MR. ABEL’S RESEARCHES ON GLJN-COTTON. 
221 
tracting considerably and afterwards, after the lapse of upwards of one year, becoming 
converted into a somewhat hard gum-like mass. 
In the case of the second and third samples, the coloured vapours disappeared at first 
almost entirely, but the atmosphere in the bottles became coloured again after one month’s 
exposure to light. The depth of colour increased so rapidly in one instance that two 
months after first exposure to light the bottle was placed in the dark. The change in 
the two bottles then proceeded at about the same rate. The specimens contracted very 
slowly, and the nitrous vapours disappeared gradually. At present, years after com- 
mencement of the experiment, the specimen which has been exposed to light is scarcely 
as much changed as the one which after a time was placed in the dark ; both have con- 
tracted to about one-half their original volumes, but have preserved their normal appear- 
ance; a few very minute crystals (probably oxalic acid) are perceptible upon the sides 
of the bottle which has been kept in the dark. 
The fourth sample (prepared at Waltham Abbey in 1863) has resisted change to a 
remarkable extent. The vapours were at first entirely absorbed, and the gun-cotton has 
become slightly bleached. A faint orange tinge was first observable in the bottle after 
it had been exposed to strong daylight for six months. Nitrous vapours were then 
slowly evolved until the depth of colour was somewhat considerable. After the lapse 
of several months they gradually diminished again, and ultimately disappeared once 
more, after about eighteen months’ exposure. After the lapse of 2 \ years the gun- 
cotton has contracted only slightly, but exhibits no other signs of change. There can 
be no doubt, however, judging from this contraction and from the evolution of vapours 
at one period of exposure, that this sample has suffered change which would not have 
occurred had it been exposed to light under ordinary conditions. 
The experiments in sealed tubes which have been described, — the results of examina- 
tion of gases collected from gun-cotton which has been exposed to heat for long periods 
in contact with them, — and the general existence of nitric acid in samples of decom- 
posed gun-cotton, appear to show that the first effect of exposure of the ordinary mate- 
rial to sufficient heat is the disengagement of pernitric oxide and the production of 
water, by which the former is converted into the nitric and nitrous acids ; the latter, if 
allowed to remain in contact with the heated gun-cotton, is gradually reduced to nitric 
oxide, and finally the nitrogen becomes deoxidized at the expense of hydrogen and 
carbon, oxalic and carbonic acids being eventually furnished by the latter. The nitric 
acid produced attacks the gun-cotton at the same time ; the presence of very small 
quantities of this substance in gun-cotton greatly accelerates the decomposition of the 
material by heat. 
Experiment 121. — One drop of concentrated nitric acid introduced into vessels con- 
taining 2 or 3 gratis, of gun-cotton, invariably brought about rapid decomposition at 
comparatively low temperatures (55° to 65°) ; and by operating at temperatures between 
70° and 100° with small samples of gun-cotton to which as small a quantity as possible 
of dilute nitric acid was added, they were in this way generally converted into the gum- 
mdccclxvii. 2 H 
