however, it was noticed that the lighter distillates were being
shipped to Germany, where lamps fitted for the consumption
of the grades of oil now known as lamp oil were being made by
Stohwasser of Berlin; some of these lamps were imported,
and similar lamps were afterwards manufactured by Laidlaw
in Edinburgh.
In Pennsylvania in 1859 Colonel E. L. Drake’s successful boring for petroleum resulted in the flooding of the market with oil at prices never before deemed possible, and led to the introduction of lamps from Germany for its consumption. Although the first American patent for a petroleum lamp is dated 1859, that year saw forty other applications, and for the next twenty years they averaged about eighty a year.
English lamp-makers were not behind in their attempts to improve on the methods in use for producing the highest results from the various grades of oil, and in 1865 Hinks introduced the duplex burner, while later improvements made in various directions, by Hinks, Silber, and Defries led to the high degree of perfection to be found in the lamps of to-day. Mineral oil for lamps as used in England at the present time may be defined as consisting of those portions of the distillate from shale oil or crude petroleum which have their flash-point above 73° F., and which are mobile enough to be fed by capillarity in sufficient quantity to the flame. The oil placed in the lamp reservoir is drawn up by the capillarity of the wick to the flame, and being there volatilized, is converted by the heat of the burning flame into a gaseous mixture of hydrogen and hydrocarbons, which is ultimately consumed by the oxygen of the air and converted into carbon dioxide and water vapour, the products of complete combustion.
To secure high illuminating power, together with a smokeless flame and only products of complete combustion, strict attention must be paid to several important factors. In the first place, the wick must be so arranged as to supply the right quantity of oil for gasification at the burner-head—the flame must be neither starved nor overfed: if the former is the case great loss of light is occasioned, while an excess of oil, by providing more hydrocarbons than the air-supply to the flame can completely burn, gives rise to smoke and products of incomplete combustion. The action of the wick depending on the capillary action of the microscopic tubes forming the cotton fibre, nothing but long-staple cotton of good quality should be employed; this should be spun into a coarse loose thread with as little twist in it as possible, and from this the wick is built up. Having obtained a wick of soft texture and loose plait, it should be well dried before the fire, and when put in position in the lamp must fill the wick-holder without being compressed. It should be of sufficient length to reach to the bottom of the oil reservoir and leave an inch or two on the bottom. Such a wick will suck up the oil in a regular and uniform way, provided that the level of the oil is not allowed to fall too low in the lamp, but it must be remembered that the wick acts as a filter for the oil, and that if any sediment be present it will be retained by and choke the capillaries upon which the action of the wick depends, so that a wick should not be used for too long a time. A good rule is that the wick should, when new, trail for 2 in. on the bottom of the oil vessel, and should be discarded when these 2 in. have been burnt off.
When the lamp is lighted the oil burns with a heavy, smoky flame, because it is not able to obtain sufficient oxygen to complete the combustion, and not only are soot flakes produced, but products of incomplete combustion, such as carbon monoxide and even petroleum vapour, escape—the first named highly injurious to health, and the second of an offensive odour. To supply the necessary amount of air to the flame, an artificial draught has to be created which shall impinge upon the bottom of the flame and sweep upwards over its surface, giving it rigidity, and by completing the combustion in a shorter period of time than could be done otherwise, increasing the calorific intensity and thus raising the carbon particles in the flame to a far higher incandescence so as to secure a greater illuminating power. This in practice has been done in two ways, first by drawing in the air by the up-suck of the heated and expanded products of combustion in a chimney fitted over the flame, and secondly by creating a draught from a small clockwork fan in the base of the lamp. It is necessary to break the initial rush of the draught: this is mostly effected by disks of perforated metal in the base of the burner, called diffusers, while the metal dome which surrounds and rises slightly above the wick-holder serves to deflect the air on to the flame, as in the Wanzer lamp. These arrangements also act to a certain extent as regenerators, the air passing over the heated metal surfaces being warmed before reaching the flame, whilst disks, cones, buttons, perforated tubes, inner air-tubes, &c., have been introduced to increase the illuminating power and complete the combustion.
| Type. | Name. | Grains of Oil per candle-power per hour. | Total Candle-power. | ||
| American. | Russian. | American. | Russian. | ||
| Circular wick | Veritas, 60-line | 64.5 | 112.5 | 122.5 | 78 |
| Veritas, 30-line | 42.5 | 50. | 60 | 60 | |
| Veritas, 20-line | 43.75 | 58.5 | 40 | 35 | |
| Ariel, 12-line center draught | 52.8 | 70.9 | 18 | 18 | |
| Reading, 14-line | 97.9 | 85.4 | 12 | 12 | |
| Kosmos, 10-line | 63.9 | 97.2 | 9 | 9 | |
| Wizard, 15-line | 56.9 | 51.3 | 18 | 19 | |
| Flat wick, single | Wanzer, no glass | 42.6 | 48.3 | 17 | 17 |
| Solid slip, gauze and cone | 84.4 | 84.4 | 8 | 8 | |
| Old slip, fixed gauze | 60.9 | 89.3 | 7 | 7 | |
| Flat wick, duplex | Feeder wick | 56.2 | 55.7 | 20 | 22 |
| Ordinary | 51.2 | 46.6 | 20 | 22 | |
| American oil—Sp. gr. 0.7904; flash-point, 110°F. Russian oil—Sp. gr. 0.823; flash-point, 83° F. | |||||
According to Sir Boverton Redwood, duplex burners which give a flame of 28 candle-power have an average oil consumption of 50 grains per candle per hour, while Argand flames of 38 candle-power consume about 45 grains of oil per candle per hour. These figures were obtained from lamps of the best types, and to obtain information as to the efficiency of the lamps used in daily practice, a number of the most popular types were examined, using both American and Russian oil. The results obtained are embodied in Table 1. The first noteworthy point in this table is the apparent superiority of the American over Russian oil in the majority of the lamps employed, and there is no doubt that the bulk of the lamps on the market are constructed to burn American or shale oil. A second interesting point is that with the flat-flame lamps the Russian oil is as good as the American. We have Redwood’s authority, moreover, for the fact that after prolonged burning the Russian oil, even in lamps least suited to it, gives highly improved results. Although the average consumption with these lamps is close upon 60 grains per candle with American oil, yet some of the burners are so manifestly wasteful that 50 grains per candle-power per hour is the fairest basis to take for any calculation as to cost.
The dangers of the mineral oil lamp, which were a grave drawback in the past, have been very much reduced by improvements in construction and quality, and if it were possible to abolish the cheap and dangerous rubbish sold in poor neighbourhoods, and to prevent the use of side-fillers and glass reservoirs in lamps of better quality, a still larger reduction in the number of accidents would take place. In the use of the lamp for domestic purposes only soft well-fitting wicks should be employed, and the lamp should be filled with oil each day so as never to allow it to burn too low and so leave a large space above the surface of the oil in the reservoir. The lamp should never be moved whilst alight, and it should only be put out by means of a proper extinguisher or by blowing across the top instead of down the chimney. By these means the risk of accident would be so reduced as to compare favourably with other illuminants.
Candles, oil and coal gas all emit the same products of complete combustion, viz. carbon dioxide and water vapour. The quantities of these compounds emitted from different illuminants for every candle of light per hour will be seen from the following table:
| Cubic Feet per Candle. | ||
| Illuminant. | Carbon Dioxide. | Water Vapour. |
| Sperm candle | 0.41 | 0.41 |
| Oil lamp | 0.24 | 0.18 |
| Gas—Flat flame | 0.26 | 0.67 |
| Argand | 0.17 | 0.45 |
| Regenerative | 0.07 | 0.19 |
| Incandescent | 0.03 | 0.08 |
From these data it appears that if the sanitary condition of the air of a dwelling-room be measured by the amount of carbon dioxide present, as is usually done, candles are the most prejudicial to health and comfort, oil lamps less so, and gas least, an assumption
