Lamp, a vessel employed for producing light, and sometimes also heat, by the combustion of inflammable fluids, grease, or wax. The simple form of these contrivances adopted by the ancient Hebrews has continued in use down to the present day; and until near the close of the last century this had hardly been improved upon among the most civilized nations. Even on the American continent may still be seen among the Canadian French the same low oval metallic vessel that was used by the ancient orientals and Europeans, furnished with a handle at one end and a beak at the other, through a hole on the upper surface of which projects the wick from the reservoir of oil or grease below. Some are made to be carried in the hand and placed upon tables, and others are kept suspended by chains in the middle of rooms. They give a dim smoky light, in consequence of the carbonaceous matter not being sufficiently spread by an open wick to be reached by the oxygen of the air before it is dissipated in sooty vapor. (See Combustion, and Flame.) The external form of the lamp was more of a study to the ancients than the principles of combustion. They gave to it the most graceful outlines, and ornamented it with grotesque figures and fanciful designs which were often of great beauty.
They suspended their lamps from the ceiling or from the hands of ornamental figures of boys or men, or they were placed upon stands. As at the present day in Aleppo and Egypt, they were kept by the Hebrews burning all night; and to this much importance was attached, the putting out of the light being significant of the extinction of the family and desertion of the house. - The first improvement in the construction of lamps was removing the beak by a long neck to a distance from the reservoir of oil, thus reducing the width of the shadow cast by the lamp. Besides this object, it was soon found by those who investigated the matter, that the following were subjects for improvement: 1, the wick, which as used presented a bundle of fibres, the inner portion of which, though saturated with oil, was removed from the reach of the air required for its combustion; 2, the level of the surface of the oil, that from first to last it should bear the same relation to the level of the burning part of the wick, thus securing uniformity in the supply of oil for combustion; and 3, the concentration of the light by reflectors at points where it is wanted.
The wick was first improved and much used in the countries bordering on the Rhine by platting its fibres together to make it flat and ribbonlike; a flat socket was provided for it, and it was made to move up and down by a horizontal spindle and toothed wheel; this is known as the Worms lamp. A greater improvement was that of the Argand burner, in which the wick was made in the form of a hollow cylinder, and so arranged that a current of air could pass up within it, as well as come to its external surface. The addition of a chimney of sheet iron, as originally made by Argand, increased the supply of air by producing an upward draught. The effect of the chimney was afterward much increased by contracting its upper portion and forming a shoulder, against which the ascending current impinges, and is turned inward upon the flame. The so-called astral lamps were provided with these wicks, and the reservoir for the oil was arranged in the form of a hollow ring encircling the hollow central stand that supported the burner, and with which it was connected by one of the tubular braces that held it up. Thus the level of the oil in the shallow ring could not undergo much change, and it Continued very nearly the same as that of the burning part of the wick until it was almost exhausted.
In consequence of the thin and peculiar shape given to the ring, the lamp cast no shadow at a little distance off, and a vase of ground glass surrounding the flame served to render the light still more diffusive or scattered. In the year 1800 Carcel devised an ingenious piece of clockwork machinery for pumping the oil from a reservoir at the foot of the lamp up to the burner, and thus supplying this always from the same point, while the excess of oil flowed back into the reservoir. This being at the base of the stand and the flame at the top, there was consequently no shadow. The lamp, afterward slightly improved by other manufacturers, was in many respects the most perfect of these contrivances; but its great cost restricted its use to the wealthy. It was moreover so inconveniently large and heavy, that it could be moved only with difficulty; and the complicated nature of its mechanism required access to skilful workmen, such as can be found only in large cities, to keep it in repair. The attention directed in the early part of the present century to the subject of producing artificial light by convenient and efficient methods caused many more forms of lamps to be introduced than can here be named.
Some were designed to burn the crude whale oil, which on account of its viscidity requires to be heated before it can pass along the fibres of the wick. Parker's hot oil or economic lamp was especially adapted for its use. The reservoir was a double cylinder of metal surrounding the upper portion of the chimney, which was also of metal, the lower part being of glass. It was supported by a side arm, which was made hollow to convey the oil to the burner below. A paper shade served to conceal the apparatus above the flame, and also to reflect the light downward. This lamp is very highly commended by Dr. Ure for its illuminating power and economy. The lamps of Benkler, constructed in Wiesbaden in 1840, introduced a peculiar contrivance in the form of the burner, which caused the draught of air to impinge at an angle upon the flame, making the combustion more vivid and the light more brilliant. It rendered practicable the use of poor qualities of oil, such as in other lamps were very imperfectly consumed, and only with the production of much smoke and disagreeable smell.
The so-called solar lamps, first made by Mr. Smith in Birmingham, depended on this principle; and it was essential to the excellent solar lamps made by Cornelius of Philadelphia, which, by means of a metallic cylinder passing from the burner down into the reservoir, permitted the use of lard instead of oil,sufficient heat being conveyed from the flame to keep it in a melted state. The solar lamps, on account of the cheap materials they consume, have been very extensively used; but they require particular care to keep them clean. The wick must be frequently changed, and always freshly trimmed with every using; and the reservoir also must be freshly filled at the same time. A report 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 R. Johnson and others, is contained in " Senate Document No. 160," 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 comparative trials referred to were, that from the same weights of the materials employed the quantity of light afforded by lard was represented by the figures 1068; by rosin gas, of specific gravity 0.8093, "or 43 Per cent. superior 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 carried 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 distillation of bituminous coals. To these succeeded a variety of lamps for the burning of camphene, and of a mixture of camphene and alcohol called burning fluid, but which, together 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, portability, and brilliancy of light that distinguished the camphene lamps, while their entire 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 reference to effecting the most thorough combustion of the oil. One of these in very general use has a flat wick half an inch to two inches 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 perforated 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 arrangement 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 variety 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, commonly of glass, furnished with a metallic tube for holding the wick and a closely fitting bell-shaped cover of glass for protecting the alcohol 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 device 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 liable to produce explosion. Their greatly increased brilliancy in this served to indicate danger; 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. R. Clanny of Sunderland, England, of the first true safety lamp. In this the communication with the external air was intercepted by water, through which the air was made to pass. This apparatus proved too cumbrous for general use. In 1815 George Stephenson and Sir Humphry Davy both invented safety lamps on other principles. 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 mines, contrived a lamp which was protected by a glass cylinder, and covered at top with a perforated metallic cap to allow the products of combustion to pass out.
The air to support combustion was admitted through small openings in the bottom, and it was supposed that the velocity of the current entering the lamp would prevent the explosion passing backward; but the protection the lamp afforded was really owing to the smallness of the apertures, continued through capillary tubes till they discharged all around and close against the circular burner. Davy's lamp is represented in tig. 1. The wire-gauze cylinder, through which the air was admitted, served also for the passage of the light, and when composed of wire 1/60 to 1/40 of an inch in diameter, and with 28 wires or 784 apertures to the inch, proved a perfect obstruction to the flame in the most explosive mixtures, unless these were blown in currents through the gauze, or the lamp was carried rapidly through the gas. The wires might even be heated red hot, as sometimes happens in very foul air, by the flame leaving the wick and burning in the upper part of the cylinder, and no explosion take place; but if a glass cover became hot it might be broken by drops of water falling upon it; and so fragile a material under any circumstances could not be regarded as a sure protection.
Among the various modifications of the Davy lamp, that known as Mackworth's safety lamp, which was contrived by one of the government inspectors of coal mines to meet the objections raised in resisting the general introduction of the Davy lamp into the fire-damp mines, is represented in fig. 2. The objections were the small light given by the Davy, which is an inconvenience in working high seams of coal; that its locks could be easily picked and opened by the workmen to obtain more light, or to light their pipes; and also the danger of breaking the glass already mentioned. The lamp has a thick outer glass, a a, and a thin inner chimney, f b. The air supplies the flame in the direction of the arrows through three wire gauzes: first the cylindrical gauze c; then through the gauze d, which supports the brass cover e of the glass chimney b; and thirdly through the conical wire gauze f, which with its frame acts as a support to the glass chimney b. This conical frame throws the air on to the flame g so as to produce a more perfect combustion and a white light. This lamp burns with a steady flame in currents of air which extinguish other lamps. It is 1 1/4 lb. heavier than the Davy, and 1 1/2 lb. lighter than the Clanny lamp.
The outside glass does not get so hot as in the latter, and if it breaks, there is still a perfect safety lamp inside.
Fig. 1. - Davy's Safety Lamp.
Fig. 2. - Mackworth's Safety Lamp.