The function of arsenious oxide on the melting of soda-lime glasses has been tested by meltings carried out in covered pots at a temperature of 1400 deg C. Contrary to general belief, the arsenious oxide added to the batch is not expelled during the melting process. Practically the whole if it is retained when the amount added is about one to two parts per 1000 parts of sand; whilst 60% or more is retained even when 250 parts per 1000 are added. In batches containing neither oxidising nor reducing agent, part of the arsenious oxide, from 40-70%, is converted to arsenic oxide and is found in this condition in the glass. No beneficial action has been found in the experiments to be exerted by arsenious oxide either on the rate of melting or on the refining of the glass. The presence of arsenious oxide in amounts greater than 2 parts per 1000 sand is liable to lead to the formation of a scum of high silica content and when present in amounts from 150 to 250 parts per 1000, opacity in varying degrees is produced. The presence of arsenious oxide does definitely reduce the green tint in glass due to iron oxide and may therefore be regarded as a decolouriser.
