occurs on the surface of Flint Glass in a species of cloudy, diminutive, white, starry crystals: it is supposed to arise from impurity of alkali. This curious semi-roughened or opaque effect is seldom found in Flint Glass of an open form, but usually on the surface of the inside of a close Glass vessel towards the bottom; the stars are much more minute in Flint than in bottle Glass, and no acid or alkaline application will remove it when the Glass has become cold. If its existence be noticed before the workman has finished the partially devitrified piece of Glass in hand, it may be remedied by thoroughly re-melting the Glass sufficiently long, until the partial opacity dissipated. This defect very rarely occurs when the American subcarbonate potash has been well purified; whereas, it is often caused by the use of the Birmingham ashes, most probably from their not being sufficiently free from sulphates or muriates. In specimens of old Venetian Glass, (without lead,) the interior surface of a vase is often found devitrified towards the bottom and centre; should it have but a small opening, a hollow handle may have its interior affected in the same manner, as if it were roughened; whereas, an open foot or lip of the same vase may be perfectly transparent and free from semi-opacity, owing to the remelting of the two open parts; whilst the body of the vase, having only a small opening, or mouth, fails to get heat enough to remelt into transparency the devitrified part.

Annealing may sometimes appear complete in Glass articles that have borne the friction of deep cutting; which, when long after exposed to the influence of the atmosphere, become fractured, as it were, spontaneously. A large quantity of Flint,