Acetylene, the Principles of Its Generation and Use / A Practical Handbook on the Production, Purification, and Subsequent Treatment of Acetylene for the Development of Light, Heat, and Power - F. H. Leeds; W. J. Atkinson Butterfield

It has already been explained that acetylene is comparatively a less efficient heating agent than it is an illuminating material, because, per unit of volume, its calorific power is not so much greater than that of coal-gas as is its illuminating capacity. It has also been shown that the high upper explosive limit of mixtures of acetylene and air--a limit so much higher than the corresponding figure with coal-gas and other gaseous fuels--renders its employment in atmospheric burners (either for lighting or for heating) somewhat troublesome, or dependent upon considerable skill in the design of the apparatus. If, therefore, either the upper explosive limit of acetylene could be reduced, or its calorific value increased (or both), by mixing with it some other gas or vapour which should not seriously affect its price and convenience as a self-luminous illuminant, acetylene would compare more favourably with coal-gas in its ready applicability to the most various purposes. Such a method has been suggested by Heil, and has been found successful on the Continent. It consists in adding to the acetylene a certain proportion of the vapour of a volatile hydrocarbon, so as to prepare what is called "carburetted acetylene." In all respects the method of making carburetted acetylene is identical with that of making "air-gas," which was outlined in Chapter I., viz., the acetylene coming from an ordinary generating plant is led over or through a mass of petroleum spirit, or other similar product, in a vessel which exposes the proper amount of superficial area to the passing gas. In all respects save one the character of the product is similar to that of air-gas, i.e., it is a mixture of a permanent gas with a vapour; the vapour may possibly condense in part within the mains if they are exposed to a falling temperature, and if the product is to be led any considerable distance, deposition of liquid may occur (conceivably followed by blockage of the mains) unless the proportion of vapour added to the gas is kept below a point governed by local climatic and similar conditions. But in one most important respect carburetted acetylene is totally different from air-gas: partial precipitation of spirit from air-gas removes more or less of the solitary useful constituent of the material, reducing its practical value, and causing the residue to approach or overpass its lower explosive limit (cf. Chapter I.); partial removal of spirit from carburetted acetylene only means a partial reconversion of the material into ordinary acetylene, increasing its natural illuminating power, lowering its calorific intensity somewhat, and causing the residue to have almost its primary high upper explosive limit, but essentially leaving its lower explosive limit unchanged. Thus while air-gas may conceivably become inefficient for every purpose if supplied from any distance in very cold weather, and may even pass into a dangerous explosive within the mains; carburetted acetylene can never become explosive, can only lose part of its special heating value, and will actually increase in illuminating power.

It is manifest that, like air-gas, carburetted acetylene is of somewhat indefinite composition, for the proportion of vapour, and the chemical nature of that vapour, may vary. 100 litres of acetylene will take up 40 grammes of petroleum spirit to yield 110 litres of carburetted acetylene evidently containing 9 per cent. of vapour, or 100 litres of acetylene may be made to absorb as much as 250 grammes of spirit yielding 200 litres of carburetted acetylene containing 50 per cent. of vapour; while the petroleum spirit may be replaced, if prices are suitable, by benzol or denatured alcohol.

The illuminating power of acetylene carburetted with petroleum spirit has been examined by Caro, whose average figures, worked out in British units, are:

ILLUMINATING POWER OF CARBURETTED ACETYLENE. HALF-FOOT BURNERS.

Those results may be compared with those referring to air-gas, which emits in incandescent burners from 3.0 to 12.4 candles per cubic foot according to the amount of spirit added to the air and the temperature to which the gas is exposed.

The calorific values of carburetted acetylene (Caro), and those of other gaseous fuels are:

Besides its relatively low upper explosive limit, carburetted acetylene exhibits a higher temperature of ignition than ordinary acetylene, which makes it appreciably safer in presence of a naked light. It also possesses a somewhat lower flame temperature and a slower speed of propagation of the explosive wave when mixed with air. These data are:

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| | | | |
| | Explosive | Temperature. | |
| | Limits. | Degrees C. | Explosive |
| |19 mm. Tube. | | Explosive |
| |_____________|__________________| Wave. |
| | | | | | Metres per |
| | | |Of Igni-| | Second. |
| |Lower.|Upper.| tion. |Of Flame.| |
|________________________|______|______|________|_________|____________|
| | | | | | |
| Acetylene (theoretical)| --- | --- | --- |1850-2420| --- |
| " (observed) | 3.35 | 52.3 | 480 |1630-2020| 0.18-100 |
| Carburetted \ from | 2.5 | 10.2 | 582 | 1620 | 3.2 |
| acetylene / . . to | 5.4 | 30.0 | 720 | 1730 | 5.3 |
| Carburetted acetylene\ | 3.4 | 22.0 | --- | 1820 | 1.3 |
| (benzol) . . . / | | | | | |
| Carburetted acetylene\ | 3.1 | 12.0 | --- | 1610 | 1.1 |
| (alcohol) . . . / | | | | | |
| Air-gas, self-luminous\|15.0 | 50.0 | --- |1510-1520| --- |
| flame . . . . /| | | | | |
| Coal-gas . . . | 7.9 | 19.1 | 600 | --- | --- |
|________________________|______|______|________|_________|____________|