Industrial and Manufacturing Chemistry; A Practical Treatise. Inorganic Volume 2 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1918 edition. Excerpt: ...for its better quality and greater stability than compounds B and C. It is here assumed that on storing or heating, the alkali groups alone change places and that the dibasic and alumina ones are more strongly bound. That there is some truth in this assumption is shown by the researches on the depression point of thermometers made of various glasses by Schott and others, indicating a change in the nature of the glass when stored or repeatedly heated and cooled. In particular, Schott found that glasses containing potassium but no sodium showed little or no depression, and the absence of depression in glasses which contain sodium but no potassium. According to the formulae given above, such glasses do not permit the alkali groups to replace each other, as would be possible if both sodium and potassium atoms were present, and the changes in the nature of the glass are thereby prevented. The effect of alumina on glass has been shown by Schott to increase the facility with which the glass can be worked in the blowpipe. Seger also studied the effect of alumina very thoroughly and found that it increases the fusibility, makes the glass easier to work, and greatly reduces the tendency to devitrify or crystallise. Many manufacturers have also found that the presence of a small proportion of alumina greatly improves the working power of the glass. It has hitherto been difiicult to explain satisfactorily how so small a proportion of alumina (seldom more than 3 or 4 per cent.) could make so much difference. Various theories of catalytic action, etc., have been proposed, but the position of the two aluminium atoms in the foregoing formula explain the effect of the alumina on the glass far more simply and satisfactorily than any previously published...