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Sheet of Glass
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and deposited on what are called the burgy banks, which are an eyesore and a nuisance and occupy about 100 acres of valuable land. The total amount of the deposit is something over 5,000,000 tons.
    There are two developments in flat glass which are of considerable public and scientific interest. These are what we call "Vitrolite" and "Armourplate."
    Vitrolite is a trade name given to fire polished sheets of opaque glass which are made in various colours. It is only a recent development in which we owe much to an American Company with whom we are associated and also to the staff of the Scientific Instrument Research Association, who have always been helpful in suggesting methods and materials for obtaining the required colour. This glass, which has a silica, soda, lime, alumina base with a certain amount of fluorine, is opaque by reason of the distribution of crystals throughout its mass. For once we have made our enemy devitrification become our servant instead of our master. These crystals which appear on cooling have been examined by X-ray analysis and although we have still a good deal to learn about their characteristics, we believe them to be sodium fluoride and calcium fluoride. We have successfully manufactured a large variety of colours ranging from crimson to mauve, and, of course, at either end the black and white.
    Armourplate is a trade name which we have given to plate glass which has undergone a heat treatment and has become toughened. The method, which is of French origin, is to heat a piece of plate glass uniformly to a temperature round about its softening point, and then cool it