318

August 18, 1916.

THE COLLIERY GUARDIAN.

________________________________________________________________________________

large a portion of the coal tar chemical industry. This
is also true of the products allied to benzol—the toluol
and xylol. The process of recovering the benzol consists
in washing the gas with a heavy oil, usually derived
from coal tar or petroleum “ straw ” oil, until this oil
is charged with the crude benzol, when it is removed
from the circulating system and distilled at such a tem-
perature as to drive over the benzol and allied vapours
without disturbing the original washing oil. This oil
may then be cooled and returned to the circulating
system. The quantity of crude benzol contained in gas
varies from 2 gals, per ton of coal carbonised to very
much less than this, according to the volatile matter in
the coal. The subsequent treatment of the crude benzol
to separate it into its various fractions is carried out by
fractional distillation between limited temperatures.
Ninety per cent, benzol, which is the usual commercial
standard, is that product 90 per cent, of which will distil
over at lOOdegs. Cent, or lower.

The production of benzol from coke oven gas has
been extensively carried on in Germany, and the large
amounts of benzol so secured have been one of the main
raw materials for their highly developed coal tar
chemical industry. The surplus benzol was used as a
motor fuel in place of gasoline, and under the present
war conditions, benzol is the principal fuel for auto-
mobiles and similar engines.

Pure benzol is also the starting point for the manu-
facture of aniline oil and a wide range of dye stuffs,
pharmaceuticals, etc., based on it. It is also important
at present as a source of pure phenol or carbolic acid
which is extensively used for making tri-nitro phenol or
picric acid, an explosive, and also for making phono-
graphic records. The separation of the toluol from the
crude benzol also supplies material for making tri-nitro-
toluol, a very important explosive.

The amount of benzol produced in the United States
was very small until subsequent to the outbreak of the
European war. If all the coal made into coke had been
treated for benzol recovery, the production would have
been about one hundred million gallons per year, on the
moderate estimate of one and one-half gals, per ton of
coal. It is stated on good authority, however, that the
total recovery in 1913 was not more than 4,500,000 gals,
outside of that used foir gas enrichment by the producer.
The European war, however, not only cut off foreign
supplies of chemical and dye stuffs based on benzols,
but immensely increased the demand for it because of
the manufacture of war munitions. Accordingly many
benzol recovery plants have sprung into being, and this
article is now in a fair way to come into its own. The
Geological Survey in a recent report states that the out-
put of benzol and light oils in 1915 was nearly
14,000,000 gals., and that with the completion of the
new plants under construction the capacity will probably
exceed 22,000,000 gals, per year. The price for refined
has risen from 25c. per gal. to 60c. or upwards, while
toluol, formerly in limited demand at 30c. per gallon, has
risen to 4-25 per gal. and upwards.

As benzol is an excellent motor fuel, it is quite pro-
bable that any surplus existing after the close of the
war can be readily absorbed for this purpose, although
it may well be hoped that the development of the
chemical industries will afford an adequate and more
remunerative market.

Cyanides.

The presence of cyanogen in coal gas is generally
attributed to the breaking down of ammonia in contact
with hot coke or oven surfaces. Therefore, while the
amount of cyanogen present depends originally on the
amount of nitrogen in the coal, it has also- an immediate
relation to the heat of the coke oven or gas retort, in
which the carbonisation is carried on. High heats and
exposure to hot surfaces encourage cyanide formation
and low heats the opposite. The usual form in which
cyanogen occurs is as hydrocyanic acid, HCN; thus,
C + NH3 = HCN + H2.

The actual amount of cyanogen in a gas is small, for
of the original nitrogen of the coal (amounting to one
or two per cent.) only between one and two per cent,
appears as cyanogen. A gas containing 130 grains of
cyanogen per cu. ft. can be worked profitably, it is said,
provided the amount of coal treated approximates 200
tons per day.

In the usual method of purifying coal gas, by the use
of iron oxide, more or less of the cyanogen is removed.
Under favourable conditions the spent oxide will be
found to contain enough to warrant treatment by
chemical manufacturing concerns purchasing the spent
oxide, on the basis of its prussian blue contents, and.
working it up, the final product being yellow prussiate
of potash, or an equivalent form.

The complete removal of cyanogen from gas as a
separate operation can be effected in accordance with
several different methods, as the Bueb, the Davis-Neill,
Feld, etc., and is carried out on a commercial scale in
a number of European gas plants. The Bueb process,
which is perhaps the best known, consists primarily in
washing the gas with a solution of ferrous sulphate,
FeSO4, in a gas washer of one of the- usual types, using
the sulphate of iron solution as the washing liquid. As
the presence of ammonia in the gas is essential to the
reaction, the point chosen is previous to the ammonia
washers. It is also necessary that the gas should be
first freed from naphthalene by passing through a
washer in which a suitable absorbing medium, as anthra-
cene oil, creosote oil or water gas tar, is used. The gas
therefore passes through the naphthalin washer first,
and then goes to the cyanide washer.

In the latter, the fresh sulphate of iron enters at one
end and the gas at the other, the currents being opposed,
lion sulphide is formed, and in turn reacts with the
cyanogen and ammonia, forming ammonium fer.ro-
forro cyanide, together with a little ammonium ferro-
cyanide.

The sludge liquor from the washer is treated in a still
and then neutralised with sulphuric acid. It then con-

tains an insoluble double ferrocyanide of ammonia and
iron, plus ammonium sulphate, ferrous sulphate and
free acid. It is run to a filter press, and the sludge
removed in the form of press cake, ammonium ferro-
ferro cyanide, or “ blue.” The final product is sold on
its equivalent to potassium ferro-cyanide, yellow
prussiate of potash; though under present conditions,
sodium ferrocyanide is made instead of potash, because
of the high price of the latter.

Tar.

The removal of tar from crude gas was long a sticking
point in methods of condensation, and is still a criterion
of good operation. As the gas cools, tar is deposited very
readily, but the last traces of tar are not so easily
removed. This is usually effected by passing the gas
through a scrubber, in which it is finely divided, together
with a reduction in temperature to about 80 degs. Fahr.,
the latter being deemed essential to success. The tem-
perature reduction has, however, been avoided by the
use of a scrubbing device in which a jet of tar acts on
the gas, and causes the tar mist to gather into drops
which readily separate out. Until (this difficulty was
overcome the presence of tar in the gas prevented the
adopting of direct saturation by which the ammonia is
removed from the gas by passing through sulphuric acid,
making sulphate of ammonia directly in place of washing
with water and redistilling.

Tans from different coals, and more especially pro-
duced in different types of apparatus, vary within wide
limits. The more highly heated the surfaces over which
the tar vapours pass on their way out of the retort and
the longer the exposure, the heavier the tar. The per-
centage of free carbon is a fair indication of its quality,
as the amount of oils and bitumens is apt to vary with
it. Generally speaking, coke oven tars are low in free
carbon, averaging around 10 per cent., while gas works
tars are apt to be high, 25 to 30 per cent, and correspond-
ingly lower in tar oils. Because of these variations, and
also because of the invariable presence of two or three or
more per cent, of water, there are few if any purposes to
which crude tar can successfully be put without preli-
minary treatment, except to burn as fuel. Therefore, for
whatever purpose the crude tar is to serve, it has to
undergo the process of distillation and probably admix-
ture with other tars to correct defects in composition.

The distillation of tar is carried out in steel plate stills
of cylindrical form, these being set vertically in Europe,
but usually horizontal in the United States. A standard
type is of half-inch plate, 9 ft. in diameter, and 20 ft.
long, holding about 10,000 gals. These are set in brick
work with a firebox beneath them, usually several stills
in a battery. The vapour from the stills is led away
through a goose-neck to a condensing coil which is
immersed in a tank of water, the temperature of which
can be regulated. The separation of the distillation
products is controlled by a thermometer placed in the
goose-neck, cuts being made at certam specified points.
For refined tar the removal of the water and -a certain
portion of the light oils is sufficient. Such refined tar
is used in the saturation of felt for roofing, waiterproofing
and insulating purposes. In combination with soft
pitch saturated felt is built into a foundation or laid on
a roof for waterproofing or roofing, in successive layers.

It is also used in the manufacture of ready roofings,
two ply, three ply, and mineral surfaced. Another very
important use of prepared tar is as good as a road appli-
cation, or binder. For this purpose several different
grades are made, each suited to a special field. They
range from a thin tar to what is really a soft pitch of
lOOdegs. melting point.

When the distillation is to be carried out to the pro-
duction of the various oils and pitch the separations are
as follows in American practice : The first fraction is
that which comes over below 200 degs. Cent., or until
the distillate sinks in water. This is called light oil or
crude naphtha. The second fraction comes over between
200 and 270 degs. Cent., and is called middle or carbolic
oil. The third fraction includes the oil above 270 degs.
until pitch of the required hardness remains in the still.
It contains naphthalene and anthracene, and is known
as heavy oil or creosote oil. It is extensively used in
wood preservation under many and more or less compli-
cated specifications.

The residue is pitch. In American practice pitch
varies greatly in hardness, the bulk of the production
being the softer grades, used for roofing, paving, water-
proofing and preservative coatings. Some hard pitch
for use in fuel briquettes and similar purposes is also
made.

The proportion of these five preliminary products in
tar varies with the tar, but is about as follows : Light
oil, 0-5 to 3 per cent.; carbolic or middle oil, 5-0 to
8 per cent.; creosote or heavy oil including anthracene
oil, 20 to 30 per cent.; pitch, 60 to 75 per cent.

Light Oil.

From this benzol, toluol, and xylol are obtained, as
already explained, and, in addition, a number of
different solvent naphthas, also some phenol, creosol and
naphthalene.

Middle or Carbolic Oil.

From this tar acids or crude creosols and crude
naphthalene are obtained, also some creosote oil, which
is added to the heavy oil fraction.

From the first two are obtained phenol or carbolic
acid, nitrophenol, the starting point for many dye stuffs,
and trinitro-phenol or picric acid. The crude products
also furnish cresylic acid, and naphthalene, which is
converted into nitro-naphthalene, from which many dye
stuffs are made.

Heavy Oil.

In addition to the naphthalene, heavy oil contains
anthracene, from which in turn come alizarine and
anthraquinone, from both of which a wide series of dye
stuffs is obtained.

MINING EMPLOYMENT STATISTICS.

The Board of Trade Labour Gazette states that
employment in coal mining continued very good during
July, and showed some improvement on the whole com-
pared with a month ago. There was an increase of
2,353, or 0-4 per cent., in the number of workpeople
employed compared with the previous month, and of
6,546, or 1'2 per cent., as compared with

Average No. of
days worked per
week by the
collieries m fort-
night ended

Districts.

July 1915.

Inc. ( *) or
dec. ( —) in
July 1916,
on a

England fy Wales.
Northumberland ...
Durham ........
Cumberland _____
South Yorkshire ...
West Yorkshire___
Lancs. & Cheshire...
Derbyshire ......
Notts and Leicester
Staffordshire .....
Warwick, Worcester
and Salop......
Gk/ster & Somerset
North Wales .....
South Wales & Mon.

Work-
people
em-

ployed t-----------A--------,---------*------

in July July June July M v_ar

1916.* 22,	24.	24, iViontJ1 Year

1916. 1916. 191'. ag0*	ag0*

Days. Days. Da\s. Days. Days.

44.453..	.5'48...5'43...5'46... 4-0'05...+0'02

92.170..	.5'53...5'60.. 5'42...-0'07... f 0*11
6,490...5'84 ..5'57...5'80... + 0'27...+0'04

61.535..	.5'82...5 81...5'74...+0'01...+0'08

25.375..	.5'78.. 5'75...5'53 ..+0'03 .. >-0'25

49.271..	5'70...5'54..5'50... + 0T6... + 020

35.385..	.5’88...5*43...5*75... +0*45... +0'13

34.759..	.5*70...5*56...5*44...+0*14... + 0*26
28,372 ..5’88...5*76...5'75... +0'12... +0'13

8.646..	.5’83...5*82...5'78... +0 01... 4-0’05

6.212..	.5 33...5*66...5*97...—0*33...—0’64
7,970 . 5 95...5'81...5'88 +0'14... 4-0'07

91,914...5'93...5'50 3'08...+0'43... r2'85

Total ...... 492,552...5 74 5'60 . 5'12... +0T4 +0'62
Scotland.

West Scotland ... . 19,826 5'46...5 47...4 44...-0'01... +1'02
The Lothians ......	2,348 5'46...5'56...4'85...-OTO...+0'61

Fife ............... 24,828 .5'51.. 5'56...3'55 ..-0'05... +1'96

Total ...... 47,002...5'48.5'52...4'00...-0'04... +1'48

Total, U.K. ... 539 554 5'71...5'59..5'0'2...+0'12... 4-0'69
* At the collieries included in the table.

Compared with the previous month, employment
showed a decline in Durham and in Gloucester and
Somerset. In Scotland, also, employment showed a
slight decline, which was accounted for by holidays. In
every other district there was an improvement, which
was most marked in Cumberland, Derbyshire, South
Wales and Monmouthshire.

Compared with a year ago, there was an improve-
ment in every district except Gloucester and Somerset;
in South Wales and Monmouth the comparison with
last year was affected by a dispute, and in Scotland by
holidays.

Description
of coal.

Work-
people
em-
ployed
in July
1916*

Average No. of
days worked per
week by the pits
in fortnight
ended
_______________

July June July
22, 24,	24,

1916. 1916. 1915.

Inc. (+) or
dec. ( —) in
July 1916
on a

__________

Month Year

ago. ago.

Anthracite	......

Coking ..

Gas......

House....

Steam....

Mixed....

Days. Days. Days. Days. Days.

5,529 . 5'99...5'63 . 3'28... + 0 36...+2'71

29.171..	.5'60...5 78...5 48...-0 18... +0T2
36,734 . 5'61 ..5'51...5'43... + OTO... t0'18

59.356..	5'66...5'54..5'35 .. + 0'12... + 0'31
189,142...5'78...5 56...4'58... * 0'22... +1'20
219,622 ..5'70...5'61...5'23... ► 0'09...+0'47

All descriptions ... 539,554 ..5'71 ...5'59...5 02... +0'12 ..+0'69

* At the collieries included in the table.

Compared with a month ago, employment showed an
improvement at pite producing all classes of coal,
except coking pits, which showed a decline. The
improvement was most marked at anthracite and at
steam coal pits. Compared with a year ago, there
was an improvement at all coal pits.

Iron Mining.—Employment in iron mines was very
good—better even than in June. Returns, relating in
each case to the same mines, show 13,312 workpeople
employed in July 1916; this is 39 less than in June, and
450 (or 3'3 per cent.) less than a year ago.

The returns are summarised by districts in the
following table :—

Work-
people

Districts. em-

ployed (------A------x	>----------______

in July	July	June	July	__

1916.	22,	24,	24,	Month	Year

1916.	1916.	19)5.	ag0'	ag0'

Days.	Days.	Days.	Days. Days.

Average No. of
days worked per
week by mines
in fortnight

Inc. (+ ) or
dec. (—) in
July 1916
on a

Cleveland........... 5,563 ...5'84...5'63...5'60...+0'21...+0'24
Cumberland and

Lancashire ....... 4,630 ...5'93 . 5 92.. 5'83... +0 01... +0'10
Scotland ...........	758 ...5'97...5'99...4'40...-0'02... +1'57

Other districts .... 2,361 .. 5'96 . 5*96...5'68... — ...+0'28

All districts... 13,312 ...5':0...5'81...5'63...+0'09... + 0'27

The weekly average number of days worked by the
mines and open works included in the returns was 5-90,
compared with 5'81 in the previous month, and 5'63 a
year ago. Compared with both a month ago and a year
ago, there was an improvement of about a quarter of a
day per week in Cleveland, the principal district. The
great increase (II days per week) in Scotland compared
with a year ago is due to the holidays which were taken
in 1915, but were not taken this year.

Pig Iron.—Employment continued good, and was
better than a month ago and a ‘year ago. There was
still much difficulty in obtaining sufficient supplies of
iron ore, limestone, and coke. There was a shortage of
workpeople, especially of general labourers.

Returns received show that 277 furnaces were in blast
at the end of July 1916, compared with 274 in the
previous month, and 264 a year ago.

Iron and Steel Works. — Further improvement
occurred in the employment at iron and steel works.
Compared with a month ago, the number of workpeople
employed showed a marked increase in Cleveland, and