OF GUN-POWDER. 2 Z

be altered in quality; and while the interior of the grains,from which the sulphur and charcoal are fallen off, continue inthe same state they were in when made, the exterior will havelost the greater part of the substances necessary to facilitate theinflammation. Thus, on applying fire to these grains, thesurface burns slowly till the fire penetrates tlie interior, andmeets a sufficient quantity of sulphur and charcoal; thepowder must therefore have become weaker. Now, if thepowder, thus reduced in strength, be manufactured again,the grains will become homogeneous both internally and ex-ternally; but, owing to the diminution of the quantity ofsulphur and charcoal, they will be altered in quality, sincethe saltpetre will be in greater proportion than either of theother two ingredients; so that if, before the powder be-came damp, it was not very strong, it will now have becomemuch stronger; but, on the contrary, if it was as strong aspossible before, and the ingredients ( 38.) well-proportionedand intimately mixed together, it will in this new operationhave loft part of its strength. Hence it may be inferred, thatgrinding serves only to mix the ingredients together; and thatwhen there is a perfect contact between the nitrous and com-bustible particles, it is useless any longer to continue theoperation,

64. Powder, however well dried and fabricated it mayhave been, loses its strength when allowed to become damp.If daily observations on powder, put into damp magazines,and carefully preserved in barrels, are not sufficient to esta-blish this fact, the following experiment will render it incon-testable.

Let a quantity of well-dried powder be nicely weighed,and put into a close room, where the air is temperate, andseemingly dry, and be left for three or four hours; on weigh-ing it again, its weight will be increased. This same pow-der, exposed to an air loaded with vapour, acquires muchadditional weight in a short time. Now the increase of theweight being proportional to the quantity of vapour con-tained in the atmosphere, and to the length of time thatthe powder is exposed to it; it follows, that powder easilyattracts moisture.

65. Wherefore, if a degree of heat, sufficient only to firedry powder be applied to powder that is damp, the moisturewill oppose the action of the fire, and the grains either willnot take fire at all, or their inflammation will be flower:thus, as the sire will spread more slowly, fewer grains will

B 4 burn;