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Pharology - How Lighthouses Work - H17

H17: Acetylene

Q: How was acetylene used in lighthouses?

Acetylene is a highly combustible gas which burns with an intensely bright flame. (Think of the very bright flame that is used when a welder joins or cuts pieces of metal.) Acetylene is easily generated by the chemical reaction of water on a mineral called calcium carbide. This principle made it an ideal method for providing light in situations where human effort was not readily available. The solid calcium carbide, is cheap, easy to store, takes up relatively little space, and its reactant - water - is also readily available. Use in buoys and other automatic systems is straightforward and it has been used in this way in these systems for many years.

The following notes were extracted from a publication by Chance Bros, Lighthouse Equipment Manufacturers (1910)

"Acetylene may also be used as an illuminant for Light-vessels. Precautions should be taken in the design of a vessel using either compressed oil gas or acetylene, to prevent the possibility of an explosion. In ordinary cases where these gases are used on shore, they are not confined in any way, and there is comparatively no danger; but in a vessel the gas is in most cases contained in cylinders below, and led up through a pipe to the top of the mast. Should there be the slightest leak anywhere, the gas will slowly collect, and being confined either in the hold, or the bottom of the mast or elsewhere, an explosive mixture will be formed. Great care should therefore be taken to give efficient ventilation, and also to prevent the possibility of such explosive mixture collecting in the proximity of any oil engines which may be fitted on board for the purpose of compressing air for a fog-signal.

"Coal Gas, as has already been mentioned, can be used for permanent lights, but the two illuminants which really hold this field are oil gas and Acetylene. Oil Gas, as also mentioned above, is compressed into the body of the buoy or into containers arranged conveniently near the beacon as the case may be, and supplied to the burner through a governor or pressure reducer. The use of Acetylene in permanent Lights has already been discussed elsewhere. The length of time during which any permanent Light will burn without attention depends essentially on the size of the containers, and the amount of gas consumed per hour; with oil gas this is usually from one to three months. With Acetylene it may vary from one month or less up to six months, or even a year. In practice, Lights are very seldom left longer than six months without examination, as among other reasons the lenses gradually become dimmed by the deposit of dust and the salt from the sea spray, and where they are fairly accessible, a period of three months is perhaps sufficient.

"The points against acetylene are : (1) Its cost if required in large Lights. (2) The danger of explosion, if it collects in an enclosed space. In the case of small Lights placed in the open, this may be neglected if reasonable care is taken, but in larger Lights, where the generator and burners are in an enclosed space, such as a Lighthouse tower or lantern, special pre-cautions are necessary.

"The points in favour of acetylene are therefore as follows : (1) Adaptability for 'permanent' Lights. (2) Ease of manipulation in the case of beacons, as compared with oil gas, it can be made on the spot and as required. (3) Ease of giving any occulting characteristic as compared with an oil burner which requires a revolving screen or other device to occult it. (4) Portability (in carbide form).

"In Buoys, which are an important type of unattended light, the Acetylene generator is arranged in the interior of the body, or else cylinders containing the gas in the Dissolved form, are inserted in it. When used for Beacons, the generator can be placed wherever convenient, and the simpler the form the less protection it will require. To give a distinctive character to a Light using either Compressed Oil Gas or Acetylene, a special "Flasher" is used. By means of these, of which there are several types, practically any character can be given, the gas being automatically cut off and allowed to pass as required. The gas of course reaches the flasher after passing through a governor, so that the pressure is constant, and in consequence there is no variation in the period of the character. It is usual to make the period of light shorter than that of darkness, as by this means the gas is economized.

"We have made a special study of acetylene burners, and have designed one employing small mantles, which can be used either singly or in a group of three, there being a special attachment which ensures that the light is practically unimpaired even if one mantle is broken by a shock or for any other reason. This burner was intended specially for use in the Revolving Portlight and when placed inside this, a very intense beam results.

"Though for reason of cost acetylene is very little used for large Lights, there is no doubt that it is well suited for an illuminant in unattended Lights of all kinds, and in this field it is now competing successfully with compressed oil gas, and in some cases taking its place. The difficulty which was at first met with was the clogging or carbonizing of the burner, but this has been overcome by passing the gas after generation through a special purifying material, and there is now no need to fear trouble on this score. Lights may be safely left to burn for six months and more without attention.

"There are many types of burners, but in our opinion the best form is that giving a small fish-tail flame; the number of burners, which can be arranged in a group as desired, varying according to the candle-power required. Such burners use from 3/4 to 3/4 of a foot of gas per hour, and give from 10 to 30 candle-power (from 1 to 3 carcels) each. Acetylene burners can be constructed for use with a mantle. This of course greatly decreases the cost per candle-power, but it is still considerably higher than that of incandescent oil.

"We have designed a special generator, working on the water to carbide principle, for use with Lights on shore, in which the water and the gas are the only things which move, there being no movable gas-holder, levers, etc., which is the case with most generators. This generator can be opened up at any time with very little waste of gas and carbide, the latter being attacked by the water in small quantities only, as gas is required. Where a high candle-power is required, such as in the case of large lights, the consumption of gas and therefore the size of the generator, make both the first cost and upkeep incomparably more expensive than that of incandescent oil, and as in such cases there is almost always a keeper in attendance during the night, there seems little need to employ acetylene.

"Acetylene is made very simply by the action of water on calcium carbide, which can now be obtained universally. The gas can either be manufactured on the spot as required which is the more usual method, and that practically always adopted where any quantity of it is used, that is, where a burner of high candle-power is required, or obtained in the form called "Dissolved," compressed into cylinders, containing a patent absorbent which renders it absolutely safe to transport them. There are a great number of different forms of acetylene generators on the market, but in our opinion the majority are rather complicated, and have too many moving parts, especially if they are to be used with unattended Lights. For Lighthouse use, where a breakdown for even a short period may be attended by such serious conse-quences, it is essential that everything should be as simple as possible.

"Acetylene has lately been introduced as an illuminant for sea lighting. It is claimed by many of its advocates that it has a specially penetrating power, and candle-power, for candle-power will show through fog further than other illuminants. This statement, however, needs further confirmation, as it has hitherto been held that the more red and yellow rays a light contains, the greater will be its penetrating power in a foggy atmosphere.

"With regard to the illuminant to be used in such Lights, for ordinary positions, the simplest is a wick burner of the capillary type, which can be left unattended all night, and gives a very satisfactory result. For positions which are close to or in a town, the ordinary gas supply may be laid on to the Light; the candle-power in this case can be greatly increased by the use of an incandescent mantle. If it is desired to leave the Light unattended for several days at a time, owing to the possibility of access to it being prevented by heavy seas, or other cause, a by-pass can be put in, by running a subsidiary pipe up to the position, so that the gas can be turned off at a distance, during the day, but in this case it would not be advisable to use a mantle. For isolated positions, or those where it is desired to leave a Light unattended for long periods, months at a time, acetylene in some form or other may be employed with great advantage."