The Analysis of Glass by the Treatment of Thin Film in the Autoclave. (1)The Determination of Soda

JSGT 1935 V19 T022 T039

A glass blown into exceedingly thin film from a platinum alloy tube, has a thickness of only about 1 µand shows bright interference colours. In this form the glass exposes an extremely large surface to a liquid reagent. Glasses ranging in soda content from 9% to 22% were treated in this form in the autoclave at temperatures up to 217°, that is up to pressures of 300 lb. per sq. inch water and aqueous solutions of caustic soda, sodium carbonate, borate and phosphate, and calcium and barium hydroxides were used as reagents. The soda extracted was determined by titration. Various indicators were used. Methyl orange was the most satisfactory. Among the difficulties encountered were the hydrolysis of the silicates of calcium and magnesium and also the absorption by them of soda. It was found possible to determine the soda content of any commercial window glass by treatment of the film with water for one hour at 200°. It was remarkable that this could be done while the film still retained much of its original form and sometimes some of its interference colours. The method was found to be accurate to 0·2% of soda for window glasses, but to attain this accuracy it was necessary to follow the technique exactly, and to use about 0·08 g of film in 50 ml of water, filtering very rapidly to free the solution from contact with the solid silicates. The film should always be freshly blown.

A. R. Wood