70

THE COLLIERY GUARDIAN.

July 12, 1918.

be recommended. If returned to the well, the free
acid and sulphate increase the proportion of “fixed”
ammonia in the liquor, with consequential increased
consumption of lime at the still, and the tar in the
well becomes contaminated with an acid arsenical tar
that may be a source of trouble to distillers. If thrown
away, the whole of the accompanying sulphate and
free acid is lost. It would appear to be better to
steam the scum, with or without addition of water,
and to pour the liquor on to a breeze filter draining
to the bubbler effluent tank or suitable receiver.
When scum is highly charged with tar, separation
can often be readily effected by addition of hot water,
followed by stirring; the tar sinks, and the super-
natant liquor can then be decanted. At one works
it was found that some 90 to 100 lb. of scum, contain-
ing 40 lb. of s/a, were being thrown away per week,
amounting on occasions to more than half a pound of
sulphate per ton of coal carbonised. The whole of this
scum is now treated, and the recovered sulphate
returned to the bubbler.

Figures for recovery of sulphate are of little value
in comparative statistics unless based on careful
measurement of stocks accompanied by analysis of
liquors, and even then results are misleading if stocks
vary widely from one period to another, since it is
obvious that the whole of the ammonia in stock cannot
be recovered in actual practice owing to working losses
in the handling and distillation of liquor, and in the
storage tanks. This is especially true of the direct
process, which is generally conducted at works of
small size, where little regard is often paid to the
importance of protecting liquor from evaporation of
ammonia during storage, and where losses at the still
are sometimes serious. At one works the loss of am-
monia in the spent effluent liquor is rarely below the
equivalent of half a pound of s/a per ton of coal;
at another the average loss at the still as determined
by analysis averaged If lb. s/a per ton of coal for
28 days, and for the four following days averaged
3| lb., and this at a time when the still was under
observation and daily samples taken. Account should
be taken also of any ammoniacal liquor retained by
the tar, an amount by no means insignificant in works
where separation of tar and liquor is imperfect. The
importance of covering in seal pots by sliding lids
and of protecting liquor during storage has been
frequently emphasised.

The recovery figure for sulphate in the direct pro-
cess undoubtedly leaves much to be desired. When
the process first came under observation, the relatively
poor yield of sulphate was attributed solely to working
losses. Investigation now shows that this view is un-
tenable, and that improvement, if such is to be
attained, must, in the better conducted works, be
sought for rather in the carbonising house than in
the bubbler.

Synthetic Production of Ammonia.

Chemical manufacturing methods for the production
of ammonia from hydrogen and nitrogen are making
rapid advances on the Continent, in the United
Kingdom, and in the United States of America.
Figures published regarding Germany in this direc-
tion state that whilst in 1913 plant for the “ Haber ”
process was calculated to be capable of producing the
equivalent of 30,000 tons of sulphate of ammonia, the
output by this process for 1917 was anticipated to
exceed the equivalent of 500,000 tons, and at a
moderate cost. There are, moreover, other processes
by which atmospheric nitrogen is utilised for the
manufacture of products from which ammonia can
readily be obtained.

Apart from “ synthetic” methods for production of
‘ammonia, there is its recovery as a by-product. In
this country this has.been hitherto the main source
of the ammonia available, but a large proportion of
the coal annually consumed is not so treated as to
permit of ammonia recovery; so that, although 458,617
tons of sulphate were produced in 1917, there is room
for a very large increase in this source of national
wealth. A recent effort of some interest is a fresh
attempt to produce profitably products from the
destructive distillation of coal at temperatures
materially lower than are customary in present prac-
tice in gas works, coke oven works, or coal carbonising
works, where gas and coke are the dominant products
aimed at. The period during which this fresh effort
has been made is still too short for a final judg-
ment ; the products obtained vary from those obtained
at higher temperatures, and experience will decide
whether a permanent addition is being made to
commercial coal products.

There are also indications of important changes
in gas works practice. The departure from estimating
the quality of coal gas from its light-giving powers
to its capacity for producing heat and sufficiently
high temperatures on combustion is leading towards
differences in the character of the gas manufactured,
the by-products obtained, and modes of carbonisation.
The use of steam in vertical retorts will, judging from
the long experience accumulated in the analogous
methods of shale distillation in Scottish oil works,
materially increase the proportion of ammonia re-
covered per ton of coal, whilst the greatly increased
volume of gas made will lessen the quantity of coal
carbonised unless a rapid and corresponding expan-
sion in the demand for coal gas arises. More than
the necessary expansion is, however, to be anticipated,
as the convenience, varied applicability and economy
of a cheap heat-giving gas leads to its wider use by
the industrial as well as the domestic consumer.

It would appear, therefore, that ammonia supplies
available from such varied sources will in the future
prove to be'ample for all requirements, even if the
price become less than in the past.

Tar Works.

The number of this class of works registered was 360,
an increase of 44 over 1916, almost entirely due to
the erection of tar dehydrating plants in gas works.
Lack of sufficient condensing power was again noted

in some of the tar dehydrating plants, leading to loss
of these light oils so greatly desiderated for high
explosives.

The complete fractional distillation of tar—as dis-
tinguished from the partial operation known as de-
hydrating—was effected in plant of the intermittent
type. It is noteworthy that in the Scottish shale oil
works continuous complete fractional distillation of
the crude oil introduced nearly 30 years ago has for
a long time been general in that industry.

The system of continuous tar distillation introduced
a number of years ago by Lennard continued in
successful operation in a limited number of works.
It is, however, different in type from ordinary frac-
tional distillation, and is more accurately to be
described as a process of fractional condensation, apart
from the preliminary heating to effect separation of
water and part of the light oils.

The means used for preventing escape of noxious
gases continued unchanged. Apart from the undue
escape of uncondensed vapours of light oils in a few
works, due to insufficient condensing power, these
works were conducted satisfactorily. Additional con-
densers were provided in those cases where this was
necessary for efficient working in accordance with Act
requirements.

The following are particulars as regards the opera-
tion in tar works in the United Kingdom: —

Tar distilled in—	Tons.

Gas works	...	...	•••	•••	1,526,209

Other works	...	...	•••	•••	126,966

Pitch produced in—

Gas works	...	...	...	•••	721,130

Other works	...	...	...	•••	74,829

Scientific Control.

Recently there has been a considerable extension
in the numbers of those who recognise the advantages
to be derived from the most efficient works control,
and progress is also evident in favour of co-operative
effort, although not always accompanied by the desire
to add special knowledge to the general store. There
is, however, a tendency in some to look to the Govern-
ment for guidance and support. Government depart-
ments will doubtless be active in their proper spheres,
and may do good service in certain directions, but it
is essential that there should not be lacking the solid
foundation of skilled, alert, scientific control, com-
bined with intelligent, sustained and willing work on
the part of everyone associated with individual works
in the various branches of manufacture, as well as
united effort on the part of the owners of these works.
To elicit willing activity on the part of all by suitable
recognition is to lay the foundations of success in the
coming strenuous competition amongst the nations.

Scotland.

The number of works registered was 168, being one
more than in 1916. The number of the registered
processes in operation was 317 (an increase of two over
1916), including 19 sulphuric acid, 19 sulphuric acid
(Class II.), 11 gas liquor, 109 sulphate and muriate
of ammonia, 5 paraffin oil, and 50 tar. The quantity
of salts of ammonia (expressed as sulphate) was H8,427
tons (114,693 tons in 1916), including gas works 22,870
tons, iron works 12,765 tons, shale works 60,560 tons,
and’bone, producer gas, coke and carbonising works
22,232 tons. The tar distilled amounted to 262,158
tons (265,482 tons), including gas and coke oven
works 142,969 tons, and other works 119,189 tons. The
pitch produced was 137,012 tons (146,153 tons), viz.,
from gas and coke oven works 66,914 tons, and from
other works 70,098 tons. Of the above total quantity
of sulphate of ammonia, the equivalent of 17,689 tons
was manufactured as concentrated ammoniacal liquor;
the balance of 100,738 tons consisted of other ammonia
products (sulphate, chloride, nitrate, etc.).

COAL PRICES ORDER.

The Board of Trade have made an Order providing
for an increase of Is. 6d. per ton in the price of all coal
despatched from the colliery for consumption in the
United Kingdom, commencing Monday, July 8, to meet
the cost of the increased war wage recently granted to
the miners.

The prices of coal for shipment for export and as
bunkers are increased by 2s. per ton in the case of all
vessels the loading of which was begun on or after
July 8, the 2s. being made up of Is. 6d. to meet the cost
of the’ war wage and 6d. to meet increased dock
charges.

The Board of Trade also issued directions under
which they assume responsibility for the payment of
the war wage as from June 30, and, to provide funds
for so doing, are to be credited by the collieries with 4s.
per ton on all coal disposed of on and alter that date.
This ensures that the whole of the increases in prices
which have been granted to meet the cost of the war
wage shall be specifically applied to that purpose.

Fuel Shortage in Argentina.—The scarcity of fuel re-
sulting from the carmen’s. strike endangers the conduct
of the public services, particularly street lighting and the
tramways. The employment of maize as fuel is seriously
contemplated.

Italy’s Coal Supplies.—Much interest is centred in heavier
coal requirements of Italy. There is some difficulty. in
apportioning the quantities to coal exporters and arranging
for shipment. To obviate this a few firms .have been
chosen to arrange for the export of the quantities desired.
These firms will work in conjunction with an exporters’
pool, and the profits resulting from the exporters’ services
will be pooled and divided amongst qualified exporters
in proportion to their percentage of trade in the pre-scheme
period. The arrangement facilitates business, inasmuch
as the Italian authorities will have one shipper only at
each district to deal with. The business which will come
into the operation of the pool will be that outside of
the quantities taken by the Italian State Railways Com-
mission, which for some years past have secured their
requirements through their resident commissioners and
exporting agencies.

EARTHING ELECTRICAL SERVICES
IN MINES.

(Specially Contributed.)

It is not too much to say that the provision of good
earth, properly connected to every metallic surface
with which users may come into contact, means the
saving of a considerable number of lives. Many fatal
accidents have been caused by workmen making con-
nection with some metal surface that has become
alive, but, fortunately, the number of these fatal
accidents is steadily decreasing, largely owing, the
writer believes, to the problem of providing good
earth and connecting it to all metallic surfaces being
better understood and more efficiently carried out.

The Hojpe Office has very wisely decreed that the
armouring of cables shall be of a certain maximum
electrical resistance, compared with the conductors it
is designed to protect, and that the continuity of the
armour, or whatever may take the place of the
armour, shall be maintained at this standard. One
of the difficulties in this connection arises where joints
have to be made. However carefully the armour is
glanded to the joint box, one can never be quite sure that
a resistance in the earth circuit is not introduced at
the joint box. The joint itself introduces a resistance
into the circuit of the conductor, however carefully
it may be made, and the joint box will almost cer-
tainly introduce a greater resistance into the earth
circuit.

The difficulty is overcome by carefully bonding the
armour on each side of and across the joint box by
substantial copper wires. It is necessary that the
bonding wires should be substantial, and on the other
hand they should be as flexible as possible; the object
to be attained is a close long contact between the
bonding wire and the armour on each side of the
joint box by means of a conductor of as low resistance
as possible. With the greatest care in the world there
will be some resistance between the armour and the
bonding wire, but this can be reduced to a minimum
by wrapping the bonding wire a good many times
round the armour, making sure that both the armour
and the bonding wire are perfectly clean, absolutely
free from oil and dirt before wrapping, and arranging
so that the bonding *wire will remain in its place under
mining conditions. A stranded wire is probably the
best, but the individual wires of the strand should
not be too small, i.e., below No. 18 S.W.G. If the
individual wires are very small, greater flexibility is
obtained, but there is a greater danger of some of
them being broken, and there is also the danger of
oxidation of the individual wires of the strand. In
bonding, the bonding wire should not be drawn tight
across the joint box, but a certain amount of slack
should be allowed, so that the wrapping shall not be
pulled away from the armour, nor the bonding wire
broken.

The same remarks apply to the matter of connecting
all metallic surfaces, such as the carcasses of motors,
the bodies of joint boxes, switch boxes, etc., to earth.
The connection made with the earthing wire should
be as large as it possibly can be, and as much as the
surface of the earthing wire should be in contact with
a similar amount of the surface of the object to be
earthed as possible—the larger the surfaces of the
metals that are making contact the better. Again,
both metallic surfaces should be made absolutely clean
before they are brought into contact. The screw con-
nection, or the screw holding the wire to the object
to be protected, should have a large flat head and a
coarse thread, so that it can be easily tightened up
and the thread will not easily strip. The earth wire
also should be very substantial, and it should follow
the same rule as that laid down for the armour; its
resistance should not be greater than twice the same
length of the largest conductor of the service, and
if it is larger—say the same size as the service con-
ductor—so much-the better.

The Ideal Earth.

The ideal earth would be a conductor of infinitely
large dimensions, or infinitely low electrical resistance,
arranged in such a position that connection could be
made to it quite easily from every metallic body with
which anyone could come into contact. The idea of the
infinitely large conductor of infinitely low resistance is
that in case of contact being made between a live con-
ductor and one of the metallic objects to be protected,
the very low resistance opposed to the flow of current
to earth, and through earth, shall reduce to safe
figures the electrical pressure tending to produce
shock. When a connection is made between a service
conductor and the armour, a joint box or the frame
of a machine, a certain current flows through the
earth circuit (where one is provided), and there
will be a fall of pressure right along the earth circuit
in proportion to the resistance of the earth path and
the current flowing. The same formula rules in this
case as is employed when calculating the size of a
conductor allowable with a given fall of pressure
between two points. This formula is E = CR, E being
the fall of pressure in volts, C the current to be pro-
vided for in amperes, and R the resistance of the
conductor in ohms. For calculating the resistance
and size of the conductor the formula is transposed,
but for the present purpose the form given above is
the one that rules. If R is reduced to 0, it will
be evident that E also becomes 0, no matter how
large the current may be; and the nearer the re-
sistance of the earth path can be reduced to 0, the
more nearly will the earthing arrangements fulfil the
ideal conditions. A case that may occur in actual
practice will render this more clear : Suppose that
the resistance of the earth path is 0-5 ohm, and that
one of the conductors of a 3,000 volt service makes
contact with the armour of the cable, the joint box,
or the carcass of a machine. Omitting the question
of the power factor, the current flowing may be as
much as 6,000 amps., and the pressure at the point
of contact will be dangerously high according to the
above formula. When the current is flowing, the fall