(3) a rotating air suction fan F, of special design ; and

(4) a small holder H, which also acts as a regulator. The driving power is obtained in small plants by means of a weight W, on a wire rope, the rope be passed through a series of pulleys and wound on to a drum D.

This weight rotates the drum, which is geared to drive the air fan, and also the feed of spirit to the carburettor, which is on the metric principle, and takes in exactly the amount of spirit required to carburet the volume of air passing through the carburettor at the same time.

To prevent the temperature falling too low, the carburettor is placed in an antifreezing mixture of glycerine and salt, kept in constant circulation by the air fan which works in the same. This fan sucks in air from the open through the carburettor.

The gas thus made is delivered to the small holder, which is sealed with glycerine and, acting as a regulator, is set to a pressure of 4 inches, and is connected by a lever L to a band brake (B) acting on the driving drum, which stops the action entirely when no gas is passing or the full pressure is on, and retards or allows acceleration according to the quantity of gas being used. From the holder the gas is delivered to the main service pipe.

To avoid constant filling of the small reservoir, and to prevent danger, in accordance with the regulations for storing petrol, the bulk of it has to be kept not less than 16 feet from a building, and therefore the petrol tank is placed outside, and is connected to the reservoir by a small feed pipe and a gauge placed on the reservoir.

From this reservoir the petrol is fed in small quantities by a thimble (Fig. 188) at the end of a pipe, and this pipe is made to rise and fall, each time dipping up the thimble full of petrol and letting it run through the pipe to a small well over the carburettor, where a similar pipe and thimble, as shown in Fig. 188, transfers an exact amount of petrol to the carburettor. These thimbles and pipes are actuated by a paul and rachet action from the driving drum, and their movements are correlated to the action of the air fan.

Fig. 187A.

Fig. 187A.

The carburettor is zigzag in form, and the air is sucked through in given volume. If necessary the air is first dried by being passed through or over calcium chloride.

This plant when put together is very compact, and can be covered up in a neat casing, taking up only a small amount of space, a 30-light plant measuring over all only 27 by 27 by 49 inches in height.

A paul and rachet allows the driving weight to be wound up with ease by hand without interrupting the action of the plant at any time. Practically this is all the attention required once it has been started to work, with the very occasional refilling of the outside petrol tank. Thus the labour to the household involved is not appreciably more than in ordinary coal-gas lighting. The effect of measuring a given amount of petrol to the carburettor ensures that the whole of the spirit is vaporised, so that there is no residue to be dealt with; and the resulting gas is practically constant in quality, no matter what the time of year or the temperature.

Oil Gas Continued 227

Fig. 188.

This apparatus has been used very successfully on the Continent even for lighting small towns and villages, which proves the permanent quality of the gas, and although quite new to this country it is meeting with a very large measure of popularity.

The general advantages of the use of petroleum gas are many, and far more than counterbalance any drawbacks.

In any system the necessary quantity of petrol required to carburet a given quantity of air varies somewhat with the specific gravity of the spirit used; but taking 0.680 spirit, such as is used for motor cars, one gallon will carburet from 850 to 1000 cubic feet of air.

This introduces the question of cost.

A 30-light plant will cost about 50, but for other sizes the price may be put at from 30s. to 25s. per burner, for the producer plants of most makes, to which must be added the cost of running the service pipes. Ordinary gas fittings are suitable, if these are not already laid in.

The whole is a very small capital outlay.

The absolute cost of producing gas depends on the price of petrol almost entirely. To-day this can be bought in bulk at certainly 1s. per gallon, and the cost of the gas would work out at about 1s. 6d. to 2s. at the utmost per 1000 cubic feet, after allowing for carriage, wages, etc., in the country,1 which compares more than favourably with coal or acetylene gas or electric lighting in any locality.

The next point is that properly proportioned petroleum gas is less dangerous to use than coal gas in the event of a leakage. The mixture of inflammable vapour and air in the gas itself should be such as to ensure perfect combustion, so that should a leak occur the addition of more air, instead of creating an explosive mixture, as is the case with coal gas, simply dilutes it and renders it compatatively harmless. Nevertheless, a leak when detected by the smell - which by the way is nothing like so unpleasant as that of coal gas - should not be sought for with a naked light.

A further source of economy, due to the purity of this gas, is that incandescent mantles will not only last very much longer than with coal gas, but they will also retain their pristine brilliancy almost unimpaired throughout, as there is no carbonising action taking place. A mantle that has been burning on a coal-gas burner for some three weeks, and from which much of the lighting power had been lost, may be placed on a petroleum gas burner for one hour with the result that the mantle will be practically burnt clean again, and have almost entirely regained its original brilliancy, and retain it even when replaced on the coal-gas burner.

As regards the question of hygiene, which is a very important one, petroleum gas, on account of its purity and proportioning to give perfect combustion, does not contaminate the atmosphere of the room in which it is burnt to anything like the same extent as coal gas or even ordinary lamps. The products of combustion are almost entirely water, a small proportion of carbonic anhydride and free nitrogen from the air.

There are none of the poisonous products due to sulphur and other impurities which are found in coal gas, no blackening of ceilings or destruction of the contents of the room; neither is there any fear of corrosion in the service pipes and fittings.

The gas burns without smell, and is pre-eminently clean and innocuous in use, and therefore especially adapted for gas-cooking stoves.

All the principal insurance companies have set the seal of their approval on its use, provided an accepted make of producer plant is used, and several railway stations are installing: this system of lighting.

1A 50-candle-power light costs about o. 1d. per hour.

Printed by Morrison & Gibb Limited, Edinburgh