Page:The American Cyclopædia (1879) Volume X.djvu/136

 130 LAMP port of comparative experiments made in 1844 for the United States treasury department with the solar lard lamp, an Argand burner for rosin gas, and an Argand oil lamp such as was used in the lighthouses, by Prof. Walter K. John- son and others, is contained in " Senate Docu- ment No. 166," 28th congress, second session. The results are also given in the American edition of Knapp's "Chemical Technology" (1848), vol. i., p. 212. The results of the com- parative trials referred to were, that from the same weights of the materials employed the quantity of light afforded by lard was repre- sented by the figures 1068 ; by rosin gas, of specific gravity 0'8093, " or 43 per cent, su- perior in density to coal gas," by 956 ; and by sperm oil (two thirds summer and one third winter strained) by 711. The forms of lamps so far noticed are not adapted for being car- ried about in the hand, and their advantageous qualities depend on their being employed for several persons together. Little progress has been made in the production of economical, safe, and convenient small lamps. The vapor lamps, made for burning the vapors arising from a mixture of oil of turpentine and alcohol, which is kept sufficiently heated by a metallic tube passing down into the mixture from the flame, promised to meet this want ; but they proved expensive in use, and not altogether free from danger and the offensive smoke and smell of burning turpentine. Similar lamps were made for burning the volatile hydro- carbons obtained from the products of the dis- tillation of bituminous coals. To these suc- ceeded a variety of lamps for the burning of camphene, and of a mixture of camphene and alcohol called burning fluid, but which, to- gether with the material, have passed out of use, as being unsafe. The oils obtained by distillation of bituminous coals and petroleum have introduced new forms of lamps called kerosene lamps, and it is believed that these present all the advantages of cheapness, por- tability, and brilliancy of light that distin- guished the camphene lamps, while their en- tire safety gives to them a preference which has caused the use of the latter to be wholly abandoned. A multitude of burners have been contrived for these lamps, all made with ref- erence to effecting the most thorough combus- tion of the oil. One of these in very general use has a flat wick half an inch to two inch- es broad, which is moved up and down by a horizontal spindle. The wick tube is held by a cap which screws upon the top of the lamp, and over the cap is fitted tightly a brass ring or cylindrical piece perforated all around with holes to let in air to the wick ; and this ring carries a dome-shaped cover of thin brass in the top of which is a slit or elongated opening a little larger than the wick and directly over it, through which the flame passes up. The dome being of smaller diameter than the ring, there is room outside of it for the base of a glass chimney to stand, and this is moreover supported outside by the extension upward of the brass cylinder. Another row of holes per- forated at the base of this extension lets in air, which passes under the foot of the glass, and circulates up the outside of the dome, meeting the flame at the top. The dome with its opening is somewhat like the peculiar ar- rangement in the solar lamp. The chimney is enlarged immediately above the flame, and is then contracted to the same diameter as below. The student lamp, used for burning kerosene, has a construction similar to the Argand lamp, and is supplied with a reservoir which keeps the wick full at nearly a constant level. Lamps in chemical operations answer the purpose of small furnaces. They are made in a great va- riety of forms, adapted to special uses and the kinds of fuel employed. Some are oil lamps designed for the use of the blowpipe, and are furnished with a broad flat wick convenient for this purpose. Others are designed to consume alcohol ; and these are either plain vessels, com- monly of glass, furnished with a metallic tube for holding the wick and a closely fitting bell- shaped cover of glass for protecting the alco- hol from evaporation when the lamp is not in use ; or they are more elaborately constructed of metal, provided with an Argand burner, and made to slide upon an upright rod. This rod also supports movable rings adapted for holding crucibles and other vessels over the flame of the lamp. The heat is concentrated by the use of a metallic chimney ; and in some lamps it can be intensified by propelling a current of air of annular form and concentric with the Argand burner, so directed as to impinge across the flame. Safety Lamps. The explosive mixture of light carburetted hydrogen and atmospheric air which is often present in coal mines long made it desirable to procure some kind of de- vice by which the ignition of the compound might be avoided. Contrivances called steel mills were first used to give light in dangerous parts of the mines, a succession of sparks being constantly elicited by the rapid revolution of little wheels of steel against pieces of flint. In an explosive mixture of gas and air these however were not safe, as the sparks were lia- ble to produce explosion. Their greatly in- creased brilliancy in this served to indicate dan- ger; and where the gas predominated above the explosive proportion the sparks were of blood- red color or ceased entirely to be emitted. The necessity of more efficient protection led to the invention in 1813, by Dr. W. K. Clanny of Sunderland, England, of the first true safe- ty lamp. In this the communication with the external air was intercepted by water, through which the air was made to pass. This appa- ratus proved too cumbrous for general use. In 1815 George Stephenson and Sir Humph: Davy both invented safety lamps on other pri ciples. The former, noticing the effect of the gaseous products of combustion to extinguish the burning jets of inflammable gas called blowers, which issue from the crevices of coal 8 I