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CAPTAIN NOBLE AND ME. F. A. ABEL ON EIEED OUNPOWDEE. 
nozzle, was led to a mercurial trough. Before the gas was taken, a sufficient quantity 
was allowed to escape to clear the tubes of air; the gas was then collected in tubes 
over mercury, and confined in the usual manner by sealing them with the blowpipe. 
The gas was generally collected in from five to fifteen minutes from the time of 
explosion. Owing to the dangerous nature of the experiments, and the precautions 
necessary to be adopted in exploding such considerable charges of powder, it was not 
generally possible to collect the gases more rapidly ; but a comparison of the analysis 
of different tubes taken from the same experiment has shown that, at all events within 
moderate limits, no change takes place in the composition of the gas by its continued 
contact with the solid products. 
6. Collection of Solid Products. 
The collection of the solid products presented much more difficulty than that of 
the gaseous products. On opening the cylinder, the whole of the solid products were 
found collected at the bottom, there being generally an exceedingly thin (in fact, with 
large charges, quite an inappreciable) deposit on the sides. Upon the firing-plug there 
was usually a button of deposit, which differed considerably both in appearance and 
in chemical composition from the rest. In the button a crystalline structure was 
quite apparent, some of the crystals being large and transparent. The surface of the 
deposit was generally perfectly smooth and of a very dark grey, almost black, colour. 
This colour, however, was only superficial, and through the black could be perceived 
what was probably the real colour of the surface, a dark olive-green. The surface of 
the deposit, and the sides of the cylinders, had a somewhat greasy appearance, and were 
indeed greasy to the touch. On the smooth surface were frequently observed very 
minute particles, in appearance like soot, but of the greasy texture to which we have 
alluded. 
The removal of the deposit was generally attended with great difficulty, as it formed 
an exceedingly hard and compact mass, which always had to be cut out with steel 
chisels. Lumps would frequently break off, but a considerable portion flew off before 
the chisel in fine dust. In various experiments, on examining the fracture as exhibited 
by the lumps, the variation in physical appearance was very striking, there being 
marked differences in colour, and also, frequently, a marked absence of homogeneity, 
patches of different colours being interspersed with the more uniform shade of the 
fracture. There was no appearance of general crystalline structure in the deposit ; but, 
on examination with a microscope and sometimes with the naked eye, shining crystals 
of metallic lustre (sulphide of iron) were observed. On the whole, the general appear- 
ance of the deposit was attended with such considerable variations, that, for minute 
details, we must refer to the account of the experiments themselves. The deposit 
always smelt powerfully of sulphuretted hydrogen, and frequently strongly of ammonia. 
It was always exceedingly deliquescent, and after a short exposure to the air became 
black on the surface, gradually passing over into an inky-looking pasty mass. As in 
