Glass is a transparent material, used for giving light through openings, while excluding the elements. It is a mixture of white sand, soda, and chalk, in various proportions, melted together at a very high temperature, and then formed into the various kinds required. These include "crown," "sheet," and "plate" glass.

Sheet glass, the most useful variety, is made by blowing the heated glass into cylinders, which have their ends cut off and periphery split down, so that the glass can be flattened out in a kiln, under the action of heat, applied to open it out, after which it is allowed gradually to cool. The various kinds of sheet glass are distinguished by their weight per foot, super., as 16 oz., 21 oz., 26 oz., and 32 oz.

Piatt glass is, of course, a superior kind, made of thicknesses varying from 1/8 inch to 1/8 inch, by which thicknesses it is described and distinguished. In the process of its manufacture the glass, when at a white heat, is placed on a table and rolled to the required thickness; after which it is polished over or left as rough-cast. Its advantages over "sheet glass" are that it is much stronger and less affected by atmospheric influences, while it cannot be cut noiselessly with the diamond - which renders it an enemy of burglars.

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Fig. 887.

Fig. 889.

Rough-cast - the resulting material without the polishing - has a rather wavy appearance, but is otherwise as strong and advantageous as the polished plate.

British polished plate glass is even superior to the ordinary "polished plate," though of the same material; its superiority being the result of grinding the surfaces down truly before polishing.

Hartleys rough rolled plate is of similar composition to the "plate," but it is rolled on a patent ribbed table, which gives it the advantage of admitting light without scorching, glare, or diminished transparency.

There are numerous other varieties of glass, chiefly made out of the different manufactured products above explained, and rendered different by the labour and colouring matters expended on them and used therewith.

Glass is cut into squares or panes of the required size, and secured by means of putty (a stiff, pasty substance of whiting and oil) into the wood or iron rebates, as Fig. 887, which shows the glass puttied and back-puttied, as at X; or it is secured and bedded in washleather, by means of wood fillets or beads, as Fig. 888.

As the putty used in glazing cannot be made of a suitable lasting material, but is perishable, the necessity has arisen of late years of employing other means of securing the glass to the framing, especially in skylights and other exposed flat or sloping surfaces.

A simple method of attaining this object is to secure it by sprigs driven into the woodwork at the bottom of the sheet and at the sides, as Fig. 889, in addition to which, if the glass is cut circularly on the bottom edge, all water will be collected, and will run down the centre of the light clear of the putty and bars, as shown by dotted lines.

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Fig. 889.

Patent Glazing

Among the many patented methods of accomplishing this result, now in vogue, may be mentioned the following: -

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Fig. 890.

Fig. 891.

The British Patent Glazing Company's Patent, consisting of steel bars and sheet lead, as illustrated by Fig. 890, from which it will be seen that no water can enter and drop through their system, as any water penetrating between the bars and the lead is collected in the groove of the bar.

Messrs. Braby's Patent, consisting of wooden bars of any size and design, and zinc, etc., is illustrated in section by Fig. 891.

Messrs. Grover's Simplex is shown in Figs. 892 and 893, from which it will be seen that their method consists of a patent lead strip, as Fig. 893, fixed to wood bars and turned down on the glass, as Fig. 893.

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Fig. 892.

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Fig. 893.

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Fig. 834.

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Fig. 896.

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The Pennycook Patent is illustrated by Figs. 894, 895, and 896, from which it will be seen that this system can be adapted to iron, wood, or metal bars.

Helliwell's Patent consists of metal bars and capping, as Fig. 897, and Rendell's of similar materials, as Fig. 898 in section.

There are many other similar patents, including that of Messrs. Mellowes (of Sheffield), which is extensively used throughout the country, though those above illustrated are quite as good and effective.

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Fig. 898.

Durolim is a substitute for glass in positions where glass would soon be broken. It consists of thin wire-woven work, covered over by a transparent thin substance of different tints. It is fixed on rafters by zinc nails, and lapped at the joints.