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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For vehicular lamps, and probably for hand lanterns, the water-to-carbide
system has practically no alternative (among actual generators), and
safety and convenience have to be gained at the expense of the carbide.
In such apparatus the supply of water is usually controlled ultimately by
pressure, though a hand-operated needle-valve is frequently put on the
water tube. The water actually reaches the carbide either by dropping
from a jet, by passing along, upwards or downwards, a "wick" such as is
used in oil-lamps, or by percolating through a mass of porous material
like felt. The carbide is held in a chamber closed except at the gas exit
to the burner and at the inlet from the water reservoir: so that if gas
is produced more rapidly than the burner takes it, more water is
prevented from entering, or the water already present is driven backwards
out of the decomposing chamber into some adjoining receptacle. It is
impossible to describe in detail all the lamps which have been
constructed or proposed for vehicular use; and therefore the subject must
be approached in general terms, discussing simply the principles involved
in the design of a safe portable generator.

In all portable apparatus, and indeed in generators of larger dimensions,
the decomposing chamber must be so constructed that it can never, even by
wrong manipulation, be sealed hermetically against the atmosphere. If
there is a cock on the water inlet tube which is capable of being
completely shut, there must be no cock between the decomposing chamber
and the burner. If there is a cock between the carbide vessel and the
burner, the water inlet tube must only be closed by the water, being
water-sealed, in fact, so that if pressure rises among the carbide the
surplus gas may blow the seal or bubble through the water in the
reservoir. If the water-supply is mainly controlled by a needle-valve, it
is useful to connect the burner with the carbide vessel through a short
length of rubber tube; and if this plan is adopted, a cock can, if
desired, be put close to the burner. The rubber should not be allowed to
form a bend hanging down, or water vapour, &c., may condense and
extinguish the flame. In any case there should be a steady fall from the
burner to the decomposing chamber, or to some separate catch-pit for the
products of condensation. Much of the success attainable with small
generators will depend on the water used. If it is contaminated with
undissolved matter, the dirt will eventually block the fine orifices,
especially the needle-valve, or will choke the pores of the wick or the
felt pad. If the water contains an appreciable amount of "temporary
hardness," and if it becomes heated much in the lamp, fur will be
deposited sooner or later, and will obviously give trouble. Where the
water reservoir is at the upper part of the lamp, and the liquid is
exposed to the heat of the flame, fur will appear quickly if the water is
hard. Considerable benefit would accrue to the user of a portable lamp by
the employment of rain water filtered, if necessary, through fabric or
paper. The danger of freezing in very severe weather may be prevented by
the use of calcium chloride, or preferably, perhaps, methylated spirit in
the water (_cf._ Chapter III., p. 92). The disfavour with which
cycle and motor acetylene lamps are frequently regarded by nocturnal
travellers, other than the users thereof, is due to thoughtless design in
the optical part of such lamps, and is no argument against the employment
of acetylene. By proper shading or deflection of the rays, the eyes of
human beings and horses can be sufficiently protected from the glare, and
the whole of the illumination concentrated more perfectly on the road
surface and the lower part of approaching objects--a beam of light never
reaching a height of 5 feet above the ground is all that is needed to
satisfy all parties.

As the size of the generator rises, conditions naturally become more
suited to the construction of a satisfactory apparatus; until generators
intended to supply light to the whole of (say) a railway carriage, or the
head and cab lamps of a locomotive, or for the outside and inside
lighting of an omnibus are essentially generators of domestic dimensions
somewhat altered in internal construction to withstand vibration and
agitation. As a rule there is plenty of space at the side of a locomotive
to carry a generator fitted with a displacement holder of sufficient
size, which is made tall rather than wide, to prevent the water moving
about more than necessary. From the boiler, too, steam can be supplied to
a coil to keep the liquid from freezing in severe weather. Such apparatus
need not be described at length, for they can be, and are, made on lines
resembling those of domestic generators, though more compactly, and
having always a governor to give a constant pressure. For carriage
lighting any ordinary type of generator, preferably, perhaps, fitted with
a displacement holder, can be erected either in each corridor carriage,
or in a brake van at the end of the train. Purifiers may be added, if
desired, to save the burners from corrosion; but the consumption of
unpurified gas will seldom be attended by hygienic disadvantages, because
the burners will be contained in closed lamps, ventilating into the
outside air. The generator, also, may conveniently be so constructed that
it is fed with carbide from above the roof, and emptied of lime sludge
from below the floor of the vehicle. It can hardly be said that the use
of acetylene generated on board adds a sensible risk in case of
collision. In the event of a subsequent fire, the gas in the generator
would burn, but not explode; but in view of the greater illuminating
power per unit volume of carbide than per equal volume of compressed oil-
gas, a portable acetylene generator should be somewhat less objectionable
than broken cylinders of oil-gas if a fire should follow a railway
accident of the usual kind. More particularly by the use of "cartridges"
of carbide, a railway carriage generator can be constructed of sufficient
capacity to afford light for a long journey, or even a double journey, so
that attention would be only required (in the ordinary way) at one end of
the line.

Passing on from the generators used for the lighting of vehicles and for
portable lamps for indoor lighting to the considerably larger portable
generators now constructed for the supply of acetylene for welding
purposes and for "flare" lamps, it will be evident that they may embody
most or all of the points which are essential to the proper working of a
fixed generator for the supply of a small establishment. The holder will
generally be of the displacement type, but some of these larger portable
generators are equipped with a rising holder. The generators are,
naturally, automatic in action, but may be either of the water-to-carbide
or carbide-to-water type--the latter being preferable in the larger sizes
intended for use with the oxy-acetylene blow-pipe for welding, &c., for
which use a relatively large though intermittent supply of acetylene is
called for. The apparatus is either carried by means of handles or poles
attached to it, or is mounted on a wheelbarrow or truck for convenience
of transport to the place where it is to be used. The so called "flare"
lamps, which are high power burners mounted, with or without a reflector,
above a portable generator, are extremely useful for lighting open spaces
where work has to be carried on temporarily after nightfall, and are
rapidly displacing oil-flares of the Lucigen type for such purposes.

The use of "cartridges" of calcium carbide has already been briefly
referred to in Chapters II. and III. These cartridges are usually either
receptacles of thin sheet-metal, say tin plate, or packages of carbide
wrapped up in grease proof paper or the like. If of metal, they may have
a lid which is detached or perforated before they are put into the
generator, or the generator (when automatic and of domestic size) may be
so arranged that a cartridge is punctured in one or more places whenever
more gas is required. If wrapped in paper, the cartridges may be dropped
into water by an automatic generator at the proper times, the liquid then
loosening the gum and so gaining access to the interior; or one spot may
be covered by a drape of porous material (felt) only, through which the
water penetrates slowly. The substance inside the cartridge may be
ordinary, granulated, or "treated" carbide. Cartridges or "sticks" of
carbide are also made without wrappings, either by moistening powdered
carbide with oil and compressing the whole into moulds, or by compressing
dry carbide dust and immersing the sticks in oil or molten grease. The
former process is said to cause the carbide to take up too much oil, so
that sticks made by the second method are reputed preferable. All these
cartridges have the advantage over common carbide of being more permanent
in damp air, of being symmetrical in shape, of decomposing at a known
speed, and of liberating acetylene in known quantity; but evidently they
are more expensive, owing to the cost of preparing them, &c. They may be
made more cheaply from the dust produced in the braking of carbide, but
in that case the yield of gas will be relatively low.

It is manifest that, where space is to spare, purifiers containing the
materials mentioned in Chapter V. can be added to any portable acetylene
apparatus, provided also that the extra weight is not prohibitive. Cycle
lamps and motor lamps must burn an unpurified gas unpurified from
phosphorus and sulphur; but it is always good and advisable to filter the
acetylene from dust by a plug of cotton wool or the like, in order to
keep the burners as clear as may be. A burner with a screwed needle for
cleaning is always advantageous. Formerly the burners used on portable
acetylene lamps were usually of the single jet or rat-tail, or the union
jet or fish tail type, and exhibited in an intensified form, on account
of their small orifices, all the faults of these types of burners for the
consumption of acetylene (see Chapter VIII.). Now, however, there are
numerous special burners adapted for use in acetylene cycle and motor
lamps, &c., and many of these are of the impinging jet type, and some
have steatite heads to prevent distortion by the heat. One such cycle-
lamp burner, as sold in England by L. Wiener, of Fore Street, London, is
shown in Fig. 21. A burner constructed like the "Kona" (Chapter VIII.) is
made in small sizes (6, 8 and 10 litres per hour) for use in vehicular
lamps, under the name of the "Konette," by Falk, Stadelmann and Co.,
Ltd., of London, who also make a number of other small impinging jet
burners. A single jet injector burner on the "Phos" principle is made in
small sizes by the Phos Co., of London, specially for use in lamps on
vehicles.

[Illustration: FIG. 21.--CYCLE-LAMP BURNER NO. 96042A.]

Nevertheless, although satisfactory medium-sized vehicular lamps for the
generation of acetylene have been constructed, the best way of using
acetylene for all such employments as these is to carry it ready made in
a state of compression. For railway purposes, where an oil-gas plant is
in existence, and where it is merely desired to obtain a somewhat
brighter light, the oil-gas may be enriched with 20 per cent. of
acetylene, and the mixed gas pumped into the same cylinders to a pressure
of 10 atmospheres, as mentioned in Chapter XI.; the only alteration
necessary being the substitution of suitable small burners for the common
oil-gas jets. As far as the plant is concerned, all that is required is a
good acetylene generator, purifier, and holder from which the acetylene
can be drawn or forced through a meter into a larger storage holder, the
meter being connected by gearing with another meter on the pipe leading
from the oil-gas holder to the common holder, so that the necessary
proportions of the two gases shall be introduced into the common holder
simultaneously. From this final holder the enriched gas will be pumped
into the cylinders or into a storage cylinder, by means of a thoroughly
cooled pump, so that the heat set free by the compression may be safely
dissipated.

Whenever still better light is required in railway carriages, as also for
the illumination of large, constantly used vehicles, such as omnibuses,
the acetone process (_cf._ Chapter XI.) exhibits notable advantages.
The light so obtained is the light of neat acetylene, but the gas is
acetylene having an upper limit of explosibility much lower than usual
because of the vapour of acetone in it. In all other respects the
presence of the acetone will be unnoticeable, for it is a fairly pure
organic chemical body, which burns in the flame completely to carbon
dioxide and water, exactly as acetylene itself does. If the acetylene is
merely compressed into porous matter without acetone, the gas burnt is
acetylene simply; but per unit of volume or weight the cylinders will not
be capable of developing so much light.

In the United States, at least one railway system (The Great Northern)
has a number of its passenger coaches lighted by means of plain acetylene
carried in a state of compression in cylinders without porous matter. The
gas is generated, filtered from dust, and stored in an ordinary rising
holder at a factory alongside the line; being drawn from this holder
through a drier to extract moisture, and through a safety device, by a
pump which, in three stages, compresses the acetylene into large storage
reservoirs. The safety device consists of a heavy steel cylinder filled
with some porous substance which, like the similar material of the
acetone cylinders, prevents any danger of the acetylene contained in the
water-sealed holder being implicated in an explosion starting backwards
from the compression, by extinguishing any spark which might be produced
there. The plant on the trains comprises a suitable number of cylinders,
filled by contact with the large stores of gas to a pressure of 10
atmospheres, pipes of fusible metal communicating with the lamps, and
ordinary half-foot acetylene burners. The cylinders are provided with
fusible plugs, so that, in the event of a fire, they and the service-
pipes would melt, allowing the gas to escape freely and burn in the air,
instead of exploding or dissociating explosively within the cylinders
should the latter be heated by any burning woodwork or the like. It is
stated that this plan of using acetylene enables a quantity of gas to be
carried under each coach which is sufficient for a run of from 53 to 70
hours' duration, or of over 3600 miles; that is to say, enables the
train, in the conditions obtaining on the line in question, to make a
complete "round trip" without exhaustion of its store of artificial
light. The system has been in operation for some years, and appears to
have been so carefully managed that no accident has arisen; but it is
clear that elements of danger are present which are eliminated when the
cylinders are loaded with porous matter and acetone. The use of a similar
system of compressed acetylene train lighting in South America has been
attended with a disastrous explosion, involving loss of life.

It may safely be said that the acetone system, or less conveniently
perhaps the mere compression into porous matter, is the best to adopt for
the table-lamp which is to be used in occupied rooms Small cylinders of
such shapes as to form an elegant base for a table-lamp on more or less
conventional lines would be easy to make. They would be perfectly safe to
handle. If accidentally or wilfully upset, no harm would arise. By
deliberate ill-treatment they might be burst, or the gas-pipe fractured
below the reducing valve, so that gas would escape under pressure for a
time; but short of this they would be as devoid of extra clangor in times
of fire as the candle or the coal-gas burner. Moreover, they would only
contaminate the air with carbon dioxide and water vapour, for the gas is
purified before compression; and modern investigations have conclusively
demonstrated that the ill effects produced in the air of an imperfectly
ventilated room by the extravagant consumption of coal-gas depend on the
accumulation of the combustion products of the sulphur in the gas rather
than upon the carbon dioxide set free.

One particular application of the portable acetylene apparatus is of
special interest. As calcium carbide evolves an inflammable gas when it
merely comes into contact with water, it becomes possible to throw into
the sea or river, by hand or by ejection from a mortar, a species of bomb
or portable generator which is capable of emitting a powerful beam of
light if only facilities are present for inflaming the acetylene
generated; and it is quite easy so to arrange the interior of such
apparatus that they can be kept ready for instant use for long periods of
time without sensible deterioration, and that they can be recharged after
employment. Three methods of firing the gas have been proposed. In one
the shock or contact with the water brings a small electric battery into
play which produces a spark between two terminals projecting across the
burner orifice; in the second, a cap at the head of the generator
contains a small quantity of metallic potassium, which decomposes water
with such energy that the hydrogen liberated catches fire; and in the
third a similar cap is filled with the necessary quantity of calcium
phosphide, or the "carbophosphide of calcium" mentioned in Chapter XI.,
which yields a flame by the immediate ignition of the liquid phosphine
produced on the attack of water. During the two or three seconds consumed
in the production of the spark or pilot flame, the water is penetrating
the main charge of calcium carbide in the interior of the apparatus,
until the whole is ready to give a bright light for a time limited only
by the capacity of the generator. It is obvious that such apparatus may
be of much service at sea: they may be thrown overboard to illuminate
separate lifebuoys in case of accident, or be attached to the lifebuoys
they are required to illuminate, or be used as lifebuoys themselves if
fitted with suitable chains or ropes; they may be shot ahead to
illuminate a difficult channel, or to render an enemy visible in time of
war. Several such apparatus have already been constructed and severely
tested; they appear to give every satisfaction. They are, of course, so
weighted that the burner floats vertically, while buoyancy is obtained
partly by the gas evolved, and partly by a hollow portion of the
structure containing air. Cartridges of carbide and caps yielding a self-
inflammable gas can be carried on board ship, by means of which the
torches or lifebuoys may be renewed after service in a few minutes' time.

CHAPTER XIV

VALUATION AND ANALYSIS OF CARBIDE

The sale and purchase of calcium carbide in this country will, under
existing conditions, usually be conducted in conformity with the set of
regulations issued by the British Acetylene Association, of which a copy,
revised to date, is given below:

"REGULATIONS AS TO CARBIDE OF CALCIUM."

1. The carbide shall be guaranteed by the seller to yield, when broken
to standard size, _i.e._, in lumps varying from 1 to 2-1/2 inches or
larger, not less than 4.8 cubic feet per lb., at a barometric pressure of
30 inches and temperature of 60 deg. Fahr. (15.55 deg. Centigrade). The
actual gas yield shall be deemed to be the gas yield ascertained by the
analyst, plus 5 per cent.

"Carbide yielding less than 4.8 cubic feet in the sizes given above shall
be paid for in proportion to the gas yield, _i.e._, the price to be
paid shall bear the same relation to the contract price as the gas yield
bears to 4.8 cubic feet per lb.

"2. The customer shall have the right to refuse to take carbide yielding
in the sizes mentioned above less than 4.2 cubic foot, per lb., and it
shall lie, in case of refusal and as from the date of the result, of the
analysis being made known to either party, at the risk and expense of the
seller.

"3. The carbide shall not contain higher figures of impurities than shall
from time to time be fixed by the Association.

"4. No guarantee shall be given for lots of less than 3 cwt., or for
carbide crushed to smaller than the above sizes.

"5. In case of dispute as to quality, either the buyer or the seller
shall have the right to have one unopened drum per ton of carbide, or
part of a ton, sent for examination to one of the analysts appointed by
the Association, and the result of the examination shall be held to apply
to the whole of the consignment to which the drum belonged.
"6. A latitude of 5 per cent, shall be allowed for analysis; consequently
differences of 5 per cent. above or below the yields mentioned in 1 and 2
shall not be taken into consideration.

"7. Should the yield of gas be less than 4.8 cubic feet less 5 per cent.,
the carriage of the carbide to and from the place of analysis and the
cost of the analysis shall be paid for by the seller. Should the yield be
more than 4.8 cubic feet less 5 per cent., the carriage and costs of
analysis shall be borne by the buyer, who, in addition, shall pay an
increase of price for the carbide proportionate to the gas yield above
4.8 cubic feet plus 5 per cent.

"8. Carbide of 1 inch mesh and above shall not contain more than 5 per
cent. of dust, such dust to be defined as carbide capable of passing
through a mesh of one-sixteenth of an inch.

"9. The seller shall not be responsible for deterioration of quality
caused by railway carriage in the United Kingdom, unless he has sold
including carriage to the destination indicated by the buyer.

"10. Carbide destined for export shall, in case the buyer desires to have
it tested, be sampled at the port of shipment, and the guarantee shall
cease after shipment.

"11. The analyst shall take a sample of not less than 1 lb. each from the
top, centre, and bottom of the drum. The carbide shall be carefully
broken up into small pieces, due care being taken to avoid exposure to
the air as much as possible, carefully screened and tested for gas yield
by decomposing it in water, previously thoroughly saturated by exposure
to acetylene for a period of not less than 48 hours.

"12. Carbide which, when properly decomposed, yields acetylene containing
from all phosphorus compounds therein more than .05 per cent. by volume
of phosphoretted hydrogen, may be refused by the buyer, and any carbide
found to contain more than this figure, with a latitude of .01 per cent.
for the analysis, shall lie at the risk and expense of the seller in the
manner described in paragraph 2.

"The rules mentioned in paragraph 7 shall apply as regards the carriage
and costs of analysis; in other words, the buyer shall pay these costs if
the figure is below 0.05 per cent. plus 0.01 per cent., and the seller if
the figure is above 0.05 per cent. plus 0.01 per cent.

"The sampling shall take place in the manner prescribed in paragraphs 5
and 11, and the analytical examination shall be effected in the manner
prescribed by the Association and obtainable upon application to the
Secretary."

* * * * *

The following is a translation of the corresponding rules issued by the
German Acetylene Association (_Der Deutsche Acetylenverein_) in
regard to business dealings in calcium carbide, as put into force on
April 1, 1909:

"REGULATIONS OF THE GERMAN ACETYLENE ASSOCIATION FOR TRADE IN CARBIDE.

"_Price_.

"The price is to be fixed per 100 kilogrammes (= 220 lb.) net weight of
carbide in packages containing about 100 kilogrammes.

"By packages containing about 100 kilogrammes are meant packages
containing within 10 per cent. above or below that weight.

"The carbide shall be packed in gas- and water-tight vessels of sheet-
iron of the strength indicated in the prescriptions of the carrying
companies.

"The prices for other descriptions of packing must be specially stated.

"_Place of Delivery_.

"For consignment for export, the last European shipping port shall be
taken as the place of delivery.

"_Quality_.

"Commercial carbide shall be of such quality that in the usual lumps of
15 to 80 mm. (about 3/5 to 3 inches) diameter it shall afford a yield of
at least 300 litres at 15 deg. C. and 760 mm. pressure of crude acetylene
per kilogramme for each consignment (= 4.81 cubic feet at 60 deg. F. and
30 inches per lb.). A margin of 2 per cent. shall be allowed for the
analysis. Carbide which yields less than 300 litres per kilogramme, but
not less than 270 litres (= 4.33 cubic feet) of crude acetylene per
kilogramme (with the above-stated 2 per cent. margin for analysis) must
be accepted by the buyer. The latter, however, is entitled to make a
proportionate deduction from the price and also to deduct the increased
freight charges to the destination or, if the latter is not settled at
the time when the transaction is completed, to the place of delivery.
Carbide which yields less than 270 litres of crude acetylene per
kilogramme need not be accepted.

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