In all common lamps the oil box is above, and while it allows the oil to flow down upon the wick and keep it moist, it casts an objectionable shadow. To ob viate this the oil box is placed in some lamps below, and the oil has to be raised this involves ingenious but complicated apparatus.
G-irard' s hydrostatic lamp is constructed on precisely the same principles as the air chamber of a fire engine, or similar to the fountain of Hero (which see). The second illustration given under that article is an ideal lamp of Girard. The air vessel, air chamber, and connecting tubes are closely packed together. Its shape is inconve nient and limits its extended use.
In 1325 Thilorier, at Paris, invented a lamp in which the principle of the equili brium of fluid pressure is made use of: if two fluids of different densities be placed in tubes connected at the bottom, they will balance each other at different heights, according to their respective den sities. Thus, a column of 1 inch high, will balance a column of sulphuric ether of 19 inches, or a column of oil 14 inches.
Thilorier used ft solution of equal parts of white vitriol and water, which is II times denser than oil. So that 10 inches of the zinc solution can balance 151 inches oil in the other tube. As the oil diminishes by burning, the zinc solution exerting its pressure upon it keeps it up to the original level. This lamp cannot well be moved or carried about, without fear of being extinguished.
In the mechanical lamp it is a pump which is used to raise the oil up. In Car eer s lamp the pump is worked by clock wheel arrangement. The case for the works and space for the supply of oil are at the foot of the lamp : the stem of the lamp contains only the ascending tube, which separates above over the capital into a forked appendage or crutch, upon which rests the burner with its two con centric tubes. The burner and ascending tube form a space connected with the oil vessel by the pump. Three little pumps, termed priest pumps, are alternately act ing, one being forcing, the second is sucking, and the third midway between the two. Motion is obtained by a spring wound up in a case and furnished with cogs, which act upon the wheel which works the pumps. This lamp burns well, but it is costly, is liable to get out of order, and cannot, always readily be repaired.
Vapor lamps are those in which the mild in the lamp is first vaporized, and the heat thus produced while burning tends to raise a fresh quantity of fluid up in the form of vapor. A little cup of
spirits of wine, or a cloth soaked with the same, and surroux ding the nozzle of the lamp, are the usual means of vaporiz ing the liquid, which is usually one part of turpentine mixed with 4 parts of alcohol of 90 per cent.
Solar lamps. The chief point in the construction of these lamps is the man ner in which the air is caused to impinge upon the flame by the adaptation of a metallic or glass cone. This admits of a crude and cheap oil being used, which in other lamps would smoke.
A very beautiful kind of miniature sokr lamp, for those who have much writing at night, is manufactured by Messrs En dicott and Sumner, N. Y. The light of one is equal to that of six sperm candles, and it can burn either oil or lard. A pound of lard lasts about twenty hours. The air is admitted to the flame all ound it, inside and out, thus supplying it with plenty of oxygen, consequently there is no part of the flame blue, but all is a bright white light.
Whale oil is so thick and coarse when cold that it does not readily ascend the wick until heated.
Parker's economic or hot oil lamp was intended to obviate this, and has the oil vessel as a double cylinder, surrounding the upper part of the chimney. This latter is slightly curved outwards, so as to re flect the heat upon the oil vessel ; the hot oil descends by the arm to the burner. A slide regulates and cuts off the supply, so that the oil vessel may be removed to be filtered. Care must be taken to fill the ves sel with oil and allow no air to remain, as its expansion would make the oil overflow.
Camphene lamps.—Oil of turpentine is the liquid in these lamps. This sub stance 3s composed in 100 parts of 88-46 of carbon and 11.54 of hydrogen, which corresponds to the formula Cio This quantity of carbon is Vastly above what is found in oils, and hence more air is requisite to burn it without sooting. This is accomplished by putting a but ton in the flame, and narrowing the glass at the point where the flame is thrown out. Sometimes the current of air whick supplies the inner part of the flame is made to pass through the reservoir of turpentine, which becomes heated 10° or 15° above the temperature of the sur rounding air.