc, 382 pvrts ; iron, 88 

 parts. Its tenacity is said to be excessive ; it is easily forged and bored : when cold, 

 it may be bent considerably without breaking, and wo are told its resistance is far 

 greater than iron of the best quality. See Bit ASS and COPPKR. 



GUNNERY. Under the heads of ARTILLERY and FIUE-ARMS, wo have included 

 all which appears necessary in a work of this description. 



GUNNY CXiOTHS or BAGS. Tho coarse sacking made in India, which is used 

 for wrapping rice, spices, &c. Tho Bengal gunny cloth is made of tho fibre of a spirits 

 of Corchorus, while that of Bombay and Madras is manufactured from different kinds 

 of sunn fibre, the Crotolaria juncea. Simmonds. 



GUNPOWDER. The discovery of gunpowder has been claimed for Juurrr I!ar..n 

 and Schwartz. The ground for this appears to bo no more than this. In their writings 

 tho earliest recorded mention of tho <!iM->vi-ry is mado in any European lai 

 .Roger Bacon, unquestionably antecedent to his German rival, was l>orn l'Jl-1 and died 

 1292 ; and his work, ' Do Nullitato Magia-.' appears to have been writen about 1270, 

 while Kjreher's account gives 1354 as tho date of the discovery by Schwartz, It ap- 



