Page:Experimental researches in chemistry and.djvu/157

142 Action of Gunpowder on Lead.

gave me also some balls from cartridges about fifteen years old, and which had probably been in a damp magazine. They were covered with white warty excrescences rising much above the surface of the bullet, and which, when removed, were found to have stood in small pits formed beneath them. These excrescences consist of carbonate of lead, and readily dissolve with effervescence in weak nitric acid, leaving the bullet in the corroded state which their formation has produced. It is evident there must have been a mutual action amongst the elements of the gunpowder itself, at the same time that it acted on the lead; and it would have been interesting, had the opportunity occurred, to have examined what changes the powder had suffered.

Purple Tint of Plate-glass affected by Light.

is well known that certain pieces of plate-glass acquire, by degrees, a purple tinge, and ultimately become of a comparatively deep colour. The change is known to be gradual, but yet so rapid as easily to be observed in the course of two or three years. Much of the plate-glass which was put a few years back into some of the houses in Bridge Street, Black friars, though at first colourless, has now acquired a violet or purple colour. Wishing to ascertain whether the sun's rays had any influence in producing this change, the following experiment was made:—Three pieces of glass were selected, which were judged capable of exhibiting this change; one of them was of a slight violet tint, the other two purple or pinkish, but the tint scarcely perceptible, except by looking at the edges. They were each broken into two pieces; three of the pieces were then wrapped up in paper and set aside in a dark place, and the corresponding pieces were exposed to air and sunshine. This was done in January last, and the middle of this month (September) they were examined. The pieces that were put away from light seemed to have undergone no change; those that were exposed to the sunbeams had increased in colour considerably;