BOLOGNA FLASK.

1£)5

There are two toys made of unannealed glass, which thoughcommonly used for the amusement of children, exhibit pheno-mena which justly interest the curiosity of the philosopher, wemean Prince Rupert's drop, and the Bologna flask, or philo-sophical phial.

Prince Rupert's drop is made by letting drops of melted glassfall into water; the drop assumes by that means an ovalform, with a tail or neck resembling a retort. These drops aresaid to have been invented by Prince Rupert, and are thereforecalled by his name. They possess the singular property, that ifa small portion of the tail is broken off, the whole bursts intopowder, with a kind of explosion, and a considerable shockis communicated to the hand that grasps it. Their explosion inthe dark is said to be attended with a flash of light, this how’everis a mistake; a flash of light indeed is produced if the drop bebroken in a glass-receiver, but in that case the flash proceeds fromthe action of the projected particles, forcibly striking against thebody of the glass, but no such phenomenon takes place if thedrop be broken in free space.

The Bologna , or philosophical phial is a small cylindrical vesselof glass which has been suddenly cooled, open at the upper end,and rounded at the bottom. It is generally made so thick at thebottom, that it will bear a smart blow against a hard body with-out breaking, but if a little pebble or piece of flint is let fallinto it, it immediately cracks, and the bottom falls into pieces.

Remark. ..Concerning the cause of the phenomena of boththese bodies, different opinions have been advanced. The mostgeneral is founded on the assumption that the dimensions of bo-dies which are suddenly cooled remain shorter than if the cool-ing had been more gradual. The dimensions therefore of thesmooth external surface of these glasses, which are suddenlycooled, are supposed to be shorter than is adapted to the accu-rate envelopement of the internal part, which is necessarilycooled in a more gradual manner; if therefore by a crack or fis-sure, a solution of the continuity takes place in the external

N 2