Mechanical an Useful arts. Curiosities of Glass Manufacture.

The Year-Book of Facts in Science and Art
Exhibiting the Most Important discoveries and Improvements of the past year,
in mechanics and the useful arts; natural philosophy; electricity; chemistry; zoology and biology; geology and geography; meteorology and astronomy.
By John Timbs,
editor of "the Arcana of Science and Art."
David Bogue, Fleet Street,
This is the title of a paper read by Mr. Apsley Pellatt at the Royal Institution, supplementarily to a communication made in 1847, and reported in the Year-book of Facts, 1848, p. 88. Mr. Pellatt explained the various processes by diagrams, models, and working instruments. Of these processes we can give but a brief outline. It was noticed that in ancient, as in modern glass, sand was the base and alkali the solvent, and the injury occasioned to the glass by an excess of the latter ingredient was pointed out. That opacity of glass, called devitrification, was explained as consisting in the formation of a multitude of minute crystals in close contact with each other on the surface of the glass. The process of annealing was then described; and it was shown that a glass tube forty inches in length contracts, if annealed, a quarter of an inch, while an unannealed tube of the same length contracts but one-eighth of an inch. The most interesting part of Mr. Pellatt's discourse referred to the mode of making Vitro di Trino, and of impressing heraldic devices, &c. on glass. In the ease of Vitro di Trino, the gathered glass, after being expanded into a bulb or cylinder of the required size, has rods of other glass or enamel, attached to it in a vertical position, at equal distances all round, and then, the bottom being held, the top part is more or less turned, so as to give an equally inclined twist to the vessel and the rods. A similar but larger vessel is made, but which is also turned inside out, and then the former is put into the lathe; and, being expanded by blowing, the two come together and adhere by the rods and their intersections, but inclose small portions of air, which, being regular in size, form, and disposition, give the character of the glass. When heraldic devices, &c. are to be impressed, a mould of the design is made in a fit earthy material (beine puzzolana or one of the volcanic deposits), and this is placed within, and forms part of the larger iron mould in which the decanter is blown: when the large mould is removed, the earthen portion still adheres to the glass, and continues in its place until the bottle is finished. After the annealing, the mould is moistened with water, and immediately separates, and the impression is found really perfect.

At the close of Mr. Pellatt's communication, Mr. Faraday called the attention of the members to two circumstances of philosophical interest which had happened during the momentary apprehension of fire from a heated furnace being, on a previous evening, placed so near a timber beam as to char it. 1. At three different times the water poured on the cinders of the temporary furnace, when, on the fire being drawn, they fell on the hearth, became decomposed by the ignited carbon, and the hydrogen, driven by the sudden expansion of steam, &c., having penetrated the hot and porous hearth-stone, found its way to the heated beams and space which were immediately beneath. 2. This gas, though not in the state of flame as it passed through the hearth-stone and pugging, was, after being mixed with the air below, sufficiently hot to enter into combustion, producing three gushes of flame downwards from beneath the hearth: and it was experimentally shown that a temperature so low as barely to scorch paper, and in which the hand may be held for some seconds without inconve-nience, is yet able to ignite a jet of coal or hydrogen gas in air.

— Athenæum, No. 1061.

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