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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"Carbide must not contain more than 5 per cent. of dust. By dust is to be
understood all which passes through a screen of 1 mm. (0.04 inch) square,
clear size of holes.

"Small carbide of from 4 to 15 mm. (= 1/6 to 3/5 inch) in size (and
intermediate sizes) must yield on the average for each delivery at least
270 litres at 15 deg. C. and 760 mm. pressure of crude acetylene per
kilogramme (= 4.33 cubic feet at 60 deg. F. and 30 inches per lb.) A margin
of 2 per cent. shall be allowed for the analysis. Small carbide of from 4
to 15 mm. in size (and intermediate sizes) which yields less than 270
litres but not less than 250 litres (= 4.01 cubic feet per lb.) 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. Small carbide of from 4 to 15 mm. in size (and intermediate
sizes) which yields less than 250 litres per kilogramme need not be
accepted.

"Carbide shall only be considered fit for delivery if the proportion of
phosphoretted hydrogen in the crude acetylene does not amount to more
than 0.04 volume per cent. A margin of 0.01 volume per cent. shall be
allowed for the analysis for phosphoretted hydrogen. The whole of the
phosphorus compounds contained in the gas are to be calculated as
phosphoretted hydrogen.

"_Period for Complaints._

"An interval of four weeks from delivery shall be allowed for complaints
for consignments of 5000 kilogrammes (= 5 tons) and over, and an interval
of two weeks for smaller consignments. A complaint shall refer only to a
quantity of carbide remaining at the time of taking the sample.

"_Determination of Quality._

"1. In case the parties do not agree that the consignee is to send to the
analyst for the determination of the quality one unopened and undamaged
drum when the consignment is less than 5000 kilogrammes, and two such
drums when it is over 5000 kilogrammes, a sample for the purpose of
testing the quality is to be taken in the following manner:

"A sample having a total weight of at least 2 kilogrammes (= 4.4 lb.) is
to be taken. If the delivery to be tested does not comprise more than ten
drums, the sample is to be taken from an unopened and undamaged drum
selected at random. With deliveries of more than ten drums, the sample is
to be drawn from not fewer than 10 per cent, of the lot, and from each of
the unopened and undamaged drums drawn for the purpose not less than 1
kilogramme (= 2.2 lb.) is to be taken.

"The sampling is to be carried out by a trustworthy person appointed by
the two parties, or by one of the experts regularly recognised by the
German Acetylene Association, thus: Each selected drum, before opening,
is to be turned over twice (to got rid of any local accumulation of dust)
and the requisite quantity is to be withdrawn with a shovel (not with the
hand) from any part of it. These samples are immediately shot into one or
more vessels which are closed air- and water-tight. The lid is secured by
a seal. No other description of package, such as cardboard cases, boxes,
&c., is permissible.

"If there is disagreement as to the choice of a trustworthy person, each
of the two parties is to take the required quantity, as specified above.

"2. The yield of gas and the proportion of phosphoretted hydrogen
contained in it are to be determined by the methods prescribed by the
German Acetylene Association. If there are different analyses giving non-
concordant results, an analysis is to be made by the German Acetylene
Association, which shall be accepted as final and binding.

"In cases, however, where the first analysis has been made in the
Laboratory of the German Acetylene Association and arbitration is
required, the decisive analysis shall be made by the Austrian Acetylene
Association. If one of the parties prevents the arbitrator's analysis
being carried out, the analysis of the other party shall be absolutely
binding on him.

"3. The whole of the cost of sampling and analysis is to be borne by the
party in the wrong."

* * * * *

The corresponding regulations issued by the Austrian Acetylene
Association (_Der Oesterreichische Acetylenverein_) are almost
identical with those of the German Association. They contain, however,
provisions that the price is to include packing, that the carbide must
not be delivered in lumps larger than the fist, that the sample may be
sealed in a glass vessel with well-ground glass stopper, that the sample
is to be transmitted to the testing laboratory with particulars of the
size of the lots and the number of drums drawn for sampling, and that the
whole of it is to be gasified in lots of upwards of 1 kilogramme (= 2.2
lb.) apiece.

In Italy, it is enacted by the Board of Agriculture, Commerce and
Industry that by calcium carbide is to be understood for legal purposes
also any other carbide, or carbide-containing mixture, which evolves
acetylene by interaction with water. Also that only calcium carbide,
which on admixture with water yields acetylene containing less than 1 per
cent. of its volume of sulphuretted hydrogen and phosphoretted hydrogen
taken together, may be put on the market.

It is evident from the regulations quoted that the determination of the
volume of gas which a particular sample of calcium carbide is capable of
yielding, when a given weight of it is decomposed under the most
favourable conditions, is a matter of the utmost practical importance to
all interested in the trafficking of carbide, _i.e._, to the makers,
vendors, brokers, and purchasers of that material, as well as to all
makers and users of acetylene generating plant. The regulations of the
British Association do not, however, give details of the method which the
analyst should pursue in determining the yield of acetylene; and while
this may to a certain extent be advantageously left to the discretion of
the competent analyst, it is desirable that the results of the experience
already won by those who have had special opportunities for practising
this branch of analytical work should be embodied in a set of directions
for the analysis of carbide, which may be followed in all ordinary
analyses of that material. By the adoption of such a set of directions as
a provisional standard method, disputes as to the quantity of carbide
will be avoided, while it will still be open to the competent analyst to
modify the method of procedure to meet the requirements of special cases.
It would certainly be unadvisable in the present state of our analytical
methods to accept any hard and fast of rules for analysis for determining
the quality of carbide, but it is nevertheless well to have the best of
existing methods codified for the guidance of analysts. The substance of
the directions issued by the German Association (_Der Deutsche
Acetylenverein_) is reproduced below.

"METHODS FOR THE DETERMINATION OF TILE YIELD OF GAS FROM CALCIUM CARBIDE.

"The greatest precision is attained when the whole of the sample
submitted to the analyst is gasified in a carbide-to-water apparatus, and
the gas evolved is measured in an accurately graduated gasholder.

"The apparatus used for this analysis must not only admit of all the
precautionary rules of gas-analytical work being observed, but must also
fulfil certain other experimental conditions incidental to the nature of
the analysis.

"(_a_) The apparatus must be provided with an accurate thermometer
to show the temperature of the confining water, and with a pressure
gauge, which is in communication with the gasholder.

"(_b_) The generator must either be provided with a gasholder which
is capable of receiving the quantity of gas evolved from the whole amount
of carbide, or the apparatus must be so constructed that it becomes
possible with a gasholder which in not too large (up to 200 litres = say
7 cubic feet capacity) to gasify a larger amount of carbide.

"(_c_) The generator must be constructed so that escape of the
evolved gas from it to the outer air is completely avoided.

"(_d_) The gasholder must be graduated in parts up to 1/4 per cent.
of its capacity, must travel easily, and be kept, as far as may be in
suspension by counterweighting.

"(_e_) The water used for decomposing the carbide and the confining
water must be saturated, before use, with acetylene, and, further, the
generator must, before the analysis proper, be put under the pressure of
the confining (or sealing) liquid."

The following is a description of a typical form of apparatus
corresponding with the foregoing requirements:

"The apparatus, shown in the annexed figure, consists of the generator A,
the washer B, and the gasholder C.

[Illustration: FIG. 22.--LARGE-SCALE APPARATUS FOR DETERMINING YIELD OF
GAS FROM CARBIDE.]

"The generator A consists of a cylindrical vessel with sloping bottom,
provided with a sludge outlet _a_, a gas exit-pipe _b_, and a
lid _b'_ fastened by screws. In the upper part ten boxes _c_
are installed for the purpose of receiving the carbide. The bottoms of
those boxes are flaps which rest through their wire projections on a
revolvable disc _d_, which is mounted on a shaft _l_. This
shaft passes through a stuffing-box to the outside of the generator and
can be rotated by moans of the chains _f_, the pulleys _g_ and
_h_, and the winch _i_. Its rotation causes rotation of the
disc _d_. The disc _d_, on which the bottoms of the carbide-
holders are supported, is provided with a slot _e_. On rotating the
disc, on which the supporting wires of the bottoms of the carbide-holders
rest, the slot is brought beneath these wires in succession; and the
bottoms, being thus deprived of their support, drop down. It is possible
in this way to effect the discharge of the several carbide-holders by
gradual turning of the winch _i_.

"The washer B is provided with a thermometer _m_ passing through a
sound stuffing-box and extending into the water.

"The gasholder C is provided with a scale and pointer, which indicate how
much gas there is in it. It is connected with the pressure-gauge
_n_, and is further provided with a control thermometer _o_.
The gas exit-pipe _q_ can be shut off by a cock. There is a cock
between the gasholder and the washer for isolating one from the other.

"The dimensions of the apparatus are such that each carbide-holder can
contain readily about half a kilogramme (say l lb.) of carbide. The
gasholder is of about 200 litres (say 7 cubic feet) capacity; and if the
bell is 850 mm. (= 33-1/2 inches) high, and 550 mm. (= 21-1/2 inches) in
diameter it will admit of the position being read off to within half a
litre (say 0.02 cubic foot)."

The directions of the German Association for sampling a consignment of
carbide packed in drums each containing 100 kilogrammes (say 2 cwt.) have
already been given in the rules of that body. They differ somewhat from
those issued by the British Association (_vide ante_), and have
evidently been compiled with a view to the systematic and rapid sampling
of larger consignments than are commonly dealt with in this country.
Drawing a portion of the whole sample from every tenth drum is
substantially the same as the British Association's regulations for cases
of dispute, viz., to have one unopened drum (_i.e._, one or two
cwt.) per ton of carbide placed at the analyst's disposal for sampling.
Actually the mode of drawing a portion of the whole sample from every
tenth vessel, or lot, where a large number is concerned, is one which
would naturally be adopted by analysts accustomed to sampling any other
products so packed or stored, and there in no reason why it should be
departed from in the case of large consignments of carbide. For lots of
less than ten drums, unless there is reason to suspect want of
uniformity, it should usually suffice to draw the sample from one drum
selected at random by the sampler. The analyst, or person who undertakes
the sampling, must, however, exercise discretion as to the scheme of
sampling to be followed, especially if want of uniformity of the several
lots constituting the consignment in suspected. The size of the lumps
constituting a sample will be referred to later.

The British Association's regulations lead to a sample weighing about 3
lb. being obtained from each drum. If only one drum is sampled, the
quantity taken from each position may be increased with advantage so as
to give a sample weighing about 10 lb., while if a large number of drums
is sampled, the several samples should be well mixed, and the ordinary
method of quartering and re-mixing followed until a representative
portion weighing about 10 lb. remains.

A sample representative of the bulk of the consignment having been
obtained, and hermetically sealed, the procedure of testing by means of
the apparatus already described may be given from the German
Association's directions:

"The first carbide receptacle is filled with 300 to 400 grammes (say 3/4
lb.) of any readily decomposable carbide, and is hung up in the apparatus
in such a position with regard to the slot _e_ on the disc _d_
that it will be the first receptacle to be discharged when the winch
_i_ is turned. The tin or bottle containing the sample for analysis
is then opened and weighed on a balance capable of weighing exactly to
1/2 gramme (say 10 grains). The carbide in it is then distributed
quickly, and as far as may be equally, into the nine remaining carbide
receptacles, which are then shut and hung up quickly in the generator.
The lid _b'_ is then screwed on the generator to close it, and the
empty tin or bottle, from which the sample of carbide has been removed,
is weighed.

"The contents of the first carbide receptacle are then discharged by
turning the winch _i_. Their decomposition ensures on the one hand
that the sealing water and the generating water are saturated with
acetylene, and on the other hand that the dead space in the generator is
brought under the pressure of the seal, so that troublesome corrections
which would otherwise be entailed are avoided. After the carbide is
completely decomposed, but not before two hours at least have elapsed,
the cock _p_ is shut, and the gasholder is run down to the zero mark
by opening the cock _q_. The cock _q_ is then shut, _p_ is
opened, and the analytical examination proper is begun by discharging the
several carbide receptacles by turning the winch _i_. After the
first receptacle has been discharged, five or ten minutes are allowed to
elapse for the main evolution of gas to occur, and the cock _p_ is
then shut. Weights are added to the gasholder until the manometer
_n_ gives the zero reading; the position of the gasholder C is then
read off, and readings of the barometer and of the thermometer _o_
are made. The gasholder is then emptied down to the zero mark by closing
the cock _p_ and opening _q_. When this is done _q_ is
closed and _p_ is opened, and the winch _i_ is turned until the
contents of the next carbide receptacle are discharged. This procedure is
followed until the carbide from the last receptacle has been gasified;
then, after waiting until all the carbide has been decomposed, but in any
case not less than two hours, the position of the gasholder is read, and
readings of the barometer and thermometer are again taken. The total of
the values obtained represents the yield of gas from the sample
examined."

The following example is quoted:

Weight of the tin received, with its contained |
carbide . . . . . ._| = 6325 grammes.
Weight of the empty tin . . . . = 1485 "
_______
Carbide used . . . = 4840 " = 10670 lb.

The carbide in question was distributed among the nine receptacles and
gasified. The readings were:

________________________________________________
| | | | |
| No. | Litres. | Degrees C. | Millimetres. |
|______|__________|______________|_______________|
| | | | |
| 1 | 152.5 | 13 | 762 |
| 2 | 136.6 | " | " |
| 3 | 138.5 | " | " |
| 4 | 161.0 | " | " |
| 5 | 131.0 | " | " |
| 6 | 182.5 | 13.5 | " |
| 7 | 146.0 | " | " |
| 8 | 163.0 | 14.0 | " |
| 9 | 178.5 | " | " |
|______|__________|______________|_______________|

After two hours, the total of the readings was 1395.0 litres at 13.5 deg. C.
and 762 mm., which is equivalent to 1403.7 litres (= 49.57 cubic feet) at
15 deg. C. and 760 mm. (or 60 deg. F. and 30 inches; there is no appreciable
change of volume of a gas when the conditions under which it is measured
are altered from 15 deg. C. and 760 mm. to 60 deg. F. and 30 inches, or
_vice versa_).

The yield of gas from this sample is therefore 1403.7/4.840 = 290 litres
at 15 deg. C. and 760 mm. per kilogramme, or 49.57/10.67 = 4.65 cubic feet at
60 deg. F. and 30 inches per pound of carbide. The apparatus described can,
of course, be used when smaller samples of carbide only are available for
gasification, but the results will be less trustworthy if much smaller
quantities than those named are taken for the test.

Other forms of carbide-to-water apparatus may of course be devised, which
will equally well fulfil the requisite conditions for the test, viz.,
complete decomposition of the whole of the carbide without excessive rise
of temperature, and no loss of gas by solution or otherwise.

An experimental wet gas-motor, of which the water-line has been
accurately set (by means of the Gas Referees' 1/12 cubic foot measure, or
a similar meter-proving apparatus), may be used in place of the graduated
gasholder for measuring the volume of the gas evolved, provided the rate
of flow of the gas does not exceed 1/6 cubic foot, or say 5 litres per
minute. If the generation of gas is irregular, as when an apparatus of
the type described above is used, it is advisable to insert a small
gasholder or large bell-governor between the washer and the meter. The
meter must be provided with a thermometer, according to the indications
of which the observed volumes must be corrected to the corresponding
volume at normal temperature.

If apparatus such as that described above is not available, fairly
trustworthy results for practical purposes may be obtained by the
decomposition of smaller samples in the manner described below, provided
these samples are representative of the average composition of the larger
sample or bulk, and a number of tests are made in succession and the
results of individual tests do not differ by more than 10 litres of gas
per kilogramme (or 0.16 cubic foot per pound) of carbide.

It is necessary at the outset to reduce large lumps of carbide in the
sample to small pieces, and this must be done with as little exposure as
possible to the (moist) air. Failing a good pulverising machine of the
coffee-mill or similar type, which does its work quickly, the lumps must
be broken as rapidly as possible in a dry iron mortar, which may with
advantage be fitted with a leather or india-rubber cover, through a hole
in which the pestle passes. As little actual dust as possible should be
made during pulverisation. The decomposition of the carbide is best
effected by dropping it into water and measuring the volume of gas
evolved with the precautions usually practised in gas analysis. An
example of one of the methods of procedure described by the German
Association will show how this test can be satisfactorily carried out:

"A Woulff's bottle, _a_ in the annexed figure, of blown glass and
holding about 1/4 litre is used as the generating vessel. One neck, about
15 mm. in internal diameter, is connected by flexible tubing with a
globular vessel _b_, having two tubulures, and this vessel is
further connected with a conical flask _c_, holding about 100 c.c.
The other neck is provided with tubing _d_, serving to convey the
gas to the inlet-tube, with tap _e_, of the 20-litre measuring
vessel _f_, which is filled with water saturated with acetylene, and
communicates through its lower tubulure with a similar large vessel
_g_. The generating vessel _a_ is charged with about 150 c.c.
of water saturated with acetylene. The vessel _f_ is filled up to
the zero mark by raising the vessel _g_; the tap _e_ is then
shut, and connexion is made with the tube _d_. Fifty grammes (or say
2 oz.) of the pulverised carbide are then weighed into the flask _c_
and this is connected by the flexible tubing with the vessel _b_.
The carbide is then decomposed by bringing it in small portions at a time
into the bulb _b_ by raising the flask _c_, and letting it drop
from _b_ into the generating vessel _a_, after having opened
the cock _e_ and slightly raised the vessel _f_. After the last
of the carbide has been introduced two hours are allowed to elapse, and
the volume of gas in _f_ is then read while the water stands at the
same level in _f_ and _g_, the temperature and pressure being
noted simultaneously."

A second, but less commendable method of decomposing the carbide is by
putting it in a dry two-necked bottle, one neck of which is connected
with _e_, and dropping water very slowly from a tap-funnel, which
enters the other neck, on to the carbide. The generating bottle should be
stood in water, in order to keep it cool, and the water should be dropped
in at the rate of about 50 c.c. in one hour. It will take about three
hours completely to gasify the 50 grammes of carbide under these
conditions. The gas is measured as before.

[Illustration: FIG. 23.--SMALL-SCALE APPARATUS FOR DETERMINING YIELD OF
GAS FROM CARBIDE.]

Cedercreutz has carried out trials to show the difference between the
yields found from large and small carbide taken from the same drum. One
sample consisted of the dust and smalls up to about 3/5 inch in size,
while the other contained large carbide as well as the small. The latter
sample was broken to the same size as the former for the analysis. Tests
were made both with a large testing apparatus, such as that shown in Fig.
22, and with a small laboratory apparatus, such as that shown in Fig. 23.
The dust was screened off for the tests made in the large apparatus. Two
sets of testings were made on different lots of carbide, distinguished
below as "A" and "B," and about 80 grammes wore taken for each
determination in the laboratory apparatus, and 500 grammes in the large
apparatus. The results are stated in litres (at normal temperature and
pressure) per kilogramme of carbide.

___________________________________________________________________
| | | |
| | "A" | "B" |
|_____________________________________________________|______|______|
| | | |
| Lot |Litres|Litres|
| Small carbide, unscreened, in laboratory \ (1) | 276 | 267 |
| apparatus . . . . . / (2) | 273 | 270 |
| Average sample of carbide, unscreened, in \ (1) | 318 | 321 |
| laboratory apparatus . . . / (2) | 320 | 321 |
| Small carbide, dust freed, in large apparatus (1) | 288 | 274 |
| Average sample of carbide, dust freed, in \ (2) | 320 | 322 |
| large apparatus . . . . / | | |
|_____________________________________________________|______|______|

As the result of the foregoing researches Cedercreutz has recommended
that in order to sample the contents of a drum, they should be tipped
out, and about a kilogramme (say 2 to 3 lb.) taken at once from them with
a shovel, put on an iron base and broken with a hammer to pieces of about
2/5 inch, mixed, and the 500 grammes required for the analysis in the
form of testing plant which he employs taken from this sample. Obviously
a larger sample can be taken in the same manner. On the other hand the
British and German Associations' directions for sampling the contents of
a drum, which have already been quoted, differ somewhat from the above,
and must generally be followed in cases of dispute.

Cedercreutz's figures, given in the above table, show that it would be
very unfair to determine the gas-making capacity of a given parcel of
carbide in which the lumps happened to vary considerably in size by
analysing only the smalls, results so obtained being possibly 15 per
cent. too low. This is due to two causes: first, however carefully it be
stored, carbide deteriorates somewhat by the attack of atmospheric
moisture; and since the superficies of a lump (where the attack occurs)
is larger in proportion to the weight of the lump as the lump itself is
smaller, small lumps deteriorate more on keeping than large ones. The
second reason, however, is more important. Not being a pure chemical
substance, the commercial material calcium carbide varies in hardness;
and when it is merely crushed (not reduced altogether to powder) the
softer portions tend to fall into smaller fragments than the hard
portions. As the hard portions are different in composition from the soft
portions, if a parcel is sampled by taking only the smalls, practically
that sample contains an excess of the softer part of the original
material, and as such is not representative. Originally the German
Acetylene Association did not lay down any rules as to the crushing of
samples by the analyst, but subsequently they specified that the material
should be tested in the size (or sizes) in which it was received. The
British Association, on the contrary, requires the sample to be broken in
small pieces. If the original sample is taken in such fashion as to
include large and small lumps as accurately as possible in the same
proportion as that in which they occur in the main parcel, no error will
be introduced if that sample is crushed to a uniform size, and then
subdivided again; but a small deficiency in gas yield will be produced,
which will be in the consumer's favour. It is not altogether easy to see
the advantage of the British idea of crushing the sample over the German
plan of leaving it alone; because the analytical generator will easily
take, or its parts could be modified to take, the largest lumps met with.
If the sample is in very large masses, and is decomposed too quickly,
polymerisation of gas may be set up; but on the other hand, the crushing
and re-sampling will cause wastage, especially in damp weather, or when
the sampling has to be done in inconvenient places. The British
Association requires the test to be made on carbide parcels ranging
between 1 and 2-1/2 inches or larger, because that is the "standard" size
for this country, and because no guarantee is to be had or expected from
the makers as to the gas-producing capacity of smaller material.
Manifestly, if a consumer employs such a form of generator that he is
obliged to use carbide below "standard" size, analyses may be made on his
behalf in the ordinary way; but he will have no redress if the yield of
acetylene is less than the normal. This may appear a defect or grievance;
but since in many ways the use of small carbide (except in portable
lamps) is not advantageous--either technically or pecuniarily--the rule
simply amounts to an additional judicious incentive to the adoption of
apparatus capable of decomposing standard-sized lumps. The German and
Austrian Associations' regulations, however, provide a standard for the
quality of granulated carbide.

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