1340

THE COLLIERY GUARDIAN

December 31, 1915.

_________________	___________________________________

CURRENT SCIENCE AND TECHNOLOGY.

Gas from Peat.

According to a Friesland newspaper, the municipal
gas works at Akkrum, in that province, are extracting
gas from peat mixed with coal. It is stated that if peat
alone were used, the retorts would become too hot,
because of the steam created by the moisture always
found in peat. Accordingly, the retorts are filled with
two parts in weight of coal to one of peat. The peat—
as well as the coal—produces about 30 cu. m. of gas
per 100 kilogs. (2201b.), and, according to a report by
the United States Consul at Amsterdam, the gas pro-
duced from this mixture is declared to be of excellent
quality. The peat is entirely consumed in the process,
and therefore yields no by-products, as coal does in tar
and coke; but the use of peat is a great saving of coal,
which is important in Holland now, where all coal, and
particularly gas coal, is scarce, and has to be imported
from a distance at heavy cost. Peat, on the other hand,
is plentiful’, particularly in Friesland, and is dug in the
vicinity of the gas works.

Dangerous Wiring in Mines.

Mr. H. J. 'Johnson (Coal Age) considers that, under
certain conditions, electricity is dangerous in mines,
especially where gas is encountered in considerable
quantities. A great number of mines are wired to-day
by connecting a feeder cable to a circuit-breaker in the
power plant, and setting this breaker to carry the entire
load of the mine, consisting of haulage motors, coal
mining machines, pumps, etc. This feeder is then con-
nected to the trolley wire at the mine entrance, and
this trolley wire is run for a mile or more underground,
and connected to machine wires, pump wires, etc. Some
of these conductors are small, and have a high resist-
ance. Furthermore, track-bonding is none too good in
mines.

Suppose one of these machine wires should fall and
cause a short circuit. The resistance of the wires, com-
bined with bad track bonding, would cause the voltage
to drop so low that it would not allow enough current to
flow back and trip the circuit breaker at the power plant.
The author has seen coal machine cables short-circuited
and catch fire, and the machine helper compelled to run
down to the heading and pull his cable off the heading
wire. Had this room contained dangerous gas, there
would probably have occurred an explosion.

He has seen a cable burn completely while coiled on
its reel. The current was cut off at the power plant,
due to a breakdown, and the runner, learning that it
would be off for several hours, went home, leaving his
cable connected to the heading wire. When the current
was turned on again, this cable short-circuited from some
cause, and burned together with the wooden frame of
the reel. This mishap was the result of having a high
resistance line and bad bonding on the return rail. The
voltage was reduced so low that it could not force enough
current back to the power plant to trip the circuit-
breaker. If there had been gas in the mine, it might
have been blown up, and no one would have known the
cause.

The remedy for such conditions is to have a magnetic
low-voltage switch installed on each machine and pump
line, so as to protect that particular circuit. The use of
open face-plate starting boxes for pumps and mining
machines, as well as the employment of open motors in
gaseous mines, should be avoided, since a spark from
either may cause an explosion.

Continuous Partial Distillation of Tar.

In a paper read before the Southern District Asso-
ciation of Gas Engineers and Managers, Mr. F. Livesey
described his experience at Maidstone with a Wilton
plant of a capacity of 4,000 gals, of crude tar per 24
hours. After a short experience of the plant, he found
that, when working at a temperature of 130 degs. Cent,
in the tar, he was unable to extract the water content
when this content was high, and some 4 or 5 per cent,
of water remained. The steam blast was increased, and
a steam heater, consisting of an old carburetter, was
added. This brought up the temperature of the tar to
100 degs. Cent, before entering the coil, and gave a
temperature of 150 degs. Cent, at the outlet of the coil,
with an output of approximately 3,000 gals, per 24
hours.

It was found that working at 150 degs. Cent., the con-
denser provided was insufficient to cool the vapours
sufficiently on entering the vapour catch box, but a
small washer was provided, and a vent was furnished
from this washer to a small oxide purifier. This arrange-
ment worked satisfactorily, and prevented loss of
ammonia, and when working up to 150 degs. Cent., cool
liquor could be run off to the well.

A good demand exists for a refined tar suitable for
road making. This tar should be free from ammoniacal
liquor, the free carbon should not exceed 16 per cent.,
the middle and heavy oils should be left in the tar, but
the naphthalene content should not be too high. Tar
produced during carbonisation at low heats is usually
preferred, because of the free carbon content; but, in
pursuit of the other features, he determined to work at
higher temperatures, and for some time past the plant
has been worked at 170 degs. Cent, in the tar. This
necessitated alterations to the condensing plant; and a
second condenser was, therefore, installed between the
washer and the vapour catch box. By a careful regu-
lation of the flow of water, which is extremely small, the
light creosote oils can be collected from the first vapour
box, and the liquor and the crude naphtha can be
removed from two cocks at different levels in the
washer. The creosote oils when the first vapour box is
kept at a temperature of 93 degs. Cent, tests as follows :
Specific gravity, 1-028; water, 3 per cent.; phenols, 9 per
cent.; naphthalene, 26-3; and is liquid at 30 degs. Cent.

200°.	190°.

225’6... 179’7

156’9... 132’8

69’5 .. 73 0

There is an airtight settling tank into which the
creosote oils are run, and a considerable amount of the
naphthalene salts allowed to crystallise. This gives a
suitable creosote for the re-mixing with the tar for the
exhausters, or for the market for the preservation of
timber. The naphtha, after two washings and three
distillations, yields 45-5 per cent, of 90 per cent, benzol.

After the outbreak of the war, it became important to
treat the tar at still higher temperatures, to remove the
entire toluol fraction. Tests at various temperatures
gave the following results :—

Temperature of still.	Toluol content.

Degs. Cent.	Per cent.

190	.................... 02

200	.................... 0’153

210	.................... 0’025

220	.................. 0'007 to nil.

230	.................... Nil

To reach a temperature of 200 degs. Cent., and at the
same time to obtain a fair output from the plant, four
more complete coils were added at the top of the still—
making 16 coils in all. When working at 230 degs. Cent,
the tar, when cool, becomes extremely thick; and as
the creosote is now wanted by the tar distiller for toluene
removal, it cannot be thinned out. In fact, unless the
tar is removed and used with reasonable speed, in cold
weather it will be impossible to get it from barrels or
underground tanks. If this difficulty becomes more
acute, it will probably be necessary for us to re-distil the
creosote out into two fractions, and return the heavier
fraction to the tar.

The cast iron coil still seems to have advantages over
other types built of mild steel or wrought iron, which
must necessarily have a short life; and the danger of fire
in the Wilton plant appears to be reduced to a minimum.
The coil contains only a small quantity of tar, and any
leakage which might take place would find its way into
the flue, not into the furnace. Below are the results of
some tests made to show the capacity of the plant at
different temperatures :—

230°.	220°.	210°.

Crude tar used per

hour ........... 222’8... 198-8... 192’8...

Dehydrated tar per

hour ............ 107’0... 138’0... 120 5.......

Dehydrated tar per

cent.............	48’0... 69’4... 62’6...

Capacity of plant

per 24 hours ... 2,568’0...3,312’0...2,892’0.3,765 6.3,187’2
Crude tar used per

24 hours ........ 5,347’2...4,771’2...4,627’2...5,414 4...4,272’8
These tests are in some respects rather anomalous, as,
not being taken on the same day, the qualities of the
crude tar treated, and also probably of the fuel, were
not identical.

One disadvantage of working at a high temperature
is the difficulty of obtaining a sufficient supply of
dehydrated tar to meet the requirements of customers
during the hot weather in the summer, when nearly all
the tar is sold for road purposes. On the other hand,
the value of the heavier fraction extracted is greater
than the value of dehydrated tar, and so it is obvious that
it pays to work at high temperatures.

The working pressure on the plant varies consider-
ably with the quality of the tar treated and the condi-
tion of the pump. With tar of 7 to 15 per cent, water
content, the pressure is from 15 to 25 lb. per sq. in.; but
with tar containing 30 per cent, of water, it is rather
higher. The pressure gauge is fixed to a 4 ft. siphon,
and sealed with cylinder oil. The heat efficiency of the
plant is from 38 to 40 per cent.

Shrinkage and Time Effects in Reinforced Concrete.

Results of tests and other investigations carried on at
•the experimental engineering laboratories of the
University of Minnesota appear in a bulletin prepared
by F. R. McMillan, the object being to determine the
shrinkage and time effects in reinforced concrete. It
was found that certain changes take place that are due
neither to poor construction nor inadequate design, but
rather to the nature of the material itself—its tendency
to shrink and yield under load. The tests are conside ad
sufficient to warrant certain statements and conclusions
which should be given consideration by those responsible
for reinforced concrete design and construction. These
conclusions should be prefaced with the statement that,
while they will prove applicable to a wide range of
conditions and structures, it is recognised that, by a
careful study of mixtures and materials, it may be
possible to produce a concrete largely free from the
defects upon which these conclusions are based.

With materials and mixtures as used in these tests it
is safe to predict a shrinkage of from j to 1 in. or more in
100 ft. when exposed to the ordinary dry air of a heated
building. It cannot be definitely stated when shrinkage
will cease under these conditions, but certainly not
within a year. However, from one-half to two-thirds of
the amount indicated may be expected within 40 to 60
days after exposure to dry air. Thorough wetting in the
early curing stage seems to have no effect in reducing
the total shrinkage, but only retards the beginning of the
action, in spite of the fact that the strength of the con-
crete is materially increased by this treatment. Slight
changes in the moisture content in the air will retard
the shrinkage or even cause a swelling which seems to
warrant the belief that structures open to the elements
would never show the same total shrinkage as found in
these tests. The continued shrinkage in beams and
slabs produces an increasing deflection, though not to
the same extent as the time yielding discussed below.

The yielding of the concrete under compressive stress
with time, a phenomenon similar to the yielding of
ductile metals when stressed beyond the yield
point, is greater as the unit stress is greater,
and seems to go on indefinitely. In the tests
the deformation due to yielding was from three to four
times that produced immediately upon the application

of the load. On the tension side of a beam or slab the
effect of time is to cause a gradual increase in the steel
stress from the breaking down of the concrete in tension
or the failure of the bond. The combination of the
extension at the bottom and a shortening at the top pro-
duces in beams and slabs a continually increasing
deflection. With the same unit changes top and bottom,
the deflection is less the deeper the beam.

A few of the possible results that may be looked for
where these time changes are in progress are suggested.
The production of cracks in floors, ceilings, and
partitions even though in no sense indicating a structural
weakness, is an undesirable feature. And in certain
places, with some types of structures or details, cracks
might leave the reinforcement accessible to moisture,
and thus prove a source of danger. Sagging of the
structural frame work may cause the binding of doors
in partitions, a feature that is both expensive and
annoying. The tilting of columns by the unequal
shrinkage in different floors might be a source of high
bending moments and column stresses. But of far more
importance than these may be mentioned the two follow-
ing possible effects, both of which might in certain
instances be of serious consequence :—

(1)	The continued yielding in the upper fibres of a
beam, coupled with the gradual breaking down of the
concrete in tension, may result in a progressive destruc-
tion of the bond from centre toward the supports. Also
the drying out incident to the large shrinkage movement
may assist in this destruction of the bond.

(2)	The possibility of high stresses in the longitudinal
steel of compression members seems to be the most
important conclusion to be drawn from these tests. The
time yielding of the concrete under stress combined with
the excessive shortening due to shrinkage may result in
deformations from five to fifteen times those expected
from the ordinary calculations. In columns of the
ordinary ratio of vertical steel in which no allowance has
been made for the spirals, the resulting steel stress is
probably well within the elastic limit, but in those
columns designed on the assumption of large loads being
carried by the hooping, the steel stresses may approach
dangerously near the yield point.

___________________________

THE GERMAN AND AUSTRIAN COAL
AND IRON TRADES.

We give below further extracts from German
periodicals that have reached us, showing the course of
the coal and iron trades in Germany and Austria :—

Wages Question in the Ruhr District.

The Miners’ Union in the Ruhr district recently
petitioned the masters for an increase in wages of 10
per cent. In their reply, the masters stated that the
increase asked for is already exceeded in the case of
that portion of the original staff which is still working
at the pits. The rise of prices on September 1 has not
been without influence on the general upward tendency
of wages, and will continue to find expression in a
further rise in the average wage. At present there is
no ground for the -assumption that wages have already
reached a maximum. The miners, in their petition,
referred to the favourable financial results obtained by
certain collieries, but it must not be forgotten that other
collieries have not done at all well; and as it is impos-
sible, in view of this inequality, to make an immediate
advance in wages based on the average results of the
year’s working, the favourable position of a few com-
panies should not be brought forward as a criterion of
the whole. In view of the great modification in the
constitution of the shifts, it is impossible to establish
any comparison with the average wage of pre-war times
—an opinion confirmed by the Minister of .Commerce.

German Steel Union.

According to the annual report, the total production
of steel products, for the year ending June 30 last,
amounted to 3,393,537 tons (a deficit of 2,730,773 tons,
as compared with the previous year), made up as
follows: Semis, 739,451 Ions; railway superstructural
material, 1,759,115 tons; sections, 894,971 tons.
During November of the present year, the distribution
attained 84*2 per cent, of the deliveries in the corre-
sponding month of 1913. Additional orders for rails
and sleepers were placed by the Prussian State Railways,
and fairly large contracts were placed for export to
neutrals. Pit rails have been in satisfactory demand,
but there is little doing in tramway rails. The price of
sections for the first quarter of 1916 has been left
unchanged. The building trade is stagnant, but an
active enquiry prevails from shipbuilders and con-
structional engineers. Deliveries in November comprised
69,099 tons (68,344 tons in October) of semis, 118,942
tons (130,981 tons) of railway superstructural material,
and 53,709 tons (57,953 tons) of sections, a total of
241,750 tons (257,278 tons) calculated on the weight of
raw steel.

Iron Market in Upper Silesia.

The situation in November is again characterised as
satisfactory, owing to the considerable orders for war
material. The difficulties due to the war were in part
accentuated, and prevented the output capacity from
being fully developed. The continued increase in the
price of raw materials, etc., heightened the cost of pro-
duction still further; but the possibilities of distribution
improved, large consignments being sent to Denmark
and Scandinavia, as also to Roumania and Bulgaria. In
these last two countries there has been a considerable
revival in the demand for rolled iron, girders, plate, and
gas pipes, and a very active demand for war material.
Heavy high-grade plate has been in strong request, for
defensive and shipbuilding purposes; and the orders in
hand for fine plate are sufficient to keep the works busy
for some months. Many articles formerly made of tin-
plate, brass, or other sheet metal, are now being made