_a._ By analysis:--
Silica, 69·70%; lime, 13·30%; soda, 15·25%; oxide of iron (and loss),
1·75%.
_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 arsenic, 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-glass' in common use.