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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It has been pointed out that the German Association's direction that the
water used in the testing should be saturated with acetylene by a
preliminary decomposition of 1/2 kilogramme of carbide is not wholly
adequate, and it has been suggested that the preliminary decomposition
should be carried out twice with charges of carbide, each weighing not
less than 1 per cent. of the weight of water used. A further possible
source of error lies in the fact that the generating water is saturated
at the prevailing temperature of the room, and liberates some of its
dissolved acetylene when the temperature rises during the subsequent
generation of gas. This error, of course, makes the yield from the sample
appear higher than it actually is. Its effects may be compensated by
allowing time for the water in the generator or gasholder to cool to its
original temperature before the final reading is made.

With regard to the measurement of the temperature of the evolved gas in
the bell gasholder, it is usual to assume that the reading of a
thermometer which passes through the crown of the gasholder suffices. If
the thermometer has a very long stem, so that the bulb is at about the
mid-height of the filled bell, this plan is satisfactory, but if an
ordinary thermometer is used, it is better to take, as the average
temperature of the gas in the holder, the mean of the readings of the
thermometer in the crown, and of one dipping into the water of the holder
seal.

The following table gives factors for correcting volumes of gas observed
at any temperature and pressure falling within its range to the normal
temperature (60 deg. F.) and normal barometric height (30 inches). The
normal volume thus found is, as already stated, not appreciably different
from the volume at 15 deg. C. and 760 mm. (the normal conditions adopted
by Continental gas chemists). To use the table, find the observed
temperature and the observed reading of the barometer in the border of
the table, and in the space where these vertical and horizontal columns
meet will be found a number by which the observed volume of gas is to be
multiplied in order to find the corresponding volume under normal
conditions. For intermediate temperatures, &c., the factors may be
readily inferred from the table by inspection. This table must only be
applied when the gas is saturated with aqueous vapour, as is ordinarily
the case, and therefore a drier must not be applied to the gas before
measurement.

Hammerschmidt has calculated a similar table for the correction of
volumes of gas measured at temperatures ranging from 0 deg. to 30 deg. C.,
and under pressures from 660 to 780 mm., to 15 deg. C. and 760 mm. It is
based on the coefficient of expansion of acetylene given in Chapter VI.,
but, as was there pointed out, this coefficient differs by so little from
that of the permanent gases for which the annexed table was compiled, that
no appreciable error results from the use of the latter for acetylene also.
A table similar to the annexed but of more extended range is given in the
"Notification of the Gas Referees," and in the text-book on "Gas
Manufacture" by one of the authors.

The determination of the amounts of other gases in crude or purified
acetylene is for the most part carried out by the methods in vogue for
the analysis of coal-gas and other illuminating gases, or by slight
modifications of them. For an account of these methods the textbook on
"Gas Manufacture" by one of the authors may be consulted. For instance,
two of the three principal impurities in acetylene, viz., ammonia and
sulphuretted hydrogen, may be detected and estimated in that gas in the
same manner as in coal gas. The detection and estimation of phosphine
are, however, analytical operations peculiar to acetylene among common
illuminating gases, and they must therefore be referred to.

_Table to facilitate the Correction of the Volume of Gas at different
Temperatures and under different Atmospheric Pressures._

_____________________________________________________
| | |
| | THERMOMETER. |
| BAR.|_______________________________________________|
| | | | | | | |
| | 46 | 48 | 50 | 52 | 54 | 56 |
| | deg. | deg. | deg. | deg. | deg. | deg. |
|_____|_______|_______|_______|_______|_______|_______|
| | | | | | | |
|28.4 | 0.979 | 0.974 | 0.970 | 0.965 | 0.960 | 0.955 |
|28.5 | 0.983 | 0.978 | 0.973 | 0.968 | 0.964 | 0.959 |
|28.6 | 0.986 | 0.981 | 0.977 | 0.972 | 0.967 | 0.962 |
|28.7 | 0.990 | 0.985 | 0.980 | 0.975 | 0.970 | 0.966 |
|28.8 | 0.993 | 0.988 | 0.984 | 0.979 | 0.974 | 0.969 |
|28.9 | 0.997 | 0.992 | 0.987 | 0.982 | 0.977 | 0.973 |
|29.0 | 1.000 | 0.995 | 0.990 | 0.986 | 0.981 | 0.976 |
|29.1 | 1.004 | 0.999 | 0.994 | 0.989 | 0.984 | 0.979 |
|29.2 | 1.007 | 1.002 | 0.997 | 0.992 | 0.988 | 0.982 |
|29.3 | 1.011 | 1.005 | 1.001 | 0.996 | 0.991 | 0.986 |
|29.4 | 1.014 | 1.009 | 1.004 | 0.999 | 0.995 | 0.990 |
|29.5 | 1.018 | 1.013 | 1.008 | 1.003 | 0.998 | 0.993 |
|29.6 | 1.021 | 1.016 | 1.011 | 1.006 | 1.001 | 0.996 |
|29.7 | 1.025 | 1.019 | 1.015 | 1.010 | 1.005 | 1.000 |
|29.8 | 1.028 | 1.023 | 1.018 | 1.013 | 1.008 | 1.003 |
|29.9 | 1.031 | 1.026 | 1.022 | 1.017 | 1.012 | 1.007 |
|30.0 | 1.035 | 1.030 | 1.025 | 1.020 | 1.015 | 1.010 |
|30.1 | 1.038 | 1.033 | 1.029 | 1.024 | 1.019 | 1.014 |
|30.2 | 1.042 | 1.037 | 1.032 | 1.027 | 1.022 | 1.017 |
|30.3 | 1.045 | 1.040 | 1.036 | 1.030 | 1.025 | 1.020 |
|30.4 | 1.049 | 1.044 | 1.039 | 1.034 | 1.029 | 1.024 |
|30.5 | 1.052 | 1.047 | 1.042 | 1.037 | 1.032 | 1.027 |
|_____|_______|_______|_______|_______|_______|_______|
_____________________________________________________
| | |
| | THERMOMETER. |
| BAR.|_______________________________________________|
| | | | | | | |
| | 58 | 60 | 62 | 64 | 66 | 68 |
| | deg. | deg. | deg. | deg. | deg. | deg. |
|_____|_______|_______|_______|_______|_______|_______|
| | | | | | | |
|28.5 | 0.954 | 0.949 | 0.944 | 0.939 | 0.934 | 0.929 |
|28.6 | 0.958 | 0.953 | 0.947 | 0.943 | 0.938 | 0.932 |
|28.7 | 0.961 | 0.956 | 0.951 | 0.946 | 0.941 | 0.936 |
|28.8 | 0.964 | 0.959 | 0.954 | 0.949 | 0.944 | 0.939 |
|28.9 | 0.968 | 0.963 | 0.958 | 0.953 | 0.948 | 0.942 |
|29.0 | 0.971 | 0.966 | 0.961 | 0.956 | 0.951 | 0.946 |
|29.1 | 0.975 | 0.969 | 0.964 | 0.959 | 0.954 | 0.949 |
|29.2 | 0.978 | 0.973 | 0.968 | 0.963 | 0.958 | 0.952 |
|29.3 | 0.981 | 0.976 | 0.971 | 0.966 | 0.961 | 0.956 |
|29.4 | 0.985 | 0.980 | 0.975 | 0.969 | 0.964 | 0.959 |
|29.5 | 0.988 | 0.983 | 0.978 | 0.973 | 0.968 | 0.962 |
|29.6 | 0.992 | 0.986 | 0.981 | 0.976 | 0.971 | 0.966 |
|29.7 | 0.995 | 0.990 | 0.985 | 0.980 | 0.974 | 0.969 |
|29.8 | 0.998 | 0.993 | 0.988 | 0.983 | 0.978 | 0.972 |
|29.9 | 1.002 | 0.997 | 0.991 | 0.986 | 0.981 | 0.976 |
|30.0 | 1.005 | 1.000 | 0.995 | 0.990 | 0.985 | 0.979 |
|30.1 | 1.009 | 1.003 | 0.998 | 0.993 | 0.988 | 0.983 |
|30.2 | 1.012 | 1.007 | 1.002 | 0.996 | 0.991 | 0.986 |
|30.3 | 1.015 | 1.010 | 1.005 | 1.000 | 0.995 | 0.989 |
|30.4 | 1.019 | 1.014 | 1.008 | 1.003 | 0.998 | 0.993 |
|30.5 | 1.022 | 1.017 | 1.012 | 1.006 | 1.001 | 0.996 |
|_____|_______|_______|_______|_______|_______|_______|
_____________________________________________
| | |
| | THERMOMETER. |
| BAR.|_______________________________________|
| | | | | | |
| | 70 | 72 | 74 | 76 | 78 |
| | deg. | deg. | deg. | deg. | deg. |
|_____|_______|_______|_______|_______|_______|
| | | | | | |
|28.4 | 0.921 | 0.915 | 0.910 | 0.905 | 0.900 |
|28.5 | 0.924 | 0.919 | 0.914 | 0.908 | 0.903 |
|28.6 | 0.927 | 0.922 | 0.917 | 0.912 | 0.906 |
|28.7 | 0.931 | 0.925 | 0.920 | 0.915 | 0.909 |
|28.8 | 0.934 | 0.929 | 0.924 | 0.918 | 0.913 |
|28.9 | 0.937 | 0.932 | 0.927 | 0.921 | 0.916 |
|29.0 | 0.941 | 0.935 | 0.930 | 0.925 | 0.919 |
|29.1 | 0.944 | 0.939 | 0.933 | 0.928 | 0.923 |
|29.2 | 0.947 | 0.942 | 0.937 | 0.931 | 0.926 |
|29.3 | 0.950 | 0.945 | 0.940 | 0.935 | 0.929 |
|29.4 | 0.954 | 0.949 | 0.943 | 0.938 | 0.932 |
|29.5 | 0.957 | 0.952 | 0.947 | 0.941 | 0.936 |
|29.6 | 0.960 | 0.955 | 0.950 | 0.944 | 0.939 |
|29.7 | 0.964 | 0.959 | 0.953 | 0.948 | 0.942 |
|29.8 | 0.967 | 0.962 | 0.957 | 0.951 | 0.946 |
|29.9 | 0.970 | 0.965 | 0.960 | 0.954 | 0.949 |
|30.0 | 0.974 | 0.968 | 0.963 | 0.958 | 0.952 |
|30.1 | 0.977 | 0.972 | 0.966 | 0.961 | 0.955 |
|30.2 | 0.980 | 0.975 | 0.970 | 0.964 | 0.959 |
|30.3 | 0.984 | 0.978 | 0.973 | 0.968 | 0.962 |
|30.4 | 0.987 | 0.982 | 0.976 | 0.971 | 0.965 |
|30.5 | 0.990 | 0.985 | 0.980 | 0.974 | 0.969 |
|_____|_______|_______|_______|_______|_______|

For the detection of phosphine, Berge's solution may be used. It is a
"solution of 8 to 10 parts of corrosive sublimate in 80 parts of water
and 20 parts of 30 per cent. hydrochloric acid." It becomes cloudy when
gas containing phosphine is passed into it. It is, however, applied most
conveniently in the form of Keppeler's test-papers, which have been
described in Chapter V. Test-papers for phosphine, the active body in
which has not yet been divulged, have recently been produced for sale by
F. B. Gatehouse.

The estimation of phosphine will usually require to be carried out either
(1) on gas directly evolved from carbide in order to ascertain if the
carbide in question yields an excessive proportion of phosphine, or (2)
upon acetylene which is presumably purified, drawn either from the outlet
of the purifier or from the service-pipes, with the object of
ascertaining whether an adequate purification in regard to phosphine has
been accomplished. In either case, the method of estimation is the same,
but in the first, acetylene should be specially generated from a small
representative sample of the carbide and led directly into the apparatus
for the absorption of the phosphine. If the acetylene passes into the
ordinary gasholder, the amount of phosphine in gas drawn off from the
holder will vary from time to time according to the temperature and the
degree of saturation of the water in the holder-tank with phosphine, as
well as according to the amount of phosphine in the gas generated at the
time.

A method frequently employed for the determination of phosphine in
acetylene is one devised by Lunge and Cedercreutz. If the acetylene is to
be evolved from a sample of carbide in order to ascertain how much
phosphine the latter yields to the gas, about 50 to 70 grammes of the
carbide, of the size of peas, are brought into a half-litre flask, and a
tap-funnel, with the mouth of its stem contracted, is passed through a
rubber plug fitting the mouth of the flask. A glass tube passing through
the plug serves to convey the gas evolved to an absorption apparatus,
which is charged with about 75 c.c. of a 2 to 3 per cent. solution of
sodium hypochlorite. The absorption apparatus may be a ten-bulbed
absorption tube or any convenient form of absorption bulbs which subject
the gas to intimate contact with the solution. If acetylene from a
service-pipe is to be tested, it is led direct from the nozzle of a gas-
tap to the absorption tube, the outlet of which is connected with an
aspirator or the inlet of an experimental meter, by which the volume of
gas passed through the solution is measured. But if the generating flask
is employed, water is allowed to drop from the tap-funnel on to the
carbide in the flask at the rate of 6 to 7 drops a minute (the tap-funnel
being filled up from time to time), and all the carbide will thus be
decomposed in 3 to 4 hours. The flask is then filled to the neck with
water, and disconnected from the absorption apparatus, through which a
little air is then drawn. The absorbing liquid is then poured, and washed
out, into a beaker; hydrochloric acid is added to it, and it is boiled in
order to expel the liberated chlorine. It is then usual to precipitate
the sulphuric acid by adding solution of barium chloride to the boiling
liquid, allowing it to cool and settle, and then filtering. The weight of
barium sulphate obtained by ignition of the filter and its contents,
multiplied by 0.137, gives the amount of sulphur present in the acetylene
in the form of sulphuretted hydrogen. The filtrate and washings from this
precipitate are rendered slightly ammoniacal, and a small excess of
"magnesia mixture" is added; the whole is stirred, left to stand for 12
hours, filtered, the precipitate washed with water rendered slightly
ammoniacal, dried, ignited, and weighed. The weight so found multiplied
by 0.278 gives the weight of phosphorus in the form of phosphine in the
volume of gas passed through the absorbent liquid.

Objection may rightly be raised to the Lunge and Cedercreutz method of
estimating the phosphine in crude acetylene on the ground that explosions
are apt to occur when the gas is being passed into the hypochlorite
solution. Also it must be borne in mind that it aims at estimating only
the phosphorus which is contained in the gas in the form of phosphine,
and that there may also be present in the gas organic compounds of
phosphorus which are not decomposed by the hypochlorite. But when the
acetylene is evolved from the carbide in proper conditions for the
avoidance of appreciable heating it appears fairly well established that
phosphorus compounds other than phosphine exist in the gas only in
practically negligible amount, unless the carbide decomposed is of an
abnormal character. Various methods of burning the acetylene and
estimating the phosphorus in the products of combustion have, however
been proposed for the purpose of determining the total amount of
phosphorus in acetylene. Some of them are applicable to the simultaneous
determination of the total sulphur in the acetylene, and in this respect
become akin to the Gas Referees' method for the determination of the
sulphur compounds in coal-gas.

Eitner and Keppeler have proposed to burn the acetylene on which the
estimation is to be made in a current of neat oxygen. But this procedure
is rather inconvenient, and by no means essential. Lidholm liberated
acetylene slowly from 10 grammes of carbide by immersing the carbide in
absolute alcohol and gradually adding water, while the gas mixed with a
stream of hydrogen leading to a burner within a flask. The flow of
hydrogen was reduced or cut off entirely while the acetylene was coming
off freely, but hydrogen was kept burning for ten minutes after the flame
had ceased to be luminous in order to ensure the burning of the last
traces of acetylene. The products of combustion were aspirated through a
condenser and a washing bottle, which at the close were rinsed out with
warm solution of ammonia. The whole of the liquid so obtained was
concentrated by evaporation, filtered in order to remove particles of
soot or other extraneous matter, and acidified with nitric acid. The
phosphoric acid was then precipitated by addition of ammonium molybdate.

J. W. Gatehouse burns the acetylene in an ordinary acetylene burner of
from 10 to 30 litres per hour capacity, and passes the products of
combustion through a spiral condensing tube through which water is
dropped at the rate of about 75 c.c. per hour, and collected in a beaker.
The burner is placed in a glass bell-shaped combustion chamber connected
at the top through a right-angled tube with the condenser, and closed
below by a metal base through which the burner is passed. The amount of
gas burnt for one determination is from 50 to 100 litres. When the gas is
extinguished, the volume consumed is noted, and after cooling, the
combustion chamber and condenser are washed out with the liquid collected
in the beaker and finally with distilled water, and the whole, amounting
to about 400 c.c., is neutralised with solution of caustic alkali (if
decinormal alkali is used, the total acidity of the liquid thus
ascertained may be taken as a convenient expression of the aggregate
amount of the sulphuric, phosphoric and silicic acids resulting from the
combustion of the total corresponding impurities in the gas), acidified
with hydrochloric acid, and evaporated to dryness with the addition
towards the end of a few drops of nitric acid. The residue is taken up in
dilute hydrochloric acid; and silica filtered off and estimated if
desired. To the filtrate, ammonia and magnesia mixture are added, and the
magnesium pyrophosphate separated and weighed with the usual precautions.
Sulphuric acid may, if desired, be estimated in the filtrate, but in that
case care must be taken that the magnesia mixture used was free from it.

Mauricheau-Beaupre has elaborated a volumetric method for the estimation
of the phosphine in crude acetylene depending on its decomposition by a
known volume of excess of centinormal solution of iodine, addition of
excess of standard solution of sodium thiosulphate, and titrating back
with decinormal solution of iodine with a few drops of starch solution as
an indicator. One c.c. of centinormal solution of iodine is equivalent to
0.0035 c.c. of phosphine. This method of estimation is quickly carried
out and is sufficiently accurate for most technical purposes.

In carrying out these analytical operations many precautions have to be
taken with which the competent analyst is familiar, and they cannot be
given in detail in this work, which is primarily intended for ordinary
users of acetylene, and not for the guidance of analysts. It may,
however, be pointed out that many useful tests in connexion with
acetylene supply can be conducted by a trained analyst, which are not of
a character to be serviceable to the untrained experimentalist. Among
such may be named the detection of traces of phosphine in acetylene which
has passed through a purifier with a view to ascertaining if the
purifying material is exhausted, and the estimation of the amount of air
or other diluents in stored acetylene or acetylene generated in a
particular manner. Advice on these points should be sought from competent
analysts, who will already have the requisite information for the
carrying out of any such tests, or know where it is to be found. The
analyses in question are not such as can be undertaken by untrained
persons. The text-book on "Gas Manufacture" by one of the authors gives
much information on the operations of gas analysis, and may be consulted,
along with Hempel's "Gas Analysis" and Winkler and Lunge's "Technical Gas
Analysis."

APPENDIX

DESCRIPTIONS OF A NUMBER OF ACETYLENE GENERATORS AS MADE IN THE YEAR 1909

(_The purpose of this Appendix is explained in Chapter IV., page 111,
and a special index to it follows the general index at the end of this
book._)

AMERICA--CANADA.

_Maker_: SICHE GAS CO., LTD., GEORGETOWN, ONTARIO.

_Type_: Automatic; carbide-to-water.

The "Siche" generator made by this firm consists of a water-tank
_A_, having at the bottom a sludge agitator _N_ and draw-off
faucet _O_, and rigidly secured within it a bell-shaped generating
chamber _B_, above which rises a barrel containing the feed chamber
_C_, surmounted by the carbide chamber _D_. The carbide used is
granulated or of uniform size. In the generating chamber _B_ is an
annular float _E_, nearly filling the area of the chamber, and
connected, by two rods passing, with some lateral play, through apertures
in the conical bottom of the feed chamber _C_, to the T-shaped
tubular valve _F_. Consequently when the float shifts vertically or
laterally the rods and valves at once move with it. The angle of the cone
of the feed chamber and the curve of the tubular valve are based on the
angle of rest of the size of carbide used, with the object of securing
sensitiveness of the feed. The feed is thus operated by a very small
movement of the float, and consequently there is but very slight rise and
fall of the water in the generating chamber. Owing to the lateral play,
the feed valve rarely becomes concentric with its seat. There is a cover
_G_ over the feed valve _F_, designed to distribute the carbide
evenly about the feed aperture and to prevent it passing down the hollow
of the valve and the holes through which the connecting-rods pass. It
also directs the course of the evolved gas on its way to the service-pipe
through the carbide in the feed chamber _C_, whereby the gas is
dried. The carbide chamber _D_ has at its bottom a conical valve,
normally open, but closed by means of the spindle _H_, which is
engaged at its upper end by the closing screw-cap _J_, which is
furnished with a safelocking device to prevent its removal until the
conical valve is closed and the hopper chamber _D_ thereby cut off
from the gas-supply. The cap _J_, in addition to a leather washer to
make a gas-tight joint when down, has a lower part fitting to make an
almost gas-tight joint. Thus when the cap is off; the conical valve fits
gas-tight; when it is on and screwed down it is gas-tight; and when on
but not screwed down, it is almost gas-tight. Escape of gas is thus
avoided. A special charging funnel _K_, shown in half-scale, is
provided for inserting in place of the screw cap. The carbide falls from
the funnel into the chamber _D_ when the chain is pulled. A fresh
charge of carbide may be put in while the apparatus is in action. The
evolved gas goes into the chamber _C_ through a pipe, with cock, to
a dust-arrester _L_, which contains a knitted stocking lightly
filled with raw sheep's wool through which the gas passes to the service-
pipe. The dust-arrester needs its contents renewing once in one, two, or
three years, according to the make of gas. The pressure of the gas is
varied as desired by altering the height of water in the tank _A_.
When cleaning the machine, the water must never be run below the top of
the generating chamber.

[Illustration: FIG. 24.--"SICHE" GENERATOR.]

AMERICA--UNITED STATES.

_Maker:_ J. B. COLT CO., 21 BARCLAY STREET, NEW YORK.

_Type:_ Automatic; carbide-to-water.

The "Colt" generator made by this firm comprises a carbide hopper mounted
above a generating tank containing water, and an equalising bell
gasholder mounted above a seal-pot having a vent-pipe _C_
communicating with the outer air. The carbide hopper is charged with 1/4
x 1/12 inch carbide, which is delivered from it into the water in the
generating tank in small portions at a time through a double valve, which
is actuated through levers connected to the crown of the equalising
gasholder. As the bell of the gasholder falls the lever rotates a rock
shaft, which enters the carbide hopper, and through a rigidly attached
lever raises the inner plunger of the feed-valve. The inner plunger in
turn raises the concentric outer stopper, thereby leaving an annular
space at the base of the carbide hopper, through which a small delivery
of carbide to the water in the generating tank then ensues. The gas
evolved follows the course shown by the arrows in the figure into the
gasholder, and raises the bell, thereby reversing the action of the
levers and allowing the valve to fall of its own weight and so cut off
the delivery of carbide. The outer stopper of the valve descends before
the inner plunger and so leaves the conical delivery mouth of the hopper
free from carbide. The inner plunger, which is capped at its lower end
with rubber, then falls and seats itself moisture-tight on the clear
delivery mouth of the hopper. The weight of the carbide in the hopper is
taken by its sides and a projecting flange of the valve casing, so that
the pressure of the carbide at the delivery point is slight and uniform.
The outside of the delivery mouth is finished by a drip collar with
double lip to prevent condensed moisture creeping upwards to the carbide
in the hopper. A float in the generating tank, by its descent when the
water falls below a certain level, automatically draws a cut off across
the delivery mouth of the carbide hopper and so prevents the delivery of
carbide either automatically or by hand until the water in the generating
tank has been restored to its proper level. Interlocking levers, (11) and
(12) in the figure, prevent the opening of the feed valve while the cap
(10) of the carbide hopper is open for recharging the hopper. There is a
stirrer actuated by a handle (9) for preventing the sludge choking the
sludge cock. The gas passes into the gasholder through a floating seal,
which serves the dual purpose of washing it in the water of the gasholder
tank and of preventing the return of gas from the holder to the
generating tank. From the gasholder the gas passes to the filter (6)
where it traverses a strainer of closely woven cotton felt for the
purpose of the removal of any lime.

[Illustration: FIG. 25.--"COLT" GENERATING PLANT.]

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