THE LATE PROFESSOR ERNEST ABBE, OF JENA.
A practical example of the benefits gained in the properties of Jena glass is exhibited by its use in measuring heat. A thermometer of common glass when first manufactured may tell the truth, and in a month or two may vary from truth so much as to be worthless. The reason is that the dimensions of the glass slowly change day by day, as in a less degree do those of many alloys. It was one of the aims of the Jena laboratory to produce a glass which should remain constant in its dimensions while exposed to varying temperatures, so that, made into thermometers, it would be thoroughly trustworthy. Here, too, success was attained, so that thermometers of Jena glass are found to be reliable as are no instruments of ordinary glass. This product is available for astronomical lenses, otherwise liable to serious changes of form as exposed successively to warmth and cold.
Heat was to be staunchly withstood not only in moderate variations, but in extreme degrees. From time immemorial heat suddenly applied to glass has riven it in pieces. Could art dismiss this ancient fault? To-day a beaker from Jena may be filled with ice and placed with safety on a gas flame. In its many varieties this glass furnishes the chemist with clean, transparent and untarnishing vessels for the delicate tasks of the laboratory, all of singular indifference to heat and cold. Yet again. Special kinds of this glass in chemical uses are attacked by cold or hot corrosive liquids only one-twelfth to one-fourth as much as good Bohemian glass, the next best material.
Not only to heat but to light Jena glass renders a service. Glass of ordinary kinds when used for the tubes of a Hewitt mercury-vapor lamp, absorbs a considerable part of the ultra-violet rays upon which photography chiefly depends. A Jena glass free from this fault is formed into Uviol lamps of great value in taking photographs, photo-copying, and photo-engraving. These lamps are also employed in ascertaining the comparative stability of inks and artificial dyes; so intense is their action that brief periods suffice for the tests. Uviol rays severely irritate the eyes and skin; they may prove useful in treating skin diseases. They moreover quickly destroy germs. In all these activities reminding us of radium.
Thus by a bold departure from traditional methods in glass-making, the eye receives aid from lenses more powerful and more nearly true than ever before swept the canopy of heaven, or peered into the structure of minutest life. Meanwhile instruments of measurement take on a new accuracy and retain it as long as they last. All this while a material invaluable for its transparency is redeemed from brittleness and corrodibility, and given a strength all but metallic; at the same time transmitting light with none of the usual subtraction from its beams.
Bliss forming die. A, bed plate. B, blank-holder. C, drawing punch. D, push-out plate. O, P, annular pressure surfaces.
Bliss process of shell making.