Acetylene, The Principles Of Its Generation And Use

F >> F. H. Leeds and W. J. Atkinson Butterfield >> Acetylene, The Principles Of Its Generation And Use

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The more important advantages of acetylene as an illuminant have now been
indicated, and it remains to discuss the cost of acetylene lighting in
comparison with other modes of procuring artificial light. At the outset
it may be stated that a very much greater reduction in the price of
calcium carbide--from which acetylene is produced--than is likely to
ensue under the present methods and conditions of manufacture will be
required to make acetylene lighting as cheap as ordinary gas lighting in
towns in this country, provided incandescent burners are used for the
gas. On the score of cheapness (and of convenience, unless the acetylene
were delivered to the premises from some central generating station)
acetylene cannot compete as an illuminant with coal-gas where the latter
costs, say, not more than 5s. per 1000 cubic feet, if only
reasonable attention is given to the gas-burners, and at least a quarter
of them are on the incandescent system. If, on the other hand, coal-gas
is misused and wasted through the employment only of interior or worn-out
flat-flame burners, while the best types of burner are used for
acetylene, the latter gas may prove as cheap for lighting as coal-gas at,
say, 2s. 6d. per 1000 cubic feet (and be far better hygienically);
whereas, contrariwise, if coal-gas is used only with good and properly
maintained incandescent burners, it may cost over 10s. per 1000 cubic
feet, and be cheaper than acetylene burned in good burners (and as good
from the hygienic standpoint). More precise figures on the relative costs
of coal-gas lighting and acetylene lighting are given in the tabular
statement at the close of this chapter.

With regard to electric lighting it is somewhat difficult to lay down a
fair basis of comparison, owing to the wide variations in the cost of
current, and in the efficiency of lamps, and to the undoubted hygienic
and aesthetic claims of electric lighting to precedence. But in towns in
this country where there is a public electricity supply, electric
lighting will be used rather than acetylene for the same reasons that it
is preferred to coal-gas. Cost is only a secondary consideration in such
cases, and where coal-gas is reasonably cheap, and nevertheless gives
place to electric lighting, acetylene clearly cannot hope to supplant the
latter. [Footnote: Where, however, as is frequently the case with small
public electricity-supply works, the voltage of the supply varies
greatly, the fluctuations in the light of the lamps, and the frequent
destruction of fuses and lamps, are such manifest inconveniences that
acetylene is in fact now being generally preferred to electric lighting
in such circumstances.] But where current cannot be had from an
electricity-supply undertaking, and it is a question, in the event of
electric lighting being adopted, of generating current by driving a
dynamo, either by means of a gas-engine supplied from public gas-mains,
by means of a special boiler installation, or by means of an oil-engine
or of a power gas-plant and gas-engine, the claims of acetylene to
preference are very strong. An important factor in the estimation of the
relative advantages of electricity and acetylene in such cases is the
cost of labour in looking after the generating plant. Where a gas-engine
supplied from public gas-mains is used for driving the dynamo, electric
lighting can be had at a relatively small expenditure for attendance on
the generating plant. But the cost of the gas consumed will be high, and
actually light could be obtained directly from the gas by means of
incandescent mantles at far loss cost than by consuming the gas in a
motor for the indirect production of light by means of electric current.
Therefore electric lighting, if adopted under these conditions, must be
preferred to gas lighting from considerations which are deemed to
outweigh those of a much higher cost, and acetylene does not present so
great advantages over coal-gas as to affect the choice of electric
lighting. But in the cases where there is no public gas-supply, and
current must be generated from coal or coke or oil consumed on the spot,
the cost of the skilled labour required to look after either a boiler,
steam-engine and dynamo, or a power gas-plant and gas-engine or oil-
engine and dynamo, will be so heavy that unless the capacity of the
installation is very great, acetylene will almost certainly prove a
cheaper and more convenient method of obtaining light. The attention
required by an acetylene installation, such as a country house of upwards
of thirty rooms would want, is limited to one or two hours' labour per
diem at any convenient time during daylight. Moreover, the attendant need
not be highly paid, as he will not have required an engineman's training,
as will the attendant on an electric lighting plant. The latter, too,
must be present throughout the hours when light is wanted unless a heavy
expenditure has been incurred on accumulators. Furthermore, the capital
outlay on generating plant will be very much less for acetylene than for
electric lighting. General considerations such as these lead to the
conclusion that in almost all country districts in this country a house
or institution could be lighted more cheaply by means of acetylene than
by electricity. In the tabular statement of comparative costs of
different modes of lighting, electric lighting has been included only on
the basis of a fixed cost per unit, as owing to the very varied cost of
generating current by small installations in different parts of the
country it would be futile to attempt to give the cost of electric
lighting on any other basis, such as the prime cost of coal or coke in a
particular district. Where current is supplied by a public electricity-
supply undertaking, the cost per unit is known, and the comparative costs
of electric light and acetylene can be arrived at with tolerable
precision. It has not been thought necessary to include in the tabular
statement electric arc-lamps, as they are only suitable for the lighting
of large spaces, where the steadiness and uniformity of the illumination
are of secondary importance. Under such conditions, it may be stated
parenthetically, the electric arc-light is much less costly than
acetylene lighting would be, but it is now in many places being
superseded by high-pressure gas or oil incandescent lights, which are
steady and generally more economical than the arc light.

The illuminant which acetylene is best fitted to supersede on the score
of convenience, cleanliness, and hygienic advantages is oil. By oil is
meant, in this connection, the ordinary burning petroleum, kerosene, or
paraffin oil, obtained by distilling and refining various natural oils
and shales, found in many countries, of which the United States
(principally Pennsylvania), Russia (the Caucasus chiefly), and Scotland
are practically the only ones which supply considerable quantities for
use in Great Britain. Attempts are often made to claim superiority for
particular grades of these oils, but it may be at once stated that so for
as actual yield of light is concerned, the same weight of any of the
commercial oils will give practically the same result. Hence in the
comparative statement of the cost of different methods of lighting, oil
will be taken at the cheapest rate at which it could ordinarily be
obtained, including delivery charges, at a country house, when bought by
the barrel. This rate at the present time is about ninepence per gallon.
A higher price may be paid for grades of mineral oil reputed to be safer
or to give a "brighter" or "clearer" light; but as the quantity of light
depends mainly upon the care and attention bestowed on the burner and
glass fittings of the lamp, and partly upon the employment of a suitable
wick, while the safety of each lamp depends at least as much upon the
design of that lamp, and the accuracy with which the wick fits the burner
tube, as upon the temperature at which the oil "flashes," the extra
expense involved in burning fancy-priced oils will not be considered
here.

The efficiency (_i.e._, the light yielded per pint or other unit
volume consumed) of oil-lamps varies greatly, and, speaking broadly,
increases with the power of the lamp. But as large or high-power lamps
are not needed throughout a house, it is fairer to assume that the light
obtainable from oil in ordinary household use is the mean of that
afforded by large and that afforded by small lamps. A large oil-lamp as
commonly used in country houses will give a light of about 20 candle-
power, while a convenient small lamp will give a light of not more than
about 5 candle-power. The large lamp will burn about 55 hours for every
gallon of oil consumed, or give an illuminating duty of about 1100
candle-hours (_i.e._, the product of candle-power by burning-hours)
per gallon. The small lamp, on the other hand, will burn about 140 hours
for every gallon of oil consumed, or give an illuminating duty of about
700 candle-hours per gallon. Actually large lamps would in most country
houses be used only in the entrance hall, living-rooms, and kitchen,
while passages and minor rooms on the lower floors would be lighted by
small lamps. Hence, making due allowance for the lower rate of
consumption of the small lamps, it will be seen that, given equal numbers
of large and small lamps in use, the mean illuminating duty of a gallon
of oil as burnt in country houses will be 987, or, in round figures, 990
candle-hours. Usually candles are used in the bedrooms of country houses
where the lower floors are lighted by means of petroleum lamps; but when
acetylene is installed in such a house it will frequently be adopted in
the principal bed- and dressing-rooms as well as in the living-rooms, as,
unless candles are employed very lavishly, they are really totally
inadequate to meet the reasonable demands for light of, _e.g._, a
lady dressing for dinner. Where acetylene displaces candles as well as
lamps in a country house, it is necessary, in comparing the cost of the
new illuminant with that of the candles and oil, to bear in mind the
superior degree of illumination which is secured in all rooms, at least
where candles were formerly used.

In regard to exhaustion and vitiation of the air, and to heat evolved,
self-luminous petroleum lamps stand on much the same footing as coal-gas
when the latter is burned in flat-flame burners, if the comparison is
based on a given yield of light. A large lamp, owing to its higher
illuminating efficiency, is better in this respect than a small one--
light for light, it is more hygienic than ordinary flat-flame coal-gas
burners, while a small lamp is less hygienic. It will therefore be
understood at once, from what has already been said about the superiority
on hygienic grounds of acetylene to flat-flame coal-gas lighting, that
acetylene is in this respect far superior to petroleum lamps. The degree
of its superiority is indicated more precisely by the figures quoted in
the tabular statement which concludes this chapter.

Before giving the tabular statement, however, it is necessary to say a
few words in regard to one method of lighting which, may possibly develop
into a more serious competitor with acetylene for the lighting of the
better class of country house than any of the illuminating agents and
modes of lighting so far referred to. The method in question is lighting
by so-called air-gas used for raising mantles to incandescence in
upturned or inverted burners of the Welsbach-Kern type. "Air-gas" is
ordinary atmospheric air, more or less completely saturated with the
vapour of some highly volatile hydrocarbon. The hydrocarbons practically
applied have so far been only "petroleum spirit" or "carburine," and
"benzol." "Petroleum spirit" or "carburine" consists of the more highly
volatile portion of petroleum, which is removed by distillation before
the kerosene or burning oil is recovered from the crude oil. Several
grades of this highly volatile petroleum distillate are distinguished in
commerce; they differ in the temperature at which they begin to distil
and the range of temperature covered by their distillation, and, speaking
more generally, in their degree of volatility, uniformity, and density.
If the petroleum distillate is sufficiently volatile and fairly uniform
in character, good air-gas may be produced merely by allowing air to pass
over an extended surface of the liquid. The vapour of the petroleum
spirit is of greater density than air, and hence, if the course of the
air-gas is downward from the apparatus at which it is produced, the flow
of air into the apparatus and over the surface of the spirit will be
automatically maintained by the "pull" of the descending air-gas when
once the flow has been started until the outlet for the air-gas is
stopped or the spirit in the apparatus is exhausted. Hence, if the
apparatus for saturating air with the vapour of the light petroleum is
placed well above all the points at which the air-gas is to be burnt--
_e.g._, on the roof of the house--the production of the air-gas may
by simple devices become automatic, and the only attention the apparatus
will require will be the replenishing of its reservoir from time to time
with light petroleum. But a number of precautions are required to make
this simple process operate without interruption or difficulty. For
instance, the evaporation of the spirit must not be so rapid relatively
to its total bulk as to lower its temperature, and thereby that of the
overflowing air, too much; the reservoir must be protected from extreme
cold and extreme heat; and the risk of fire from the presence of a highly
volatile and highly inflammable liquid on or near the roof of the house
must be met. This risk is one to which fire insurance companies take
exception.

More commonly, however, air-gas is made non-automatically, or more or
less automatically by the employment of some mechanical means. The light
petroleum, benzol, or other suitable volatile hydrocarbon is volatilised,
where necessary, by the application of gentle heat, while air is driven
over or through it by means of a small motor, which in some cases is a
hot-air engine operated by heat supplied by a flame of the air-gas
produced. These air-gas producers, or at least the reservoir of volatile
hydrocarbon, may be placed in an outbuilding, so that the risk of fire in
the house itself is minimised. They require, however, as much attention
as an acetylene generator, usually more. It is difficult to give reliable
data as to the cost of air-gas, inclusive of the expenses of production.
It varies considerably with the description of hydrocarbon employed, and
its market price. Air-gas is only slightly inferior hygienically to
acetylene, and the colour of its light is that of the incandescent light
as produced by coal-gas or acetylene. Air-gas of a certain grade may be
used for lighting by flat-flame burners, but it has been available thus
for very many years, and has failed to achieve even moderate success. But
the advent of the incandescent burner has completely changed its position
relatively to most other illuminants, and under certain conditions it
seems likely to be the most formidable competitor with acetylene. Since
air-gas, and the numerous chemically identical products offered under
different proprietary names, is simply atmospheric air more or less
loaded with the vapour of a volatile hydrocarbon which is normally
liquid, it possesses no definite chemical constitution, but varies in
composition according to the design of the generating plant, the
atmospheric temperature at the time of preparation, the original degree
of volatility of the hydrocarbon, the remaining degree of volatility
after the more volatile portions have been vaporised, and the speed at
which the air is passed through the carburettor. The illuminating power
and the calorific value of air-gas, unless the manufacture is very
precisely controlled, are apt to be variable, and the amount of light,
emitted, either in self-luminous or in incandescent burners, is somewhat
indeterminate. The generating plant must be so constructed that the air
cannot at any time be mixed with as much hydrocarbon vapour as
constitutes an explosive mixture with it, otherwise the pipes and
apparatus will contain a gas which will forthwith explode if it is
ignited, _i.e._, if an attempt is made to consume it otherwise than
in burners with specially small orifices. The safely permissible mixtures
are (1) air with less hydrocarbon vapour than constitutes an explosive
mixture, and (2) air with more hydrocarbon vapour than constitutes an
explosive mixture. The first of these two mixtures is available for
illuminating purposes only with incandescent mantles, and to ensure a
reasonable margin of safety the mixing apparatus must be so devised that
the proportion of hydrocarbon vapour in the air-gas can never exceed 2
per cent. From Chapter VI. it will be evident that a little more than 2
per cent. of benzene, pentane or benzoline vapour in air forms an
explosive mixture. What is the lowest proportion of such vapours in
admixture with air which will serve on combustion to maintain a mantle in
a state of incandescence, or even to afford a flame at all, does not
appear to have been precisely determined, but it cannot be much below 1-
1/2 per cent. Hence the apparatus for producing air-gas of this first
class must be provided with controlling or governing devices of such
nicety that the proportion of hydrocarbon vapour in the air-gas is
maintained between about 1-1/2 and 2 per cent. It is fair to say that in
normal working conditions a number of devices appear to fulfil this
requirement satisfactorily. The second of the two mixtures referred to
above, viz., air with more hydrocarbon vapour than constitutes an
explosive mixture, is primarily suitable for combustion in self-luminous
burners, but may also be consumed in properly designed incandescent
burners. But the generating apparatus for such air-gas must be equipped
with some governing or controlling device which will ensure the
proportion of hydrocarbon vapour in the mixture never falling below, say,
7 per cent. On the other hand, if saturation of the air with the vapour
is practically attained, should the temperature of the gas fall before it
arrives at the point of combustion, part of the spirit will condense out,
and the product will thus lose part of its illuminating or calorific
intensity, besides partially filling the pipes with liquid products of
condensation. The loss of intensity in the gas during cold weather may or
may not be inconvenient according to circumstances; but the removal of
part of the combustible material brings the residual air-gas nearer to
its limit of explosibility--for it is simply a mixture of combustible
vapour with air, which, normally, is not explosive because the proportion
of spirit is too high--and thus, when led into an atmospheric burner, the
extra amount of air introduced at the injector jets may cause the mixture
to be an explosive mixture of air and spirit, so that it will take fire
within the burner tube instead of burning quietly at the proper orifice.
This matter will be made clearer on studying what is said about explosive
limits in Chapter VI., and what is stated about incandescent acetylene
(carburetted or not) in Chapters IX. and X. Clearly, however, high-grade
air-gas is only suitable for preparation at the immediate spot where it
is to be consumed; it cannot be supplied to a complete district unless it
is intentionally made of such lower intensity that the proportion of
spirit is too small ever to allow of partial deposition in the mains
during the winter.

It is perhaps necessary to refer to the more extended use of candles for
lighting in some few houses in which lamps are disliked on aesthetic, or,
in some cases, ostensibly on hygienic grounds. Candle lighting, speaking
broadly, is either very inadequate so far as ordinary living-rooms are
concerned, or, if adequate, is very costly. Tests specially carried out
by one of the authors to determine some of the figures required in the
ensuing table show that ordinary paraffin or "wax" candles usually emit
about 20 per cent. more light than that given by the standard spermaceti
candle, whose luminosity is the unit by which the intensity of other
lights is reckoned in Great Britain; and also that the light so emitted
by domestic candles is practically unaffected by the sizes--"sixes,"
"eights," or "twelves"--burnt. In the sizes examined the light evolved
has varied between 1.145 and 1.298 "candles," perhaps tending to increase
slightly with the diameter of the candle tested. Hence, to obtain
illumination in a room equal on the average to that afforded by 100
standard candles, or some other light or lights aggregating 100 candle-
power, would require the use of only 80 to 85 ordinary paraffin,
ozokerite, or wax candles. But actually the essential objects in a room
could be equally well illuminated by, say, 30 candles well distributed,
as by two or three incandescent gas-burners, or four or five large oil-
lamps. Lights of high intensity, such as powerful gas-burners or oil-
lamps, must give a higher degree of illumination in their immediate
vicinity than is really necessary, if they are to illuminate adequately
the more distant objects. The dissemination and diffusion of their light
can be greatly aided by suitable colouring of ceilings, walls and
drapings; but unless the illumination by means of lights of relatively
high intensity is made almost wholly indirect, candles or other lights of
low intensity, such as small electric glow-lamps, can, by proper
distribution, be made to give more uniform or more suitably apportioned
illumination. In this respect candles have an economical and, in some
measure, a material advantage over acetylene also. (But when the method
of lighting is by flames--candle or other--the multiplication of the
number of units which is involved when they are of low intensity,
seriously increases the risk of fire through accidental contact of
inflammable material with any one of the flames. This risk is much
greater with naked flames, such as candles, than with, say, inverted
incandescent gas flames, which are to all intents and purposes fully
protected by a closed glass globe.) Hence, in the tabular statement which
follows of the comparative cost, &c., of different illuminants, it will
be assumed that 30 good candles would in practice be equally efficient in
regard to the illumination of a room as large oil-lamps, acetylene
flames, or incandescent gas-burners aggregating 100 candle-power.

For the same reason it will be assumed that electric glow-lamps of low
intensity (nominally of 8 candle-power or less), aggregating 70-80
candle-power, will practically serve, if suitably distributed, equally as
well as 100 candle-power obtained from more powerful sources of light.
Electric glow-lamps of a nominal intensity of 16 candles or thereabouts,
and good flat-flame gas-burners, aggregating 90-95 candle-power, will
similarly be taken as equivalent, if suitably distributed, to 100 candle-
power from more powerful sources of light. Of the latter it will be
assumed that each source has an intensity between 20 and 30 candle-power,
such as is afforded by a large oil-lamp, a No. 1 Welsbach-Kern upturned,
or a "Bijou" inverted incandescent gas-burner, or a 0.70-cubic-foot-per-
hour acetylene burner. Either of these sources of light, when used in
sufficient numbers, so that with proper distribution they light a room
adequately, will be taken in the tabular statement which follows as
affording, per candle-power evolved, the standard illuminating effect
required in that room. The same illuminating effect will be regarded as
attainable by means of candles aggregating only 35 per cent., or small
electric glow-lamps aggregating 77 per cent., or large electric glow-
lamps and flat-flame gas-burners aggregating 90 to 95 per cent. of this
candle-power; while if sources of light of higher intensity are used,
such as Osram or Tantalum electric lamps, or the larger incandescent gas-
burners (the Welsbach "C" or "York," or the Nos. 3 or 4 Welsbach-Kern
upturned, or the No. 1 or larger size inverted burners) or incandescent
acetylene burners, it will be assumed that their aggregate candle-power
must be in excess by about 15 per cent., in order to compensate for the
impossibility of obtaining equally well distributed illumination. These
assumptions are based on general considerations and data as to the effect
of sources of light of different intensities in giving practically the
same degree of illumination in a room; it would occupy too much space
here to discuss more fully the grounds on which they have been made. It
must suffice to say that they have been adopted with the object of being
perfectly fair to each means of illumination.

COST PER HOUR AND HYGIENIC EFFECT OF LIGHTING BY DIFFERENT MEANS

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