Johanna Spyri - "Heidi"

John. T. Morse - "John Quincy Adams"

Walter Horatio Pater - "Appreciations, With An Essay on Style"

Edward William Thomson - "Old Man Savarin and Other Stories"

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




REGULATIONS AS TO PURIFICATION.--The British Acetylene
Association has issued the following set of regulations as to purifying
material and purifiers for acetylene:

Efficient purifying material and purifiers shall comply with the
following requirements:

(1) The purifying material shall remove phosphorus and sulphur compounds
to a commercially satisfactory degree; _i.e._, not to a greater
degree than will allow easy detection of escaping gas through its odour.

(2) The purifying material shall not yield any products capable of
corroding the gas-mains or fittings.

(3) The purifying material shall, if possible, be efficient as a drying
agent, but the Association does not consider this an absolute necessity.

(4) The purifying material shall not, under working conditions, be
capable of forming explosive compounds or mixtures. It is understood,
naturally, that this condition does not apply to the unavoidable mixture
of acetylene and air formed when recharging the purifier.

(5) The apparatus containing the purifying material shall be simple in
construction, and capable of being recharged by an inexperienced person
without trouble. It shall be so designed as to bring the gas into proper
contact with the material.

(6) The containers in purifiers shall be made of such materials as are
not dangerously affected by the respective purifying materials used.

(7) No purifier shall be sold without a card of instructions suitable or
hanging up in some convenient place. Such instructions shall be of the
most detailed nature, and shall not presuppose any expert knowledge
whatever on the part of the operator.

Reference also to the abstracts of the official regulations as to
acetylene installations in foreign countries given in Chapter IV. will
show that they contain brief rules as to purifiers.

DRYING.--It has been stated in Chapter III. that the proper position for
the chemical purifiers of an acetylene plant is after the holder; and
they therefore form the last items in the installation unless a "station"
governor and meter are fitted. It is therefore possible to use them also
to remove the moisture in the gas, if a material hygroscopic in nature is
employed to charge them. This should be true more particularly with
puratylene, which contains a notable proportion of the very hygroscopic
body calcium chloride. If a separate drier is desirable, there are two
methods of charging it. It may be filled either with some hygroscopic
substance such as porous calcium chloride or quicklime in very coarse
powder, which retains the water by combining with it; or the gas may be
led through a vessel loaded with calcium carbide, which will manifestly
hold all the moisture, replacing it by an equivalent quantity of
(unpurified) acetylene. The objection is sometimes urged against this
latter method, that it restores to the gas the nauseous odour and the
otherwise harmful impurities it had more or less completely lost in the
purifiers; but as regards the first point, a nauseous odour is not, as
has previously been shown, objectionable in itself, and as regards the
second, the amount of impurities added by a carbide drier, being strictly
limited by the proportion of moisture in the damp gas, is too small to be
noticeable at the burners or elsewhere. As is the case with purification,
absolute removal of moisture is not called for; all that is needed is to
extract so much that the gas shall never reach its saturation-point in
the inaccessible parts of the service during the coldest winter's night.
Any accessible length of main specially exposed to cold may be
safeguarded by itself; being given a steady fall to a certain point
(preferably in a frost-free situation), and there provided with a
collecting-box from which the deposited liquid can be removed
periodically with a pump or otherwise.

FILTRATION.--The gas issuing from the purifier or drier is very liable to
hold in suspension fine dust derived from the purifying or drying
material used. It is essential that thin dust should be abstracted before
the gas reaches the burners, otherwise it will choke the orifices and
prevent them functioning properly. Consequently the gas should pass
through a sufficient layer of filtering material after it has traversed
the purifying material (and drier if one is used). This filtering
material may be put either as a final layer in the purifier (or drier),
or in a separate vessel known as a filter. Among filtering materials in
common use may be named cotton-wool, fine canvas or gauze, felt and
asbestos-wool. The gas must be fairly well dried before it enters the
filter, otherwise the latter will become choked with deposited moisture,
and obstruct the passage of the gas.

Having now described the various items which go to form a well-designed
acetylene installation, it may be useful to recapitulate briefly, with
the object of showing the order in which they should be placed. From the
generator the gas passes into a condenser to cool it and to remove any
tarry products and large quantities of water. Next it enters a washing
apparatus filled with water to extract water-soluble impurities. If the
generator is of the carbide-to-water pattern, the condenser may be
omitted, and the washer is only required to retain any lime froth and to
act as a water-seal or non-return valve. If the generator does not wash
the gas, the washer must be large enough to act efficiently as such, and
between it and the condenser should be put a mechanical filter to extract
any dust. From the washer the acetylene travels to the holder. From the
holder it passes through one or two purifiers, and from there travels to
the drier and filter. If the holder does not throw a constant pressure,
or if the purifier and drier are liable to cause irregularities, a
governor or pressure regulator must be added after the drier. The
acetylene is then ready to enter the service; but a station meter (the
last item in the plant) is useful as giving a means of detecting any leak
in the delivery-pipes and in checking the make of gas from the amount of
carbide consumed. If the gas is required for the supply of a district, a
station meter becomes quite necessary, because the public lamps will be
fed with gas at a contract rate, and without the meter there would be no
control over the volume of acetylene they consume. Where the gas finally
leaves the generating-house, or where it enters the residence, a full-way
stopcock should be put on the main.

GENERATOR RESIDUES.--According to the type of generator employed the
waste product removed therefrom may vary from a dry or moist powder to a
thin cream or milk of lime. Any waste product which is quite liquid in
its consistency must be completely decomposed and free from particles of
calcium carbide of sensible magnitude; in the case of more solid
residues, the less fluid they are the greater is the improbability (or
the less is the evidence) that the carbide has been wholly spent within
the apparatus. Imperfect decomposition of the carbide inside the
generator not only means an obvious loss of economy, but its presence
among the residues makes a careful handling of them essential to avoid
accident owing to a subsequent liberation of acetylene in some
unsuitable, and perhaps closed, situation. A residue which is not
conspicuously saturated with water must be taken out of the generator-
house into the open air and there flooded with water, being left in some
uncovered receptacle for a sufficient time to ensure all the acetylene
being given off. A residue which is liquid enough to flow should be run
directly from the draw-off cock of the generator through a closed pipe to
the outside; where, if it does not discharge into an open conduit, the
waste-pipe must be trapped, and a ventilating shaft provided so that no
gas can blow back into the generator-house.

DISPOSAL OF RESIDUES.--These residues have now to be disposed of. In some
circumstances they can be put to a useful purpose, as will be explained
in Chapter XII.; otherwise, and always perhaps on the small scale--
certainly always if the generator overheats the gas and yields tar among
the spent lime--they must be thrown into a convenient place. It should be
remembered that although methods of precipitating sewage by adding lime,
or lime water, to it have frequently been used, they have not proved
satisfactory, partly because the sludge so obtained is peculiarly
objectionable in odour, and partly because an excess of lime yields an
effluent containing dissolved lime, which among other disadvantages is
harmful to fish. The plan of running the liquid residues of acetylene
manufacture into any local sewerage system which may be found in the
neighbourhood of the consumer's premises, therefore, is very convenient
to the consumer; but is liable to produce complaints if the sewage is
afterwards treated chemically, or if its effluent is passed untreated
into a highly preserved river; and the same remark applies in a lesser
degree if the residues are run into a private cesspool the liquid
contents of which automatically flow away into a stream. If, however, the
cesspool empties itself of liquid matter by filtration or percolation
through earth, there can be no objection to using it to hold the lime
sludge, except in so far as it will require more frequent emptying. On
the whole, perhaps the best method of disposing of these residues is to
run them into some open pit, allowing the liquid to disappear by
evaporation and percolation, finally burying the solid in some spot where
it will be out of the way. When a large carbide-to-water generator is
worked systematically so as to avoid more loss of acetylene by solution
in the excess of liquid than is absolutely necessary, the liquid residues
coming from it will be collected in some ventilated closed tank where
they can settle quietly. The clear lime-water will then be pumped back
into the generator for further use, and the almost solid sludge will be
ready to be carried to the pit where it is to be buried. Special care
must be taken in disposing of the residues from a generator in which oil
is used to control evolution of gas. Such oil floats on the aqueous
liquid; and a very few drops spread for an incredible distance as an
exceedingly thin film, causing those brilliant rainbow-like colours which
are sometimes imagined to be a sign of decomposing organic matter. The
liquid portions of these residues must be led through a pit fitted with a
depending partition projecting below the level at which the water is
constantly maintained; all the oil then collects on the first side of the
partition, only water passing underneath, and the oil may be withdrawn
and thrown away at intervals.



CHAPTER VI

THE CHEMICAL AND PHYSICAL PROPERTIES OF ACETYLENE

It will only be necessary for the purpose of this book to indicate the
more important chemical and physical properties of acetylene, and, in
particular, those which have any bearing on the application of acetylene
for lighting purposes. Moreover, it has been found convenient to discuss
fully in other chapters certain properties of acetylene, and in regard to
such properties the reader is referred to the chapters mentioned.

PHYSICAL PROPERTIES.--Acetylene is a gas at ordinary temperatures,
colourless, and, when pure, having a not unpleasant, so-called "ethereal"
odour. Its density, or specific gravity, referred to air as unity, has
been found experimentally by Leduc to be 0.9056. It is customary to adopt
the value 0.91 for calculations into which the density of the gas enters
(_vide_ Chapter VII.). The density of a gas is important not only
for the determination of the size of mains needed to convey it at a given
rate of flow under a given pressure, as explained in Chapter VII., but
also because the volume of gas which will pass through small orifices in
a given time depends on its density. According to Graham's well-known law
of the effusion of gases, the velocity with which a gas effuses varies
directly as the square root of the difference of pressure on the two
sides of the opening, and inversely as the square root of the density of
the gas. Hence it follows that the volume of gas which escapes through a
porous pipe, an imperfect joint, or a burner orifice is, provided the
pressure in the gas-pipe is the same, a function of the square root of
the density of the gas. Hence this density has to be taken into
consideration in the construction of burners, i.e., a burner required to
pass a gas of high density must have a larger orifice than one for a gas
of low density, if the rate of flow of gas is to be the same under the
same pressure. This, however, is a question for the burner manufacturers,
who already make special burners for gases of different densities, and it
need not trouble the consumer of acetylene, who should always use burners
devised for the consumption of that gas. But the Law of effusion
indicates that the volume of acetylene which can escape from a leaky
supply-pipe will be less than the volume of a gas of lower density,
_e.g._, coal-gas, if the pressure in the pipe is the same for both.
This implies that on an extensive distributing system, in which for
practical reasons leakage is not wholly avoidable, the loss of gas
through leakage will be less for acetylene than for coal-gas, given the
same distributing pressure. If _v_ = the loss of acetylene from a
distributing system and _v'_ = the loss of coal-gas from a similar
system worked at the same pressure, both losses being expressed in
volumes (cubic feet) per hour, and the coal-gas being assumed to have a
density of 0.04, then

(1) (_v_/_v'_) = (0.40 / 0.91)^(1/2) = 0.663

or, _v_ = 0.663_v'_,

which signifies that the loss of acetylene by leakage under the same
conditions of pressure, &c., will be only 0.663 times that of the loss of
coal-gas. In practice, however, the pressures at which the gases are
usually sent through mains are not identical, being greater in the case
of acetylene than in that of coal-gas. Formula (1) therefore requires
correction whenever the pressures are different, and calling the pressure
at which the acetylene exists in the main _p_, and the corresponding
pressure of the coal-gas _p'_, the relative losses by leakage are--

(2) (_v_/_v'_) = (0.40 / 0.91)^(1/2) x (_p_/_p'_)^(1/2)

_v_ = 0.663_v'_ x (_p_/_p'_)^(1/2)

It will be evident that whenever the value of the fraction
(_p_/_p'_)^(1/2), is less than 1.5, _i.e._, whenever the pressure of
the acetylene does not exceed double that of the coal-gas present in
pipes of given porosity or unsoundness, the loss of acetylene will be
less than that of coal-gas. This is important, especially in the case of
large village acetylene installations, where after a time it would be
impossible to avoid some imperfect joints, fractured pipes, &c.,
throughout the extensive distributing mains. The same loss of gas by
leakage would represent a far higher pecuniary value with acetylene than
with coal-gas, because the former must always be more costly per unit of
volume than the latter. Hence it is important to recognise that the rate
of leakage, _coeteris paribus_, is less with acetylene, and it is
also important to observe the economical advantage, at least in terms of
gas or calcium carbide, of sending the acetylene into the mains at as low
a pressure as is compatible with the length of those mains and the
character of the consumers' burners. As follows from what will be said in
Chapter VII., a high initial pressure makes for economy in the prime cost
of, and in the expense of laying, the mains, by enabling the diameter of
those mains to be diminished; but the purchase and erection of the
distributing system are capital expenses, while a constant expenditure
upon carbide to meet loss by leakage falls upon revenue.

The critical temperature of acetylene, _i.e._, the temperature below
which an abrupt change from the gaseous to the liquid state takes place
if the pressure is sufficiently high, is 37 deg. C., and the critical
pressure, _i.e._, the pressure under which that change takes place
at that temperature, is nearly 68 atmospheres. Below the critical
temperature, a lower pressure than this effects liquefaction of the gas,
_i.e._, at 13.5 deg. C. a pressure of 32.77 atmospheres, at 0 deg. C.,
21.53 atmospheres (Ansdell, _cf._ Chapter XI.). These data are of
comparatively little practical importance, owing to the fact that, as
explained in Chapter XI., liquefied acetylene cannot be safely utilised.

The mean coefficient of expansion of gaseous acetylene between 0 deg. C.
and 100 deg. C., is, under constant pressure, 0.003738; under constant
volume, 0.003724. This means that, if the pressure is constant, 0.003738
represents the increase in volume of a given mass of gaseous acetylene
when its temperature is raised one degree (C.), divided by the volume of
the same mass at 0 deg. C. The coefficients of expansion of air are: under
constant pressure, 0.003671; under constant volume, 0.003665; and those
of the simple gases (nitrogen, hydrogen, oxygen) are very nearly the
same. Strictly speaking the table given in Chapter XIV., for facilitating
the correction of the volume of gas measured over water, is not quite
correct for acetylene, owing to the difference in the coefficients of
expansion of acetylene and the simple gases for which the table was drawn
up, but practically no appreciable error can ensue from its use. It is,
however, for the correction of volumes of gases measured at different
temperatures to one (normal) temperature, and, broadly, for determining
the change of volume which a given mass of the gas will undergo with
change of temperature, that the coefficient of expansion of a gas becomes
an important factor industrially.

Ansdell has found the density of liquid acetylene to range from 0.460 at
-7 deg. C. to 0.364 at +35.8 deg. C., being 0.451 at 0 deg. C. Taking the
volume of the liquid at -7 deg. as unity, it becomes 1.264 at 35.8 deg.,
and thence Ansdell infers that the mean coefficient of expansion per degree
is 0.00489 deg. for the total range of pressure." Assuming that the liquid
was under the same pressure at the two temperatures, the coefficient of
expansion per degree Centigrade would be 0.00605, which agrees more nearly
with the figure 0.007 which is quoted, by Fouche As mentioned before, data
referring to liquid (_i.e._, liquefied) acetylene are of no practical
importance, because the substance is too dangerous to use. They are,
however, interesting in so far as they indicate the differences in
properties between acetylene converted into the liquid state by great
pressure, and acetylene dissolved in acetone under less pressure; which
differences make the solution fit for employment. It may be observed that
as the solution of acetylene in acetone is a liquid, the acetylene must
exist therein as a liquid; it is, in fact, liquid acetylene in a state of
dilution, the diluent being an exothermic and comparatively stable body.

The specific heat of acetylene is given by M. A. Morel at 0.310, though
he has not stated by whom the value was determined. For the purpose of a
calculation in Chapter III. the specific heat at constant pressure was
assumed to be 0.25, which, in the absence of precise information, appears
somewhat more probable as an approximation to the truth. The ratio
(_k_ or C_p/C_v ) of the specific heat at constant pressure to that
at constant volume has been found by Maneuvrier and Fournier to be 1.26;
but they did not measure the specific heat itself. [Footnote: The ratio
1.26 _k_ or (C_p/C_v) has been given in many text-books as the value
of the specific heat of acetylene, whereas this value should obviously be
only about one-fourth or one-fifth of 1.26.

By employing the ordinary gas laws it is possible approximately to
calculate the specific heat of acetylene from Maneuvrier and Fournier's
ratio. Taking the molecular weight of acetylene as 26, we have

26 C_p - 26 C_v = 2 cal.,

and

C_p = 1.26 C_v.

From this it follows that C_p, _i.e._, the specific heat at constant
pressure of acetylene, should be 0.373.] It will be seen that this value
for _k_ differs considerably from the corresponding ratio in the
case of air and many common gases, where it is usually 1.41; the figure
approaches more closely that given for nitrous oxide. For the specific
heat of calcium carbide Carlson quotes the following figures:

0 deg. 1000 deg. 1500 deg. 2000 deg. 2500 deg. 3000 deg. 3500 deg.
0.247 0.271 0.296 0.325 0.344 0.363 0.381

The molecular volume of acetylene is 0.8132 (oxygen = 1).

According to the international atomic weights adopted in 1908, the
molecular weight of acetylene is 26.016 if O = 16; in round numbers, as
ordinarily used, it is 26. Employing the latest data for the weight of 1
litre of dry hydrogen and of dry normal air containing 0.04 per cent. of
carbon dioxide at a temperature of 0 deg. C. and a barometric pressure of
760 mm. in the latitude of London, viz., 0.089916 and 1.29395 grammes
respectively (Castell-Evans), it now becomes possible to give the weight
of a known volume of dry or moist acetylene as measured under stated
conditions with some degree of accuracy. Using 26.016 as the molecular
weight of the gas (O = 16), 1 litre of dry acetylene at 0 deg. C. and 760 mm.
weighs 1.16963 grammes, or 1 gramme measures 0.854973 litre. From this it
follows that the theoretical specific gravity of the gas at 0 deg./0 deg. C.
is 0.9039 (air = 1), a figure which may be compared with Leduc's
experimental value of 0.9056. Taking as the coefficient of expansion at
constant pressure the figure already given, viz., 0.003738, the weights
and measures of dry and moist acetylene observed under British conditions
(60 deg. F. and 30 inches of mercury) become approximately:

Dry. Saturated.
1 litre . . . 1.108 grm. . . 1.102 grm.
1 gramme . . . 0.902 litre. . . 0.907 litre.
1000 cubic feet . 69.18 lb. . . . 68.83 lb.

It should be remembered that unless the gas has been passed through a
chemical drier, it is always saturated with aqueous vapour, the amount of
water present being governed by the temperature and pressure. The 1 litre
of moist acetylene which weighs 1.102 gramme at 60 deg. F. and 30 inches of
mercury, contains 0.013 gramme of water vapour; and therefore the weight
of dry acetylene in the 1 litre of moist gas is 1.089 gramme. Similarly,
the 68.83 pounds which constitute the weight of 1000 cubic feet of moist
acetylene, as measured under British standard conditions, are composed of
almost exactly 68 pounds of dry acetylene and 0.83 pound of water vapour.
The data required in calculating the mass of vapour in a known volume of
a saturated gas at any observed temperature and pressure, _i.e._, in
reducing the figures to those which represent the dry gas at any other
(standard) temperature and pressure, will be found in the text-books of
physical chemistry. It is necessary to recollect that since coal-gas is
measured wet, the factors given in the table quoted in Chapter XIV. from
the "Notification of the Gas Referees" simply serve to convert the volume
of a wet gas observed under stated conditions to the equivalent volume of
the same wet gas at the standard conditions mentioned.

HEAT OF COMBUSTION, &C--Based on Berthelot and Matignon's value for the
heat of combustion which is given on a subsequent page, viz., 315.7 large
calories per molecular weight of 26.016 grammes, the calorific power of
acetylene under different conditions is shown in the following table:

Dry. Dry. Saturated.
0 deg. C. & 760 mm. 60 deg. F & 30 ins. 60 deg. F. & 30 ins.

1 gramme 12.14 cals. 12.14 cals. 12.0 cals.
1 litre 14.l9 " 13.45 " 13.22 "
1 cubic foot 40.19 " 380.8 " 374.4 "

The figures in the last column refer to the dry acetylene in the gas, no
correction having been made for the heat absorbed by the water vapour
present. As will appear in Chapter X., the average of actual
determinations of the calorific value of ordinary acetylene is 363 large
calories or 1440 B.Th.U. per cubic foot. The temperature of ignition of
acetylene has been generally stated to be about 480 deg. C. V. Meyer and
Muench in 1893 found that a mixture of acetylene and oxygen ignited
between 509 deg. and 515 deg. C. Recent (1909) investigations by H. B. Dixon
and H. F. Coward show, however, that the ignition temperature in neat oxygen
is between 416 deg. and 440 deg. (mean 428 deg. C.) and in air between
406 deg. and 440 deg., with a mean of 429 deg. C. The corresponding mean
temperature of ignition found by the same investigators for other gases are:
hydrogen, 585 deg.; carbon monoxide, moist 664 deg., dry 692 deg.; ethylene,
in oxygen 510 deg., in air 543 deg.; and methane, in oxygen between 550 deg.
and 700 deg., and in air, between 650 deg. and 750 deg. C.

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