222 
ME. ABEL’S EESEAECHES ON GUN-COTTON. 
like product, in a few hours, though instances occurred occasionally in which, even under 
these severe conditions, the material resisted decomposition to a remarkable extent. 
In many experiments instituted with ordinary gun-cotton at 90° and 100° it was found 
that, if the mode of operating were such as to facilitate the escape from the apparatus 
of any acid vapours evolved, the gun-cotton would frequently resist decomposition in 
a remarkable manner, being only very gradually converted into the final products ; the 
two following experiments demonstrate how greatly decomposition at 100° C. can be 
retarded by impeding the destructive action of acid generated by the exposure to a high 
temperature. 
Experiment 121“. — Weighed quantities (about T5 grm.) of dry gun-cotton were 
loosely packed into two narrow U-tubes, which were immersed in a water-bath and con- 
nected with an aspirator. The gun-cotton was in both instances maintained during the 
day at 100° C. A moderately rapid current of air was passed through one tube, and air 
was allowed to circulate very slowly through the other. At night both tubes were 
closed up with corks. Their weight was determined at intervals ; the following were 
the results obtained : — 
Loss sustained by gun-cotton exposed to 
Duration of exposure. slow current. rapid current. 
24 hours (4 days) 17 *47 per cent. 4- 8 per cent. 
40 hours additional (7 days) . 32'43 „ 4T2 „ 
196 hours additional (28 days). 5 - 04 „ 
Total loss of weight, in 11 days 5090 „ In 39 days 13*96 „ 
The results of these and the preceding experiment warrant the conclusion, that as 
soon as acid becomes liberated in gun-cotton changes are developed in the material 
which would not be brought about by its simple exposure to heat, provided no free acid 
were present in it. If therefore it be possible to neutralize, at the instant of its liberation, 
any acid which may be produced by the effect of elevated temperatures upon the com- 
paratively unstable impurities contained in small quantities in gun-cotton, the latter 
might be expected to resist alteration under circumstances which, if the first acidity were 
not counteracted, must determine the decomposition of the material. 
Reference has been made in this paper, on more than one occasion, to the influence 
which certain mineral impurities of general occurrence in gun-cotton (earthy .carbonates) 
were observed to exert upon the rapidity with which the substance sustained alteration, 
upon exposure to heat. Some samples, which were heated for comparatively considerable 
periods without exhibiting signs of change, were found to contain much larger propor- 
tions of calcic and magnesian carbonates than specimens with which, in other respects, 
they were identical. 
This observation led, at an early stage of these investigations, to careful observations 
of the comparative effects of high temperatures (100° and 90° C.) upon a variety of 
samples, which were known to vary as regards the proportions of earthy and alkaline 
carbonates distributed through them. Some specimens were repeatedly rinsed in distilled 
