Broad Glass is an inferior kind of window glass, made with a cheaper kind of alkali. It is blown to a cylindrical form, cut open, and spread into a flat plate.
Bottle Glass is still inferior in quality to broad glass, the alkali employed being the cheapest that can be procured, with the addi• tion of a portion of lime to assist fusion. Bottle glass is fashioned by blowing into hollow moulds.
Plate Glass is both blown and cast. The following proportions and ingredients are given by Parkes : Lynn sand, well washed and dried 720 parts. Alkaline salt, containing 40 per cent.
of soda . 450 „ Lime, slaked and sifted . SO „ Nitre . . 25 „ Broken plate glass . . 4_25 „ 1700 parts.
It requires 40 hours' exposure to the full heat of the furnace to reduce the materials to the proper state of fusion and vitrification. When this is accomplished, the glass is trans ferred from the melting pot to a large vessel called a cuveite, and from this to a large cast ing table, where it is distributed by means of a roller over the whole surface of the table, bars of metal being placed at each side along its entire length, and across the bottom, in order to prevent the glass from running upon the floor. The casting of large plates of glass is one of the most beautiful processes in the arts: the large mass of melted glass, ren dered in a high degree luminous by heat, ex hibits changing colours in the sheet after the roller has been passed over it.
When annealed, which all glass requires to be before using [..9.NNE.1L.tqc], the plates of glass are ground with powdered flints, and then with emery powder, and are afterward t polished with oxide of iron laid upon woollen pads. Plate glass is silvered for looking glasses with an amalgam of mercury and tin. foil.
There has perhaps never been known more signal effect produced on a manufacture by fiscal arrangements, than that which has resulted from the removal of the glass duty in 1840. What is the amount of this effect, it would be difficult to say, as there is no account now kept by the excise of the quantity of glass manufactured. Until 1840 the excise regulations were most vexatious to the glass manufacturer. The annealing ovens were under lock and key, and no glass could be put in or taken out of them without the presence and sanction of the excise officers. The efforts of the manufacturers to improve their wares were paralysed ; for they could not even institute experiments without paying duty for the glass wasted in so doing. The sum rea lised to the revenue in 1845 amounted to 113,000/. The export has very largely in creased since the remission of the excise duty; in 1850 it amounted to 330,014 cwts. of flint, window, and bottle glass, besides plate glass, which is estimated by measure and not by weight: the value of all the four kinds was 308,340/.
It may be safely asserted, that without the remission of the glass duty in 1816, the Palace of Industry in Hyde Park could not have been constructed on Mr. Paxton's plan ; what
ever the building might else have been, it would not have been crystal' palace. Un til the duty was removed, the successful experiments in making large sheets on the broad glass method would hardly have been made; and it is only on this method, and at the cheap prices which now prevail, that the acres of glass could have been provided for this beautiful structure. The vast establish ment of Messrs. Chance at Birmingham is now one of the most interesting centres of industry in the country: the many hundreds of men employed ; the surprising skill with which the workmen (Englishmen and French men working in harmony) make the cylinders which afterwards become sheets of broad glass ; and the rapidity with which the im. mense supply for the Hyde Park building has been furnished— all have tended to render these works lately well worthy of study.
Nor are there wanting examples of the beneficial results of the fiscal change in other directions. Dairy glass is now an important article ; and we find that in London and other large towns establishments have been opened for the sale of glass—coarse but strong— : t fashioned into an amazing variety of utensils t and implements. Rough plate for skylights ; and conservatories, and rough plate for floors - (as much as an inch and a half in thickness); glass tiles and slates ; perforated glass Sor 4 ventilation ; glass milk pans, cream pots, lac : tometers, preserve jars, pastry slabs, rolling , pins, glass syringes, leech glasses, and pill making slabs ; bee glasses, propagating glasses, , wasp traps, cucumber glasses, hyacinth cups, flower dishes, crocus glasses, peach and grape ' protecting glasses, and fern shades ; glass cor nice poles; glass churns, glass syphons—these are some among the many articles now made of this beautiful and useful substance.
An important modern application of glass is as a material for pipes, in cases where iron, stone, and wood would be less efficient. Several hundred feet of glass pipes have been recently laid down on the estate of the Earl of Zetland.
A very remarkable and brilliant effect is now produced in cut glass by coating parts of the interior with silver, on a plan recently pa tented. A brief notice of this, and of the ordinary mode of silvering looking glasses, will be found under SILVERING.
The glass manufacturers of the Tyne dis trict are expected to make a worthy display of their art at the approaching Exhibition. They will send specimens of plate glass in all the stages of progress, some of them alnost un paralleled in size ; and the other kinds of glass will be fittingly illustrated. From St. Helen's we are promised other specimens ; and there can be little doubt that this depart merit of our national manufacture will be well represented. Our manufacturers, in return, will be eager to see what Bohemia and Ba varia and France can produce, in this beauti ful branch of industry.