[655] Farup, E. 3649, 1910; F. 412563, May, 1910.
[656] E. 10368, 1911.
In connection with the colouring properties of the oxides of titanium, it is interesting to note that the blue colour of sapphires is probably due to the presence of compounds of trivalent titanium; Verneuil[657] has succeeded in preparing artificial sapphires in all respects identical with the natural stones by fusing alumina with small quantities of titanium dioxide and ferric oxide in the flame of the oxyhydrogen blowpipe, which effects the reduction.
[657] Compt. rend. 1910, 150, 185.
Other Uses of Titanium Compounds.
—Owing to the high price of the tin dioxide which is largely employed for the preparation of enamels and opaque glasses, innumerable suggestions have been made for the employment of the oxides of titanium and zirconium in this direction.[658] A critical examination of the question has been made by Grünwald;[659] he finds that the opacity consequent on addition of these compounds increases with the amount of clay used, within limits, and concludes that the effect is due to displacement of alumina by the oxides, with formation of silicates of titanium and zirconium, which dissolve in the melt. He states that the results obtained from the use of these oxides are not comparable with those given when stannic oxide is employed, and that therefore the former oxides are of little use for this purpose.
[658] Vide, e.g. D. R. P. 189364, 218316, 115016, 207001; F. 438908, etc.
[659] Sprechsaal, 1911, 44, 72.
These two oxides find employment to a small extent in the manufacture of ‘Siloxide’ quartz glass.[660] Quantities up to 1·5 per cent., added to the molten silica, reduce the difficulty of working the material. Exhaustive tests carried out by Thomas[661] indicate that the vessels made from this material are, on the whole, to be preferred to ordinary quartz glass, resisting high temperature better, and showing less tendency to become crystalline and therefore brittle when maintained for considerable times at high temperature.
[660] Wolf-Burckhardt and Borchers, F. 432786, October, 1911.