Lamps

Lamps are contrivances in which to utilise the illuminating power of fluid light-giving material. The most primitive lamps were probably skulls of animals, or certain kinds of sea-shells. The principle of these natural lamps was long retained in the ancient earthenware and metal lamps of Egypt, Greece, and Rome, and in the stone cups and boxes of northern nations. Such lamps were called lychna by the Greeks, and lucerne by the Romans. Specimens obtained from the excavations of the ruins of Tarsus, Pompeii, and Herculaneum, and from other sources, show that they were made in considerable variety. A very primitive form of lamp, called a 'crusie,' was in use in Scotland until mineral oils were introduced by James Young about 1850. Animal fats and fish oils were the principal substances used in all parts of the world for burning in lamps till vegetable oils were introduced—viz. colza or rape, and other seed oils and nut oils of various kinds. The vegetable oils, being more limpid in character, admitted of improved and more complex means of burning them. Progress in this direction began in France with Leger, who in 1783 adopted flat ribbon wicks in place of the old round, thick, and smoky wick. He was followed in 1784 by Aimé Argand (q.v.), who introduced round cylindrical burners; and round burners, whether for oil or gas, are still known by his name as Argand burners.

In the use of fatty oils, the ordinary capillary attraction of the wick was insufficient to maintain a uniform flow of oil to the flame, and various con- trivances were used to keep the oil as nearly as possible at one level. In 1803 M. Carcel introduced an excellent mechanical method of forcing the oil up by means of clockwork. This lamp, however, was too easily disarranged, and too expensive to come into general use. It was not till 1836 that Franchot invented his lamp, known as the 'French Moderator.' The main features of this lamp are a cylinder or oil-container with a tubular piston resting on the surface of the oil. This piston, being acted upon by a spiral spring placed between it and the top of the cylinder, forces the oil up through the piston and so maintains a constant supply of oil to the flame. The spring was wound up by rack and pinion. The unequal tension of such a spring, and the correspondingly unequal flow of oil, was counteracted (or 'moderated')—hence the name of the lamp) by placing a tapering iron rod in the ascending tube. This lamp was simple and effective, and soon supplanted all other mechanical arrangements for controlling the flow of oil to the burner; and it is the lamp still used by the few people who burn colza or rape oil in preference to mineral oils.

Mineral oils are known under various names, such as paraffin, petroleum, kerosene, crystal oils, &c., for the lighter sorts; and for the heavier or specially high list kinds such names as mineral sperm or mineral colza are used. These oils, being much more limpid and volatile than the fatty oils, rise freely in lamps by the ordinary suction of the wicks, and, being rich in carbon, a plentiful supply of oxygen is absolutely necessary to perfect combustion. The main problem, therefore, to be solved in the construction of a good paraffin or petroleum lamp was to secure a current of air powerful enough to consume the carbon contained in the oil, and so prevent its passing off in the form of smoke.

Previous to the introduction of mineral oils, camphire, which is a volatile hydrocarbon spirit distilled from turpentine, was burned in Young's 'Vesta' lamp, introduced in 1834. His lamp was constructed on the round or Argand principle, with a button or deflector over the central air-tube, and a constricted chimney. The leading features of this lamp have been followed in many of the later developments of mineral oil lamps with circular wicks. But the common flat-wick paraffin lamps now so familiar to every one were first made by Stobwasser in Berlin, and introduced into Great Britain in 1854. Since then the manufacture of paraffin lamps has grown to be an industry of great importance, and is carried on largely in England, Germany, and the United States. The number of patents in all these countries for paraffin or kerosene lamps has been enormous, but most of them refer simply to slight modifications of existing types. We cannot do more here than mention some of the chief improvements effected.

Mineral oil lamps are made with flat wicks and with circular wicks. The circular or Argand form of lamp has been generally adopted in continental countries. The body of the lamp or oil-container is made of glassware or metal, mounted on a pedestal. The outward casing of the burner is made of brass perforated for the admission of air. In the centre of the burner the wick-tube or holder is inserted. Over the wick-tube in flat-wick burners a metal dome is placed to deflect the air into the flame. Across the dome there is a slit or oblong opening for the flame to pass through, and a chimney 8 or 10 inches high, resting on a gallery at the base of the dome, creates the current of air necessary to perfect combustion of the oil.

Flat-wick burners have the advantage of being more easily trimmed and the flame more easily controlled than round burners. They admit also of a better supply of oxygen to all parts of the flame than has been possible with ordinary round burners, and are in consequence less liable to smoke. The most successful lamp developments in Great Britain have therefore hitherto been in flat-wick burners. In 1865 Messrs Hinks of Birmingham introduced the Duplex lamp, with two parallel wicks and two openings in the dome, producing two flames. This form of lamp rapidly became very popular, and still deservedly continues so. In 1874 Captain Doty patented his Triplex lamp, with three flat wicks arranged in the form of a triangle, open at each corner, so that an abundance of air circulates freely all round each of the three wick-tubes. There are three openings in the dome, and three flames which distribute the light nearly equally in all directions; and this no other flat-wick burner does. This is a powerful burner; it has little tendency to smoke, and is easily managed.

The great difficulty with round-wick burners has been to procure a sufficient supply of oxygen to the inside circumference of the flame, so that they are very liable to smoke after burning for a short time. To obviate this very serious objection a round burner was introduced, with a circular air-channel passing up from the base of the lamp through the reservoir and through the burner, which supplied a good current of air to the inner side of the circular flame. This lamp of necessity was made of metal, and, having a metal tube passing from the burner down through the oil-container, was thus liable to raise unduly the temperature of the oil, and was considered too unsafe for general use. In 1885, however, Messrs Defries introduced an improved lamp of this type, with a thin metal casing enclosing the portion of the wick inside the oil reservoir, and open only at the bottom, so that no oil or oil vapour can escape from the lamp except by passing up through the wick from the bottom of the reservoir. By this means the Defries lamp becomes a perfectly safe lamp for domestic use. But it is still not free from the drawback which attaches to all circular burners—viz. the difficulty in ordinary domestic use of trimming the wick quite level all round.

A still later advance in lamps for burning mineral oils economically is a lamp patented by Messrs Ross & Atkins, which applies to oil illumination the regenerative inverted Argand principle so successfully employed by Siemens in gas-lighting. The mechanical difficulties of producing an inverted shadowless flame with oil are obviously very much greater than with gas; but these difficulties have been successfully overcome in this lamp, now introduced to the public by the Wanzer Company, under the name of the Down-flame Shadowless Lamp. The essential features are an annular reservoir, with three converging flat wicks, which unite to form a circular flame; a glass cup underneath the flame; and a compound chimney above. The flame curves inwards, and the products of combustion passing up through the centre of the burner heat the fresh air on its passage through the burner to the flame. It is doubtless this feature which gives to this lamp its greater economy in the consumption of oil, considering the intensity of light produced.

Mineral oils are now extensively used for heating and cooking, and the burners employed for these purposes are generally adaptations of the flat-wick type. Captain Doty in 1868 patented a lighthouse lamp for burning mineral oils, and this method of lighting has since been adopted by all the important lighthouse services of the world, with much advantage to the mariner, and great economy as compared with the use of rape or colza oil (see LIGHTHOUSE). These lamps consist of one or more concentric wicks, and are capable of producing a very powerful light; one by Sir James Douglass, engineer to the corporation of the Trinity House, has eight concentric wicks, and produces a flame whose intensity is equal to 1400 candles.

COMPARATIVE TABLE.

To burn mineral oils successfully both theory and experience teach the absolute necessity of keeping all parts of the burner perfectly clean, so that the ingress of air to the flame may not be lessened or impeded by deposits of carbonised wick, which accumulate unless removed from time to time when lamps are in use, and which moreover become a source of danger from their liability to ignite. Long experience has also shown that a most fruitful source of annoyance in burning these oils arises from the presence of water or moisture in the oil or in the lamp. The greatest care should therefore be taken to keep the oil and the lamps perfectly free from water, and new wicks should be carefully dried before being inserted in the burner. See also SAFETY-LAMP, LUCIGEN.