Page:Popular Science Monthly Volume 7.djvu/574

556 was foiled in every attempt to regain it. There was the hard fact staring him in the face, that he had succeeded in depriving glass of its brittleness, as shown by specimens around him; but there was the harder fact before him, that he had lost the key of his success. Nevertheless he labored on, and at the end of the period above mentioned he had the satisfaction of finding all his anxieties at an end; his toils were requited by the rediscovery of his secret. He has since worked at it most assiduously, and has now brought it into practical working order, rendering the process as certain of success as any in use in the arts and manufactures in the present day.

As already observed, M. de la Bastie is not a glass-manufacturer; he therefore had to reheat glass articles when toughening them. It, however, by no means follows that the toughening process cannot be applied in the course of manufacture, thus avoiding reheating. On the contrary, it not only can be, but has been, applied at glass-works to glass just made, and so saves the costly and time-absorbing process of annealing. But, for reasons stated, M. de la Bastie had to apply the process to the manufactured article; and the method adopted, and the apparatus used in its application, next merit attention. In the first place, the glass to be toughened had to be raised to a very high



temperature—the higher the temperature the better—the risk of breaking the glass being thereby reduced, and the shrinkage or condensation being increased. It was therefore advantageous, and often necessary, to heat the glass to the point of softening; but in that condition glass articles readily lost their shape, and had to be plunged into the