a method of feeding glass to a glass - melting furnace for making a vitreous material , a heated airstream containing air at a temperature in excess of 1 , 000 ° c . is passed down vertical cylinders towards the crown of the glass - melting furnace . powdered glass batch is introduced into the vertically moving heated airstream in the lower and wider cylinder and infra - sound is applied to the vertically moving heated airstream by an infra - sound generator to vibrate the heated airstream and effect heat transfer from the airstream to the glass batch particles so that the glass batch particles are heated and the temperature of the heated airstream is reduced to a temperature below 700 ° c ., thereby reducing the propensity of the air to produce nitrogen oxides . fuel is subsequently added as the heated glass batch particles and the cooled airstream move downwardly towards the crown of the furnace and a stream of glass batch , burning fuel and air is passed downwardly through the crown of the furnace in a manner such that there is a direct contact between the flame of the burning fuel and the surface of molten glass within the furnace , and the glass batch is melted .