1. Yellow sand, 20%; kelp, 8%; lixiviated wood-ashes, 30%; fresh wood-ashes, 8%; pale clay, 16%; 'cullet' (broken gla.s.s), 18%. This is the common mixture for coa.r.s.e bottles, in Belgium, France, and Germany.

2. To the last add of black oxide of manganese, 2-1/2 to 3%. Has a rich yellowish colour; used for Rhenish-wine bottles.

3. Pale sand, 51%; lixiviated wood-ashes, 33%; pearl-ashes (dried), 8%; common salt, 7-1/2%; white a.r.s.enic, 1/2%; charcoal, q. s. Very pale green.

4. Siliceous sand (pale), 68-1/2%; potash (or its equiv.), 4%; lime, 23-1/2%; heavy spar, 2-1/2%; peroxide of manganese, 1-1/2%. This forms the celebrated 'flask-gla.s.s' of St. Etienne.

GLa.s.s, BROAD, SPREAD WINDOW GLa.s.s. Sp. gr. 2642.--

_a._ By a.n.a.lysis:--

Silica, 6970%; lime, 1330%; soda, 1525%; oxide of iron (and loss), 175%.

_b._ Materials used:--

1. White sand, 50%; dried sulphate of soda, 22%; charcoal (in powder), 9%; 'cullet,' 41%; peroxide of manganese, a little. Pale.

2. White sand, 60%; potashes (good), 24%; common salt, 10%; nitre, 5%; white a.r.s.enic, 1%; peroxide of manganese, a little (1/12 to 1/10%); pale 'cullet,' at will (10 to 30%). Very pale. This is the 'spread' or 'sheet window-gla.s.s' in common use.

GLa.s.s, CHEMICAL. Sp. gr. 2390 to 2396.--

_a._ By a.n.a.lysis:--

1. Silica, 7280%; pota.s.sa, 1680%; lime (with a trace of alumina), 968%; magnesia, 40%; traces of oxide of manganese and iron (and loss) 32%. This is the difficultly fusible 'Bohemian tube-gla.s.s,' so valuable in chemical manipulations.

2. Silica, 693%; pota.s.sa, 158%; soda, 3%; lime, 76%; alumina, 12%; magnesia, 2%; oxide of iron, 5%; oxide of manganese (and loss), 6%.

English chemical gla.s.s (without lead). More fusible than the last.

_b._ Materials used:--

1. Quartz (hyalin, in powder), 60%; calcined purified pearlash, 30%; fresh-burnt lime (very pure), 9%; nitre (dried), 3/4%; a.r.s.enious acid or peroxide of manganese, 1/4%. Said to be the proportions used in the production of _a_, 1 (_above_).

2. (M. Peligot.) Quartz, 71-1/2%; carbonate of pota.s.sa (or its equiv., dry), 20%; quicklime, 8-1/2%; (manganese, a little). Said to be the formula for the hardest and least fusible 'Bohemian tube-gla.s.s.' It is very intractable and infusible, except at a very high temperature; but the addition of an exceedingly small quant.i.ty of boracic acid, borax, or a.r.s.enious acid, causes it to flow into a gla.s.s possessing great brilliancy and hardness, and capable of being wrought at the highest heat of the ordinary furnace.

GLa.s.s, CROWN, WHITE WINDOW-GLa.s.s. Sp. gr. 2486 to 2488.--

_a._ By a.n.a.lysis:--

1. Silica, 628%; pota.s.sa, 221%; lime, 155%; alumina (with traces of oxide of iron and manganese), 26%. Crown-gla.s.s of Bohemia, according to Dumas. Very beautiful.

2. Silica, 725%; soda, 1775%; lime, 975%. English crown-gla.s.s; excellent quality, but not so white as the last.

_b._ Materials used:--

1. Finest white siliceous sand, 64%; purified potashes (dry), 23%; lime, 12%; white a.r.s.enic, 3/4%; oxide of manganese, 1/4%. Said to be used in Bohemia.

2. (Schweigger.) Pure sand, 57%; dry sulphate of soda, 28-1/2%; quicklime, 11-1/2%; powdered charcoal, 3 or 4%. Corresponds to _a_, 2, _above_ (nearly).

3. Pure sand, 40%; soda ash, 24%; lime, 5%; white 'cullet,' 31%, Rather superior to the last.

CRYSTAL, CRYSTAL GLa.s.s. The 'crystal gla.s.s' of England is flint gla.s.s' of superior quality; that of Bohemia is noticed under TABLE GLa.s.s.

GLa.s.s, FLINT, CRYSTAL. Sp. gr. 3000 to 3620.--

_a._ By a.n.a.lysis:--

1. (Berthier.) Silica, 5919%; oxide of lead, 2868%; pota.s.sa, 1213%; oxides of iron and manganese, traces. Finest colourless English crystal.

2. (Brande; Faraday.) Silica, 52%; oxide of lead, 34%; pota.s.sa, 34%.

Crystal.

3. (Faraday.) Silica, 4430%; oxide of lead, 4305%; pota.s.sa, 1175%; alumina, 50%; oxides of iron and manganese, 12%; (loss 28%). Heaviest of three samples of flint gla.s.s examined.

_b._ Materials used:--

1. Finest Lynn-sand (calcined, sifted, and washed), 51%; litharge (purest), 28% (or red lead, 29%), refined pearlashes (calcined before being weighed), 16%; nitre (purified), 4-3/4% a.r.s.enious acid and peroxide of manganese, of each, 1/8%. Very fine crystal.

2. (M. Payen.) Fine sand, 46%; red lead, 31%; purified carbonate of potash, 23%. French crystal.

3. (Geddes.) White Lynn-sand, 51%; red lead or litharge, 33%; refined pearlashes, 13%; nitre, 3%; a very little a.r.s.enious acid and peroxide of manganese. Ordinary English flint-gla.s.s. Crystal 'cullet' may be added at will to the above. This gla.s.s was originally prepared from powdered flints, a fact to which it owes its common name.

GLa.s.s, OPTICAL. 1. (Crown gla.s.s.) Purest siliceous sand, 55%; carbonate of soda (dry), 12%; chalk (dry), 11%; carbonate of baryta, 22%.

2. (Flint gla.s.s.)--

_a._ By a.n.a.lysis:--

Silica, 4430%; oxide of lead, 4305%; pota.s.sa, 1175%. This is Guinand's 'dense optical gla.s.s.'

_b._ Materials used:--

1. Purest quartz, 42%; red lead (finest), 42%; purified potash, 14-3/4%; purified nitre, 1-1/4%. These are the proportions used for the last.

2. (Korner.) Finest quartz (reduced to powder, treated with hydrochloric acid, washed, and dried), 47-1/2%; red lead, 38-1/4%; cream of tartar, 14-1/2%. The above are used by opticians in the construction of achromatic object-gla.s.ses.

GLa.s.s, PLATE. Sp. gr. 2488 to 2600.--

_a._ By a.n.a.lysis:--

1. (Dumas.) Silica, 759%; soda, 175%; lime, 38%; alumina, 28%. French mirror-gla.s.s.

2. (Mitscherlich.) Silica, 60%; pota.s.sa, 25%; lime, 125%; loss, 25%(?).

Finest Bohemian plate.

_b._ Materials used:--

1. Finest siliceous sand, 45%; dried carbonate of soda, 25%; lime, 5%; nitre (purified), 2%; plate-gla.s.s cullet, 23%; peroxide of manganese and cobalt azure, a very little. Ordinary English plate.

2. Whitish quartz sand, 60%; purified carbonate of soda (dried), 20%; lime (slaked by exposure to the air), 9%; plate-gla.s.s cullet, 11% (or more).