ME. ABEL’S EESEAECHES ON GUN-COTTON. 
217 
it would be more seriously affected, and that the changes which would ultimately be 
developed by the free acid accumulating in the gun-cotton might give rise to spontaneous 
heating of the mass. On the other hand, it must be borne in mind that even the lowest 
of those temperatures occurs in nature only under exceptional circumstances, and for 
brief periods. 
It may perhaps be considered that the arrangement of heating the gun-cotton over a 
column of mercury, adopted in the foregoing experiments with the view of obtaining 
continuous records of the progress of change, was of a nature somewhat favourable to 
the material operated upon, because a small surface of mercury was exposed in direct 
contact with the gases or vapours evolved, and might, by its own oxidation, remove a 
portion of the generated acid which would otherwise have reacted injuriously upon the 
gun-cotton. It has indeed been stated, in the description of the experiments, that 
a few crystals of mercurous salt were always formed upon the exposed surface of 
the mercury, the production of the salt being favoured by the condensation over the 
metal of a small quantity of water, produced as the experiment proceeded. But it must 
be borne in mind that the surface of mercury exposed was always very small (only from 
78-100 sq. millims.), while the quantity of cotton operated upon was considerable, and 
that, between each consecutive period of exposure to heat, the gun-cotton absorbed, as 
it cooled during the night, the water impregnated with acid which had been previously 
expelled from it. Experimental proof was, however, obtained that ordinary gun-cotton, 
when exposed to 65° in vessels not closed by mercury, and so arranged that any libe- 
rated acid would not escape from contact with the material, was more rapidly and seri- 
ously affected than was the case in the globe-experiments. 
Experiment 110. — Four specimens taken from different samples of gun-cotton, ex- 
posed in a dry state to 65° in very long and narrow-necked flasks, seven hours daily 
for seven days, sustained no loss of weight. From the tenth to the fourteenth day after 
the first exposure all showed slight signs of decomposition, which proceeded with some- 
what different rapidity in the several samples ; two of them were completely decom- 
posed in three weeks after first exposure, the other two resisted for very considerably 
longer periods. 
Experiment 111. — Two other samples were similarly exposed to heat side by side; 
nitrous vapours became distinctly apparent six days after first exposure to 65°, and conti- 
nued visible until the twelfth day’s exposure. After three weeks’ exposure, the specimens 
hacl lost 30 per cent, in weight, and were converted chiefly into soluble gun-cotton. 
Experiment 112. — The protracted exposure of air-dry gun-cotton to a temperature 
ranging between 60° and 55° in a vessel to which air had access, did not effect any greater 
alteration in the material than was observed in the globe-experiments. Thus 53 - 9GS 
grms. of air-dry gun-cotton, after exposure to heat seven hours daily for ten days, 
weighed 53’902 grms. ; after a further exposure for seven days it weighed 53 - 882 grms., 
and after a third exposure for five days it weighed 53 - 881 grms. The sample had there- 
fore only sustained a loss of 0T0 per cent, 
