RECENT DEVELOPMENTS IN GAS LIGHTING

BY ROBERT FFRENCH PIERCE

For the purpose of this lecture the term "recent developments," will be applied to changes and improvements in gas lighting appliances effected and reduced to commercial practice since 1910, progress prior to that year having been set forth in the lectures at Johns Hopkins University.

The economic position of the gas industry has tended to restrict development to the refinement and elaboration of existing types rather than to encourage increasing diversity in the application of gas to lighting.

Gas was the first central station illuminant and until 1880 the only one. At the present time, in the older communities of the East there are from four to seven times as many gas meters as electric meters in use, while even in the newer communities of the West, where cheap hydro-electric power and dear coal place the gas industry under a severe handicap, the number of gas meters usually exceeds that of electric meters in use. Following the line of least resistance the gas industry has directed such of its energies as have been devoted to lighting toward those improvements which would best protect its existing lighting business, while the commercial exigencies of electrical development have favored the creation of new uses and excursions into new fields.

During the past five years the principal developments in gas lighting have had for their objects increased economy in light production through more efficient utilization of the gas and decreased maintenance expense, and the elimination of inconvenience in the use and maintenance of gas lighting units, with the purpose of forestalling, overcoming or reducing the users' inclination toward providing facilities for the use of competing illuminants.

The gas lamp is composed of two essential parts-the burner and the mantle, the former usually being fitted with a glass chimney to secure satisfactory and efficient operation.

Possibilities of increased economy of light production lie in obtaining higher temperatures through improved burner design; in

securing a larger proportion of luminous radiation through the selection of mantle materials having a more favorable selective radiation characteristics; in prolonging the useful life of the mantle by the utilization of less fragile base fabrics; and in eliminating such accessories as chimneys the maintenance of which is an item of

expense.

Opportunities for securing added convenience in the use of gas lamps lie in such of the above developments as reduce the number of parts requiring attention and the frequency with which essential parts need replacement, and in the provision of simple, inexpensive and reliable means of ignition and distance control.

THE MANTLE

The physical character of the mantle is determined by the two essential substances which enter into its manufacture, (1) the organic fabric which is impregnated with solutions of salts of the (2) rare earths (ceria and thoria) that form the ultimate mantle structure, the organic matter being burned out in the process of manufacture. The character of the fabric used determines the mechanical strength of the mantle, its shrinkage under the continued heat of the flame, and to a small extent the luminosity of the mantle. The rare earths employed determine the radiant efficiency of the mantle, and the color of the light emitted.

No significant change in the proportions of ceria and thoria employed has taken place in the past twenty years, and although a theoretical consideration of the physics of rare earths radiation indicates the possibility of greatly increased efficiency through the employment of hitherto unused elements, no promising experimental results have as yet been recorded.

The utilization of "artificial silk" as a base fabric was noted by Whittaker in his Johns Hopkins lecture, but this material had not at that time been brought to such a commercial stage as would warrant specific quantitative statements as to its performance, and the employment of this substance may for the purposes of this lecture be regarded as a subsequent development. Mantles made upon this base have been used in large quantities during the past three years and exhibit a great superiority over previous types in tensile strength, flexibility, permanence of form and maintenance of luminosity. The artificial silk mantle of the upright type after several hundred hours service will support a suspended weight of

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Candle Power

itself

one ounce, may with care and skill be folded and crumpled upon and restored to its original form without apparent damage and will maintain its initial candle-power practically unimpaired for an indefinite period-5000 hours actual service producing a depreciation of less than 10 per cent. These facts while exemplifying no practical condition, are highly significant as indicating most desirable and important physical properties. It should be understood, of course, that the rather theatrical demonstrations of desirable physical qualities referred to are not to be attempted by the user unless he wishes to purchase a new mantle.

% Ceria

The desirable qualities of artificial silk are due to the fact that the fibers are solid and continuous, instead of cellular and comparatively short.

Figs. 3, 4 and 5 showing magnified sections of different mantle fabrics illustrate the steel-cable-like structure of the artificial silk mantles compared to that of mantles based upon vegetable fibers more resembling a hempen rope. The cellular structure is largely responsible for the shrinkage during burning which characterizes cotton mantles.

Due to causes not altogether apparent the luminosity of a mantle is considerably influenced by proportioning of the rare earth contents with relation to the physical structure of the mantle fabric, and refinements in manufacturing processes have resulted not only in