Ignatius Donnelly - "Atlantis: The Antideluvian World"

Charles Morris - "Historical Tales, Vol. 6 (of 15)"

Charles Dudley Warner - "The Complete Writings of Charles Dudley Warner Volume 1"

Florence Holbrook - "Northland Heroes"

Annual Bibliography of Commonwealth Literature 2007
This paper argues that discourses of love in Ghanaian market literature for youth offer a view into complex negotiations of agency and empowerment. Drawing on Deborah Durham's notion of youth as "social `shifters'" and Francis Nyamnjoh's conception of the "interconnectedness" of agency, I take Ghanaian market literature as one specific case of how African literature for youth foregrounds questions of continuity and change as African societies enter into increasingly complex global relations. In this literature for youth, received notions of love, often constructed out of impressions from American pop and hip hop music, carry new notions of agency that compete with existing "domesticated" forms. Authors like Ike Tandoh and Evelyn Tay employ discourses of love to offer youth alternative avenues for empowerment in a context of socio-economic disenfranchizement. In a creative process of "straddling", this writing both reveals and reproduces the contradictions that obtain in youth configurations of agency.

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




EFFECT OF HEAT ON ACETYLENE.--The effect of excessive retention of heat
in an acetylene generator upon the gas itself is very marked, as
acetylene begins spontaneously to suffer change, and to be converted into
other compounds at elevated temperatures. Being a purely chemical
phenomenon, the behaviour of acetylene when exposed to heat will be fully
discussed in Chapter VI. when the properties of the gas are being
systematically dealt with. Here it will be sufficient to assume that the
character of the changes taking place is understood, and only the
practical results of those changes as affecting the various components of
an acetylene installation have to be studied. According to Lewes,
acetylene commences to "polymerise" at a temperature of about 600 deg. C.,
when it is converted into other hydrocarbons having the same percentage
composition, but containing more atoms of carbon and hydrogen in their
molecules. The formula of acetylene is C_2H_2 which means that 2 atoms of
carbon and 2 atoms of hydrogen unite to form 1 molecule of acetylene, a
body evidently containing roughly 92.3 per cent. by weight of carbon and
7.7 per cent. by weight of hydrogen. One of the most noteworthy
substances produced by the polymerisation of acetylene is benzene, the
formula of which is C_6H_6, and this is formed in the manner indicated by
the equation--

(4) 3C_2H_2 = C_6H_6.

Now benzene also contains 92.3 per cent. of carbon and 7.7 per cent. by
weight of hydrogen in its composition, but its molecule contains 6 atoms
of each element. When the chemical formula representing a compound body
indicates a substance which is, or can be obtained as, a gas or vapour,
it convoys another idea over and above those mentioned on a previous
page. The formula "C_2H_2," for example, means 1 molecule, or 26 parts by
weight of acetylene, just as "H_2" means 1 molecule, or 2 parts by weight
of hydrogen; but both formulae also mean equal parts by volume of the
respective substances, and since H_2 must mean 2 volumes, being twice H,
which is manifestly 1, C_2H_2 must mean 2 volumes of acetylene as well.
Thus equation (4) states that 6 volumes of acetylene, or 3 x 26 parts by
weight, unite to form 2 volumes of benzene, or 78 parts by weight. If
these hydrocarbons are burnt in air, both are indifferently converted
into carbon dioxide (carbonic acid gas) and water vapour; and, neglecting
for the sake of simplicity the nitrogen of the atmosphere, the processes
may be shown thus:

(5) 2C_2H_2 + 5O_2 = 4CO_2 + 2H_2O.

(6) 2C_6H_6 + 15O_2 = 12CO_2 + 6H_2O.

Equation (5) shows that 4 volumes of acetylene combine with 10 volumes of
oxygen to produce 8 volumes of carbon dioxide and 4 of water vapour;
while equation (6) indicates that 4 volumes of benzene combine with 30
volumes of oxygen to yield 24 volumes of carbon dioxide and 12 of water
vapour. Two parts by volume of acetylene therefore require 5 parts by
volume of oxygen for perfect combustion, whereas two parts by volume of
benzene need 15--_i.e._, exactly three times as much. In order to
work satisfactorily, and to develop the maximum of illuminating power
from any kind of gas consumed, a gas-burner has to be designed with
considerable skill so as to attract to the base of the flame precisely
that volume of air which contains the quantity of oxygen necessary to
insure complete combustion, for an excess of air in a flame is only less
objectionable than a deficiency thereof. If, then, an acetylene burner is
properly constructed, as most modern ones are, it draws into the flame
air corresponding with two and a half volumes of oxygen for every one
volume of acetylene passing from the jets; whereas if it were intended
for the combustion of benzene vapour it would have to attract three times
that quantity. Since any flame supplied with too little air tends to emit
free carbon or soot, it follows that any well-made acetylene burner
delivering a gas containing benzene vapour will yield a more or lens
smoky flame according to the proportion of benzene in the acetylene.
Moreover, at ordinary temperatures benzene is a liquid, for it boils at
81 deg. C., and although, as was explained above in the case of water, it is
capable of remaining in the state of vapour far below its boiling-point
so long as it is suspended in a sufficiency of some permanent gas like
acetylene, if the proportion of vapour in the gas at any given
temperature exceeds a certain amount the excess will be precipitated in
the liquid form; while as the temperature falls the proportion of vapour
which can be retained in a given volume of gas also diminishes to a
noteworthy extent. Should any liquid, be it water or benzene, or any
other substance, separate from the acetylene under the influence of cold
while the gas is passing through pipes, the liquid will run downwards to
the lowest points in those pipes; and unless due precautions are taken,
by the insertion of draw-off cocks, collecting wells, or the like, to
withdraw the deposited water or other liquid, it will accumulate in all
bends, angles, and dips till the pipes are partly or completely sealed
against the passage of gas, and the lights will either "jump" or be
extinguished altogether. In the specific case of an acetylene generator
this trouble is very likely to arise, even when the gas is not heated
sufficiently during evolution for polymerisation to occur and benzene or
other liquid hydrocarbons to be formed, because any excess of water
present in the decomposing vessel is liable to be vaporised by the heat
of the reaction--as already stated it is desirable that water shall be so
vaporised--and will remain safely vaporised as long as the pipes are kept
warm inside or near the generator; but directly the pipes pass away from
the hot generator the cooling action of the air begins, and some liquid
water will be immediately produced. Like the phenomenon of after-
generation, this equally inevitable phenomenon of water condensation will
be either an inconvenience or source of positive danger, or will be a
matter of no consequence whatever, simply as the whole acetylene
installation, including the service-pipes, is ignorantly or intelligently
built.

As long as nothing but pure polymerisation happens to the acetylene, as
long, that is to say, as it is merely converted into other hydrocarbons
also having the general formula C_(2n)H_(2n), no harm will be done to the
gas as regards illuminating power, for benzene burns with a still more
luminous flame than acetylene itself; nor will any injury result to the
gas if it is required for combustion in heating or cooking stoves beyond
the fact that the burners, luminous or atmospheric, will be delivering a
material for the consumption of which they are not properly designed. But
if the temperature should rise much above the point at which benzene is
the most conspicuous product of polymerisation, other far more
complicated changes occur, and harmful effects may be produced in two
separate ways. Some of the new hydrocarbons formed may interact to yield
a mixture of one or more other hydrocarbons containing a higher
proportion of carbon than that which is present in acetylene and benzene,
together with a corresponding proportion of free hydrogen; the former
will probably be either liquids or solids, while the latter burns with a
perfectly non-luminous flame. Thus the quantity of gas evolved from the
carbide and passed into the holder is less than it should be, owing to
the condensation of its non-gaseous constituents. To quote an instance of
this, Haber has found 15 litres of acetylene to be reduced in volume to
10 litres when the gas was heated to 638 deg. C. By other changes, some
"saturated hydrocarbons," _i.e._, bodies having the general formula
C_nH_(2n+2), of which methane or marsh-gas, CH_4 is the best known, may
be produced; and those all possess lower illuminating powers than
acetylene. In two of those experiments already described, where Lewes
observed maximum temperatures ranging from 703 deg. to 807 deg. C.,
samples of the gas which issued when the heat was greatest were submitted
to chemical analysis, and their illuminating powers were determined. The
figures he gives are as follows:

I. II.
Per Cent. Per Cent.
Acetylene 70.0 69.7
Saturated hydrocarbons 11.3 11.4
Hydrogen 18.7 18.9
_____ _____

100.0 100.0

The average illuminating power of these mixed gases is about 126 candles
per 5 cubic feet, whereas that of pure acetylene burnt under good
laboratory conditions is 240 candles per 5 cubic feet. The product, it
will be seen, had lost almost exactly 50 per cent. of its value as an
illuminant, owing to the excessive heating to which it had been, exposed.
Some of the liquid hydrocarbons formed at the same time are not limpid
fluids like benzene, which is less viscous than water, but are thick oily
substances, or even tars. They therefore tend to block the tubes of the
apparatus with great persistence, while the tar adheres to the calcium
carbide and causes its further attack by water to be very irregular, or
even altogether impossible. In some of the very badly designed generators
of a few years back this tarry matter was distinctly visible when the
apparatus was disconnected for recharging, for the spent carbide was
exceptionally yellow, brown, or blackish in colour, [Footnote: As will be
pointed out later, the colour of the spent lime cannot always be employed
as a means for judging whether overheating has occurred in a generator.]
and the odour of tar was as noticeable as that of crude acetylene.

There is another effect of heat upon acetylene, more calculated to be
dangerous than any of those just mentioned, which must not be lost sight
of. Being an endothermic substance, acetylene is prone to decompose into
its elements--

(7) C_2H_2 -> C_2 + H_2

whenever it has the opportunity; and the opportunity arrives if the
temperature of the gas risen to 780 deg. C., or if the pressure under which
the gas is stored exceeds two atmospheres absolute (roughly 30 lb. per
square inch). It decomposes, be it carefully understood, in the complete
absence of air, directly the smallest spark of red-hot material or of
electricity, or directly a gentle shock, such as that of a fall or blow
on the vessel holding it, is applied to any volume of acetylene existing
at a temperature exceeding 780 deg. or at a gross pressure of 30 lb. per
square inch; and however large that volume may be, unless it is contained
in tubes of very small diameter, as will appear hereafter, the
decomposition or dissociation into its elements will extend throughout
the whole of the gas. Equation (7) states that 2 volumes of acetylene
yield 2 volumes of hydrogen and a quantity of carbon which would measure
2 volumes were it obtained in the state of gas, but which, being a solid,
occupies a space that may be neglected. Apparently, therefore, the
dissociation of acetylene involves no alteration in volume, and should
not exhibit explosive effects. This is erroneous, because 2 volumes of
acetylene only yield exactly 2 volumes of hydrogen when both gases are
measured at the same temperature, and all gases increase in volume as
their temperature rises. As acetylene is endothermic and evolves much
heat on decomposition, and as that heat must primarily be communicated to
the hydrogen, it follows that the latter must be much hotter than the
original acetylene; the hydrogen accordingly strives to fill a much
larger space than that occupied by the undecomposed gas, and if that gas
is contained in a closed vessel, considerable internal pressure will be
set up, which may or may not cause the vessel to burst.

What has been said in the preceding paragraph about the temperature at
which acetylene decomposes is only true when the gas is free from any
notable quantity of air. In presence of air, acetylene inflames at a much
lower temperature, viz., 480 deg. C. In a manner precisely similar to that
of all other combustible gases, if a stream of acetylene issues into the
atmosphere, as from the orifices of a burner, the gas catches fire and
burns quietly directly any substance having a temperature of 480 deg. C. or
upwards is brought near it; but if acetylene in bulk is mixed with the
necessary quantity of air to support combustion, and any object exceeding
480 deg. C. in temperature comes in contact with it, the oxidation of the
hydrocarbon proceeds at such a high rate of speed as to be termed an
explosion. The proportion of air needed to support combustion varies with
every combustible material within known limits (_cf._ Chapter VI.),
and according to Eitner the smallest quantity of air required to make
acetylene burn or explode, as the case may be, is 25 per cent. If, by
ignorant design or by careless manipulation, the first batches of
acetylene evolved from a freshly charged generator should contain more
than 25 per cent. of air; or if in the inauguration of a new installation
the air should not be swept out of the pipes, and the first makes of gas
should become diluted with 25 to 50 per cent. of air, any glowing body
whose temperature exceeds 480 deg. C. will fire the gas; and, as in the
former instance, the flame will extend all through the mass of acetylene
with disastrous violence and at enormous speed unless the gas is stored
in narrow pipes of extremely small diameter. Three practical lessons are
to be learnt from this circumstance: first, tobacco-smoking must never be
permitted in any building where an escape of raw acetylene is possible,
because the temperature of a lighted cigar, &c., exceeds 480 deg. C.;
secondly, a light must never be applied to a pipe delivering acetylene
until a proper acetylene burner has been screwed into the aperture;
thirdly, if any appreciable amount of acetylene is present in the air, no
operation should be performed upon any portion of an acetylene plant
which involves such processes as scraping or chipping with the aid of a
steel tool or shovel. If, for example, the iron or stoneware sludge-pipe
is choked, or the interior of the dismantled generator is blocked, and
attempts are made to remove the obstruction with a hard steel tool, a
spark is very likely to be formed which, granting the existence of
sufficient acetylene in the air, is perfectly able to fire the gas. For
all such purposes wooden implements only are best employed; but the
remark does not apply to the hand-charging of a carbide-to-water
generator through its proper shoot. Before passing to another subject, it
may be remarked that a quantity of air far less than that which causes
acetylene to become dangerous is objectionable, as its presence is apt to
reduce the illuminating power of the gas unduly.

EFFECT OF HEAT ON CARBIDE.--Chemically speaking, no amount of heat
possible of attainment in the worst acetylene generator can affect
calcium carbide in the slightest degree, because that substance may be
raised to almost any temperature short of those distinguishing the
electric furnace, without suffering any change or deterioration. In the
absence of water, calcium carbide is as inert a substance as can well be
imagined: it cannot be made to catch fire, for it is absolutely
incombustible, and it can be heated in any ordinary flame for reasonable
periods of time, or thrown into any non-electrical furnace without
suffering in the least. But in presence of water, or of any liquid
containing water, matters are different. If the temperature of an
acetylene generator rises to such an extent that part of the gas is
polymerised into tar, that tar naturally tends to coat the residual
carbide lumps, and, being greasy in character, more or less completely
protects the interior from further attack. Action of this nature not only
means that the acetylene is diminished in quantity and quality by partial
decomposition, but it also means that the make is smaller owing to
imperfect decomposition of the carbide: while over and above this is the
liability to nuisance or danger when a mass of solid residue containing
some unaltered calcium carbide is removed from the apparatus and thrown
away. In fact, whenever the residue of a generator is not so saturated
with excess of water as to be of a creamy consistency, it should be put
into an uncovered vessel in the open air, and treated with some ten times
its volume of water before being run into any drain or closed pipe where
an accumulation of acetylene may occur. Even at temperatures far below
those needed to determine a production of tar or an oily coating on the
carbide, if water attacks an excess of calcium carbide somewhat rapidly,
there is a marked tendency for the carbide to be "baked" by the heat
produced; the slaked lime adhering to the lumps as a hard skin which
greatly retards the penetration of more water to the interior.

COLOUR OF SPENT CARBIDE.--In the early days of the industry, it was
frequently taken for granted that any degradation in the colour of the
spent lime left in an acetylene generator was proof that overheating had
taken place during the decomposition of the carbide. Since both calcium
oxide and hydroxide are white substances, it was thought that a brownish,
greyish, or blackish residue must necessarily point to incipient
polymerisation of the gas. This view would be correct if calcium carbide
were prepared in a state of chemical purity, for it also is a white body.
Commercial carbide, however, is not pure; it usually contains some
foreign matter which tints the residue remaining after gasification. When
a manufacturer strives to give his carbide the highest gas-making power
possible he frequently increases the proportion of carbon in the charge
submitted to electric smelting, until a small excess is reached, which
remains in the free state amongst the finished carbide. After
decomposition the fine particles of carbon stain the moist lime a bluish
grey tint, the depth of shade manifestly depending upon the amount
present. If such a sludge is copiously diluted with water, particles of
carbon having the appearance and gritty or flaky nature of coke often
rise to the surface or fall to the bottom of the liquid; whence they can
easily be picked out and identified as pure or impure carbon by simple
tests. Similarly the lime or carbon put into the electric furnace may
contain small quantities of compounds which are naturally coloured; and
which, reappearing in the sludge either in their original or in a
different state of combination, confer upon the sludge their
characteristic tinge. Spent lime of a yellowish brown colour is
frequently to be met with in circumstances that are clearly no reproach
to the generator. Doubtless the tint is due to the presence of some
coloured metallic oxide or other compound which has escaped reduction in
the electric furnace. The colour which the residual lime afterwards
assumes may not be noticeable in the dry carbide before decomposition,
either because some change in the colour-giving impurity takes place
during the chemical reactions in the generator or because the tint is
simply masked by the greyish white of the carbide and its free carbon.
Hence it follows that a bad colour in the waste lime removed from a
generator only points to overheating and polymerisation of the acetylene
when corroborative evidence is obtained--such as a distinct tarry smell,
the actual discovery of oily or tarry matters elsewhere, or a grave
reduction in the illuminating power of the gas.

MAXIMUM ATTAINABLE TEMPERATURES.--In order to discover the maximum
temperature which can be reached in or about an acetylene generator when
an apparatus belonging to one of the best types is fed at a proper rate
with calcium carbide in lumps of the most suitable size, the following
calculation may be made. In the first place, it will be assumed that no
loss of heat by radiation occurs from the walls of the generator;
secondly, the small quantity of heat taken up by the calcium hydroxide
produced will be ignored; and, thirdly, the specific heat of acetylene
will be assumed to be 0.25, which is about its most probable value. Now,
a hand-fed carbide-to-water generator will work with half a gallon of
water for every 1 lb. of carbide decomposed, quantities which correspond
with 320 grammes of water per 64 grammes (1 molecular weight) of carbide.
Of those 320 grammes of water, 18 are chemically destroyed, leaving 302.
The decomposition of 64 grammes of commercial carbide evolves 28 large
calories of heat. Assuming all the heat to be absorbed by the water, 28
calories would raise 302 grammes through (28 X 1000 / 302) = 93 deg. C.,
_i.e._, from 44.6 deg. F. to the boiling-point. Assuming all the heat to
be communicated to the acetylene, those 28 calories would raise the 26
grammes of gas liberated through (28 X 1000 / 26 / 0.25) = 4308 deg. C., if
that were possible. But if, as would actually be the case, the heat were
distributed uniformly amongst the 302 grammes of water and the 20 grammes
of acetylene, both gas and water would be raised through the same number
of degrees, viz., 90.8 deg. C. [Footnote: Let x = the number of large
calories absorbed by the water; then 28 - x = those taken up by the gas.
Then--

1000x / 302 = 1000 (28 - x) / (26 X 0.25)

whence x = 27.41; and 28 - x = 0.59.

Therefore, for water, the rise in temperature is--

27.41 X 1000 / 302 = 90.8 deg. C.;

and for acetylene the rise is--

0.59 X 1000 / 26 / 0.25 = 90.8 deg. C.]

If the generator were designed on lines to satisfy the United States Fire
Underwriters, it would contain 8.33 lb. of water to every 1 lb. of
carbide attacked; identical calculations then showing that the original
temperature of the water and gas would be raised through 53.7 deg. C.
Provided the carbide is not charged into such an apparatus in lumps of
too large a size, nor at too high a rate, there will be no appreciable
amount of local overheating developed; and nowhere, therefore, will the
rise in temperature exceed 91 deg. in the first instance, or 54 deg. C. in
the second. Indeed it will be considerably smaller than this, because a
large proportion of the heat evolved will be lost by radiation through the
generator walls, while another portion will be converted from sensible
into latent heat by causing part of the water to pass off as vapour with
the acetylene.

EFFECT OF HIGH TEMPERATURES ON GENERATORS.--As the temperature amongst
the carbide in any generator in which water is not present in large
excess may easily reach 200 deg. C. or upwards, no material ought to be
employed in the construction of such generators which is not competent to
withstand a considerable amount of heat in perfect safety. The ordinary
varieties of soft solder applied with the bitt in all kinds of light
metal-work usually melt, according to their composition, at about 180 deg.
C.; and therefore this method of making joints is only suitable for
objects that are never raised appreciably in temperature above the
boiling-point of water. No joint in an acetylene generator, the partial
or complete failure of which would radically affect the behaviour of the
apparatus, by permitting the charges of carbide and of water to come into
contact at an abnormal rate of speed, by allowing the acetylene to escape
directly through the crack into the atmosphere, or by enabling the water
to run out of the seal of any vessel containing gas so as to set up a
free communication between that vessel and the air, ought ever to be made
of soft solder--every joint of this character should be constructed
either by riveting, by bolting, or by doubly folding the metal sheets.
Apparently, a joint constantly immersed in water on one side cannot rise
in temperature above the boiling-point of the liquid, even when its other
side is heated strongly; but since, even if a generator is not charged
with naturally hard water, its fluid contents soon become "hard" by
dissolution of lime, there is always a liability to the deposition of
water scale over the joint. Such water scale is a very bad heat
conductor, as is seen in steam boilers, so that a seam coated with an
exceedingly thin layer of scale, and heated sharply on one side, will
rise above the boiling-point of water even if the liquid on its opposite
side is ice-cold. For a while the film of scale may be quite water-tight,
but after it has been heated by contact with the hot metal several times
it becomes brittle and cracks without warning. But there is a more
important reason for avoiding the use of plumbers' solder. It might seem
that as the natural hard, protective skin of the metal is liable to be
injured or removed by the bending or by the drilling or punching which
precedes the insertion of the rivets or studs, an application of soft
solder to such a joint should be advantageous. This is not true because
of the influence of galvanic action. As all soft solders consist largely
of lead, if a joint is soldered, a "galvanic couple" of lead and iron, or
of lead and zinc (when the apparatus is built of galvanised steel), is
exposed to the liquid bathing it; and since in both cases the lead is
highly electro-negative to the iron or zinc, it is the iron or zinc which
suffers attack, assuming the liquid to possess any corrosive properties
whatever. Galvanised iron which has been injured during the joint-making
presents a zinc-iron couple to the water, but the zinc protects the iron;
if a lead solder is present, the iron will begin to corrode immediately
the zinc has disappeared. In the absence of lead it is the less important
metal, but in the presence of lead it is the more important (the
foundation) metal which is the soluble element of the couple. Where
practicable, joints in an acetylene generator may safely be made by
welding or by autogenous soldering ("burning"), because no other metal is
introduced into the system; any other process, except that of riveting or
folding, only hastens destruction of the plant. The ideal method of
making joints about an acetylene generator is manifestly that of
autogenous soldering, because, as will appear in Chapter IX. of this
book, the most convenient and efficient apparatus for performing the
operation is the oxy-acetylene blow-pipe, which can be employed so as to
convert two separate pieces of similar metal into one homogeneous whole.

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