220 
ME. ABEL’S EESEAECHES ON GUN-COTTON. 
Experiment 117. — Gun-cotton, purified as usual, has been confined in stoppered glass 
bottles, having previously been rendered slightly acid with nitric acid. In these instances 
the gun-cotton has always undergone decomposition upon exposure to light, the rapidity 
of its change varying with the quality of the material. 
Experiment 118. — Two specimens of Waltham Abbey gun-cotton (coarse and fine 
yarn) were introduced into well-stoppered bottles, and pernitric oxide was then passed 
into those for a short time. The bottles were then tightly closed and placed in a dark 
cupboard, being inspected from time to time. The gas was rapidly absorbed by the- 
gun-cotton, which assumed a green tinge and gradually contracted, the colour of the 
vapours in the bottles slowly becoming deeper again. After the lapse of two months 
both samples had contracted into compact masses, occupying less than one-fourth the 
original volume. Both were coloured green, and dark orange vapours filled the vessels. 
From this period the pernitric oxide diminished in quantity very gradually, until, about 
eighteen months after commencing the experiment, the atmosphere in the bottles was 
perfectly colourless. The coarse gun-cotton had passed into a viscid mass, exhibiting 
the usual characters ; the fine gun-cotton, though it contracted to about one-tenth of its 
original volume, still retained to some extent its original appearance ; crystals of oxalic 
acid were dispersed through the mass. 
Experiment 11 9. — Two other samples of gun-cotton employed in the preceding expe- 
riment were placed in bottles into which nitrous acid, produced by means of starch, was 
passed. These bottles were afterwards also placed in the dark. The gas was gradually 
absorbed by the gun-cotton, the atmosphere in the bottles became colourless, and both 
samples were highly bleached. After the lapse of two months, a faint orange colour was 
exhibited, but the specimens of gun-cotton had undergone no apparent change whatever. 
Three months later, the bottle containing the coarse yarn exhibited deep orange vapours, 
the gun-cotton had contracted somewhat and assumed a green tinge. The other sample 
exhibited no signs of change, but a faint orange tinge was manifest in the bottle, which 
did not increase afterwards. Twenty-eight months after the commencement of the expe- 
riment this sample exhibits no signs of change beyond a very slight contraction. The 
coarse yarn has contracted to about one-third its original volume, is friable, and partly 
soluble in water. 
Pernitric oxide, if left in contact with gun-cotton, is therefore much more rapid in 
its destructive action than nitrous acid ; gun-cotton when confined together with either 
of them, undergoes gradual decomposition even in the dark. 
Experiment 120. — A sample of gun-cotton which had been found to decompose very 
readily at 100°, was placed in a retort suitably fitted with a delivery-tube, and the gases 
disengaged from it were passed into four bottles containing different samples of gun- 
cotton. These were then perfectly closed and exposed to strong daylight. 
The first sample soon began to exhibit signs of change. The colour of the vapours 
increased in depth, and in one month’s time had become very deep-coloured, the gun- 
cotton having assumed a greenish tinge from absorption of gas. The sample was then 
placed in the dark, after which it underwent further change very gradually, first con- 
