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Patents: 121 of 530	UNITED STATES PATENT OFFICE THADDEUS HYATT, OF NEW YORK, N. Y., ASSIGNOR TO ELIZABETH A. L. HYATT, OF SAME PLACE. CONCRETED ILLUMINATING-GRATING.	Thaddeus Hyatt 41 of 67
SPECIFICATION forming part of Letters Patent No. 243,266, dated June 21, 1881. Application filed January 3, 1881. (No model.)

To all whom it may concern:     Be it known that I, THADDEUS HYATT, of the city, county, and State of New York, have invented certain new and useful improvements in the application of hydraulic cements and concretes combined with illuminating-gratings or perforated metal plates, and in means, modes, and processes connected therewith, of which the following is a specification.     The object of my invention, as to "concrete lights," is to prevent the breakage of the glasses which now takes place when they are embedded in concrete. The glasses being then inclosed by a rigid and unyielding wall are supposed to fracture because of the unequal expansions and contractions that take place between the two under the influences of heat and cold, and the circumstance that the same glasses when set in iron grating by means of coal-tar cement do not break has given rise to the idea of interposing some yielding material between the concrete and the glasses. The actual method adopted has been to employ lead-belted glasses; but in practice the plan has proved a failure in the way it has been done, and it has proved a failure because the contraction and expansion theory is unsound. The popular notions on this subject are totally wrong; but the theory is a handy one for the manufacturer of badly-annealed glass. If contractions and expansions, produced by the sun's rays or otherwise, were the cause, every glass in the damaged grating should be broken; whereas many, and in some cases most, of them remain sound. Moreover, it is well known that glasses may be set in the gratings with no cement or other packing about them, as in case of the Walter's illuminating-gratings, where the iron plates, heated to redness at the glass-house, have the glasses pressed into their holes with metal right from the pot. Here we have naked glass directly in contact with naked iron, and these gratings, to the best of my knowledge and belief, have withstood all weathers and seasons. The contraction and expansion theory, therefore, not being supported by facts, we need a better one, and this we may get by considering the nature of the glasses employed in patent-light making and the mode of manufacturing such glasses, a true cure for their breakage being possible whenever we

succeed in ascertaining the true cause of the same.     Pressed or flint glass is the article in common use for making illuminating-gratings. From the character of the materials employed in its manufacture, this glass should be stronger and tougher than plate; but it is not so, on the contrary, and this because of the difference in the mode of annealing. On plate-glass manufacture I quote from the Encyclopædia Britannica, as follows, viz: "To anneal glass perfectly, the glass, when first made, must be kept for some time in a state approaching fluidity, and admitting of a uniform molecular arrangement throughout, * * * * the particles of glass having a cohesive polarity which dictates a certain regularity in their arrangement, but which requires time for its development." The article proceeds to say that the glass plates remain sometimes as long as two weeks shut up in hermetically-sealed ovens, during which time the temperature is allowed to gradually sink, no external air being admitted to interfere with the process. But in the manufacture of flint-glass the case is entirely different. The ovens are-open at two ends-- one, the "hot," where the goods are put in, and the other, the "cold," end, where they are taken out of the leer-- the glass during the process being moved constantly forward from the hot to the cold end of the oven. Under these circumstances it is conceivable that currents of air may enter the leer from the cold end that, sweeping in waves over the articles, may injuriously affect the process, causing all to differ and preventing the perfect annealing of any, (it is said that old hands in flint-glass works will often predict a bad lot of glass on a change in the wind;) and yet glasses of this description do not break when hot coal-tar cement is poured around them during the process of fixing in the gratings. Neither do they when molten lead is poured around them during the process of belting them with this metal, the explanation of which is that the heat of the lead and of the coal-tar is so intense and the flow so instantaneous as to flash, as it were, like lightning through the entire glass from circumference to center, causing an instantaneous expansion of the whole; and the surrounding medium being at the same