Purified Lynn sand 100 parts. Litharge or red lead 60 Purified pearlash 30 To this is added black manganese, to correct the colour, and sometimes nitre and arsenic. Plate glass is formed of Pure sand, 43.0 parts. Dry carbonate of soda, 26.5 Pure quicklime, 4.0 Nitre, 1.5 Broken plate glass, 25.0 ------ 100. Crown, or fine window glass, is composed of Fine sand, 200 lbs. Best kelp, ground, 330 lbs. To this is added, if the vitrification is not complete, some muriate of soda. Good glass, according to Pajot des Charmes, may be made by fusing equal parts of carbonate of lime, sand, and sulphate of soda. The glass is clear, solid, and of a pale yellow. Professor Scheweigger found, that the following proportions were the best: Sand, 100 Dry sulphate of soda, 50 Dry quicklime in powder, 17 to 20 Charcoal, 4 Broad glass is made of a mixture of soap-boilers' waste, kelp, and sand. Two of waste, one of kelp, and one of sand are the proportions generally employed. Common bottle glass is usually made of waste and river sand, to which lime, and clay, and common salt are occasionally added. The coloured glasses are produced by various metallic oxides. The colour and beauty of precious stones are thus imitated. These colours are communicated by sundry metallic preparations, as the following: The purple powder of Cassius, with oxide of manganese, will give a red or purple according to the proportions used; zaffre, an oxide of cobalt, a blue; a mixture of oxide of cobalt, muriate of silver, or glass of antimony, a green; and oxide of manganese, a violet, &c. The basis of all artificial precious stones, is composed of what is called glass-paste, a compound of silica, potash, borax, red lead, and sometimes arsenic. These substances are melted together. The glass, which forms the body of the artificial gem, is pulverized, and the colouring substances are blended with it by sifting; and then the whole must be carefully fused, being left on the fire for from 24 to 30 hours, and cooled very slowly. The following proportions are used for this purpose: _Pastes._ 1. 2. 3. 4. Rock crystal, 4056 gr. ---- 3456 360 Minium, 6300 ---- 5328 ---- Potash, 2154 1260 1944 1260 Borax, 276 360 216 360 Arsenic, 12 12 6 ---- Ceruse of clichy, -- 8508 ---- 8508 Sand, -- 3600 ---- ----