The glass was required to furnish the eye-pieces to the masks. These were circular in shape, and about 2¹⁄₂ inches in diameter. Each eye-piece was made from two discs of glass which were superimposed, with a thin layer of xylonite between. The last-named was introduced to extend enhanced safety to the fighting men. A ricocheting shell splinter might strike the goggle, shattering the outer layer, but the inner section might possibly escape all injury. Even if the blow were sufficiently severe to smash both sections of a single eye-piece the goggle was not certain to be shivered like the window-pane struck by a stone. The intermediate layer of xylonite nullified the force of the impact to a striking degree, any starring that might be communicated to the inner disc not necessarily being in line with that produced on the outer glass, except, of course, in instances of a direct hit. Moreover, the glass was deprived of its characteristic tendency to splinter under a blow, owing to the intervening thin film of xylonite. Photographers will appreciate the situation from their experience with their glass negatives. When dropped the glass may be smashed into a hundred fragments, but they are invariably held in position by the attached film. The glass required for this purpose had to be of a certain standard, not exceeding one-sixteenth of an inch in thickness, and free from flaws. The authorities discovered that photographic negatives were made of the very material desired, and realized that here was a peculiar opportunity to remedy the deficiency they were experiencing in regard to the supply of new material from the accepted manufacturing sources. Accordingly, appeal was made to all photographers to turn out their stocks of dismal failures and negatives which need be retained no longer, and to surrender them to the Government. The demand was certainly pretentious. The eye-pieces were required at the rate of 500,000 a week. As two quarter-plate negatives were required to produce a single goggle--four for each mask--it will be seen that 2,000,000 discarded quarter-plate negatives were sought weekly to keep pace with demand. Of course, larger-sized plates enabled the discs to be cut more economically, but it is the quarter-plate which has the biggest vogue among the huge army of amateur photographic enthusiasts, owing to questions of expense, and so appeal was especially made for plates of this size, in the feeling that here was the richest mine to be tapped. The negatives were stripped, the emulsion being dissolved from the foundation by the aid of chemicals. In this manner the nitrate of silver content was recovered to be turned to profitable account. The metallic yield from the individual plate is negligible, but, under quantitative treatment, as in this instance, the reclamation was rendered profitable. No attempt was made to exploit the emulsion, but there seems to be no reason why this should not have been utilized.