See also Ceramics.

The blue tint of the common poison bottle is got by the addition of black oxide of cobalt to the molten glass; the green tint of the actinic glass bottle is obtained in the same way by the addition of potassium bichromate, which is reduced to the basylous condition, and the amber tint is produced by the addition of impure manganese dioxide, a superior tint being produced by suphur in one form or another. The formulas for various kinds of bottle glass, which indicate the general composition of almost all glasses, are:

White Glass for Ordinary Molded Bottles

Sand.................. 64 Parts

Lime.................. 6 by

Carbonate of sodium.............. 23 weight

Nitrate of sodium....... 5

White Flint Glass Containing Lead

Sand.................. 63

Lime.................. 5 Parts

Carbonate of sodium ............... 21 by

Nitrate of sodium....... 3 weight.

Red lead............... 8

Ordinary Green Glass for Dispensing Bottles

Sand.................. 63 Parts

Carbonate of sodium ............. 26 by

Lime.................. 11 weight.

A mixture for producing a good green flint glass is much the same as that for the ordinary white flint glass, except that the lime, instead of being the purest, is ordinary slaked lime, and the sodium nitrate is omitted. Sand, lime, and sodium carbonate are the ordinary bases of glass, while the sodium nitrate is the decolorizing agent.

Glass Refractory to Heat

Fine sand, 70 parts; potash, 30 parts; kaolin, 25 parts.

Transparent Ground Glass

Take hold of the glass by one corner with an ordinary pair of fire tongs. Hold it in front of a clear fire, and heat to about 98° F., or just hot enough to be held comfortably in the hand. Then hold the glass horizontally, ground side uppermost, and pour in the center a little photographer's dry-plate negative varnish. Tilt the glass so that the varnish spreads over it evenly, then drain back the surplus varnish into the bottle from one corner of the glass. Hold the glass in front of the fire again for a few minutes and the varnish will crystallize on its surface, making it transparent. The glass should not be made too hot before the varnish is put on, or the varnish will not run evenly. This method answers very well for self-made magic-lantern slides. Ground glass may be made temporarily transparent by wiping with a sponge dipped in paraffine or glycerine.