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LHE BY-PRODUCTS
OF COAL-GAS MANUFACTURE

THE BY-PRODUCTS

COAL-GAS MANUFACTURE

MGs, LANGE, Px.D.

TRANSLATED FROM THE GERMAN BY

CHAS. SALTER

WITH THIRTEEN ILLUSTRATIONS AND DIAGRAMS

LONDON
SCOTT, GREENWOOD & SON
8 BROADWAY, LUDGATE, E.C.

1915

[ Zhe sole rights of translation into English remain with
Scott, Greenwood & Son]

D. VAN NOSTRAND COMPANY
NEW YORE

TABLE OF CONTENTS

PAGE —
INTRODUCTION . ‘ ; F ‘ 1
CHAPTER I

PURIFICATION OF Coan Gas. ; , 4

CHAPTER II
CoKE : ; ‘ ; - 23

CHAPTER III
ReTORT GRAPHITE. : é ‘ioe

CHAPTER 1V
Gas Tar. : ‘ é o BS

CHAPTER V
THE Gas Liquor i ‘ : et eee
Testing Gas Liquor . : ; : d 2 ; ; . 54
Treating the Gas Liquor . ; , ‘ : ‘ ; eae
The Distillation of Gas Liquor . ‘ , ; : 3 ae: |
Working the Still . ; P ; ; eae
Preparation of Concentrated Gas Liquor . : ‘ : ; Ns S|
Preparation of Ammonia . ‘ ; ; j : : aoe «|
Liquefied Ammonia . P . ; ; ; ° ; a 88
Sulphate of Ammonia ‘ ‘ : ; : : ‘ ens OO

CHAPTER VI
‘Tot TREATMENT OF THE GAS-PURIFYING AGENTS . 105
Eliminating the Sulphur by Extracticn . ; : : < HERE
Lixiviating the Purifying Material . ‘ : , ‘ «8
Treating the Liquor . j 2 é ‘ P Frege be S
Treating the Extracted Material : é : i ; . oe

vi TABLE OF CONTENTS

CHAPTER VII
TREATING THE CYANOGEN SLUDGE

CHAPTER VIII

TREATING THE CRUDE Liquors . ;

1. Precipitation with Iron Salts
2. Precipitation with Ammonium Salts
3. Precipitation with Potassium Salts

CHAPTER IX

Tur TREATMENT OF CRUDE AMMONIUM THIOCYANATE AND
Cuprous THIOCYANATE .

CHAPTER X
PorTassiumM F'ERRICYANIDE

CHAPTER XI
THE CYANOGEN PIGMENTS

CHAPTER XII

SULPHUR AND SULPHURIC ACID

INDEX

137

139

144

COAL GAS BY-PRODUCTS.

INTRODUCTION.

THE gas which issues when a gas burner is turned
on is not the only product furnished by the dry dis-
tillation of coal, the crude gas, as it leaves the re-
torts, containing substances the combustion of which
has an unsalutary effect on the human organism, so
that these substances must be removed from the gas
before it reaches the consumer. The bodies in ques-
tion are, chiefly, sulphuretted hydrogen, hydrocyanic
acid and ammonia.

The distillation of coal is conducted at a very high
temperature ; and some of the gaseous products thus
formed do not remain in the state of gas at: the or-
dinary room temperature. Consequently, a partial -
condensation of the gaseous mixture occurs on the
way to the gasholder, coal-tar and gas liquor being
deposited. Their complete separation is effected by
suitable cooling, in order to prevent obstruction in
the pipes. Naphthalene, in particular, tends to
choke up the pipes to an unpleasant extent in cold
weather, by crystallization. The substances to be
regarded as the raw material of the by-products in
coal-gas making are the coke and graphite left in the
retorts, and the tar, gas liquor, sulphuretted hydro-
gen and hydrocyanie acid in the distillate. As coal

3 1

a. 2255145 GOAL GAS BY-PRODUCTS —
gas there remain hydrocarbons, carbon monoxide and
carbon dioxide.

The relative proportions of these various constitu-
ents depend ,on the temperature, the arrangement of
the retorts and the length of the gasifying period.
At present, coal is usually distilled at 1100-13002 C.
With regard to the relative proportions of the con-
stituents of coal, very extensive experiments were
carried on by Drehschmidt in 1904 with the experi-
mental plant at the Berlin municipal gasworks, at
Tegel. Since this plant is constructed to scale and
modelled on the lines of practice, the experiments
furnish an accurate illustration of the percentage com-
position of the gasification products. The following
table gives the maximum and minimum values in
the case of sixty-eight kinds of coal and the gasi-
fication products of same. The moisture content of
the raw coal was 2 per cent. The percentage of gas
liquor is confined to the amount of water produced
during distillation. The gasifiable sulphur could not
be determined direct, but was calculated from the
difference between the original sulphur in the coal
and that found remaining in the coke.

The experiments show that the percentage content
of cyanogen and ammonia is independent of the
origin and composition of the coal; but that the
sulphur, on the other hand, is generally more abun-
dant in English coals. Before going into the treat-
ment of the recovered substances, brief consideration
may be given to the gas works, to gain some idea of ~
how the substances mentioned above are eliminated
from the gas. :

INTRODUCTION

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CHAPTER I.

PURIFICATION OF COAL GAS.

THE crude coal gas passes from the retorts through
upcast and trapped pipes into a sloping receiver (the
hydraulic main) in which the heaviest condensation
products of the tar, and a portion of the gas liquor,
begin to separate out. - Next follows a tubular or
annular apparatus in which the gas is cooled, by air,
to a temperature of about 40° C. (104° F.), and is
thus caused to part with the bulk of the contained
water, part of the ammonia, and most of the residual
tar. The gas is then put through a process of wet
purification which removes the bulk of the ammonia,
and part.of the sulphuretted hydrogen and cyanogen,
by absorption. On the counter-flow principle, the -
gas is introduced into the bottom of cylindrical
vessels, down which water is allowed to flow from
above. In order to present a large wetting surface
to the gas, superimposed gratings are laid on bars
at intervals in the interior of the cylinder, or else
prismatic bars are laid over one another cross- —
wise. In place of these upright cylinders, or
scrubbers, inclined cylinders are now sometimes

(4)

PURIFICATION OF COAL GAS 5

used. These are filled about one-third full of water,
a horizontal rotary shaft carrying bars with faggots
of wood bringing the gas into intimate contact with
that liquid. By the aid of a suction and pressure
apparatus, the gas is delivered to the purifying boxes
for the dry treatment. These boxes are rectangular
and are provided at the upper rim with a groove in
which the lid engages, a tight joint being made by
filling the groove with water. ‘These boxes also are
provided with gratings on which the purifying agent
is loosely spread. The gas enters the box at a suit-
able point, flows through the interior and issues at
the opposite side. To ensure complete purification, |
several boxes are arranged in series. In this case
also the counterflow system has been found satis-
factory, the fresh gas being brought into contact
with the purifying material which has been most
used, and the almost completely purified gas pass-
ing through fresh material. When the purifying
material is no longer capable of taking up any more
sulphuretted hydrogen, it is regenerated, the iron
‘sulphide formed being reconverted into ferric hy-
droxide by atmospheric oxygen and moisture, whilst
sulphur separates out. Repeated turning over with
a shovel facilitates the process and prevents local
heating through the heat generated by the reaction.
The material regenerated in this way is used over
again, until finally it has become so impregnated
with sulphur that its value as an absorbent has sunk
very low, whereupon it is put aside to be treated for
the recovery of its valuable constituents. By the

aa COAL GAS BY-PRODUCTS

above treatment the gas is freed from most of its
injurious constituents, and is then passed on to the
gasholder, for distribution in the mains. Whilst the
reactions in the wet purification process are simple,
those of the processes in the purifying boxes are of
a complex nature, and have been the cause of much
divergence of opinion among experts.

In the wet process, ammonia, sulphuretted hydro-
gen and hydrocyanic acid pass directly into solution.
A small portion of the sulphuretted hydrogen is
oxidized by the oxygen present, so that oxygen com-
pounds of ammonia are found in the gas _ liquor.
Pfeiffer detected the following products in gas liquor
from the Magdeburg gasworks :—

Totalammonia . ; ‘ s . 1:935 per cent
Combined ammonia . ; : . 0°642 fe
Free ammonia . ; : ° . 1293 -s

If the combined ammonia be allocated to the acids
absorbed in the gas liquor, the following values are
obtained :—

Ammonium carbonate . ; ‘ . 1°293 per cent
Ammonium sulphydrate . ; , 0086. -,,
Ammonium thiosulphate . , i ik i) enn
Ammonium sulphate . ; : ; 978. “e,,
Ammonium thiocyanate... se RO os
Ammonium ferrocyanide . ; . 0034 ,,

Information as to the distribution of these con-
stituents in the different absorption apparatus is
afforded by the researches of Lunge and Cox :—

PURIFICATION OF COAL GAS 7

Ss ae 5 ey La} »
Ammoniain | 3% o-.|202| 082] oc eo% | 25 2D
Grms. per EE 43 Se3 Sas | 328 3 RS Sa 34
‘ ° ea -) °
Mitre,as: | £2 |a58|885| 228 | see | 2E5| BE | ge
oat oat RYO 24D oie) ueO Ps =)
le eit” | at | ed ea? | & ES
fo se)
Ammonium
sulphide .| 2°60 | 3°14 | 17°36 | 35°71 119-93 {| 60°30 11:37 | 8°81
Carbonate .| 2°75 | 1°16 | 17:14| 41-14 61°43 | 22°86 | 8°57
Thiosulphate | 0°40 | 0°27 |trace| 0°59 1:16 2°53 | 0°73 | 0°44
Sulphate .| 0°03 |013 | — — — — — —
Thiocyanate | 0°36 | 0:41 | 0°03 | trace ~~ “— | 0°36 | 0:09
Chloride __.| 7:04 | 0°60 | 0°54 | 0-71 | 0°91 0°48 | 0°40 | 0°17
Ferrocyanide| — | — | 0°07 | 0:14 0°43 Pao sm
Total . . | 18-29 | 18°14 | 85°13 | 78°29 | 115°43 | 126-00 | 35-71 | 18°00
Percentage of
stable salts| 59 £6 | 1:8 | 1°85 2°92 3°4 4:2 | 4:0
Sp. gr. at
15°5° C. =. | 1°011 | 1:012 | 1035 | 1°075 | 1:115 | 1°120 | 1022} 1-010

The amount of these salts naturally varies ac-
cording to the origin of the coal, the sulphur com-
pounds containing a higher percentage of the
ammonia in the case of coals high in sulphur. The
construction and arrangement of the retorts also
affect the ammonia content of the gas liquor. Thus,
Carpenter obtained the values shown on next page
for horizontal, sloping, and vertical retorts respectively.

Since the absorption of the hydrocyanic acid, in
the wet process as detailed below, is effected pre-
vious to the absorption of the ammonia in purifying
the gas, it naturally produces changes in the per-
centage composition of the gas liquor. On this
point information is afforded by the values obtained
in comparative experiments by Linder, which show

8 COAL GAS BY-PRODUCTS

64 tp Ammonia Grms per e 3 5

S85) a & | Total. | Decom- | Stable.) ¢ QZ S

BOR] OS posable. .) x =

Horizontal | 0°17 | 3°13 | 34°68 | 2°21 | 32°47 | 40°87 | 3°84 | 0:34
Sloping ./ trace | 5°25 | 25°54) 523 | 20°31 | 36°96 | 1°95 | 0-17
Vertical .| trace | 6°21 | 17°16| 4°32 | 13°28 | 13°86 | 4:06 | 0°50

that the removal of cyanogen as a preliminary
treatment, lowers the percentage of cyanogen,
hydrocyanic acid and ammonia, but considerably
increases the proportion of sulphate. Only small
quantities of the cyanogen compounds present in
the gas are absorbed during the wet purification,
the reason being that the gas contains sufficient
carbon dioxide to prevent the formation of am-
monium cyanide. lLeybold found that 8-02 per
cent of the total hydrocyanic acid was removed in
the cooling process, and 6:55 per cent in the
scrubbers.

The main object of the dry treatment is the
removal of sulphuretted hydrogen; and it is only
of late years that importance has also been attached
to a thorough absorption of the hydrocyanic acid as
well, on recognizing the latter as being an injurious
constituent of coal gas. At the same time it con-
siderably improves the value of the spent purifying
materials, and helps to recoup the cost of purifying
the gas through the sale of the eliminated con-
_ stituents. The older methods of freeing gas from

PURIFICATION OF COAL GAS

CONSTITUENTS OF Gas Liquor: GrMs. PER LITRE.

Without Re- | With Removal
moval of the of the
Cyanogen. Cyanogen.
Ammonium ferrocyanide. 12 1:01
Chloride cal. as HCl 7°76 3°26
Carbon dioxide ‘ 25°51 20°57
Sulphuretted hydrogen 6°61 2°68
Hydrocyanic acid 0°68 0°03
Ammonia:
readily decomposable 21°76 14°68
stable . 5°76 4°47
total . 27°52 19°15
Allocation of the Sulphur:
as sulphide 72°8 per cent | 38°5 per cent
as Sulphate . 0'7 per cent | 26°9 per cent
as thiocyanate . 23-4 per cent | 22°4 per cent
as sulphite and thiosulphate 3°1 per cent | 12°2 per cent

sulphuretted hydrogen employed milk of lime, this
being afterwards replaced by dry quicklime. ‘This
- method, however, was abandoned as long ago as the
sixties and is now employed only in England. The
first effect of quicklime is to absorb the carbon
dioxide in the gas, the carbonate thus formed
then combining with the sulphuretted hydrogen to
form calcium sulphydrate. The hydrocyanic acid is_
chiefly retained in the form of calcium thiozyanate.
Laming introduced materials containing ferric oxide
as absorbents for sulphuretted hydrogen, using an
artificial preparation which still contained some
lime. Later on, however, it was found that the
material could be regenerated by exposure to air,
even without addition of lime. As already men-
tioned, considerable divergences of opinion prevailed

10 COAL GAS BY-PRODUCTS

on the subject of the absorption processes.; but since
a discussion of these views would be outside the
scope of the present work, further reference in this
connection may be confined to Berteslmann’s review
of the question.

According to the view of that authority, «the
absorption of sulphuretted hydrogen by the ferric
hydroxide of the purifying material is largely accom-
panied by the formation of iron sesquisulphide. A
portion of the ferric-hydroxide is reduced by the
conjoint action of sulphuretted hydrogen and am-
monia, so that ferric sulphide is formed, together
with free sulphur, the extent of this reduction
varying directly with the amount of ammonia
present.

‘‘'The hydrocyanic acid in the gas is not absorbed °
by materials which do not-contain ferrous oxide,
the absorption not commencing until the hydroxide
has been reduced by sulphuretted hydrogen and
ammonia.

‘*Regenerated material absorbs hydrocyanic acid,
owing to the formation of ferrous hydroxide in the
regenerative process, which hydroxide is not fully
converted into the ferric condition. The cyanogen
is contained in the purifying material as iron
cyanide compounds and ammonium thiocyanate.

‘“‘ Thiocyanogen is formed in the purifier by the
absorption of hydrocyanic acid in presence of oxygen
and ammonia, and consequently more thiocyanogen
is formed when air is added to the crude gas than
when such air is lacking. Moreover, thiocyanogen

PURIFICATION OF COAL GAS 11

compounds are formed during the regeneration of
the purifying material if the latter be rich in free
ammonia and becomes strongly heated spontaneously
in the process of regeneration.”

The absorbent capacity of various natural and
artificial materials used in gas purification is set
forth in the following Table :—

About 10-20 per cent of the total hydrocyanic
acid remains in the purified gas, chiefly because a
reaction between a solid and a gaseous bedy is here
in question. Since, in addition, about 15-25 per
cent of the cyanogen content is lost in treating the
purifying material, attempts have been made to
effect the absorption of cyanogen by the wet
method. The first step in this direction can be
traced in a process (German Patent 9409) for the
conversion of trimethylamine into hydrocyanic acid,
the methylamine being distilled by passing it through
red-hot pipes, an operation which results in the
formation of hydrocyanic acid, ammonium cyanide

ios = COAL GAS BY-PRODUCTS

and an illuminating gas. The ammonium salt is
then decomposed by passing the mixture through
dilute sulphuric acid; and the hydrocyanic acid is
absorbed by means of caustic soda or potash.

The next Patent dealing with the absorption of
hydrocyanic acid by the wet method is that of
Knublauch (Ger. Pat. 41930). This process is
based on the absorption of hydrocyanic acid by a
liquid containing an iron salt in solution, together
with alkalis and alkaline earths. When these
substances are present in certain relative pro-
portions, the carbon dioxide and_ sulphuretted
hydrogen passing through along with the gas are
absorbed to only a minimum extent, and the
quantity of iron sulphide formed in the operation
is in perfectly definite relation to the potassium
ferrocyanide and entirely independent of the carbon
dioxide and sulphuretted hydrogen traversing the
liquid. This means that, under certain conditions,
it is possible to absorb nearly the whole of the
cyanogen, without enriching the absorbent material
with carbon dioxide and sulphuretted hydrogen.

The Patent Specification, which relates to an
improved method of -recovering cyanogen~ com-
pounds, states that the gases obtained by the dry
distillation of coal, coke, brown coal, bituminous
shale, peat. or wocd, as also blast-furnace gas, are
brought into intimate contact with a liquid (water
or saline solution) containing one or more of the
substances in group A (see below), together with
one or more of those in group B, or else—given a

PURIFICATION OF COAL GAS 13

sufficiency of ammonia in the gas—one or more of
the group B substances.

Group A. Alkalis, ammonia (gas liquor), alkaline
earths, magnesia and the carbonates of the said
bases.

Group B. Iron, manganese and zinc, as also the
native or artificially prepared oxides, hydroxides,
and carbonates of these metals.

The proportions to be employed per molecule of
the cyanogen present in the gas, are approximately
1 molecule of alkali, alkaline earth (magnesia) or
their carbonates, with less than one molecule of the
metallic compounds mentioned under group B.° If
ores or metals be used, the quantity should be in-
creased in accordance with their lower activity, the
amount of alkali, is ates being still approximately
1 molecule.

The object of this process was to absorb all the
cyanogen in a soluble form ; but, owing to the readiness
with which iron oxidizes, this could not be effected
completely, small quantities of Prussian Blue being
always found in the iron sulphide sludge. The
Knublauch process never made headway in practice,
the reason probably being that the demand for
cyanogen salts was then too small. To this
inventor, however, belongs the credit of having, by
his careful researches, pointed out the way to
absorb cyanogen by the wet method. A few years
later, W. Foulis embodied a modification of the
process in his English Patent 9474/1892, according
to which the hydrocyanic acid is recovered, in the

14 COAL GAS BY-PRODUCTS

form of potassium ferrocyanide, or the correspond-
ing sodium salt, by treating ammonia-free coal gas
with freshly prepared ferric carbonate, held in
suspension in bell scrubbers. This form of scrubber
was afterwards replaced—in the same inventor's
Patent 15168/1895—by scrubbers in which the
charge was kept in motion by mechanical devices,
an arrangement more suitable for sludgy liquids.
For carrying out the process, 5 gals. of a solution
of ferrous chloride—containing about 11 lb. of
Fe per gallon—are treated with a solution of 15 lb.
of calcined soda in 30 gals. of water. After stir-
ring the whole thoroughly, the precipitate of ferrous
carbonate is allowed to subside, the supernatant
liquid being poured off and the deposit washed until
all the sodium chloride has been removed ; 27 Ib.
of calcined soda, or 35 lb. of potash, are then added,
the volume of the suspension is made up to 40 gals.
with water, and the charge is placed in the
scrubber. A report of the results obtained with the
process, in practical use, at the Hague gasworks,
was published by Rutten (‘‘ Journal of Gas Lighting,”
1902, vol. 80, p. 879) who used ferrous sulphate
instead of ferrous chloride, and employed as ab-
sorption vessel a Kirkham scrubber, the first
chamber of which was charged with heavy tar oil
for the purpose of retaining the naphthalene.
Whereas both Knublauch and Foulis prescribed the
removal of ammonia from the gas before absorbing
the hydrocyanic acid, the gas in the Hague trials
was merely freed from tar before being passed

PURIFICATION OF COAL GAS 15

through the absorbent charge. When the first
chamber was found to be saturated with hydro-
cyanic acid, it was emptied, and the liquid from the
second chamber was pumped into the first one, that
from the third into the second, and so on, the
operation being repeated as soon as the first
chamber became saturated again. The counterflow
principle was thus observed; and it was found that
the absorption of hydrocyanic acid was practically
complete. In the case of a crude gas containing,
on the average, per 100 cubic centimetres :—

Hydrocyanic acid. : ; : 185 grams
Ammonia . 3 ; ‘ ‘ é 325,
Carbon dioxide . ; : : . 4000-6000 ,,
Salphuretted hydrogen. : ; 1500 _,,

8-5 per cent of ammonia and ‘37-67 per cent of
cyanogen were found in the sludge of a slightly
oxidized preparation. Jorrissen and Rutten also
found that, in the absence of carbon dioxide, all the
cyanogen can be recovered in the soluble form, and
that the presence of ammonia does not lead to the
formation of thiocyanate. In this cyanogen sludge,
the cyanogen is present as Prussian Blue and as
potassium ferricyanide. The failure of Knublauch’s
attempts to absorb the cyanogen merely as salts in
soluble form is attributable to the presence of carbon
dioxide, on which account Bueb proceeded in such a
way as to prevent the formation of soluble salts
entirely, and to obtain the cyanogen in the sludge
only, whereas in the previous methods both the
sludge and the solution required to be treated for

16 COAL GAS BY-PRODUCTS

the preparation of cyanogen ‘salts. Bueb’s process
(Ger. Pat. 112459) is worked with a solution of
iron salts, of such high concentration that no ab-
sorption of ammonia takes place, and the amount of
iron is very large in proportion to the ammonia.
The hydrocyanic acid is thrown down as insoluble
ammonium ferrocyanide. The absorbent liquid is
prepared from a cold-saturated solution of ferrous
sulphate, containing about 280 grams of sulphate
per litre; and the apparatus consists of a horizontal
cylinder the liquid contents of which are kept in
motion by mechanical stirrers. This cylinder is set
up between the tar separator and the ammonia
scrubbers, and consists of several chambers, the first
two of which are used for absorbing naphthalene by
means of a.charge of heavy tar oil containing up to.
about 3 per cent of benzol. The next four
chambers are filled one-third full with the cold-
saturated solution of ferrous sulphate. In order to —
present a maximum wetting surface to the gas, a
shaft passing horizontally through the cylinder is
provided with wood faggots in the. naphthalene
chambers and sheet metal discs in the cyanogen
absorption chambers. The shaft is set in, rotation
by a worm and worm-wheel gear. The gas passes
first of-all through the chambers charged with
heavy tar oil, where the naphthalene is retained :
and from these it enters the cyanogen absorption
chambers. ‘The scrubbing liquid does not flow
through these chambers continuously, but is station-
ary. After the liquid in the first chamber is

PURIFICATION OF COAL GAS 17

completely saturated with hydrocyanic acid—which
takes about nine hours in large plants—it is run out,
the liquid from the second chamber being pumped
in in its place, whilst the liquid in each of the other
chambers is advanced a stage, and the final cham-
ber is recharged with fresh liquid. The method of
working is therefore exactly the same as in the
Foulis process. The absorption of the cyanogen is
based on the following reactions.

The ammonia decomposes the sulphate into
hydroxide, sulphate of ammonia beng formed :—

(1) FeSO, + 2NH, + 2H,O = Fe(OH), + (NH,),80,

Sulphuretted hydrogen acts on the hydroxide,
ferro1s sulphide being formed :-—

(2) Fe(OH), + H,S = FeS + 2H,0.

In presence of ammonia and hydrocyanic acid,
the ferrous sulphide is converted into ferrous cyanide,
ammonium ferricyanide being also formed.

(3) FeS + 2NH, + 2HCN = Fe(ON), + (NH,),S.
(4) 2FeS + 6NH, + 6HCN =
(NH,),Fe,(CN), + 2(NH,),S.

Both these cyanogen compounds are insoluble
in water and are precipitated as sludge. If, how-
ever, they are allowed to remain in prolonged con-
tact with the liquid, they are gradually converted,
by the further action of hydrocyanic acid, into
soluble ammonium ferrocyanide, according to the
equations :—

18 COAL GAS BY-PRODUCTS

(5) Fe(CN), + 4HCN + 4NH, = (NH)),Fe(CN),
and :—

(6) (NH,),Fe,(CN), + 6NH, + 6HCN =
2(NH,),Fe(CN),.

As is evident from these reactions, the Bueb
process also furnishes small quantities of cyanogen
in a soluble form in practice. The sludge obtained
is dark brown to black in colour and contains an
amount of cyanogen equivalent to 18-20 per cent
of potassium ferrocyanide. According to the re-
searches of Hand, Ost, and Kirchten, the insoluble
salt has the formula: (NH,) He[ Fe(CN), i. The
ammonia present in the sludge is partly combined
with iron cyanide and partly as sulphate, and
amounts to about 5-7 per cent. Owing to the im-
possibility of entirely excluding oxygen, a small
quantity of thiocyanate is also formed, according to
the equation :—

2NH, + 2H,8 + O = (NH))S + H,O+ 5.
(NH,),5 5 S = (NH,).8,
(NH,),S, + NH, + HCN = (NH,)CNS + (NH,),S.

The free sulphur is deposited from the. ferrous
sulphide and water in presence of air. Feld has
confirmed that the formation of thiocyanate takes
place chiefly in the chamber nearest to the gas
outlet, and that there is very little further increase
when the liquid is transferred to the penultimate
chamber.

A combined system of cyanogen absorption, anal-

PURIFICATION OF COAL’ GAS | 19

ogous In some respects to the Solvay soda process,
has been developed from the Foulis and Buéb pro-
cesses by Feld. According to his German Patent
151820, he uses as the absorbent liquid a saline
solution, the oxides, hydroxides, sulphides or car-
bonates in which are capable of displacing ammonia.
To these solutions he adds sufficient ferrous salt- to
ensure that for each atom of iron present the
liquid will contain at least 4 atoms of a monovalent.
salt or 2 atoms of a divalent salt. The gas must
be rich in ammonia, and when this is not the case
an ammoniacal saline solution is used. This pro- -
cess is intended to prevent the formation of thio-
cyanogen entirely. The ammonia and carbon
dioxide of the flowing gas transform the salt into
the carbonate, and this reacts with the ferrous
hydroxide and cyanogen to form ferrocyanides. In
carrying out the process in practice, use 1s made of
the Buéb ammonium cyanide washer, into which
the gas enriched with ammonia is passed. The
process was formerly used at the Billwarder gas-
works, in Hamburg, but as it has now been discon-
tinued in practice, there is no need to describe it
further.

Up to the present no practical process has been
evolved for the absorption of the cyanogen as
cyanide, though Feld patented a process of this
kind (Ger. Pat. 141626). The gas, freed from tar,
is passed through hot solutions of compounds of
iron, manganese or lead, to remove the sulphuretted
hydrogen, the carbon dioxide having been previously

20 COAL GAS BY-PRODUCTS

absorbed by a hot solution of basic magnesium salt.
The cyanogen is next absorbed in a cold, neutral or
basic carbonate solution, or by hydroxides or oxides
of magnesium, zinc, aluminium, manganese or lead,
the hydrocyanic acid being liberated from the solu-
tion by distillation, and absorbed in the form of any
cyanide. No practical experience with this process
is at present available.

The last method of cyanide absorption by the
wet process that need be mentioned consists in
converting it into thiocyanogen. However, since
the thiocyanogen compounds are far less valuable
than those of cyanogen, this method is of interest
only to gasworks which have to deal with coals very
high in sulphur, for which reason it has found ap-
plication in some English gasworks. It is based
on the conversion of the cyanogen into thiocyanogen
by means of polysulphides in presence of ammonia.
With this object the gas is washed with an aqueous
suspension of flowers of sulphur (10 per cent by
weight). The following reactions take place :—

(NH,),8 + 8 = (NH),S,.
(NH,),8, + NH, + HCN = NH,CNS + (NH,,S.

Up to 90 per cent of the cyanogen is absorbed
as thiocyanogen; but the presence of large quan-
tities of carbon dioxide is said to have an adverse
effect. Patents for processes of this kind have been
taken out by: Smith, Gidde, Salomon and Albright
(Eng. Pat. 138653/1901); Carpenter (HKng. Pat.
22710/1902), and the British Cyanides Co. Lim.
(Ger. Pat. 136367).

PURIFICATION OF COAL GAS 21

An attempt has been made, in the foregoing, to
give an idea of the manner and the chemical con-
dition in which the originating materials for the
by-products of gas-making are obtained. These
by-products are: coke, retort graphite, ammonia,
sulphate of ammonia, sulphur, ferrocyanic acid and
thiocyanic acid.

CHAPTER II.
COKE.

CokE is the first product obtained in the retorts as
the distillation residue from coal. In large gas-
works, the retorts are emptied by mechanical ap-
pliances, and the glowing coke is removed by belt
conveyers, which pass through water in order to
quench same. In small works’ it is wheeled in
barrows to a large heap where the quenching is
performed.

Gas coke forms a porous mass, ranging from silver
grey to a dark colour. It is very brittle and hard.
Its chemical composition has not yet been identified.
It does not, however, form ‘a mixture of pure car-
bon and ash constituents—the non-volatile mineral
constituents of the coal—but is a mixture of
high-molecular compounds of carbon with hydrogen,
nitrogen, oxygen and sulphur. Apart from the ash,
the composition naturally differs according to the
kind of coal; and it also depends on the coking
temperature employed, the proportion of carbon in-
creasing with the temperature. ‘The porosity de- |
pends on the method of distillation, that is to say,
on the position of the retorts. Thus, as a rule,
| (22)

COKE 23

vertical retorts furnish the densest coke, because in
these it sinters together more, under the influence
of its own weight. The range of percentage of the
various constituents of gas coke, referred to dry and
ash-free matter, are as follows :—

Carbon. ; ; ‘ . 92°70-96°09 per cent.
Hydrogen ; ‘ ‘ . 0°60-1°22 rs

Oxygen ; ; 0:29-3°60 < e
Nitrogen . ; : : si FOL-1-70 aD
Sulphur . _ : ‘es, OSB=E62 + 5,

Heating value . ; : . 7708-8022 cal.

The ash content fluctuates considerably, and
ranges between 3:72 and 11-60 per cent. The
above figures are taken from a Table compiled by
Bunte from samples of coke from the gasworks of
Berlin, Hamburg, Breslau and Munich, in 1897.

The examination of coke is directed to its fragil-
ity, the determination of the volatile constituents,
sulphur, ash, and, above all, the heating value.

The test for ascertaining the fragility of coke is
applied in the following manner: One portion of the
sample is separated by sifting, and the remainder
is dropped from a certain height on to a paved floor,
and then sifted again. The amount of the screen-
ings gives an idea of the fragility of the coke.

The determination of the ash, volatile matters and
sulphur need not be gone into here, since it does not
present any special features.

The heating value may be determined by means
of empirical formule or by accurate experimental
examination. Dulong ascertains the heating value

24 COAL GAS BY-PRODUCTS

from the chemical composition by means of the
formula :-—

H = 81C + 290 (H, - 0/8) + 258 - 6W.

in ie H represents the heating value in calories
per kilogram; C is the percentage of carbon in
the substance; H, the percentage of hydrogen; O
the percentage of oxygen, § that of sulphur, and W
the percentage of moisture present, both originally
and as produced by the combustion of the sample.
The recognized method of determining heating
values is by means of.the calorimeter, which is a
steel bomb filled with oxygen under pressure.
The substance under examination is powdered, and
compressed into a tablet, in which an iron wire, of
known carbon content, or one of platinum, is em-
bedded at the same time. This wire is raised to
incandescence by the aid of an electric current, and
thus ignites the tablet which has been placed in-
side the bomb. The heat thus liberated is trans-
mitted to water in which the bomb is immersed:
and the rise in the temperature of the water forms
a measure of the heating value of the substance.
The water is kept in constant motion to ensure a
uniform distribution of the heat ; and the whole ap-
paratus is placed in a second vessel containing water,
in order to protect it from the influence of external
heat. However, since the heat is transmitted to all
parts of the apparatus and not merely to the water
alone, it is necessary to take into consideration the
‘‘ water value,” as regards heat, of such parts. If

COKE 25

the water value of the vessel be taken as X, and the
weighed quantity of water be represented by Y, the
correction for radiation—according to the formula of
Ostwald—being set down as Z, the initial water
temperature as 'T, and the maximum temperature of
the water during the experiment as T,, then the
heating value, expressed as heat units (calories), will
be: Cal. = Y (X + Y) (T, - T, + Z,). From this
result there must be deducted the heat generated
by the iron wire and the nitrogen; and since the
heating value is referred to 1 kilo. of substance, this
value must be recalculated accordingly. Moreover,
the evaporation value of the water of combustion
must be deducted, for which purpose the quantity
of the water of combustion must be determined— |
which can be effected in the same experiment, the
bomb being constructed in such a way that the con-
tents can be completely emptied out and collected
after the combustion process. The water produced
is retained by a calcium chloride tube, and the carbon
dioxide by a potash apparatus arranged in succession
to said tube. With this object the bomb is heated to
105-110° C., and, after the pressure has become
equalized, dried air is passed through it for a short
time. The increase in weight ofthe calcium chloride
tube gives the weight of the water of combustion
formed ; and for every kilogram of water of combus-
tion, 606-6 cal. must be deducted from the heating
value found by the formula.

The coke coming from the retorts is not homo-
geneous in character, and is in lumps of different

26 COAL GAS BY-PRODUCTS

sizes. In order to obtain a product of uniform ap-
pearance, the large lumps are broken, either by hand
or,more generally, in coke-breaking machines after
the style of that illustrated in Fig, 1. This machine
consists of a shaft provided with interchangeable
teeth or cutters to which the coke is fed down an
inclined plate, which also forms an abutment. The
broken coke is passed over mechanically operated
screens of different mesh, and is thus classified at
once into various sizes. The coke fines (frag-
ments below 4-inch diameter) can be worked up in
a briquetting machine,

The ash from the fuel used in heating the retorts
also contains unconsumed particles of coke, which can
be separated by hand, and constitute the so-called
«coke breeze,” which forms an inferior, cheap
gerade of coke, of about one-third the value of gas
coke.

There is no need to dilate upon the use of coke as
a heating agent, but a good deal is consumed by the
gasworks themselves as fuel, particularly for charg-
ing the producers, |

In the gasworks of large towns the consumption of
gas varies considerably at different times of the day,
but increases very quickly at short intervals towards
evening, and this increased consumption cannot be
met at once by the retorts alone. It may, however,
be dealt with quickly by mixing the coal gas with
water gas, the output of which can be regulated more
easily, Another important factor in the case of water
_ gas is the amount of floor space required, it being

COKE 27

possible to produce more than five times as much
water gas with a plant occupying only one-third the

Fig 1.—Coke breaker.

floor space required by the retorts used in making
coal gas.

28 COAL GAS BY-PRODUCTS

Water gas is made by passing steam through
glowing coke; but though the process dates back
about a century, it is only within the last few de-
cades that a usable product has been obtainable.
If the charge of coke be heated to about 500° C.,
hydrogen and carbon dioxide are formed when the
steam is blown in; whereas if the temperature of
the coke be raised above 1000° C., the carbon dioxide
formed is reduced to monoxide in passing through
the upper layers of glowing coke. There are, conse-
quently, two processes for making water gas; the
carbon monoxide process, which furnishes a fuel gas,
and the carbon dioxide process.

Thus, at 500°C., the reaction is:

C+ 2H,O = 2H, + CO,,
whilst at 1000° C. it is:
C+ CO, +2H, ~2C0O+ 2H,.

In practice the process is carried out on the follow-
ing general lines. Coke is ignited in a retort and
raised to incandescence by means of a bottom blast.
The air is then shut off, and steam is forced through
the glowing coke, by which it is decomposed into
hydrogen and oxygen. So soon as the temperature
again falls below 1000°, or 500°, the coke is raised
to incandescence once more by restarting the blast.
These two operations are known respectively as
“blowing” and “ gasifying ”’.

Schafer gives the following as the eee (by
volume) of a water gas :—

COKE 29

Hydrogen... ‘ : . . 50 per cent
Carbon monoxide . ; : : . A” -
Carbon dioxide : ; : Pe. “a
Nitrogen ; ; : : : . 36 =
Oxygen . ; i ; 1 mR

The heat of combustion of such a water gas
amounts to about 2500 cal. and its heating value is
about 12 per cent lower than that of coal gas.

CHAPTER. II.
RETORT GRAPHITE.

ReEToRT graphite or retort residue is formed by the
decomposition of the hydrocarbons produced in the
distillation of coal in the retorts, a portion of the
gases being decomposed into their constituent ele-
ments by the high temperature. The carbon formed
in this way is also deposited on the firebrick walls,
and furnishes a hard mass which resembles graphite
‘and will even give out sparks when struck by a piece
of steel. This graphite is a very bad conductor of
heat, and therefore has to be taken out of the retorts at
intervals of four or five months. The thickness of the
deposit is sometimes considerable, that from English
coals being not infrequently 24-3 ins. thick. The
mass is cleared away either by purely mechanical
means or by burning, the latter being generally pre-
ferred, because the extreme hardness of the deposit
renders the material of the retorts liable to injury
when mechanical means are employed. ‘To burn
out the graphite, half-moon bricks are placed in the
hot, empty retorts, so as to form troughs, the open-
ings in which are closed, together with the retort
heads, whilst the cap of the upcast pipe is opened.
| (30)

RETORT GRAPHITE 31

The air flowing through the retorts then burns the
deposit and loosens its hold on the walls, which
operation takes from four to sixteen hours. When
cold the loosened graphite can be seme y removed
by mechanical means.

The specific gravity of retort graphite varies be-
tween 1-72 and 2-35 according to the pressure
which has prevailed in the retorts. The degree of
hardness also varies considerably. The ash content
is about 2-5 per cent.

Bunsen proposed to use retort graphite for carbon
electrodes for electrical purposes, and thus opened
up a large market for the article. In fact practic-
ally all carbon electrodes and rods are made of retort
sraphite. The raw material, however, is not per-
fectly homogeneous, and the shape of the retorts is
adverse to the production of any but comparatively
small plates androds. On this account, and because
the direct treatment of the raw material would give .
rise to a good deal of waste, the crude graphite is
first hand-picked and cleaned, and is then ground
down to a coarse powder. This is next worked up
into a plastic mass, along with lampblack and coal
tar, In a mixer, and from this mass the carbon rods
are shaped in hydraulic presses under a pressure of
several hundred atmospheres, the plates being treated
in a similar manner. The resulting mass, however,
has not yet attained its full strength, which is im-
parted by baking in circular kilns similar to those used
in brickmaking, The heat of the kiln decomposes the
coal tar, and the resulting graphitic carbon binds

32 COAL GAS BY-PRODUCTS

the grains of the retort graphite together. The
product is used for the carbon rods of are lamps,
chiefly on account of its very low combustibility,
Most of the works engaged in the manufacture of
electric carbons are situated in the district round
Nuremberg, though the largest firm, Gebr. Siemens
& Co., is in Berlin. |

CHAPTER IV.
GAS TAR.

THE third product met with between the retort and
the gas holder and having to be extracted from the
gas, is tar. This tar is deposited in three chief
places; the hydraulic main, the air condenser and the
water-cooled condenser, a portion of the gas liquor
also separating out at the same time. On this
account, the gas tar and gas liquor, together with
that from the scrubbers, are collected in one pit,
where their different density causes them to separ-
ate into two layers, the specifically heavier tar
being at the bottom. By means of a siphon, which
reaches down to the bottom of the pit, the tar is
drawn off from the supernatant liquor and is then
pumped up into a high-level tank.

A full description of the treatment of this tar is
beyond the scope of the present work ; and it need
only be mentioned that the entire dyestuff industry
employs gas tar as the raw material for the preparation
of all the crude products of that industry. All that
will be dealt with here is the direct utilization of the
crude tar, and its fractional distillation into light,
medium and heavy oils, anthracene oil and pitch.

(33) 3

34 COAL GAS BY-PRODUCTS

The yield of tar obtained in gasworks depends on
the origin and character of the coal, and ranges (see
Table below) between 4 and 8 per cent, coals rich in
oxygen usually furnishing the highest tar output.
The following data were compiled by Bunte as the
result of a large number of experiments :—

Origin of Coal. Retort Temperature. st pa of "Gis Liteon f
Wesphalia . ‘ 1360-1385°.C. 4:09 4°44
Saar district -| . 1205-1290° C. 5°33 6:90
Bohemia . : 1240-1350° C. 5:79 9°06
Zwickau. 1180-1240° C. 5°22 11°86
Bohemian cannel 1180-1350° C. 8°81 6°45

Gas tar is a thick, deep-black greasy liquid, but is
not a homogeneous substance, being a mixture of
highly divergent hydrocarbon compounds. In ad-
dition to water it contains hydrocarbons of the
methane, ethylene and acetylene series; naphthy-
lenes; terpenes; naphthenes; aromatic hydrocar-
bons of the benzol, naphthalene and anthracene
homologue series; phenols; aromatic acids and
sulphur compounds; basic and non-basic aromatic
nitro-compounds and free carbon.

Kramer has found samples of German gas tar to
contain :—

Benzol and its homologues, CnH.n- 5 . «. 2°50 per cent.
Phenol and its homologues, CnHon — ,;OH po PO yy ee
Pyridin and chinolin bases, — - N ; Sared p> Wer obep et:

Naphthalene, CpHon - 32 .« i ; . 6:00

93 bP]

GAS TAR 35
— oils, CpHn ss. : ; . 20°00 per cent.
Anthracene, phenanthrene, On Hoe - og} | Sen aie
Asphaltum (soluble constituents of the pitch),
ConHn S000 35 (ss
Carbonaceous matter (insoluble. constituents of
the pitch), C.nHn =. : : ‘ 7 OR de
Water : 3 ; ; nt QO es te
Gas (loss on distillation) . : : 4 AEDES es Se aes

This Table is merely intended to give an approxi-
mate idea of the relative proportions of the various

constituents of gas tar.

The tar from coal distilled in vertical retorts is
richer in light oils, and is also more fluid. The in-
fluence of the retort arrangement on the various
fractions of the tar is shown by the results obtained
by Buéb with New Leverson and Leverson Walls- -

end Coals :—
Tar from Vertical | Tar from Horizontal

Retorts. Retorts.
Water . ‘ - 2-7 3°50
Light oil ‘ a 5°85 3°10
Medium oil . : 12-32 7°68
Heavy oil . 11°95 10°15
Anthracene oil . 15-96 11°54
Pitch . : 49°75 62 00
Loss in distillation 2-00 2°03

In the examination of tars obtained by distill-
ing coal in vertical and slanting retorts, Karting
obtained the following values for the several frac-

tions :—

36 COAL GAS BY-PRODUCTS

Temperature. From Vertical Retorts. From Slanting Retorts.

per cent : per cent
0-100° C. 8°8 of oil, 5°7 of water | 10 of oil, 0°85 of water

100-170° C. Re — Sikes & Geeta § a
170-230° C. | 13°5 ,, — 30°97 >=, —-
230-270° C. Yi ae — a eee —
Over 270° ©. | 29°38 __,, — 18°80 _,, —
- Residue 34:1 5 — 58°13 ,, —

According to the use for which it is intended, the
tar is examined for water content, percentage of
ash, heating value, specific gravity and carbon con-
tent. Gas tar itself is not a homogeneous substance,
a whole series of bodies separating out, in accord-
ance with their specific gravity, especially on pro-
longed standing.

For this reason, it is essential to employ great
care in obtaining a good average sample for the
purpose of judging the value of a tar. The best
method of sampling is to mix the tar in the vessel
by blowing air through it, and then taking samples
from different places. Ahrens and Senger recom-
mend, as an efficient tar sampling device, a tube
which is long enough to reach to the bottom of the
tar vessel, and is traversed by a rod provided on its
lower end with a conical or flat valve member, so
that the sampler can be closed by a pull on the rod.
In taking samples, the tube, in the open condition,
is worked slowly down as far as the bottom of the
vessel, and is then closed at its lower end by pulling
on the rod. In this way a complete sample of the
several layers of tar in the vessel is obtained. By

GAS TAR 37

repeating the operation in different parts of the
vessel an average sample is obtained.

For determining the percentage of water, Mai-
wald recommends distilling 100 grms. of the tar in
a copper still, capable of holding 200 grms. and con-
nected to a Liebig condenser, 50 grms. of benzol
being added to the tar to prevent it from frothing up
and boiling over, By the time the still temperature
attains 190° C. all the water will have passed over.
The distillate is collected in a measuring cylinder,
in which the layer of oil separates from the water, so
that the percentage amount of the latter can be read
off direct. Merchantable tar should not contain
more than 4 per cent of water; and if found to
have more than this amount, an allowance-should be
claimed on account of the unnecessarily increased
cost of carriage.

According to Senger, 500 grms. should be distilled
ina 1 litre copper still, without addition of benzol, the
frothing of the tar being prevented by the applica-
tion of heat from above, by means of a ring burner
arranged under the upper rim of the still. Con-
ducted in this way the operation requires no super-
vision, and is completed in about three or four hours.
In the Maiwald method the distillation is finished in
half an hour.

The heating value is determined by means of
the Berthelot bomb, in the same way as for coal.
According to Allner, it is advisable to soak the tar
up in cellulose cubes, in order to obtain complete
combustion of the carbon, the heat of combustion of

38 COAL GAS BY-PRODUCTS

the added material being determined beforehand and
deducted. from the result furnished by the calcula-
tion. Bertelsmann, however, has found no difficulty
in effecting the direct combustion of the tar.

The specific gravity is determined by the method
of Lunge. A small weighing glass is used .as
pyknometer, and a notch, about 2 mm. wide and of
the same depth, is filed in the edge. The following
_ weighings have to be performed :—

The tare weight of the vessel = a,

The weight of the vessel filled with water at 15°
C.=0;

The Hesacee of the vessel filled about two-thirds
full of tar = ¢ ;

The weight of the vessel now filled up completely
with water = q.

C —*&

b+c- (a+ dad)

Before making this determination, it is necessary,
of course, that the tar should be freed from water.
This can be effected by leaving the tar to stand in
a covered glass beaker for about twenty-four hours
at 40° C., under which conditions the tar and’ water
separate from each other. The supernatant water
is then poured off, the final traces being soaked up
with filter paper.

In determining the value of c, the vessel should
be allowed to stand in hot water for some consider-
able time, to expel all air bubbles from the tar.

For determining the carbon content, Kohler pre-

Then : Sp. gr. =

GAS TAR 39

scribes heating 10 grms. of the tar with a mixture of
25 grms. each of glacial acetic acid and toluol for
some time, and then passing the whole through a
tared filter, the residue being washed with benzol
until the washings are free from colouring matter.
The carbon remains on the filter and is determined
by weighing.

Kramer and Spilker warm 1 part of tar with 3 of
aniline, and pour the mixture on to a plate of unglazed
earthenware, which absorbs: the liquid constituents of
the tar. The residual carbon is then transferred to
a tared watch glass by means of a spatula and
weighed.

For the determination of the various fractions in
tar, Kramer and Spilker recommend a method
adopted directly from practical working on the large
scale, 5 kilos. of the tar under examination being
placed in a cast-iron still, holding about 8 kilos., and
distilled in a partial vacuum, the fractions being
collected at definite intervals of time.

The ash content is ascertained by warming | grm.
of tar in a platinum dish, then igniting it, and when
the flame has subsided, heating the residue in a
muffle until of constant weight. The ash seldom
exceeds about 0:05 grm.

As already mentioned, the tar collected in the tar
tanks still contains a large amount of water, from which
it must be separated. According to the method of the
Deutsche Continental Gas Gesellschaft (Ger. Pat.
191342/1907), the mixed tar and water is allowed
to flow down an incline of 45° in a thin stratum.

40 COAL GAS BY PRODUCTS

During this operation the tar and. water separate,
the tar collecting in a pit at the bottom of the slope,
whilst the water floats on the surface. Schlosser’s
tar-separator is based on the same principle, the tar
being allowed to flow over the edge of a high-level
‘ tank on to a vertical corrugated plate, below which
is a collecting tank in which the tar and water form
separate strata.

Another method, frequently employed in large
gasworks and tar distilleries, consists in the applica-
tion of centrifugal force. Burmeister and Wain
proposed to use a centrifugal tar separator con-
structed on the same principle as the milk separator.
The drum is run at a speed of about 2000 revolu-
tions per minute, and the tar, which is fed into it as
a continuous stream, at a temperature of about 30-
40° C, (86-104° F.) separates from the water, which
rises to the top, inside the tar, and is retained in the
central space of the drum by a partition, over which
the tar flows outward,. the two ee ae being thus
forced apart.

One very simple method consists in merely warm-
ing the tar, in which case the temperature should not
exceed 50° C. (122° F.),in order to prevent loss. In
this state of increased fluidity a separation of the tar
and water takes place automatically.

According to Klénne (Ger. Pat. 196240/1906),
tar can be freed from water by forcing it between
rollers, which are heated if necessary, this treatment .
freeing the imprisoned particles of water from the
adherent tar by pressure and friction.

GAS TAR 41

The Weil method (Ger. Pat. 217659 and 218780/
1908) is performed in a partial vacuum. The tar
flows, as a continuous current, round a system of
pipes heated by waste gases. ‘To prevent loss of
readily volatile constituents, a condenser and washer
for their absorption are arranged in the rear of the
vacuum pump.

In a large number of systems the device for re-
moving the water from the tar is placed in direct
connection with the distillation apparatus. A method
of this kind is that patented by the Riitgerswerke
A. G. (Ger. Pat. 161524/1904) in which, by the
application of heat from above downwards, the float-
ing water is got rid of first, then that emulsified with
the tar, and finally the chemically combined water.
The flue gases from the retorts are utilized as the
heating agent.

The crude tar obtained in this way is used for
painting cast-iron articles, for making lampblack and
for roofing-felt. For application to metal surfaces
the tar is made fluid by heat, and then laid on the
- metal direct, producing a lustrous and durable black .
coating. This paint is used on cast-iron pipes. in-
tended to be exposed to corrosive vapours, for ex-
ample in chemical works. Kuhlmann also recom-
mends gas tar as an acid-resisting paint for stone
and brickwork; but it is not much used as a preser-
vative for wood. One of the most important direct
applications of gas tar is in the manufacture of roof-
ing felt. This is a very simple process, the mill-
board or felt being boiled in water-free tar or passed

42 GOAL GAS BY-PRODUCTS

continuously through hot tar solutions, whilst the
surplus tar is removed by pressing the material be-
tween rollers. It is more economical to carry on
the work in closed cylinders, instead of open pans,
in order that the readily volatile constituents may be.
recovered by condensation. The crude tar may also
be replaced by a mixture of tar pitch and heavy oil,
in which case the roofing felt will have to be fre-
quently recoated with the same preparation during
the first few years it is in use.

Crude gas tar is also used for making lampblack ;
but a better product can be obtained from the heavy
oil. Of late years, tar has also found advantageous
employment for dressing the surface of highways, in
order to render them dustless and more durable.

Crude tar, from which the constituents boiling up
to 150° C. have been distilled off, is made into arti-
ficial stone (Dérrite stone) with dried and crushed
gravel, furnishing a product characterized by great
hardness and strength.

The possibility of producing an illuminating gas
by passing coal tar through red-hot pipes has not
found any practical application; but, on the other
hand, this tar is utilized as fuel, having a heating
value of about 8500 cal. The tar flows through a
nozzle to the burner and is forced into the combus-
tion chamber by a mixture of steam and air.

As already mentioned in the introductory chapter,
gas tar is likewise used for absorbing gases; and it
also serves to absorb naphthalene in naphthalene
and cyanogen washers.

GAS TAR 43

The bulk of the tar, however, is distilled, for the
purpose of fractionating it into the four grades:
light oil, medium oil, heavy oil and anthracene oil,
pitch being left behind in the retorts as residue.
The relative yield under the same treatment na-
turally differs with tars of divergent origin. The
following percentage values are given by Kramer
and Spilker for the yields obtained in distilling the
gas tar from: (1) Upper and Lower Silesian gas
coals; (2) Zwickau coal, with addition of paraffin
coal; (8) English coal; (4) Saar gas coal, with
addition of paraffin coal :-—

;
Retort : Light | Medium | Heavy | Anthracene Total
Pitch. | Water. Oil.

No. | Oil. Oil. Oil. Distillate.
1 | 551 | 8-0 24 | 12:0 92 | 18:0 41°3
| 592 | 49 25 | 129 | 11°2 15-2 41°8
3 | 599 | 3-1 3-4 |. O4 7-0 17-0 36-7
4°) Od 24 Be 1108. | 86} 184 35:3

The first runnings, which distil over between 9
and 100° C., contain water and volatile gases-—_the
light hydrocarbons absorbed by the tar, and also
sulphuretted hydrogen, ammonia and carbon dioxide.

The lhght oil comes over between 100 and 180° C.
It contains phenols, bases, sulphur compounds,
nitriles, neutral oxygen compounds, olefines, paraf-
fins, unsaturated and cyclic compounds, and aro-
matic hydrocarbons. The medium oil, which distils
over between 180 and 240° C., consists chiefly of
naphthalene and phenols. The next distillation

44 COAL GAS BY-PRODUCTS

product, the heavy oil, comes over up to 300° C.,
and, in addition to naphthalene, consists mainly of
creosote oils. Anthracene oil, the final distillate,
comes over at temperatures up to 400° C., and
contains crude anthracene, which is solid at the
ordinary temperature. The filtrate from this de-
posit is redistilled and furnishes an additional
quantity of crude anthracene, together with carbo-
lineum, which latter is used as a preservative for
timber. The pitch forming the residue in the still,
is a product of varying consistence and is composed
of carbon compounds of unknown composition,
mixed with carbon.

The apparatus used for tar distilling varies con-
siderably in appearance, but not greatly in principle.
A distinction may be drawn between three main
systems of distillation : with direct fire heat or flue
gases; with indirect steam; and vacuum distilla-
tion. Recently, continuous distillation has also
come into favour.

The water-free tar is distilled in iron stills, pre-
ferably of wrought iron, which material is more
easily workable than cast iron and is also able to
withstand greater fluctuations of temperature. The
more general use of cast iron is, moreover, precluded
owing to the narrow limits of size possible with this
material; though wrought iron is more lable to
suffer from the heat. In order to protect the still
from direct contact with the heating flame, a pro-
tective casing is provided under the still bottom, so
that only the hot gases come in contact with the

GAS TAR 45

apparatus, which is, therefore, to some extent, in a
kind of air bath. The flues must be arranged in
such a manner that, during the whole of the dis-
tillation process, down to the pitch—which, it is
true, occupies about two-thirds the total volume of
the tar-—the heating gases only come in contact
with those parts of the still which are filled with
liquid.

Tar stills differ considerably in shape, both
vertical cylinders, as high as they are wide, and
horizontal cylinders, being used. In the case of
upright cylinders the bottom is domed (concave)
and the upper end is of similar shape, this latter
being provided with an outlet for the liberated ,
gases. ‘The reason for using a domed bottom in-
stead of a flat one is that the former is able to give
better under the influence of the high and con-
siderably fluctuating temperature, whereas a flat
bottom would soon get out of shape and make the
complete removal of the pitch from the still a
difficult matter. Very often the still is made in
one piece, in which case the dome at the top is pro-
vided with a manhole for charging and cleaning out
the still. In another form of still the whole dome
is detachable, and the flanged joints have to be re-
packed every time a fresh charged is distilled. The
best packing material is asbestos. In the case of
horizontal stills, the question of distortion does not
have to be considered. A cock for drawing off the
pitch is provided at the deepest point of the still,
which is usually set on the brickwork so ‘as to have

46 COAL GAS BY PRODUCTS

a slight tilt. Internally, the still is provided with
stirring mechanism—adapted to the shape of the
still—in order to facilitate uniform heating of the
liquid, and also to prevent the charge burning on to
the still walls; but these stirrers are not set to
work until the higher distillation temperatures are
reached and the residual charge has become very
thick. A better method of keeping the charge in
motion is by blowing in dry, superheated steam,
because this facilitates distillation at the same time.
In place of vertical stills, the horizontal pattern is
used, especially in Scotland, the cylinders being
about 21 ft. in length and 8 ft. in diameter. The
.still is protected from direct contact with the fire
by an arch, the flame passing through about twenty
openings in the sides into flues which surround the
cylinder up to about its middle line. The stirring
mechanism used consists of a shaft carrying horizon-
tal rods, on the ends of which are attached short
chains which scrape along the bottom of the still,
in alternate positions, so that one chain scrapes
along a part which has been left untouched by the
preceding one. In large works a still charge is
about 20 tons, but in smaller works, 12- ten stills
are used. Though the larger sizes are the more
economical in working, it is not desirable to go above
a capacity of 18-22 tons, since this quantity can be
finished off in about twelve to fourteen hours, whereas
larger charges require night shifts. The heavy oil
and anthracene oil are mostly distilled by the aid of
steam and a partial vacuum.

GAS TAR 47

In all the foregoing stills the tar must first be
freed from water before distilling; but latterly
methods have arisen in which the heat produced
during distillation is utilized for removing the water
from the crude tar at the same time. ‘Thus,
Respier drys the tar in a column still, of exactly
the same type as that for distilling ammonia liquor
(q.v.) and mounted on the cover of the dehydrating
retort. The tar is run into the column through an
intermediate member situated between the three
lower and the two upper chambers. The gaseous
distillates, water and light oil issue through a pipe
connection mounted on the cover, and pass away to
a condenser. In addition to this continuous. dehy-
drating retort, are three stills for the separation of
medium, heavy and anthracene oil respectively.
The method of working is as follows: In starting
operations, crude tar is slowly heated to about
200° C. in the dehydrating retort; and the disen-
gaged gases flow through the column. Crude tar
enters through a lateral pipe and is heated by the
exhaust gases so that the bulk of its contained water
and light oil are expelled, this tar then passing into
the retort, where the final traces of this fraction
are distilled off. The dehydrated tar is drawn off,
at a rate corresponding to the rate of feed, into a
storage tank, whence it is passed into one of the
other retorts, for fractional distillation into medium,
heavy and anthracene oil. The distillation of these
fractions is carried on in vacuo, and proceeds in a
very simple and rapid manner. The dehydrating

48 COAL GAS BY-PRODUCTS

retort dries sufficient tar daily for two or three 18-
ton stills, and the whole operation is performed in
about ten to twelve hours,

In another method, according to Biapie: the gases
issuing from the still are cooled by crude tar, the
heat thus transferred serving at the same time to
free the crude tar from water and light oil. The
apparatus is arranged in the following manner: A
completely closed, rectangular iron tank is fitted up
with a coil, composed of straight pipes with short
bends, which coil is traversed by the still gases.
Over this coil is a pipe bent to the same shape, but
perforated ; and through this pipe the crude tar flows
in a thin stream on to the heated coil, and parts
with its water and light oil, which escape to the con-
denser through a connection in the cover of the tank.
The dehydrated tar, on the other hand, collects in
the bottom and runs off through a connection to the
still. 'The mouth of this outlet is closed by a bell
seal, to prevent any vapours being carried along by
the tar. The medium and heavy oils are distilled by
fire heat: but in distilling off the anthracene oil, a
partial vacuum is used, and superheated steam is
forced through the mass.

The prevention of the risk of fire in tar distilling
is the subject of a process patented by Opitz and
Klotz (Ger. Pat. 188,635/1906), in which super-
heated water is employed as heat transmitter. An
endless coil is arranged so that one portion is situ-
ated in a heating stove and the remainder inside the
still. The hot water ascends through the coil, gives

GAS TAR 49

up its heat in the still and flows back, in a cooled
state, to the heater. Unless the heater is under-
neath the still a pump has to be connected up with
the coil so as to keep the water in proper circulation
and utilize its heat effectually, For complete dis-
tillation it is necessary that the water should be
raised to a temperature of 400° C., a result which
is possible of attainment, since, by increasing the
pressure, the critical temperature of water can be
raised without converting it into steam. With this
object the coil, which is made of special steel tubing,
must be tested to stand a pressure of 1000 atmo-
spheres ; and by this means the water can be heated
to 400° C., which is sufficiently high for the distilla-
tion of all the tar fractions. By providing suitable
gauges and safety appliances, any desired temperature
up to the above maximum can be produced and
automatically maintained. In consequence of the
advantageous manner in which the transference of
heat is accomplished, this process is economical in
operation; and by the separation of the heating
chamber from the distillation chamber the risk of
fire is considerably lessened.

For the last stage of distillation, the recovery of
creosote oil, a vacuum (up to 15 mm. mercury gauge)
isused with great success. At the same time, steam
is introduced into the still, to prevent the contents
from burning on to the walls. The employment of
the vacuum makes the process work more regularly,
and, in particular, prevents obstruction of the con-

denser.
4

50 COAL GAS BY-PRODUCTS

Continuous fractional distillation, 7 vacuo, has
been considerably improved by Krey, who arranges
two receivers behind the condenser, with interposi-
tion of a bulb provided with a three-way cock and
air-tight bell seal with gauge glasses. Both receivers
are connected to the air-pump, and are also provided
with gauge glasses to enable the progress of the dis-
tillation to be observed. Distillation is conducted
without vacuum until the creosote oil stage is reached.
By setting the three-way cock accordingly, the frac-
tions can be collected separately. After each fraction
has been collected, the receiver must, of course, be
emptied into a vessel underneath. When the
vacuum is employed, the two receivers must be
brought to the same pressure before reversing the
cock—a result which can be controlled by means of
the pressure gauge.

Of late years continuous distillation has -made
great progress. In this system, a continuous supply
of fresh tar is introduced and the corresponding
quantity of pitch is removed. Numerous proposals
have been made in this connection. 7

Hirzel (Ger. Pat. 115,921/1899) uses a column
still of similar pattern to that employed in distilling
ammonia. The various cells are heated to 155-160°
C. by a coil through which superheated steam under
a pressure of 6-64 atmospheres is passed. The tar
is screened, to free it from solid fragments, and is
then fed into the top of the column, whilst the soft
pitch runs out at the lower end into a montejus ap-
paratus. The distillate escapes through an opening

GAS TAR 51

in the cover, and after condensation is run into a
trap in which the heavy oils are separated from the
light oil and water, these two latter being separated
in turn in a second trap. ‘The heavy oil and light
oil are collected in a common tank.

The distillate at 160° C. contains all the constitu-
ents which come over up to 300° C. in the ordinary
process of distillation, but no anthracene oil, this
being contained in the soft pitch. The distillate can
be fractionated in the usual way. Hirzel separates
the naphthalene by means of a refrigerator, and dis-
tils off the anthracene oil with superheated steam at
250° C., separating it from the water after cooling.
The advantage of the Hirzel process is that the dis-
tillation temperatures are considerably lower, the
heavy oils coming over at 155-160° C. instead of at
300° C.,and even the anthracene oil being recovered
at 250° C. instead of 400° C. Owing to the lower
temperature, the distillates are in a much purer con-
dition.

The Lennard continuous distillation process is based
on continuous condensation. ‘The crude tar is pre-
heated by the anthracene-oil distillate and thus serves
at the same time as a condensing medium. The
warmed tar is passed through a scrubber, in which it
gives up its contained water and ammonia, together
with a little light oil which is then recovered in a
- condenser. The dehydrated tar is collected in tanks
and forced from these, in a constant stream, to the
still. This latter consists of a cast-iron coil of many
turns, mounted in a special furnace which is heated —

52 COAL GAS BY-PRODUCTS

by producer gas or by means of an oil burner, in order
to obtain a constant temperature. The preheated tar
flows through this still at a temperature of about
300° C., passing thence toa scrubber which is heated
to the same temperature and into which superheated
steam is blown in order to extract the volatile con-
stituents from the tar. The residue collecting in
the bottom of the scrubber consists entirely of pitch.
The distillate is then fractionated by cooling it in
stages, and the various fractions are collected separ-
ately. ,

The only other systems which need be mentioned
here are: the Wernecke process (Ger. Pat. 201,372/
1907), in which the tar is allowed to flow over a
number of annular troughs, arranged in steps in a
hopper-shaped vessel,in order to obtain more com-
plete utilisation of the heat; and the Béckelmann and
Sachse vacuum process (Ger. Pat. 154,755/1903).

CHAPTER \V.
THE GAS LIQUOR.

THE gas liquor consists of the constituents which
collect in the form of an aqueous liquid, together
with the tar, in the hydraulic main and condensers,
and as the tar-free drainings from the ammonia
washer. The liquor obtained by condensation, as
mentioned in the preceding chapter, is separated from
the tar in the tar pit, and is run into a collecting
pit with the washing water.

Gas liquor is yellowish to deep orange in colour.
In addition to ammonia, it smells of sulphuretted
hydrogen and tar. Chemically speaking, gas liquor
consists of ammonia, ammonium salts and volatile
constituents of tar, especially pyridin and phenols.
The ammonium salts may be divided into two
groups according to the relative difficulty ex-
perienced in decomposing them. ‘To the readily
decomposable salts belong: ammonium sulphide,
ammonium cyanide, ammonium sulphydrate and the
three forms of ammonium carbonate. The more
stable salts are: ammonium chloride, sulphate, sul-
phite, thiosulphate, thiocarbonate and ferrocyanide.

(53)

D4. COAL GAS BY-PRODUCTS

It is not advisable to store gas liquor very long,
because, as Lindner has shown, in these circum-
stances the proportion of the more stable salts
increases. In such case the consumption of lime
also increases, thus adding to the cost of pro-
duction.

TESTING GAS LiIQuorR.

The most valuable constituent of gas liquor is
the ammonia. Attempts to recover the cyanogen
compounds have not proved successful in practice,
owing to the small proportion present, especially
when the cyanogen washing process has been carried
out beforehand. Before proceeding to recover the
ammonia it is necessary to know both how much is
present in the free state and how much is com-
bined as stable salts; and it is to ascertain these
data that the examination of the liquor is chiefly
directed. The amount of the stable salts indicates
the quantity of lime that must be added for their
decomposition. There is no need to go into the
examination for the acids with which the ammonia
is combined, these being unimportant and non-
essential. 3

The total ammonia is determined by distillation
in presence of lime. Caustic soda should not be
used for this purpose, because this reagent also
liberates as ammonia the nitrogen of the cyanides
and thiocyanates present, and thus gives results in
excess of the truth.

THE GAS LIQUOR ci

The distillate is cooled, and then collected in acid
of known strength, the excess of acid being after-
wards titrated with equally strong caustic soda.
The percentage of ammonia is obtained from the
difference between the original volume of the acid
and the excess as found by the titration, 1 c.c. of
normal acid corresponding to 0-017 grm. of
ammonia.

To determine the ammonia in combination as
unstable salts, that is to say salts which split up at
100° C. into ammonia and free acid, the same
apparatus is used as in the total ammonia deter-
mination; but a correspondingly larger volume of
test liquor is taken and no milk of lime is added.

To determine the fixed ammonia, the residue
from this last distillation may be diluted with water
and redistilled after adding milk of lime; but in
many cases it is sufficient to calculate the fixed
ammonia from the difference between the total and
that in unstable combination.

The amount of active substance (CaQO) in the
lime is ascertained by rubbing down an average
sample, and placing a weighed quantity (70 grms.)
in boiling distilled water. After stirring the mix-
ture thoroughly and allowing the liquid to cool, the
volume is made up to 1000 c.c., and an aliquot part
(20 c.c.) of the well-shaken liquid is treated with
two to three drops of phenolphthalein and titrated
with normal sulphuric acid until the red coloration
disappears. For the proportions given above, 1 c.c.
of normal acid corresponds to 2 per cent of active lime.

56 COAL GAS BY-PRODUCTS

TREATING THE GAs LIQUOR.

The gas liquor from the pit or tank contains
1-3 per cent of ammonia. As this quantity is too
small to make the carriage of the crude liquor to a
distance profitable, the liquor must be concentrated,
no matter for what purpose it is intended. It is
therefore customary in gasworks to concentrate the
liquor to a strength of 10 per cent or 25 per cent of
ammonia, or else to convert the whole of the
ammonia into sulphate. In some large works,
strong ammonia is produced, but in the majority of
cases the concentrated liquor is sold to firms who
make a special feature of treating this material.

The simplest way to concentrate the ammonia,
and one which dispenses with distillation, is to
convert it into sulphate of ammonia; but this
process is mostly confined to small works, where the
quantity of gas-liquor to be dealt with is not large.

. Commercial sulphuric acid (66° Bé. strength) or
waste acid is diluted by running it through a siphon,
as a thin stream into gas liquor in a wooden vat.
This dilute acid is then added to the gas liquor in
the pit until the mixture just turns blue~ litmus
paper red. Since sulphuretted hydrogen is liberated
in this operation, the work should be carried on
out of doors, a cowl being placed over the pit, to
carry off the poisonous fumes. The sulphate of
ammonia liquor thus obtained is concentrated by
means of the heat of the flue gases from the retort
fires, a number of long iron pans, lined with lead,

THE GAS LIQUOR 57

being placed in the flue and charged with the liquor,
which evaporates until the salt crystallizes out.
The sulphate crystals are separated from the
mother liquor by means of a centrifugal separator
(««whizzer”). The product is an inferior grade of
sulphate of ammonia, though containing about
20 per cent of ammonia, the colour being a dirty
dark grey from the presence of tarry matters derived
from the gas liquor.

THE DISTILLATION OF GAS LiIQuoR.

The process almost exclusively used for concentrat-
ing gas liquor is one of distillation. As already
mentioned the liquor contains stable ammonium
salts in addition to free ammonia and easily decom-
posable salts. The principle of the treatment is to
distil the ammonia and unstable salts off first, by
warming the liquor to the boiling point of water.
When this has been done, the stable salts are
decomposed with lime, and the ammonia set free is
recovered by distillation. The reason for not add-
ing the lime until this second stage is because, in
this way, the lune is utilized to the best advantage
for liberating ammonia from the more stable salts;
whereas if it were added before the first distillation.
a large proportion would be consumed in combining
with the carbon dioxide—a considerable quantity of
which is contained in the gas liquor and is expelled
at the same time as the free ammonia—without
producing any corresponding yield of ammonia.

58 COAL GAS BY-PRODUCTS

At one time any old boiler was considered good
enough for the first distillation of gas liquor. The
boiler was charged with liquor and fired until all
the volatile ammonia had been driven off, after
which it was filled up again and the operation
repeated, until the remaining liquor had become
sufficiently concentrated in fixed salts. On this
stage being reached, the lime was added, and the
fixed ammonia distilled off.

This method was improved by arranging a
number of boilers side by side, and utilizing the
flue gases from the first one to heat the others.
The distilled vapours passed through the whole
series of boilers in succession and thus became
enriched with ammonia. When all the readily
decomposable ammonia had been expelled in this
way, the. whole of the residual liquor was pumped
into the first boiler of the series, and there freed
from the ammonia in the stable salts after addition
of the calculated amount of lime needed for their
decomposition.

This intermittent method is now practically dis-
continued in favour of continuous distillation. The
apparatus constructed by Franke (Bremen) for this
purpose consists of a still, divided into two compart-
ments (approximate ratio 3 : 2) by a horizontal parti-
tion. From the lower compartment a pipe for
carrying off the ammonia vapours ascends through
the upper compartment, and leads thence to the
condenser and concentrated liquor tank. Both com-
partments of the still are fitted with pressure gauges,

THE GAS LIQUOR 59

safety valves and upcast pipes. The still is enclosed in
a wrought-iron jacket traversed by the hot gases from
the fireplace which is situated underneath the still.

In working the apparatus, the lower compartment
of the still is charged with about 90 galls. of gas
liquor, the ammonia vapours from which pass
through the exhaust pipe to the condenser, furnish-
ing a 10 per cent ammonia liquor which runs into
the collecting tank. When the ammonia has been
expelled, the cock leading to the condenser is turned
off, and the hot liquor rises through an upcast pipe
into the upper compartment of the still, its place be-
ing taken by a fresh. charge of gas liquor, which is
distilled as before, after opening the condenser cock
again. While this fresh charge is’being treated, the
liquor in the upper compartment remains at boiling
temperature; and when this compartment has been
filled with the residual liquor from several such
charges, its contents are drawn off, cooled, and
used as washing liquor in the ammonia washer. In
this way the gas liquor passes through a continuous
cycle of operations, and gradually becomes enriched
with fixed ammonia salts, whereupon it is treated
with lime and distilled in one operation.

In works where the amount of gas liquor avail-
able is large, the distillation of the ammonia is now
almost exclusively performed by the continuous pro-
cess, the heat being utilized ina very complete
manner, and the method enabling far larger quanti-
ties of liquor to be dealt with, per unit of time, than
in the old method of distillation in boilers.

60 COAL GAS BY-PRODUCTS

The plant is arranged in such a way that the lime
is not added until all the volatile ammonia has been
driven off. ‘The steam used for heating the appa-
ratus is derived either from the gas liquor itself or
else from a steam boiler. lt is employed, in the
first place, for expelling the ammonia liberated by
the lime treatment; then for mixing the lime charge
with water; and finally for driving off the free
ammonia in the gas liquor, after which, laden with
the whole of the ammonia from the gas liquor, it
passes to the condenser. ‘The heat liberated during
condensation serves for preheating fresh quantities of
gas liquor, for which purpose the heat of the spent
gas liquor.—effluent—can also be utilized.

The continuous distillation of the ammonia liquor
is based on the same principle which led Savalle to
devise the column still for rectifying alcohol. The
whole system of the distillation of gas liquor is based
on three phases: expulsion of the volatile ammonia ;
addition of lime; expulsion of the ammonia com-
bined as stable salts.

This subdivision of the working process necessarily
implies a corresponding subdivision in the arrange-
ment of the column still. The three parts. of the
apparatus are disposed in such a manner that the
gas liquor from a high-level tank traverses them in
succession. Both the upper and lower parts of the
column are divided into a number of superimposed
cells, whilst the middle portion is occupied by the
lime mixer, which in the newest patterns consists
of only a single cell. The gas lquor is led away

THE GAS LIQUOR 61

through tubular connections which project a short
distance above the floor of each cell, so that acertain
depth of the liquor remains in each, whilst the sur-
plus overflows into the cell next below. Each tube
is long enough to dip below the level of the liquor in
each case; and the tubes are arranged so that the
liquor traverses the cells in a zig-zag course. The
steam which carries off the ammonia vapour passes
upward from one cell to another through perforations
arranged in the cell bottoms and extending upward
through same in the form of short trunco-conical
tubes which are long enough to project above the
level of the gas liquor and are surmounted by loose
caps supported by tripods resting on the cell floor.
These caps dip below the level of the gas liquor and
are provided with notches. In passing from one
cell to another the steam is compelled to make its
way through the liquor in the upper cell, and as it
does this by bubbling through each of the notches
provided in the caps, it comes into intimate contact
with the liquor and becomes enriched with ammonia.
The steam enters the apparatus by the- bottom cell
and leaves it at the top one, whilst the warmed gas
liquor travels in the opposite direction, and parts with
the whole of its ammonia before issuing from the
bottom cell. The counterflow principle is thus am-
ply made use of in this arrangement, the hot fresh
steam coming into contact with the warm liquor
which is poor in ammonia, and taking up from the
latter merely the fixed ammonia which has just been
liberated by the lime, whilst the steam that is fully

62 COAL GAS BY-PRODUCTS

laden with ammonia comes in contact with the fresh
gas liquor.

A few types of this kind of apparatus will now be
described. :

_Fig. 2 represents a column still made by the
Berlin-Anhalt Maschinenbau Aktiengesellschaft. It
is built up of a number of flanged cast-iron rings,
superimposed on a pan which is provided with a
sloping bottom, the whole being surmounted by a
cover. The steam and ammonia escape through A.
The cell bottoms already mentioned are mounted
on the internal flanges of the rings. The cells are
provided with openings, for cleaning purposes, and
the whole interior is accessible, so that the whole still
can be cleaned out without having to be taken apart.
The preheated gas liquor enters the top cell through
a lateral feed pipe, B, and flows downwards from cell
to cell, meeting a current of steam on its way. The
course taken by the steam is indicated by the light-
coloured arrows, and that of the gas liquor by the
black ones. As the steam flows through the crude
liquor at the loose caps it gradually raises the same
to boiling, so that, in the upper part of the apparatus,
the volatile ammonia and the other gases pass into
the steam. ‘The lime is added in the third cell from
bottom, in which section the tubes and caps are
made higher, so as to provide for the increased
volume of liquor due to the addition of the milk of
lime. The deeper immersion of the caps causes the
liquor to be kept in active movement by the steam.
The milk of lime, in slight excess, is introduced

THE GAS LIQUOR 63

through a lateral pipe C, and mixed with the water.
In the two bottom cells the fixed ammonia is ex-

mf ky ed = me —~ B

Br) A wd gs
nN
/

Fig. 2.—Column still.

A—A = steam and ammonia gas; B=

ammoniacal liquor; C= milk of lime; D=steam; E = to

spent lime pit.

tracted from the gas liquor.

The effluent, which

should contain only about 0-005 per cent of ammonia,

64 COAL GAS BY-PRODUCTS

issues from the apparatus through a self-adjusting
draw-off valve, g, which consists of a movable float
made of sheet-iron, faced with lead, and carries the
cone valve on an iron rod. ‘The float is housed in a
cast-iron casing and is subjected to the same steam
pressure as the rest of the lower portion of the still,
so that the water level at which the valve opens
remains constant. The steam admission pipe D is
provided with a pressure gauge, a throttle valve and
a safety valve. The working steam pressure of the
apparatus is only 11-4} lb., and the safety valve is
set to blow off should that pressure be exceeded.
The effluent gas liquor has a temperature of 212° F.,

and is used for preheating the fresh liquor in an
apparatus of the kind shown in Fig. 3, which is
made by the same firm as the still. This is of the
tubular pattern, and the tubes are traversed from
above downwards, by the hot effluent hquor from
the still, whilst the fresh gas liquor flows upward
through the cylinder, and is thereby warmed to about
60-70° C. (140-158° F.) before entering the column
- still. The admission of the gas liquor is adjusted
by a feed regulator ; whilst the supply of lime to the
still is controlled by a hand-pump or an automatic
steam pump.

The -Koppers still differs from the one just
described, both externally and internally. It con-
sists of two portions ; and only the volatile ammonia
is expelled, and the mixing of the lime and gas
liquor effected, in the main column. The vessel
for mixing the milk of lime consists of a single,

THE GAS LIQUOR 65

funnel-shaped chamber. The gas liquor, deprived of
its volatile ammonia, enters the mixing vessel, along
with the milk of lime, at the lowest point ; and at

>»

Frq. 3.—Tubular preheater.

a point about half. way up the side of the vessel
the mixture runs off through a pipe into an inde-
pendent auxiliary column, in which the fixed
ammonia is expelled. The escaping gases pass under-
neath the lowermost cell into the mixing vessel. The

5 :

66 COAL GAS BY-PRODUCTS

openings in the cells, for the passage of the mixed
steam and gases, consist of two long, narrow slits,
with loose caps of corresponding shape; and those
in the various cells are arranged crosswise with
relation to those above and below. Distillation
proceeds in the manner already described. The
- separation of the two stages of the process has the
advantage that the auxiliary column can be cleaned
without taking apart the whole of the apparatus.

The gaseous mixture issuing from the column
contains a large proportion of steam, together with
ammonia, sulphuretted hydrogen and carbon dioxide.
A water-cooled condenser, for concentrating the
ammonia, is mounted over the column. The gas
liquor may also be utilized for condensing. The
condensed steam runs back into the top cell of the
still. A reflux condenser of this kind is illustrated
in Fig. 4, in which the pipe A is shown at right
angles to its real position.

The gas issuing from the still is mostly con-
taminated with carbon dioxide and sulphuretted hy-
drogen. If strong ammonia liquor were produced,
the carbonates would be lable to deposit in the
condenser and choke it, so that continuous. working |
could only be obtained at the cost of very careful
supervision. On leaving the apparatus, the gases
are pumped to their further destination. Any ob-
struction in the condenser would set up increased
pressure in the still, on the one hand, and on the
other a vacuum would be produced between there
and the pump. It follows therefore that any such

THE GAS LIQUOR

Fic. 4.—Reflux condenser. A = pipe turned at right angles.

68 COAL GAS BY-PRODUCTS

deposition of salts would upset the whole series
of operations. Consequently, the concentrated gas
liquor must be freed from carbon dioxide before
entering the condenser.

Two principal methods have been proposed for
eliminating the carbon dioxide from the still gases.
Hither the carbon dioxide is absorbed by passing
the effluent gases from the still through milk of
lime, or else use is made of the fact—which will be
more fully explained later on—that the gas liquor
gives off carbon dioxide and sulphuretted hydrogen
when warmed, whereas the ammonia is retained.

The first-named principle is embodied in a carbon-
dioxide separator, manufactured by the Berlin-
Anhaltischer Maschinenbau A. G. and illustrated in
Fig. 5. :

This separator consists of a cylindrical cast-iron
vessel, provided with a conical bottom. The cover
is provided with two openings, of which the one in
the centre is traversed by a pipe (T’) which extends
nearly to the bottom of the vessel, where it is
flared and notched. Through this pipe, at B, the efflu-
ent gases from the column still enter the separator.
The pipe itself is surrounded by a number of plates
sloping at an angle to the horizontal. The milk of
lime is introduced from the bottom (D) and flows away
through a lateral pipe (C) half-way up the vessel. The
gas, freed from carbon dioxide, issues from the
purifier through the second pipe (A) in the cover. The
plates are arranged in such a way that the gas is
compelled to describe a zig-zag course through the

THE GAS LIQUOR 69

liquid. The milk of lime runs into the lime vessel
of the column still, and is there freed from the

D
Fia. 5.—Carbon-dioxide separator. A = purified ammonia gas;

B = ammonia gas and CO,; C = to still ; D = milk of lime.
ammonia it has absorbed, thereafter serving to
liberate the fixed ammonia. The purified gas is

then forwarded to the condenser.
The separation of the carbon dioxide by warming

70 COAL GAS BY-PRODUCTS

the gas liquor is based on the following considera-
tions: Ammonium sulphide and ammonium carbonate
belong to the most readily decomposable class of
salts, that is to say they are decomposed by heat
into ammonia and carbon dioxide, or sulphuretted
hydrogen, respectively. Now, warm water has a
greater capacity for absorbing ammonia than it has
for carbon dioxide and sulphuretted hydrogen, so
that if a solution of ammonium sulphide or am-
monium carbonate be warmed, it becomes enriched
in ammonia at the expense of the sulphuretted
hydrogen and carbon dioxide. Experiments per-
formed by Bertelsmann with gas liquor in a Feld-
mann column still showed that gas liquor ceases
to absorb carbon dioxide when the temperature
reaches 96° C. (205° F.)—see the subjoined Table,
in which the content of ammonia, carbon dioxide
and sulphuretted hydrogen is set down as 100. The
column still was composed of eleven cells; and during
the experiment, determinations were made of the
temperature in each cell, and also of the amounts of
ammonia, carbon dioxide and sulphuretted hydrogen
in the liquid.

In the first five cells, in which the temperature
rose to 93° C., the gas content in the water increases
continually, the ascending vapour giving up a
portion of the gases to the water again. In the
sixth cell, in which the temperature attains 96° C.,
the percentage of carbon dioxide diminishes by one-
half, and that of the sulphuretted falls by more than
50 per cent, whereas the water still contains 170

THE GAS LIQUOR : v1

per cent of ammonia. Up to the ninth cell the
temperature rises to 97° C., and whilst practically
the whole of the carbon dioxide has been expelled,
the ammonia content still amounts to 26 per cent.

Gas Content of the Water in Percentages of
Original Amount,
Water Sample | Temperature
from Intake of °C.
Ammonia. | Carbon Dioxide. i podinge
Cell 1 55 142 144 144
ee | 87 380 187 269
A 90 377 168 165
psn 93 359 134 181
ee 93 307 109 126
Pee 96 170 57 50
» 0 96 89 39 4°3
Rta 97 49 18 3°4
rica 97 26 0°3 1:9

Hence, if the crude gas liquor be kept at this
temperature before it is admitted to the column
still, a liquor very low in carbon dioxide will be
obtained. The Feldmann-Pintsch separator is based
on this principle, and consists of a cast-iron cylinder
divided into two parts. The gas liquor, preheated
by the effluent from the column still, is introduced
into the lower part of the apparatus and is heated
by a steam coil to 88-95° C., which causes it to
give off carbon dioxide, sulphuretted hydrogen and
also ammonia. ‘The liberated gases pass into the
upper part of the separator, where they come in
contact with a current of cold gas liquor, which
absorbs the ammonia completely, leaving the carbon

72 : COAL GAS BY-PRODUCTS

dioxide and sulphuretted hydrogen to escape into
the open air.

WORKING THE STILU.

Starting the apparatus for the continuous dis-
tillation of the gas lquor is a very simple operation,
all that is necessary beforehand being to employ the
usual precautions to see that none of the apparatus
is leaky. Heating up should be effected slowly, and
‘it is not until the entire contents of the still are
properly warmed through that the fire should be
quickened, to raise the liquid to boiling. When the
contents are drawn off, the fire should be ex-
tinguished. |

If milk of hme be used from the start, the liquid
should be stirred up from time to time, to prevent
the lime burning on to the metal, since, in addition
to the loss of heat, this would give rise to the usual
dangers of boiler incrustation.

The continuous column stills are heated by direct
- steam. Before starting, the still should be warmed
up in the dry state, the water of condensation from
the heating steam collecting in the bottom, of the
cells. The admission of steam is gradually in-
creased, and at the end of about two hours, the
pressure should attain 13-3 lb. per square inch. The
gas liquor is then admitted, and the pressure is
maintained by controlling the supply of steam. As
soon as the effluent water begins to drain off, the
milk of lime is added; and the temperature is

THE GAS LIQUOR 73

raised, by admitting more steam, until no more
volatile ammonia can be detected in the cell above
the lime-mixing vessel. The inflow of milk of lime
is then regulated in such a manner that the effluent
water is free from combined ammonia as well.
This condition can be ascertained by testing a
sample of the effluent with a little fresh lime, under
which conditions no smell of ammonia should be
noticeable. After the admission of the steam, gas
liquor and milk of lime has been properly adjusted,
care must be taken to see that the supply of each
remains constant throughout the whole of the
distillation process, the effluent liquor being tested
from time to time to make sure that everything is
in order. If the steam pressure be too high, the
gas liquor is liable to be forced into the gas delivery
pipe. ‘To test whether this is the case, a hole. is
bored in the ammonia pipe, and.if the steam which
then escapes contains moisture—which may be
ascertained by holding the hand in the escaping
current, whereupon any moisture present will make
the hand wet—the supply of steam must be re-
duced.

In the course of distillation the temperature will
fall unless the supply of steam be increased, owing
to the walls and bottom of the cells becoming
incrusted with lime. For this reason the column
should be cleaned out, by means of the manholes,
at the end of every month or two.

One of the most troublesome obstructions to the
working of the still is caused by tar passing into

74 COAL GAS BY-PRODUCTS

the column; but this drawback can be prevented by
careful supervision of the pumps and the ammonia
liquor pits. If, notwithstanding, any considerable
quantity of tar finds its way in, about the only
thing that can be done is to dismount the apparatus
entirely and clean it out.

The consumption of fuel depends on the nature of
the fuel and the construction of the still. With
the Feldmann-Pintsch apparatus, 4 cwt. of steam
will be required for the distillation of 220 gals. of
gas liquor, so that, given an evaporative power of
7:1, 483 tons of coal will be needed in treating
330,000 gals. of gas liquor.

PREPARATION OF CONCENTRATED GAS LIQUOR.

Although a method of obtaining 10 per cent gas
liquor has‘ long been known, a higher concentration
is generally desired, and for this purpose a con-
tinuous process is exclusively employed.

As a rule, two grades of concentrated liquor are
produced: a weak liquor containing 16-20 per cent
of ammonia, and a stronger liquor with 18-25 per cent.

The weaker liquor has a density of 15-18" Bé.,
and contains a large proportion of amnionia in
combination, chiefly as carbonate. It is prepared
without the employment of a carbon-dioxide separa-
tor. The manufacturing process may be illustrated
by reference to the plant made for this purpose
by the Julius Pintsch A. G. (Ger. Pat. 179,080) and
illustrated in Fig. 6.

The crude liquor runs from a high-level tank to

THE GAS: LIQUOR 75

the ball-cock tank b, which serves to keep the gas
liquor at a constant level and ensure uniform feed.
From this tank the liquor flows through the cock c
to the condenser n, which it enters from below and
in whichit plays the part of condensing agent. The
gases from the still enter the top of this condenser
and are cooled down, the crude liquor being preheated
at the same time. The condenser is composed of
several members united together to form a double
worm, the cooling agent, the crude gas liquor,
flowing upward through the one coil, whilst the hot
gases pass down inside the other and are condensed.
To ensure complete condensation, the condenser is
divided into two parts, cooling water being used in
the smaller, upper compartment. ‘The preheated
crude liquor next enters the top cell of the column
still, d. In the upper part, h, the volatile ammonia
is expelled, whilst the crude liquor runs off into the
lime mixer, g. Here it is mixed with milk of lime,
which is admitted, either at stated intervals by
means of a hand pump, or else continuously by
means of a steam pump, k, the delivery of which
can be carefully adjusted. The intimate mixture of
the lime and gas liquor is effected by means of a
steam spider. ‘The resulting mixture is then run
into the auxiliary column still, f, and thence to the
bottom chamber, e, where the final traces of the
combined ammonia are driven off. From this cham-
ber the spent mixture is discharged, as effluent, to
the settling tank, threugh a cock, J, which may. be
either operated by hand, or else self-acting.

COAL GAS BY-PRODUCTS

‘zonbiy se8 = M ‘4URq [ode] YSty utory Aonbry svs = A {yuea = J {z0q9eM
Suljooo = § ‘Sdonbiy vruouUIe poyerqueou0D = yy {! WBeys = JX ‘4B pesserdwioo = ry fount, jo yp = y
‘Inodva BIuoTIUIY = | ‘10}vM JQUONJo = YW ‘Aonbi, eruouure yvom Zutrederd 10; guvid yo weaseiq—'g ‘rg

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Vos

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be SSS SS SS Se

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HD
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mutt
$33:

THE GAS LIQUOR 77

The steam enters the lower chamber, e, flows
through the cap-covered openings in the bottom of
the several cells, and becomes saturated with am-
monia, ammonium carbonate and small quantities
of ammonium sulphide. The ammoniacal vapours
are condensed in a condenser, m, and are delivered
to the storage vessel, p. This vessel is emptied by
compressed air, furnished by the compressor, q.

This plant will produce a liquor containing up to
18 per cent of ammonia, assuming the crude liquor
to have an average content of 20 per cent of com-
bined ammonia.

In order to obtain the stronger grade of ammoni-
acal liquor (up to 6° Bé. strength), it is necessary to
free the gas liquor from carbon dioxide. As has
already been seen, this elimination of carbon dioxide
can be effected in two principal ways. One of these
—the warming of the gas liquor—forms the basis of
the apparatus illustrated in Fig. 7 and embodying
the Feldmann-Pintsch system. It differs from the
apparatus Just described, for the production of weak
ammonia liquor, by containing a carbon-dioxide
separator, ¢, and a reflux condenser, x, mounted on |
the column still: Clarified water alone is used for
condensing the waste bases in s.

The crude liquor flows from the ball-cock tank
into the ammonia absorber, 7, of the carbon dioxide
separator, t, whence it is passed through the pre-
heater, v, to be warmed by the effluent water from
the column still. The preheated liquor is next
heated to 88-95° C. in the heating chamber, s, of the

COAL GAS BY-PRODUCTS

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: I Roe : = 0 ‘41098 Sul[ooo = ry $quea =
‘inodva viuomUe = | : sv oysem = g ‘ronby eruowure Suo1ys Sursederd 107 sted Jo tavatane =>) ‘DI

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THE GAS LIQUOR 79

separator, t, by a steam coil, and parts with its
carbon dioxide. Any ammonia carried off at the
same time is reabsorbed by the crude liquor in r.
The liquor freed from carbon dioxide is distilled in
the column still, d. In order to concentrate the
ammoniacal vapours, a portion of the steam is con-
densed in the reflux condenser, x, mounted on the
still. The further course of the process is identical
with that given in connection with the preparation of
the weaker grade of liquor.

To prepare concentrated ammonia liquor by re-
moving the carbon dioxide with lime, the separator
illustrated in Fig. 5 is employed. The gas liquor
flows from the high-level tank through a cellular
condenser of the kind shown in Fig. 8, where it is
preheated, and at the same time the still gases are
condensed. ‘The preheated liquor is distilled in the
column still, and the gases from the latter are freed
from steam by the reflux condenser, from which they
pass into the carbon dioxide separator, in which
both the carbon-dioxide and the sulphuretted hydro-
gen are absorbed. The outflowing gases are
condensed in the cellular condenser and conveyed to
the storage vessel. ~ The milk of lme used for
purifying the gases is run into the lime mixer of the
still, and there serves to expel the combined am-
monia.

The concentrated ammonia liquor resembles the
crude gas liquor in appearance, and, like the latter,
darkens in colour on standing. Its value is ascer- |
tained by a simple titration, 10 c.c. being diluted to

80 COAL GAS BY-PRODUCTS

y Musas YY,

Fic. 8.—Cellular condenser. A-=crude liquor to still; B=
crude liquor from tank.

THE GAS LIQUOR 81

1000 c.c. and an aliquot part being treated with an
excess of normal sulphuric acid. After boiling for a
short time the excess of sulphuric acid is titrated
back with normal caustic soda, methyl orange being
used as indicator.

The concentrated liquor is not, in itself, a com-
mercial article, but forms the raw material for the
manufacture of ammonia preparations, and is there-
fore a semi-manufactured product.

PREPARATION OF AMMONIA.

The most valuable products recoverable from gas
liquor are aqueous ammonia and liquefiedammonia, the
former being a chemically pure product obtained by
absorbing ammonia in distilled water. It is re-
covered direct from the gas liquor, without the assist-
ance of any other chemical agents, such as acids or
salts, and differs from the crude gas liquor in being
free from any contamination with carbon dioxide,
sulphuretted hydrogen or organic (empyreumatic)
substances. Jn connection with the preparation of
aqueous ammonia, Pfeiffer of Magdeburg has rendered
valuable service. It is prepared, either by the in-
termittent process in boiling pans, or by the continu-
ous process in column stills. The gases from the
pans or stills are freed from contained acids by milk

of lime and are then dried, the dried gases being |

filtered through wood charcoal (and also through
vaseline oil if necessary) to eliminate organic sub-
stances, chemically pure gaseous ammonia being

82 COAL GAS BY-PRODUCTS

finally left. The further treatment of this gas can
be carried out in two ways. For the production of
aqueous ammonia it is- passed into distilled water,
whilst for making liquefied ammonia it is put through
a compressor.

The intermittent process of preparing aqueous
ammonia is carried on in the following manner :—

The still is charged half full with the crude liquor
and slowly heated, the gases liberated during this
stage being returned to the crude liquor tank. When
the liquor has reached distillation temperature (100°
C.), a calculated quantity of milk of lime is added at
once. ‘The gases disengaged are passed into a high
reflux condenser, two cells, provided with loose caps,
being interposed between the still and condenser, in
order to prevent any lime from being carried off with
the gases. The addition of the milk of lime before
distillation causes practically the whole of the car-
bon dioxide and sulphuretted hydrogen to be retained
in the still. The high reflux condenser condenses
the whole of the steam, which then flows back into
the still, carrying with it a portion of the ammonia
and the final traces of carbon dioxide and sulphuretted |
hydrogen. The gas, dried in this way, is next passed
through several cylinders charged with wood char-
coal, in which the empyreumatic substances are ab-
sorbed. The final traces of carbon dioxide and
sulphuretted hydrogen are extracted with caustic
soda, leaving the gaseous ammonia chemically pure.
To prepare aqueous ammonia, this gas is introduced
into a cylinder containing distilled water, the ab-

THE GAS LIQUOR 83

sorption being effected by the acid, on the counter-
flow system. The absorption of ammonia by water
is based on a chemical reaction accompanied by the
disengagement of heat :—

NH, + H,O = NH,HO + 8435 cal.

In order to enable the water to take up as much
ammonia as possible it must be cooled, preferably by
immersing a cooling worm in the liquid. The ab-
sorption vessel is composed of several cells, communi-
cating by means of syphons. The pure ammonia
gas enters the liquid in the lowest cell first, where
the bulk of the absorption takes place. The un-
absorbed gas traverses the superimposed cells in
succession, so that the water which is poorest in
ammonia has only to absorb the final traces of the
gas. When the water in the lowest cell is com-
pletely saturated with ammonia it is drawn off into
carboys or drums. The liquid charge in each of the
higher cells is transferred to the one next below, and
the top cell is recharged with fresh water. With a
plant of this kind a solution containing 25-28 per
cent of ammonia can be prepared. The still is
heated by steam, the exposure of the still directly to
fire heat necessitating careful supervision on account
of the addition of lime. The charcoal filters must
be renewed every five or six weeks ; and the charcoal
can be regenerated, for which purpose steam is blown
through the filter before the latter is emptied, the
steamed charcoal being then heated to incandescence
out of contact with air, whereupon it is ready for
use again. The process of making aqueous ammonia

84 COAL GAS BY-PRODUCTS

requires to be carefully controlled, the gases being
subjected to constant examination, for the presence
of sulphuretted hydrogen, after the washing with
caustic soda.

It is only of late years that the preparation of
aqueous ammonia by the continuous process has
been carried on with success. The Berlin-Anhaltische
Maschinenbau A. G., in collaboration with Griine-
berg, Tieftrunk and Buhe, was the first to devise a
process of this kind on the large scale, with which
it was found practicable, in an Upper Silesian works,
to treat nearly 1800 galls. of gas liquor in twenty-
four hours.

From that time:-onwards, the continuous process
has developed progressively. The plant now supplied
by the above firm is based mainly on the patented
carbon-dioxide separator and the grouping of the
apparatus in such a way that, throughout the process,
the milk of lime flows in the opposite direction to
that taken by the ammoniacal gases.

The working of the process is checked by testing
the effluent ; and so long as the latter contains an
excess of lime, it is evident that such excess is also
present throughout the process. The ammoniacal
gases issuing from the still are passed through a re-
flux condenser which eliminates all but a slight trace
of steam from the gas. The latter still contains
carbon dioxide, sulphuretted hydrogen and empyreu-
matic substances, the first two of which are com-
pletely removed by passing the gas through a series
of three milk-of-lme vessels (Hig. 9), such as are

THE GAS LIQUOR 85

used in concentrating the crude gas liquor, and in
which the milk of lime flows in the opposite direction
to that of the gas and runs off into the still. The
gas passes through two condensers and a coke filter,

SNS

| y
4 | “all J
Uy, x “9 Y
tk Be if a ee a
| ed mee | :
Lt yet —e

Fic. 9.—Lime washer.

after which the bulk of the chief organic impurities
is removed by an oil washer, and the remaining im-
purities of all kinds by charcoal filters. The gas issu-
ing from the last named is pure ammonia, and is

86 COAL GAS BY-PRODUCTS

passed into distilled water in a cooling apparatus
which enables aqueous ammonia of any desired con-
centration to be obtained.

The carbon dioxide and sulphuretted hydrogen can
also be eliminated by the application of heat ;. and a
Feldmann-Pintsch plant for this purpose is illustrated,
diagrammatically, in Fig. 10. The column still
differs from that already described in that the milk-
of-lime mixer is abolished, the lime reagent being
applied prior to the distillation process. Up to the
stage of issuing from the heating chamber of the
carbon-dioxide separator, the course taken by the
crude liquor is exactly the same as in the preparation
of concentrated gas liquor; and there is also no need,
in this case, to warm the gas liquor before it enters
the heating chamber. The liquor is passed alter-
nately into two mixing vessels, f, which are charged
with the necessary amount of milk of lime by means
of a steam syphon, it being the intention that the
lime shall combine with the acids of both the fixed
and more volatile ammonia salts, the latter of which
are present in smaller quantity, and thus furnish
perfectly pure ammonia gas. The arrangement of
the plant enables the mixture of milk of lime and
gas liquor to be introduced into the still whilst still hot.
The preliminary elimination of the carbon dioxide
and sulphuretted hydrogen by heat enables up to 90
per cent of the consumption of quicklime to be
saved, if the operations be accurately performed. By
means of the steam pump, g (shown in the Figure as
situated between the two mixers, f), the power of

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quonyye = AA + oUt] Jo ¥[TU pus zonbiy ses Jo ornjxtul = g {4109eM poT[ysip = yz { Suryerodveas 10; uveys = g
OUI] JO Y[IUL = JL 109BM Sul[ooo = J ‘1098M posuepuoos = y !yueq, [oaoy, YSIy Woy ronbip ses = F {ses
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THE GAS LIQUOR

88 COAL GAS BY-PRODUCTS

which is also utilized for stirring the contents of
the mixers, the mixture is pumped into the
column still, d, where the distillation is carried on in
the known manner. ‘The reflux condenser, z, retains
nearly the whole of the water vapour carried over
with the gases. The dried gas passes through the
safety device, h, into the washer, 7, which is charged
with caustic-soda lye, which absorbs the residual
traces of carbon dioxide and sulphuretted hydrogen
present. In & the gas is cooled in order to remove
the heat acquired in 7. Wood charcoal or bone
black, in lumps about the size of peas, is employed
in two cylinders, o, for the purpose of absorbing the
empyreumatic constituents. ‘The purified gas is
absorbed by distilled water in the two absorption
vessels, p, which can be connected up alternately,
the heat liberated by the absorption process being
removed by means of a water coil.

The requisite distilled water is recovered, in the
heating chamber s, of the carbon-dioxide separator ¢,
this water being distilled in q, freed from mechanical
admixtures of iron by filtration through sand and
charcoal in y, and collected in wu. This apparatus
enables technically pure aqueous ammonia, that is
to say, a water-white product free from chlorine, to
be obtained. For preparing the chemically pure
article, the absorption vessels must be of earthenware,
and the purifymg agents must be renewed at more
frequent intervals.

THE GAS LIQUOR 89

LIQUEFIED AMMONIA.

The highest-grade product obtainable from gas
liquor is liquefied ammonia. It is prepared in exactly
the same way as chemically pure aqueous ammonia,
up to the absorption stage, this latter operation be-
ing replaced by compressing the gas into the liquid
condition, after having passed it over quicklime in
order to make certain that the gas is perfectly dry.
For the purpose of compensating the fluctuations in
pressure between the still and the compressor, the
gas is usually stored in a gasholder provided with an
oil seal. According to the practice recently adopted
by the Pintsch Company, the gas is conveyed direct
from the still to the compressor, and any considerable
fluctuations in the pressure are avoided by means of
several closed storage vessels, provided with suitable
pressure gauges.

The dried gas still always contains impurities, such
as pyridin, methyl alcohol, benzol and organic sub-
stances. These are removed by repeated com-
pression and re-evaporation of the ammonia, the
impurities remaining behind in the liquid condi-
tion.

There is nothing essentially different between the
manufacture of liquefied ammonia and that of liquefied
gases; and therefore there is no need to go into de-
tail on the subject. The liquefication is entirely on
a par with that of carbon dioxide and sulphur dioxide.
At 10° C., the vapour tension of ammonia is about
6{ atmospheres; and any pressure exceeding this

90 COAL GAS BY-PRODUCTS

value liquefies the gas, at said temperature. In the
compressor, the thoroughly cooled gas is subjected to
a pressure of 8 atmospheres. The nearly colourless
liquid is forced by the pressure in the compressor
through an oil separator and a steel cooling coil, into
the usual steel flasks met with in commerce. In
charging these flasks, an allowance of about 58 cub.
inches should be made for each 1 lb. of ammonia,
under which conditions the filled flasks may be ex-
posed to any temperature up to 65°C. (149° F.)
without exceeding the pressure they have been tested
to stand (1420 lb. per sq. inch).

The chief use of liquefied ammonia is in refrigerating
machines (Linde ice machines). In consequence
of the handy nature of the steel flasks, and the fact
that the ammonia is 99-100 per cent pure, liquefied
_ ammonia is now used instead of aqueous ammonia.
It forms a water-white aqueous. liquid, having a high
refractive index, and has the sp. gr. 0:-6362 at zero

C., the boiling-point under normal pressure being
a fie. 6

SULPHATE OF AMMONIA.

Sulphate of ammonia is the product most usually
obtained from gas liquor, because, in contrast to con-
centrated gas liquor, it is an article of direct com-
mercial value, and is also more convenient to store.
It is prepared by passing the gases from the column
still into dilute sulphuric acid, ammonium bisulphate,
which is readily soluble in water, béing formed

THE GAS LIQUOR | 91

at first. On continuing the introduction of ammonia
until the whole of the acid is neutralized, the neutral
sulphate of ammonia, which is only sparingly soluble
in water, is obtained. These reactions are accom-
panied by the disengagement of heat (100 calories
per lb. of salt). The liquid becomes heated, so that
not only is the condensation of the water vapour
coming over from the still prevented, but even more
water is evaporated. Consequently, the cooling of
the gases from the still can be dispensed with.
Moreover, the gases need not be freed from sulphur-
etted hydrogen or carbon dioxide, since these sub-
stances are not absorbed by theacid solution. Hence,
in the manufacture of sulphate of ammonia, carbon
dioxide, sulphuretted hydrogen and hydrocyanic acid
escape from the absorption apparatus, a point which
must be remembered, and precautions taken to
render these gases innocuous. ‘The most primitive
method of obtaining sulphate of ammonia has al-
ready been mentioned in dealing with the treatment
of gas liquor. The absorption of the ammonia is
generally effected in rectangular wooden vats, lined
with sheet lead and charged with sulphuric acid. The
gases from the column still are conveyed to the vats
through iron pipes, the last length of piping, how-
ever, being of lead and extending nearly to the
bottom of the vat, being notched at the lower end.
This pipe is surrounded by a bell cover, which dips
into the acid and is provided with an outlet pipe for
the residual gases, which, since they still contain
small quantities of ammonia, are passed through a

92 : COAL GAS BY-PRODUCTS

lead-lined separator, in which parallel surfaces are
arranged in such a manner as to compel the gases to
traverse a zig-zag course. If necessary, the effluent
gases are re-washed with sulphuric acid.

This type of plant enables sulphate of ammonia
to be produced by the intermittent process, at least
two absorption vats being provided, so that when
the charge in one is saturated, the other can be
connected up, and vice versa, without interrupting
the distillation of the ammonia.

A Pintsch plant for the intermittent production
of sulphate of ammonia is illustrated in Fig. 11.
The arrangement for distilling the gas lquor is
similar to that used in making concentrated gas
liquor, except that, whereas in that case the crude
liquor is warmed up by the gases escaping from the
- column still, the same effect is produced here by
the spent gases from the absorption vats (saturators)
p, 1 o. The gases from the still are admitted,
under a leaden bell, into the saturator. The small
amount of ammonia not taken up by the sulphuric
acid in the saturators passes, along with steam,
carbon dioxide and sulphuretted hydrogen, into the
acid receiver, g, to retain the ammonia, which comes
over more particularly toward the end of the satura-
tion process in p. The acid receiver, qg (see Fig. 12)
—Pintsch’s Ger. Pat. 134,967—consists of. a closed
vessel, lined throughout with lead, and provided
with an internal vertical partition. The second
or discharge chamber contains a number of sloping
baffles, which prevent any of the sulphuric acid

THE GAS LIQUOR

“tonbiy ses = MA ‘plo o1mnydns = g

‘ YUey [OAay YSiy wor conbiy ses = oO fanodva viuowue = N foautly, jo yp = T { ureeys =

= ‘4oy8m poesuopauoo = q ‘ses ojsem = gq ‘od, = Vy ‘gueid Biuomue jo ayeydins jo welseIq—'TT ‘DLT

UNE ta Eg

Se oe

Wf 1eyem yuenyyo

DRE RY | L }

94 COAL GAS BY-PRODUCTS _

from being carried away by the effluent gases. The
receiver is filled, to about a quarter of its height,
with dilute sulphuric acid. The ammoniacal gases
from the saturator are obliged to pass underneath
the partition in order to reach the second chamber ;

Fia, 12.—Acid receiver for sulphate of ammonia plant. A=
waste gas containing ammonia; K = waste gas free from am-
monia; U = lye; W = sulphuric acid.

and in this way the whole of their ammonia is com-

bined by the acid. When the charge in the one

saturator has been neutralized by the ammonia in
the gases, the latter coming from the still are
diverted into the second saturator. The sulphate of

THE GAS LIQUOR 95

ammonia which precipitates in the saturator—es-
pecially towards the end of the saturation process—
is taken out and placed on the drainer; 7, where the
bulk of the adherent liquor runs away. The salt is
then purified by whizzing it in a centrifugal machine,
and washing it until almost entirely free from acid.

The spent. gases from the receiver, g, pass into
the crude liquor preheater, 0, and are then led into
a purifier, charged with ferric hydroxide, for the
recovery of the sulphur, or else are allowed to escape
direct into the chimney stack.

Towards the close of the reaction, the absorption
of ammonia in the saturators proceeds very slowly,
so that a thorough washing of the effluent gases is
essential for preventing loss of ammonia. On this
account, various proposals have been made of late -
for ensuring complete absorption of the ammonia.

Zimpel washes the gases at once in the bell, for
which purpose he provides a second bell, e (Fig. 13),
of the same construction as the bell G. The acid
is introduced at r, filling the vessel sufficiently to
cover the notches in the bell, e. Consequently, the
gases coming from G are rewashed in exactly the
same way, before passing off into the trap by way of
d. When the washing acid is renewed, the previ-
ous charge is run off, through f, into the saturators.

The counterflow principle is employed in the
absorption apparatus of Rosenkranz, in which two
saturators are used. So long as the ammonia is
absorbed in the form of an acid salt in the saturator,
the absorption is complete; and it is only during
the second stage of the reaction that any ammonia

96 COAL GAS BY-PRODUCTS

escapes with the waste gases. On this account,
therefore, Rosenkranz allows the exhaust gases to
escape during the first stage, but when the second
stage is reached, diverts these gases into a fresh
saturator which is charged with fresh acid. As
soon as saturation in the first saturator is complete,
it is disconnected and replaced by the second one.

So
PR et

=
int

ry : Ga (3

Fia. 18.—Zimpel double bell washer.

The salt in the first saturator is taken out, and the
apparatus is recharged with fresh acid, to be ready
for the exhaust gases from the other saturator to be
passed through it when the proper moment arrives.

The acid charge of the saturators should have a
density of about 42° Bé., under which conditions

THE GAS LIQUOR 97

the sulphate of ammonia is deposited as large
crystals when the saturation stage is reached; and
the resulting product is of a high degree of purity.
It has mostly a greyish or yellowish tinge, which,
however, is not objected to in commerce, whereas
if the salt is of a blue shade, it must be sold at a
loss, although the blue colour—which is due to
Prussian blue from the cyanogen impurities—is
quite harmless when the salt is used as a fertilizer.
A. blue tinge also appears when local supersatura-
tion of the acid has occurred; and for some unex-
plained reason, the salt obtained from imperfectly
saturated liquor turns blue in draining. Sulphate
of ammonia is sold on the basis of its ammonia
content only, this amounting as a rule to 24-5 per
cent. The following Table gives the solubility of
sulphate of ammonia per 100 parts of water, at
various temperatures :— |

at 0° C. 71°00 parts at 60° CO. 86°90 parts

mG || piaee 73°65, ye IO ss 89°55 4s

” 20° ” 76°30 ” ” 80° ” 92°20. ”

OO 3 78°95. ,, aa ae 94°85 ,,

ae ler 81:60 _,, sa SOOT x 97°50 ,,
° 84:25,

” 3?

The manufacture of sulphate of ammonia in
saturators, as described above, entails stoppages for
the purpose of emptying the apparatus and re-
charging it with fresh acid; but the process may be
carried on in a continuous manner by means of the
same plant, by introducing both the mother liquor
and acid in the form of continuous thin streams.
The acid, however, must not be so strong as in the
intermittent process, the strength employed being

98 COAL GAS BY-PRODUCTS

32° Bé. The crystallized salt is scraped out at inter-
vals, or else is transported, by mechanical means, along
with the mother liquor, to a centrifugal machine,
where the two are separated, the mother liquor being
run back into the saturators. ,

Latterly, a number of gasworks have taken up
the manufacture of by-products; and, so far as the
manufacture of sulphate of ammonia is concerned,
the problem may be regarded as solved.

The two methods of Burkheiser and Feld enable
sulphate of ammonia to be produced simultaneously
with the purification of the gas, thus rendering the
operation independent of the sulphuric acid manu-
facturer.

The idea of combining the sulphuretted hydrogen
and ammonia in such a manner as to form sulphate
of ammonia, dates back as far as the fifties of the
last century, though no practical solution of the prob-
lem was effected. The attempts were all wrecked
in the endeavour to convert the sulphite into sulphate,
and consequently trials were made for utilizing the
sulphite as a fertilizer. This step was rightly charac-
terized by Feld as merely an emergency remedy.

The Burkheiser process is described in »German
Patents 212,209/07, 215,907/08 and 217,315/08.
This inventor oxidizes the iron sulphide of the gas-
purifying agent to sulphurous acid by a current of
air, and absorbs the product in a neutral solution of
ammonium sulphite, ammonium bisulphite being
formed. The ammonia of the gas liquor is distilled
in a column still, and is returned, in a dried state, to
the crude coal gas before the sulphuretted hydrogen

THE GAS LIQUOR 99

absorption stage is reached. After the removal of
the sulphuretted hydrogen, the gas parts: with its
ammonia to the ammonium bisulphite liquor and,
thus purified, is passed on to the gasholder. The
sulphite of ammonia deposited from the liquor, and
already containing 10 per cent of sulphate of
ammonia, 1s completely oxidized by the oxygen of
the air.

The method of operating may be explained by
reference to the accompanying diagram. The gas
liquor is distilled in a column still, and the dried
ammonia is returned to the crude gas before the
sulphuretted hydrogen is absorbed, so that the gas
contains the same quantity of ammonia as it did
before the ammonia absorption stage.

In absorbing the sulphuretted hydrogen, the gas
purifying agent in the No. I H,S purifier is heated
above 100° C., in contrast to the ordinary pro-
cedure. ‘The gas, freed from H,S, next passes to
the saturators, which will be mentioned again later.
Here it is freed from the bulk of the ammonia, and
passed on to the No. I scrubber, where it comes in
contact with a flow of acid ammonium sulphide

liquor, produced in No. II scrubber. While the
purifier I is absorbing sulphuretted hydrogen from
the crude gas, the purifier I] is being regenerated
by a blast of air. The heat generated by the
oxidation of the iron sulphide to ferric oxide and
sulphur dioxide is partly nullified and partly serves
to keep the purifier I heated to above 100° C.
during the absorption of the sulphuretted hydrogen.
The mixture of sulphur dioxide and air is passed

COAL GAS BY-PRODUCTS

100

through scrubber II, where it encounters a flow

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of ammonium sulphite liquor, which absorbs the

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dioxide and becomes bisulphite, in which condition
it is run through scrubber I and arrests the
residual ammonia in the coal gas. The. resulting
semi-neutral liquor passes to the saturators, where
the bulk of the ammonia of the coal gas is absorbed,
neutral sulphite of ammonia being formed. This
salt, being very sparingly soluble, is deposited for
the most part, and the residual neutral mother
liquor is used again for absorbing sulphur dioxide in
scrubber II. The deposited salt, about 60 per cent of
which is already oxidized into sulphate of ammonia,
is centrifugalized, dried and completely oxidized in a_
conveyor stove.

This stove consists chiefly of a horizontal drum,
provided at one side with a charging hopper for the
admission of the mixture of sulphite and sulphate,
another opening, for the discharge of the completely
oxidized salt, being provided at the other side.
Inside the drum is a worm conveyor which trans-
ports the salt from the charging end to the deliv-
ery end, whilst a current of air traverses the drum
in the opposite direction. For half its length,
measured from the charging end, the drum is cooled,
whilst the other half is heated. When the mixed
salt enters the heated end of the drum, the sulphite
of ammonia is decomposed into ammonia and —
sulphur dioxide, and is carried back by the current
of air—which partially oxidizes it at the same time—
into the cooled end of the drum, where it recon-
denses and is moved onward again, together with
the mixed salt, into the heated end of the drum, and

. a) *
24°83

DT ee 6) Ts » 2° 9

02° 328° GOA -GAS BY-PRODUCTS

so on. The salt discharged from the drum is
perfectly free from sulphite.

Of course, the whole purifying plantis arranged in
such a way that the H,S purifiers can be connected
and disconnected, according as they are regenerated
or exhausted. A small amount of sulphur trioxide
is formed along with the dioxide in the purifiers
and combines with the ferric oxide to form sulphate.
As soon as any considerable accumulation of this sul-
phate collects in the purifying agent it is extracted
by lixiviation.

The oxidation in the conveyor stove seems, how-
ever, to be not quite complete, or else a considerable
amount of sulphur dioxide is carried away by the
current of air and lost, for, according to a more
recent process (Ger. Pat. 223,713/09) Burkheiser
does away with the supplementary oxidation process,
and converts the sulphur dioxide into trioxide
direct, by interposing between the purifier and
scrubber a contact mass of platinum or ferric oxide,
as in sulphuric acid making. In other respects the
procedure is the same, except that sulphate liquors
replace the sulphite liquors.

The Burkheiser process has emerged beyond the
experimental stage and is already in use at the
Tegel gasworks, Berlin, and at several other gas-
works and by-product cokeries in Germany, etc.
(Aachen, Hamburg and Liége).

Whereas, in the Burkheiser process, the trans-
formation into sulphate is effected directly, by the
aid of atmospheric oxygen, Feld employs poly-

THE GAS LIQUOR 103

thionates as the carriers of oxygen, these being
decomposed again into sulphate and sulphur. The
Feld process passed through a series of experimental
stages before a practically usable method was ob-
tained. These experiments afforded, at the same
time, an opportunity for elucidating the reactions
of the complex polythionates.

Of the four stages of development of the process,
namely the tar-oil absorption process, zinc thionate
process, iron thionate process and_ polythionate
process, only the two last named have found ap-
plication in practice. The iron thionate process is
used at the East Hull gasworks, but is found to
be attended by certain defects, the absorption not
being always complete and proving nearly an entire
failure in presence of an excess of ammonia. Rises
in temperature ‘decompose the ferric thiosulphate
into ferric sulphate, sulphur dioxide and sulphur,
in .consequence of which the absorption of the
sulphuretted hydrogen (but not that of the ammo-
nia) is Impaired.

The polythionate process (Hing. Pat. 5838/11) is
employed at the Konigsberg gasworks, and is free
from the above-named defects. The principle is as
follows: When led into even a moderately concen-
trated solution of ammonium thiosulphate, sulphur
dioxide is absorbed, quantitatively, with formation
of ammonium tetrathionate and trithionate:

(a) 2(NH,),8,0, + 880, = (NH,),5,0, + (NH,),530..

The resulting solution serves as absorbent for the
ammonia and sulphuretted hydrogen in coal gas,

104 COAL GAS BY-PRODUCTS

sulphate of ammonia and sulphur being formed,
together with some ammonium thiosulphate. The
deposited sulphur is burned off as sulphur dioxide
and serves for regenerating the absorbent liquid
from the thiosulphate (reaction q@) :—
(b) (NH,),8,0, + 2NH, + H,O = (NH,),SO, +
(NH,). 8 yt SS.
(c) NH),8,0, + 3H,S = 3H,0 + (NH), $0, + 58.
(d) (NH,),8 Oct (NH,),5 = 2(NH,),S, O,+ .

When the liquor is sufficiently enriched with
sulphate of ammonia, a portion of it is worked up
for.the recovery of sulphate, by treating it with
sulphur dioxide and heat, thus converting the
polythionate into sulphate, accompanied with de-
position of granular sulphur :—

(NH_,),5,0, (hot) = (NH,),8O0,.+ 5O, + 25.

The sulphur is separated from the liquor, which
is then concentrated to allow the sulphate of am-
monia to crystallize out. The mother liquor, sulphur
dioxide and sulphur are used over again in the manu-
facturing process.

The only direct oxidation occurring throughout
the whole process is the combustion of the sulphur
to sulphur dioxide, the further oxidation of the
thiosulphate to sulphate being based on a reaction
of displacement between the thiosulphate and.sulphur
dioxide, accompanied by the deposition of sulphur.

The Feld process has enabled a wet purification
for washing out the sulphuretted hydrogen to be
introduced in addition to purifying the coal gas and
producing sulphate of ammonia.

CHAPTER VI.»
THE TREATMENT OF THE GAS-PURIFYING AGENTS.

THE spent purifying agents contain, as valuable
constituents: ammonia, cyanogen, sulphur, sul-
phuric acid and thiocyanogen, the cyanogen being
perhaps the most valuable at all. This substance is
present in the spent mass in the form of compounds
of still unknown composition. The percentage of
cyanogen varies considerably according to the origin
of the mass, and it is therefore important, in con-
nection with the sale of spent gas purifying agents,
to have a good method for the determination of the
cyanogen. Consequently, the divergent character
and chemical composition of the purifying agents
have led to the elaboration of a whole series of
methods of determination, the most customary of
which will now be briefly described. In valuing the
article it is important that both buyer and seller
should agree on the method of determination to be
employed, since otherwise it will be difficult for
concordant results to be obtained.

One of the oldest methods for the determination
of ferrocyanogen is that introduced by Zulkowsky
in 1883 (Dingler, No. 249, p. 168). It was origin-

(105)

106 COAL GAS BY-PRODUCTS

ally intended for application to ferrocyanide melts,
but was afterwards used also for determining
cyanogen in gas-purifying agents.

The mass is extracted with caustic potash, the
filtrate being then acidified with sulphuric acid, and
the cyanogen determined by titration with zinc
sulphate solution of known strength. The end
point of the titration is ascertained with ferric
chloride solution:as indicator. .

Leybold and Moldenhauer («Journal fiir Gas-
beleuchtung,” 1899, p. 155) ascertain the percentage
of ferrocyanogen by determining the combined iron
volumetrically. The mass is treated with caustic
potash in the warm, and is then made up to a
definite volume. An aliquot part of the filtrate is
concentrated, and is evaporated with sulphuric acid
and calcined, to eliminate the cyanogen. The
residue is taken up with a little sulphuric acid in
water, and the iron is determined in the solution,
with potassium permanganate, in known manner,
after reduction with zinc.

De Koningh (« Zeitschrift fiir angewandte Chemie,”
1898, p. 463) evaporates the alkaline extract to
dryness and eliminates the cyanogen by fusion with
sodium carbonate and saltpetre, the iron being
determined, gravimetrically, in the melt. The
determination of the cyanogen in _ gas-purifying
agents by estimating the iron in the alkaline ex-
tract has also been proposed by others; but since
this extract contains other iron in addition to that
in combination with cyanogen, the ferrocyanogen

TREATMENT OF THE GAS-PURIFYING AGENTS — 107

content comes out higher than the truth; and
seeing that the cyanogen content in the mass is
always small, even slight sources of error are suf-
ficient to produce a considerable percentage dif-
ference.

A method which is based on the technical pro-
cess of treatment has been elaborated by Dr.
Knublauch (‘‘ Chemiker Zeitung,” 1902, p. 1039), and
as this is largely employed in practice, it may be
described in a somewhat fuller manner. According
to Knublauch, the ferrocyanogen is determined as
Prussian blue, in the alkaline extract, by means of
-copper-sulphate solution.

T'wo hundred to two hundred and fifty grms. of a
good average sample of the spent purifying material
under examination are dried on a weighed sieve,
covered with paper, for five to six hours at 50°-
60° C. The mass it then left exposed to the air for
four hours until of constant weight, the hygroscopic
moisture being ascertained from the difference in
weight. The sample is next crushed to powder
and passed through a sieve with 360 meshes per
square centimetre, the residual fragments of wood
being cut up with a knife so that they too pass
through the screen. Ten grms. of this air-dry
powder are suffused with 250 cc. of 10 per
cent caustic potash in a 250-c.c. flask, and left
to stand for about sixteen hours at room tempera-
ture, the liquid being shaken up repeatedly at first
and towards the end. In order to prevent the
formation of lumps or nodules, the extraction may

108 COAL GAS BY-PRODUCTS

also be effected in a porcelain mortar, the liquid
being stirred, at the prescribed times, with the
. pestle. At the end of the sixteen hours, the thorough-
ly triturated mixture is rinsed into a 250-c.c. flask,
which is then filled up with distilled water, to 5 c.c.
above the mark (to allow for the space occupied by
the solids). The flask is then shaken up well, and
the contents passed through a dry filter. Owing
to the presence of impurities, mainly of an organic
character, the potassium ferrocyanide cannot be
determined direct by titrating the filtrate, but the
extract must first be re-purified by precipitating the
cyanogen as Prussian blue. The ferric chloride
solution used for this precipitation contains 60 grms.
of Fe,Cl, per litre, along with 200 c.c. of concen-
pee hydrochloric acid. One hundred c.c. of the
alkaline extract are run (with stirring) into 25 c.c.
of the ferric solution, which has been warmed to
80° C. The ferrocyanide is thrown down as Prus-
sian blue, which is filtered through a folded filter in
a hot-water funnel, this latter being kept covered
up and the solution warmed before each portion
is poured in. The precipitate is washed two or
three times with hot water, and is then stirred
up well, in a glass beaker, along with 20 c.c. of
10 per cent caustic potash, in order to decom-
pose all the Prussian blue, this process being assisted
by a careful, gentle warming. When all the blue is
decomposed, the contents of the beaker are rinsed
into a 250-c.c. flask, which is then filled up to the
mark Any sulphuretted hydrogen present is pre-

TREATMENT OF THE GAS-PURIFYING AGENTS — 109

cipitated by the addition of 1 grm. of freshly pre-
pared lead carbonate. After a thorough shaking,
the liquid is passed through a folded filter, and an
aliquot part of same, in acid solution, is titrated
with copper sulphate, ferric chloride being used as
indicator.

The copper reagent is prepared as follows: 12-
13 grms. of pure copper sulphate are dissolved in 1
litre of water, and the solution is standardized with
a 0-4 per cent solution of pure potassium ferro-
cyanide. With this object, 50 c.c. of this latter
solution are treated, in a beaker, with 5 c.c. of dilute
sulphuric acid (1:5). Copper sulphate solution is
next allowed to run in from a burette until the ap-
plication of a strip of test paper no longer reveals
the formation of Prussian blue. This test paper is
prepared by allowing one drop of the test liquid to
fall on to a strip of absorbent paper (free from iron),
and then letting one drop of ferric chloride fall
on the paper so that the edges of the two liquids
coalesce. In presence of potassium ferrocyanide, a
blue coloration is produced at the plane of contact.
Since copper ferrocyanide also reacts with ferric
chloride, care must be taken to see that the ferric
chloride solution comes in contact with the test
liquid orily.

Another method of ascertaining the end point of
the reaction consists in filtering off 1 c.c. of the test
liquid, after each application of the copper solution,
and adding ferric chloride solution to the filtrate. If
no blue coloration appears after the solution has

110 COAL GAS BY-PRODUCTS

been observed on white paper for half a minute, then
the reaction is complete.

A sharp distinction must be made between ‘thens
two methods of determining the end point, the re-
sulting values not being identical. In both cases it
is desirable to repeat the titration, adding, in a single
dose, a slightly smaller quantity of the copper solution
than was consumed in the first test, and ascertain-
ing the end point in the same way as before. In
these circumstances the difference between the two.
methods is reduced; but in any event the filtration
method gives higher values than the other. The
standardized copper-sulphate solution, prepared as
above, corresponds to 0-0,04 grm. of

K,Fe(CN), + 3H,0.

In order to calculate the results to cyanogen com-
pounds other than potassium ferrocyanide, the
values obtained must be multiplied by the following
factors :—

For Cyanogen CN = 0°3696
Hydrocyanic acid, HON = 0°3839
Hydroferrocyanic acid, H,Fe(CN),; = 0°5118
Prussian blue, Fe; (CN); = 0°6792.

Dreschmidt found that the unfavourable influence
exerted on the titration by the re-solution of the
Prussian blue cannot be avoided entirely; and he
therefore proposes to determine the ferrocyanide in
the spent purifying agent by means of mercuric
oxide. When cyanogen compounds are boiled along
with mercuric oxide, soluble mercuric cyanide is
formed ; but since the purifying agent also contains

TREATMENT OF THE GAS-PURIFYING AGENTS 111

thiocyanogen, which likewise enters into soluble
combination with mercuric oxide, this reaction must
be prevented by the addition of a reducing agent to
transform the product into insoluble mercurous thio-
cyanate. By reduction with zinc dust, the mercuric
cyanide is transformed into ammonium cyanide,
which can be determined, volumetrically, by the
Volhard method. |

For the determination of cyanogen in gas purify-
ing agents by the Dreschmidt method, 10 grms. of
the thoroughly pulverized, air-dry average sample
(as already described) are mixed with 150 c.c. of
water in a 500-c.c. flask, and treated with 1 grm. of
ammonium sulphate and 15 grms. of mercuric oxide,
the former reagent being added to obviate the dis-
turbing influence of the fixed alkali on the decom-
position. The mixture is kept boiling for fifteen
minutes and, when cooled, is treated with about
1 c.c. of a saturated solution of mercurous nitrate
until all the mercuric thiocyanate has been thrown
down as the corresponding mercurous salt. The
flask is then filled with distilled water up to about
6-8 c.c. above the mark (to allow for the space
occupied by the solids), and well shaken. Two
hundred c.c. of the solution, passed through a dry
filter, are treated, in a 400-c.c. flask, with 6 c.c.
of ammonia solution (0-910) and 7 grms. of zinc
dust (free from chlorine). The whole is shaken up
well for a short time, and then treated with 2 c.c. of
a 30 per cent solution of caustic potash. The flask
is filled up again with water to 1 c.c. above the

112 COAL GAS BY-PRODUCTS

mark, and after being well mixed, the liquid is
filtered through a dry filter. Of the filtrate, 100 c.c.
are run into a 400-c.c. flask containing 40 c.c. of
decinormal silver solution and 80 c.c. of a 10 per
cent solution of nitric acid (free from chlorine). The
cyanogen, thrown down as silver cyanide, is collected
together by shaking, and the flask is filled up to the
mark. The contents are next filtered again through
a dry filter, and the excess of silver nitrate in 200 c.c.
of the filtrate is titrated back with 1/20-normal
thiocyanate solution, by the Volhard method, in pre-
sence of ferric sulphate as indicator. The difference
between the number of c.c. of thiocyanate solution
consumed and the 40 c.c. of silver nitrate solution
taken gives the consumption of decinormal silver
solution per 1 grm. of air-dry purifying material.

One c.c. of decinormal silver solution corres-
ponds to :— |

0°002598 grm. of CN,
0°007042 grm. of K,Fe(CN), + 3H,0,
0°004782 orm. of Fe,(CN),3.

A quick method which gives values only slightly
higher than those of Knublauch and Dreschmidt has
been worked out by Witzeck, in consequence of an
exhaustive examination of Feld’s method of deter-
mining cyanogen. According to his proposal, 2 grms.
of the gas-purifying materials are triturated for
about five minutes in a porcelain mortar with 1 c.c,
of asolution of ferrous sulphate (containing 278 grms.
of ferrous sulphate per litre) and 5 c.c. of caustic
soda (320 grms. per litre). Into this mixture, 30 c.c.

TREATMENT OF THE GAS-PURIFYING AGENTS _ 113

of magnesium chloride solution (600 germs. of MgCl,
per litre) are run by degrees with continued stir-
ring, the whole being swilled with a large volume
of hot water into a 200 c.c. retort. In presence of
30 c.c. of sulphuric acid (of four times the normal
strength), the liberated hydrocyanic acid is dis-
tilled over, the distillate being collected in 2-normal
caustic soda and titrated with decinormal silver nitrate
solution in presence of 5 c.c. of i-normal potassium
iodide solution. One c.c. of decinormal silver solu-
tion corresponds to 0:00956 grm. of Prussian blue.
The selling value of the spent purifying material
depends on its cyanogen content, though the amount
of the other utilizable substances present must also
be determined, for manufacturing reasons. The de-
termination of the sulphur, sulphuric acid, thio-
cyanogen and ammonia does not differ essentially
from the methods generally used for these substances,
and therefore need not be gone into in detail here.
In determining the sulphur by extracting the air-
dry material with carbon disulphide in the Soxhlet
apparatus, the sulphur content can be ascertained
direct, from the loss.in weight of the flask after the
expulsion of the solvent. Gas purifying materials,
however, always contain small quantities of organic
substances, which pass into solution during the ex-
traction process. Unless very accurate results are
required, it will be sufficient to suffuse the residue
with ether, and to pour off the organic substances
thus dissolved along with those from.the sulphur. - For
accurate determinations, the sulphur must be con-
8

114 COAL GAS BY-PRODUCTS

verted into sulphuric acid, by oxidation with potas-
sium chlorate or fuming. nitric acid, and determined
as barium sulphate.

The products recovered from the spent purifying
material are: cyanogen compounds, thiocyanogen
compounds, ammonia and sulphur, or sulphuric acid.
The ammonia is almost entirely in a state of com-
bination.

~The preparation of cyanogen compounds from the
spent purifying materials is not altogether among
the simplest of operations. The large content of
sulphur, which, on account of its low market value,
cannot be extracted at a profit, has to be carried
through the whole process as ballast, and, in the
basic dissociation of the materials, favours the forma-
tion of thiocyanogen—of course at the expense of the
cyanogen. In spite, however, of the fact that the
extraction of sulphur is prescribed in many processes,
it is seldom carried out in practice.

A large number of methods have been proposed
for the recovery of the cyanogen compounds, only
a few of which, however, have been adopted into
practice. The most important and the one almost
exclusively in use at present is that described in
Kunheim and Zimmermann’s German Patent 26,884/
83. The spent purifying material is first lixiviated
with water, to extract the soluble ammonia salts,
and is then dried in the air. The sulphur is
recovered by extraction with carbon disulphide,
and -the residual mass is intimately mixed with
ground caustic lime and warmed to 40-100° C.

TREATMENT OF THE GAS-PURIFYING AGENTS — 115

(104-212° F.) in a closed vessel provided with
stirrers. The dissociated mass is placed in filter
boxes and leached systematically with water, an
ammoniacal solution of calcium ferrocyanide being
obtained, which, on concentration, deposits the spar-
ingly soluble double salt Ca (NH,),Fe(CN),. This is
filtered off, and transformed into calcium ferrocyan-
ide by boiling the calcium hydroxide, this compound
being, in turn, transformed, by the aid of potassium
chloride, into the sparingly soluble potassium-calcium
ferrocyanide, K,Cal'e(CN),, from which potassium
ferrocyanide is: finally obtained by treatment with
potassium carbonate.

Valentine (Eng. Pat. 3908/74) proposed to dis-
sociate the lixiviated purifying material with calcium
.and magnesium carbonates at boiling temperature, —
recovering the corresponding ferrocyanide compounds
from the clear solution, and transforming them into
Prussian blue for the production of potassium ferro-
cyanide. ‘The dissociation is, however, very imper-
fect and takes a long time to effect.

Proposals have been made by O’Neill and Johnson,
and also by Griineberg, to use caustic soda as the
dissociating agent; but the high cost of the reagent
and the risk of producing thiocyanogen render the
process unprofitable.

More recently, it has been proposed to extract the
Prussian blue by means of acids. Donat and Orn-
stein (Ger. Pat. 110,097), after eliminating the sol-
uble salts and sulphur, treat the residue with dilute
hydrochloric acid (1:3), and thus get rid of all the

116 COAL GAS BY-PRODUCTS

ferric hydroxide. .'The Prussian blue is then extracted
with concentrated hydrochloric acid and is thrown
down, in a pure state, on dilution with water.

Another possible method of treating spent purify-
ing materials consists in converting the cyanogen
compounds into thiocyanogen compounds, with quick
lime (Marrasses, Ger. Pat. 28,137), or with baryta or
barium sulphide (Hélbling), under pressure. Since,
however, the demand for thiocyanogen compounds
is far smaller than that for cyanogen compounds,
and can, in fact, be met by the compounds already
present in the spent purifying materials, there is no
need to go into the details of these processes.

For the treatment of spent purifying materials
there is a choice of three systems :—

1. Extracting the sulphur with carbon disulphide.
and then treating the material further as under 2
and 3.

2. The material is first freed from the soluble
ammonium thiocyanate and sulphate by lixiviation,
and the residue is dissociated with lime or alkalis.

3. The material is treated direct with lime or
alkalis, so as to obtain cyanogen, thiocyanogen, and
sulphuric acid in the same extract.

In 2 and 3, the sulphur content (about 30-40 per
cent) of the material is carried, as ballast, right
through the process. It would, therefore, from the
ideal standpoint, be preferable to extract the sulphur
first; but in spite of the attractiveness of the idea,
the preliminary extraction of the sulphur is rarely
carried out, the operation requiring very careful

TREATMENT OF 'THE GAS-PURIFYING AGENTS — 117

supervision, owing to the high fire risk and injurious
action of the solvent (carbon dioxide) on the human
organism.

ELIMINATING THE SULPHUR BY EXTRACTION.

The air-dry spent purifying material is first ground
ina disintegrator, so as to pass through a 4-m.m.
sieve. The apparatus used for extracting the sul-
phur consists of the extractor, the condenser, a still,
a tank for the solvent and a trap for the separation
of water. The cylindrical extractor is provided with
a perforated false bottom covered with a filter cloth,
on which the purifying material is spread so as to fil
the vessel, being introduced through a manhole for
this purpose. ‘The material is then covered over
with another filter cloth and the manhole is closed.
The carbon disulphide in the still is vaporized by
means of a steam coil and admitted into the charged
extractor, where most of it condenses, draining down
through the charge and extracting the sulphur, after
which it is run through a second pipe back to the
still. The uncondensed carbon disulphide passes
away to the condenser, where it condenses in a
water-cooled worm and collects in a receiver, whence
it can be led off to the still as required. All the
connections are provided with valves. In conducting
the distillation, a quantity of solvent equal to the
amount condensed in the condenser is run from the
storage tank into the still. The extraction is con-
tinued until a sample of the carbon disulphide, taken
from between the extractor and the still, no longer

118 COAL GAS BY-PRODUCTS

leaves any sulphur behind on evaporation. After all
the sulphur has been extracted, the valves are set
so that all the carbon disulphide vapour coming from
the still passes into the condenser, whilst at the
same time the supply from:the storage tank to the
still is cut off. In this way the sulphur is freed from
the solvent, and is drawn off when melted. Steam is
then blown through the extraction residue, in order to
expel the carbon disulphide completely.

The residual material is treated, for the extraction
of the ammonium salts, in exactly the same way as
when the sulphur is left in.

LIXIVIATING THE PURIFYING MATERIAL.

In the course of treatment for recovering the
cyanogen compounds, the usual practice now is to
extract the material with water first, the method of
extraction in an apparatus fitted with stirrers, for the
purpose of obtaining a concentrated liquor which
can be worked up for thiocyanogen compounds, hav-
ing been entirely abandoned in favour of filter
boxes in which the material is lixiviated systematic-
ally. The usual dimensions of the filter boxes are
7 feet by 6 feet by 3 feet, and the holding capacity is
about 3 tons. The boxes are of iron, or preferably
wood, the bottom being of six to seven baulks, ar-
ranged at uniform intervals and provided on the
upper face with V-shaped grooves, 2 inches deep and
6 inches apart, to allow the liquid to drain away un-
impeded. On the bottom, and at right angles to
the timbers, is a grating of laths (about 1} inches

TREATMENT OF THE GAS-PURIFYING AGENTS 119

in width), covered by a filtering layer of twigs or
straw, the whole being topped by a filter cloth of
loosely woven cotton or jute fabric. In one part of
the box a pipe extends down through the filtering
material to the bottom timbers; and in this. place
the filter cloth is preferably provided with a double
iron ring, fitted with an internal thread in which
the pipe is screwed to hold it in position. The ob-
ject of this pipe is, first of all, to allow free outlet to
any imprisoned air when the water is poured on to
the charge, and, secondly, to prevent suction, which
would compress the charge and hinder filtration
when the water is being run off. At one side of the
box, and below the level of the grating, is an earth-
enware cock for drawing off the liquor. The box is
charged with spent gas-purifying material, nearly up
to the rim, the charge being merely shovelled in and
not stamped down. Water is next admitted through
a hose.. The air escapes through the upcast pipe,
and the material is uniformly penetrated by the
water, which is allowed to fill the box until the level
is a little above the surface of the charge. The box
is left for fifteen to twenty hours, during which time
the soluble salts are taken up by the water, where-
upon the liquor is drawn off through the cock. Since
a single extraction is not sufficient to remove all the
soluble salts, the operation must be repeated several
times; but since these repeated extractions in the |
same box would give: very dilute liquors, several
boxes are connected up in series to form a battery,
and the lixiviation is performed on the counterflow

120 COAL GAS BY-PRODUCTS

principle. After leaching the contents of the first
box, the liquid passes into the second and there be-
comes enriched by extracting further quantities of
soluble salts, and so on until the end box is reached.
In this way the box containing the most exhausted
material receives the fresh water, whilst the freshly
charged box is first extracted with the most concen-
trated liquor, the succeeding extractions being effected
with progressively weaker liquors, until, finally, fresh
water comes into action on the nearly spent charge.
As a rule, eight boxes are connected together to form
a battery, so that the material in each is extracted
eight times.

Assuming, in the first place, that all the boxes are
charged with fresh spent material. Fresh water is
admitted into box No. 1, and left to stand for about
twenty hours, the liquor being then run off into a
collecting basin, and transferred thence to box No. 2
by a pump or injector. Owing to the fact thata
certain quantity of water is retained by the material
in the first box, a corresponding amount of fresh water
must be supplied to No. 2. Box No. 1 is recharged
with fresh water. At the end of twenty hours the
liquor from box 2 is run off into a collecting basin,
and at the same time that from No. 1 is discharged
into another basin. The two liquids are transferred
to boxes Nos. 3 and 2 respectively, and No. 1 is re-
charged with fresh water. These operations are
repeated until the first liquor is discharged from the
eighth box. No. 1 box is now disconnected and re-
ceives a fresh charge of spent purifying material,

TREATMENT OF THE GAS-PURIFYING AGENTS — 121

the liquor from. box 8 is admitted into box 1, and
all the other liquors are advanced a stage to corre-
spond. ‘The liquor discharged from box I after a
further sojourn of twenty hours therein is almost
-completely saturated with soluble salts. It has a
density of 12-14° Bé., and is run off into a collecting
tank for further treatment, whilst box No. 2 now re-
ceives a charge of fresh water. By proceeding in
this way a charge of liquor can be drawn off into the
collecting tank each day, and one unit of the battery
must be recharged. With a battery of this kind,
24 tons of spent purifying material can be leached
in a week.
TREATING THE LIQuoR.

The valuable contents of the liquor from the lix-
iviation of the spent purifying material consist of
ammonium thiocyanate and sulphate. The liquor
can be treated direct in a column still of the kind
already described, thus recovering the bulk of the
ammonia contained in the spent purifying material.
If, however, it be desired to prepare thiocyanates from
the liquor, this latter is concentrated in evaporating
pans, and the two salts are separated by fractional
crystallization. The sulphate of ammonia is deposited
first, and the bulk of the thiocyanate is afterwards
recovered by further concentration and crystallization.
Neither of the salts is as yet in a marketable con-
dition. ‘The sulphate is freed from ammonia in a
.column still and is then obtained in a pure state,
whilst the thiocyanate is purified by recrystallization.
The thiccyanate can also be recovered from the

122 COAL GAS BY-PRODUCTS

mother liquor of the sulphate of ammonia, as cuprous
thiocyanate, by treatment with copper sulphate and
sulphurous acid, and is squeezed in the filter press.
Further particulars on the treatment of the crude
salt and the copper salt will be given later.

TREATING THE EXTRACTED MATERIAL.

The lixiviated purifying material is next subjected
to further treatment for the recovery of cyanogen,
which is present in the form of insoluble ferrocyan-
ide. Treatment with alkalis or lime converts it into
the soluble alkali- or calcium ferrocyanide compound.
The transformation takes place in the cold, but is
accelerated and rendered more complete by warming.
In practice, of course, lime alone—or perhaps soda
—is used as the dissociating agent, the other alkalis
being too expensive. The process is carried on
either in vessels provided with mechanical stirrers
or in filter boxes.

At the first glance, the former method would seem
the more suitable, the object being attained more ©
quickly by constant stirring, whilst at the same time
a smaller excess of reagent is sufficient. This treat-
ment, however, results in a portion of the material
being converted into a fine sludge, which cannot be
separated into liquor and residue, either by settling
or by suction filters, filter presses being necessary.
Moreover, the homogeneity of the material is de-
stroyed, nearly 1-4 being still in the condition of
coarse granules; and in these circumstances the.
filter press is very liable to be choked up. To pre-

TREATMENT OF THE GAS-PURIFYING AGENTS — 123

vent this, the material has to be diluted with
the drainings from previous pressings, and the
coarser ingredients must be allowed to settle down.
Before washing, the press cakes still contain about
4 per cent of potassium ferroeyanide and about 35
per cent of water. Since the spent purifying mass
originally contains from 7 to 14 per cent of cyanogen,
it follows that nearly one half this has to be recovered
from the press cakes by washing. The chief draw-
back of the stirring process therefore consists in the
very weak liquors obtained ; and for this reason the.
_method has, in most works, been superseded by the
filter-box process.

' The apparatus used for the stirring process con-
sists chiefly of a closed iron cylinder, the bottom of
which slopes toward the periphery. The cover is.
_ provided with a stuffing box for the rotary shaft, and
with a manhole for charging and emptying, a pipe
connection being arranged for carrying off any gases
that may be liberated ; whilst a draw-off cock is fitted
in the bottom. For treating 3-ton charges of spent
purifying material, the cylinder should have a capa-
city of about 230 cub. feet, of which the material oc-
cupies about 53 cub. feet; so that, to fill the cylinder
about three-quarters full, there is room for about
550 galls. of liquor. The cylinder is traversed by a
pinion-driven vertical shaft, carrying, at the bottom
end, a set of rakes adapted to the shape of the
cylinder bottom, whilst a number of horizontal vanes
are arranged at certain intervals on the shaft, in
order to keep the uppcr layers of material in motion.

124 COAL GAS BY-PRODUCTS

To start the apparatus, the cylinder is charged with
a corresponding quantity of weak liquor, and the
stirrers are set in motion, the material to be treated
being then introduced through the manhole, and
the steam turned on.. The dissociation takes two to
three hours, according to the quantity treated. At
this stage the mass is diluted with weak liquor, the
stirrers are stopped, and the whole is left at rest for
about half an hour, to allow the coarser material to
settle down. ‘The sludge is next drawn off into a
filter press by a siphon, which extends down to the
level of the coarse material, and in this press the
material is washed until the “washings no longer ex-
hibit any traces of cyanogen. A sufficient quantity
of the weak liquor to dissociate a fresh charge is in-
troduced into the cylinder, and a fresh quantity of.
spent purifying material is treated. When, in this
way, a sufficient amount of coarse material has ac-
cumulated in the cylinder it is drawn off through
the cock and completely extracted in the filter press.
The various liquors are collected in a tank. Accord-
ing to the dissociating agent used, they contain
sodium ferrocyanide or calcium ferrocyanide.
Béssner, in his work on the utilization of spent
gas purifying materials, reports on a number of ex-
periments made in the dissociation of the material
with lime and soda,. the method adopted being similar
to that described above. The lime was used in the
form of slaked lime containing about 50 per cent of
CaO, 11 parts of CaO being added to every 100
parts of material in order to provide for the insol-

TREATMENT OF THE GAS-PURIFYING AGENTS 125

uble sulphates in the lixiviated mass. The actual
consumption of lime ranged from one and a half to
three times the theoretical quantity. At the ordinary
temperature, although a threefold quantity of lime was
used, the dissociation amounted to only 66 per cent,
corresponding to the formula K,Fe(CN),.3H,O; but
was increased to 80 per cent cn raising the tempera-
ture to 55°C. (131° F.). Further rises in temperature
greatly facilitated the formation of thiocyanogen
compounds, all the requisite components of which
(lime, cyanogen and sulphur) are present in the
material. To increase the dissociation at the tem-
perature mentioned, a mixture of lime and soda was
added towards the end of the operation, the addition
of lime being naturally reduced accordingly; and in
this way the dissociation was increased to 96 per
cent. The addition of soda converts the calcium
ferrocyanide into Na,CaFe(CN),; but a sufficient
amount of soda must be used to dissociate the
ferrocyanogen as well. A very important factor in-
fluencing the success of the treatment is not to work
with very large charges.

As already mentioned, the stirring process has
now been superseded by the filter-box method,
because it enables a dissociation of 87 per cent to
be obtained with lime alone, without the use of
complicated apparatus. The filter boxes are of
exactly the same pattern as those used for lixiviat-
ing the spent purifying material; and the process
is carried out in just the same way. After the
operation, the material is left to drain for several

126 COAL GAS BY-PRODUCTS

days in the boxes, and is then spread out to dry on
a cement or asphalted floor and turned over fre--
quently with a shovel. As soon as it no longer
‘“‘balls”” when squeezed, it is air-dry, whereupon a
definite quantity of powdered lime is strewn over it,
and the two are thoroughly mixed with the shovel.
The amount of lime thus added is equal to the
quantity of potassium ferrocyanide present. The
mixture is screened in a 4 mm. sieve, and the
residual lumps are also crushed and screened. ‘This
mixture is again placed in the filter boxes, sufficient
water being added to cover the mass. The leach-
ing process is precisely the same as in the original
lixiviation in the filter-box battery. The resulting
liquor has a density of 12-14° Bé. and contains
120 grms. of K,Fe(CN),.3H,O per litre. Irre-
spective of the original content of potassium ferro-
cyanide, 0-8-1-5 per cent of that salt is left behind
in the residue, the percentage referring to the mass
in the condition in which it was, as regards
moisture, previous to the addition of the lime. .
With the filter-box method the cyanogen obtained
in the liquor is in the form of calcium ferrocyanide
exclusively. The further treatment of the liquor
will be described later, in connection with that of
the liquor obtained from the cyanogen sludge.

The third system of treatment, by dissociation
without previous lixiviation, is applied when the
spent purifying material is very low in soluble am-
monium salts; and the operation is carried on in
closed filter boxes, in order to prevent inconvenience

TREATMENT OF THE GAS-PURIFYING AGENTS — 127

from the fumes of ammonia. When sufficiently
rich in ammonia, the liquor is treated in a column
still and then concentrated, the potassium ferro-
cyanide being precipitated direct with potassium
chloride.

CHAPTER VIL.
TREATING THE CYANOGEN SLUDGE.

THIS operation is comparatively simple, since one
has only to deal with substances of known com-
position, and the work is rendered easier by the
absence of sulphur.

Up to the present, only the methods of Foulis
and Buéb have to be considered in the absorption of
cyanogen by the wet process in the course of gas
purification.

According to the Foulis method, the washing
liquor contains Prussian blue, potassium ferroferri-
cyanide and ammonium ferroferricyanide, together:
with soluble cyanogen compounds. ‘The sludge is
squeezed in the filter press, and the ammonia in the
clear filtrate is expelled in a column still. The
residual liquor from the latter contains calcium
ferrocyanide in solution. The residue from the
filter is dissociated with caustic lime in an apparatus
fitted with stirrers, and the resulting clear liquor is
united with that from the column still, to be treated
for recovering ferrocyanide salts. According to the
Buéb method, the soluble portion of the sludge con-

(128)

TREATING THE CYANOGEN SLUDGE 129

- tims ammonium ferrocyanide, whilst the insoluble
portion corresponds to the formula

2NH,(CN) : Fe(CN), (Hand),

or (NH,),Fe,(CN,), (Feld).

The cyanogen of the soluble ammonium ferro-
cyanide is converted into the insoluble form by boil-
ing the sludge in closed iron vessels, fitted with
condensing apparatus. In this process all the free
ammonia is liberated, and is worked up in the
manner already described. The sludge is next
squeezed in filter presses, and the sulphate of am-
monia contained in the filtrate is worked up as such,
whilst the press cakes are dissociated with lime in a
stirrer apparatus, the resulting calcium ferrocyanide
liquor being subjected to further treatment.

CHAPTER VIII.

TREATING THE CRUDE LIQUORS.

THE crude liquors from the dissociation process
contain a variable mixture of saline matters, accord-
ing to the previous treatment of the material.
When the preliminary lixiviation has been omitted,
the material will contain calcium thiocyanate and
gypsum, in addition to the cyanogen compounds,
whereas if dissociated with caustic soda and lime,
the hydroferrocyanic acid will be in combination
with calcium, sodium, and sometimes ammonium.
as well. Irrespective of the preliminary treatment,
this acid must be separated from the other con-
stituents of the liquor, by precipitation or crystalliza-
tion, three systems being available :—

1. Precipitation with iron salts, as a blue pre-
cipitate which varies in composition and is commonly
termed ‘‘ blue”,

2. Precipitation, as a double calcium-ammonium
salt, by means of ammonium salts. |

3. Precipitation, with potassium chloride, as a
double, calcium-potassium salt.

(130)

TREATING THE CRUDE LIQUORS 131

1. PRECIPITATION witH IRON SALTS.

The crude liquor is slightly acidified, with hydro-
chloric acid, in wooden or lead-lined vats, the
sulphur resulting from the dissociation of the sul-
phides being thrown down. This will subside to the
bottom of the vat inside twenty-four hours, and the
clear liquor can then be drawn off. The liquor is
next treated with ferrous chloride or ferric sulphate
—which latter salt should not be used when the dis-
sociation has been effected with lime, since other-
wise gypsum would be formed—until a sample,
taken from the filtrate, no longer gives a precipitate
with the iron salt. In such case the amount of iron
is not sufficient to convert the whole of the ferro-
cyanogen salt into Prussian blue, the white pre-
cipitate obtained containing in addition substances
corresponding to the formula Na,FeFe(CN),. The
reaction 1s expressed by the equations :—

K Fe(CN), + 2FeCl, = Fe,Fe(CN), + 4KCl:
Na sHe(CN), 4 FeCl, = Na »HeFe(CN), + 2NaCl.

The white eR however, contains com-
pounds of a more complex nature, since calcium (and
also ammonium) is present, in addition to sodium,
in the crude liquor.

The precipitate is left to settle for twenty-four oats,
and, after the clear liquor has been siphoned off, is
squeezed in filter presses. Owing to the slimy
character of the precipitate, the pressing 1s accom-
panied with difficulties. On account of the acidity
of the liquor, diaphragm pumps have to be used,

132 COAL GAS BY-PRODUCTS

and the resulting pulsating action of the pump is
liable to tear the filter cloths, so that the use of a
pressure vessel is preferable. The washing, too, is
a protracted operation and is always attended with
loss. The resulting press cakes, which contain
about 30 per cent of K,Fe(CN),.3H,O are decom-
posed with caustic potash or soda, in a stirrer
apparatus, the reaction being expressed by the
equations :—

‘Na, FeFe(GN), + 2NaOH = Na, Fe(CN),+ Fe(OH), ;
Fe,Fe(ON), + 4NaOH = Na, Fe(CN), + 2Fe(OH), -

The precipitated ferrous hydroxide presents the
unwelcome feature of causing difficulties in respect
of settling down and filtration, and necessitates re-
course to the filter press again, in which connection
the protracted washing of the press cakes—-which,
moreover, yield a very weak liquor—is highly incon-
venient, the further concentration of the liquor tak-
ing up much time and patience. Jor these
reasons the method is now seldom used, unless it be
desired to extract further small quantities of cyanogen
from the spent liquors.

The Kunheim and Zimmermann process accom-
plishes the same object in a much simpler and
quicker way. In presence of alkali- or ammonium
salts, in the warm, calcium ferrocyanide furnishes in-
soluble double salts, according to the equations :—

Ca,Fe(CN), + 2NH,Cl = Ca(NH,),Fe(CN), + CaCl,
Ca,Fe(CN), + 2KCl = CaK,Fe(ON), + CAC.

(REATING THE CRUDE LIQUORS i33
2. PRECIPITATION WITH AMMONIUM SALTS.

The reagent consists of a solution of ammonium
chloride, which, according to the character of the pre-
liminary dissociation process, is either added per se,
or else the liquor from the filter boxes is manipulated ©
in such a way that it contains sufficient ammonia to
carry out the reaction. This latter will generally be
the case when the spent purifying material has
not been lixiviated before dissociation. In these cir-
cumstances, sufficient hydrochloric acid is added to
neutralize the ammonia, but if the material has been
previously lixiviated, a sufficient amount of unlixiviated
material is added, for the dissociation treatment, to
introduce sufficient ammonia to precipitate the
double salt from the whole of the crude liquor. The
precipitation is effected in apparatus provided with
mechanical stirrers. The liquor is heated by direct
steam, and the precipitation of the double salt begins
when the temperature reaches 75°C. When the de-
position is completed, the steam is turned off and
the stirrers are stopped, the clear liquor being drawn
off when the salt has settled down. ‘This latter is
repeatedly washed with water, by decantation, and is
finally put through the filter press. It may occa-
sionally be profitable to precipitate the cyanogen,
present in the washings and mother liquor, in the
form of ‘‘blue”. The precipitated double salt
is a white substance with a bluish tinge, and it may
either be reconverted into the calcium salt, or else
transformed direct into potassium ferrocyanide. In

134 COAL GAS BY-PRODUCTS

the case of very good double salt, a marketable ai'ticle
can be produced direct ; but in other cases the cal-
cium salt has to be prepared as the intermediate
product. For this purpose a suitable quantity of
lime is added to the solution of the double salt, in
a stirrer apparatus of the kind already described, the
liberated ammonia being worked up into one or other
of the preparations referred to earlier. The reaction
corresponds to the equation :—
Ca(NH,),Fe(CN), + CaO =Ca,Fe(CN),+ 2NH,+H,0.
When all the ammonia has been driven off, the re-
sulting liquor is concentrated to 20-21° Bé. and put
aside to crystallize, the black sludge formed during con-
centration being removed in a filter press. The
calcium ferrocyanide is treated in exactly the same
way as the crude liquor precipitated with potassium
chloride. As already stated, the ammonium double
salt can be converted direct into potassium ferro-
cyanide, for which purpose a corresponding quantity
of potassium carbonate is placed in the stirrer ap-
paratus, together with the requisite amount of lime.
The reaction corresponds to the equation :—

Ca(NH,),Fe(CN), + CaO + 2K,CO,

= K,Fe(CN,) + 2CaCO, + H,O + 2NH,.
After the expulsion of the ammonia, the liquor is con-
centrated to 31° Bé., filtered and set to crystallize.

3. PRECIPITATION WITH POTASSIUM SALTS.

The best method of obtaining good salts from the
crude liquors is through the potassium double salt.

TREATING THE CRUDE LIQUORS 135

In the methods discussed above, hydrochloric acid—
and sometimes ammonia—-must be added and then
got rid of again, on which account it is preferable to
make direct use of the salts which are required to
furnish the end product. It is true that the potash
salt can also be prepared direct from the calcium salt
by means of potassium carbonate; but, for reasons of
economy, cheaper potassium salts should be em-
ployed wherever possible. This can be done, up to
the formation of the double salt, with potassium
chloride. The crude liquor is either treated direct
with potassium chloride in the stirring apparatus, or
else the liquor can first be concentrated to 23-25° Bé.,
separated from the deposited impurities, and run into
the apparatus. In this latter it is treated with an
addition of solid potassium chloride (3-5 per cent
more than the theoretical quantity) at about 80° C.,
the mixture being stirred continuously. The double
salt, formed in accordance with the equation :—

Ca,Fe(CN), + 2KCl = CakK,Fe(CN),+ CaCl,

settles down quickly after the stirring ceases, and the
clear supernatant liquor can then be drawn off. ‘The
salt is placed on a filter, and washed with a little
water, whilst the liquor is treated for the production
of ‘‘blue,” by precipitation with iron salts, after which
it is discharged ‘as effluent. When a sufficient
quantity of “blue” has accumulated, it is pressed,
and treated further by one or other of the methods
described. The double salt is converted into potas-

136 COAL GAS BY-PRODUCTS

sium ferrocyanide by boiling it with potassium car-
bonate, in accordance with the reaction :—

CaK,Fe(CN), + K,CO, = K,Fe(CN), + CaCO,.

After the calcium carbonate has settled down, the
clear liquor (density 27° Bé.} is concentrated to 30-
31° Bé. in iron pans, and is then set to crystallize,
whilst still hot, in pans, about 41 feet deep and 34
feet across, which are lagged with wood to prevent
loss of heat. Across the top of each pan a number
of rods are laid, to which are attached strings lead-
ing nearly to the bottom of the vessel. The crystals
collect in clusters on these strings. The pans must
be kept free from vibration during the crystallizing
process, which takes about a fortnight to complete.
The crystals are broken up and whizzed, the mother
liquor being returned to the crystallizing pans until it
is so rich in potassium sulphate that this salt begins
to crystallize out first, whereupon the liquors are
placed aside and concentrated separately. The re-
sulting crystals still contain about.60-80 per cent of
K,Fe(CN),.3H,O.

CHAPTER IX.

THE TREATMENT OF CRUDE AMMONIUM THIOCY-
ANATE AND CUPROUS THIOCYANATE.

THE crude ammonium thiocyanate obtained in the
lixiviation of spent purifying material is dissolved in
water, and the heavy metals are thrown down, as
sulphides, by means of barium sulphide, the sulphuric
acid present precipitating the barium at the same
time. The addition of barium sulphide is continued
until the filtrate no longer gives a precipitate with
the same reagent. The mixture is squeezed in the
filter press, after which the liquor is concentrated to
20-25° Bé. and left to crystallize. The resulting
salt is not a marketable commodity, but has to be
recrystallized. This is done by dissolving it, throw-
ing down any heavy metals, still present, with am-
monium sulphide, drawing off the clear liquor and
concentrating it to 18-20° Bé. ‘The crystals separat-
ing out as the solution cools are removed from the
mother liquor, whizzed and dried. The product is a
pure, white ammonium salt.

In connexion with the lixiviation of the purifying
materials it has been mentioned that the thio-
cyanogen in the liquor can also be thrown down by

(137)

138 COAL GAS BY-PRODUCTS

copper sulphate. This product, cuprous thiocyanate,
serves as the raw material for other thiocyanates.
Treated with barium sulphide solution in a stirrer
apparatus, it is decomposed as follows :—

20uCNS + BaS = Ba(CNS), + Cu,S.

The copper sulphide is separated by pressing,
whilst the barium thiocyanate liquor is passed
through a charcoal filter, concentrated to about 60°
- Bé., and placed in iron pans to crystallize. The
salt is separated from the mother liquor by whizzing,
and forms a marketable product.

To prepare potassium thiocyanate, the purified
barium thiocyanate solution is treated with a corre-
sponding amount of potassium sulphate, separated
from the precipitated barium sulphate by pressing,
and the liquor is concentrated to about 40°. Bé.
The salt obtained on crystallization is purified by
recrystallizing.

CHAPTER X.
POTASSIUM FERRICYANIDE.

THis salt is not prepared direct, but is obtained
by the oxidation of potassium ferrocyanide :—
2K ,Fe(CN), + O = 2K,Fe(CN), + K,0.

The means of oxidation include chlorine, per-
oxides, persulphates, and finally electrolysis. The
oldest process is that of oxidation with chlorine.
It may be carried on in the dry, or even in the
dissolved state. T'o oxidize the dry product, it is
reduced to fine powder, and spread on racks in a
chamber, a current of dry chlorine being passed
over it until a sample is found no longer to contain
any ferrocyanide. ‘This test is applied by dissolving
a crystal in water, dropping it on an unglazed tile
and seeing whether any blue coloration is produced
by ferric chloride solution. The potassium ferri-
cyanide obtained by this process contains, of course,
all the potassium chloride produced in the operation.
It is, however, not customary to separate the two
salts in this method, by fractional crystallization,
the product being usually worked up into Turnbull’s
blue.

In oxidation with chlorine by the wet process, a

(139)

140 COAL GAS BY-PRODUCTS

current of washed chlorine is passed through a cold
10 per cent solution until the whole of the ferro-
cyanide has been oxidized. The end point of the
decomposition must be carefully watched for, or
difficulties will occur during crystallization. If the
oxidation be insufficient, the resulting salt will be con-
taminated with ferrocyanide; whilst if carried too
far, Prussian green will be formed, which adheres
to the product with equal tenacity. When oxidation
is complete, the solution is concentrated to 27° Bé
(hot), and put aside to crystallize, an operation taking
about five days. The mother liquor is further
concentrated to 29° Bé. (hot). The crystals from
the mother liquor are contaminated with potass-
ium chloride; and this salt serves for concentrating
a newly oxidized patch. A number of mother
liquors from the second crystallization are concen-
trated until the potassium chloride separates out,
the bulk of this salt being washed out of the crystals
with cold water. In this method of working, a yield
of 88-90 per cent is obtained.

The oxidation of potassium ferrocyanide by means
of peroxides was introduced into practice by
Schénbein. When the ferrocyanide is treated, at
boiling temperature, with lead peroxide, it is oxi-
dized, lead oxide and caustic potash being also
formed. ‘These two compounds are converted into
carbonates by the introduction of carbon dioxide, the
lead carbonate being precipitated. The potassium
ferricyanide and potassium carbonate can be easily
separated by fractional crystallization. The lead

POTASSIUM FERRICYANIDE 141

carbonate is reconverted into the peroxide, by means
of bleaching powder.

_A modification of this process has béen brought
forward by Kassner, who replaces the lead p2roxide
by calcium plumbate and carbon dioxide. The de-
composition proceeds according to the equation :—

2K,Fe(CN), + Ca,PbO, + 4CO,
= 2K,Fe(CN), + 2CaCO, + PbCO, + K,CO..

The potassium carbonate left in solution is utilized
by oxidizing an equivalent amount of ferrocyanide
without addition of carbon dioxide, and adding the
product to this solution, whereupon potassium ferri-
cyanide and calcium carbonate are formed. The
latter settles down, and the clear supernatant liquor
is siphoned off and concentrated to crystallization
point. Since the calcium plumbate is prepared by
calcining lead oxide and calcium carbonate, it serves
to some extent as a carrier of atmospheric oxygen.

The method which is probably most widely used
at present for preparing ferricyanide is that of
oxidation by electrolysis. In the electrolysis of
water, the oxygen is separated at the anode, and
the hydrogen at the cathode ; and it is this nascent
oxygen which is utilized for oxidizing potassium
ferrocyanide. The reactions are expressed by the
following equations :—

H,O = H,+ 0.
2K,Fe(CN), + O = 2K,Fe(CN), + K,O
K,0 + H,O = 2KOH.
aK Fe(ON), + 2H,0 = 2K,Fe(CN), + IKOH + H,.

142 COAL GAS BY-PRODUCTS

The potassium ferricyanide is deposited, in a pure
state, on the anode, the yield amounting to 95 per
cent and over. A number of patents are based on
this process (Buschweiler, Petrie, Dubosq, etc.).
The electrolysis is suspended as soon as all the
ferrocyanide has been oxidized, a condition which
is recognized by the circumstance that the liquor no
longer decolorizes potassium permanganate solution.

According to the process of the Deutsche Gold
und Silberscheideanstalt (Ger. Pat. 59,014), a mix-
ture of potassium ferrocyanide and calcium ferro-
cyanide is oxidized. The use of calcium salts, in
addition to potassium salts, in the decompositions
corresponding to the reaction, is stated to ensure
a purer product being obtained, since the whole
of the potassium combines with the ferricyanic acid,
and any lime that may be left behind in solution
can be completely precipitated with carbon dioxide.
The reactions are expressed by the equations :—
3K,Fe(CN), + Ca,Fe(CN), + O,

= 4K,Fe(CN), + 2CaO; 2CaO + 2CO, = 2CaCO,.

The use of ammonium- and sodium persulphates
for oxidation is dealt with in Beck’s German Patents
81,927 and 83,966, the reaction corresponding to
the equation :—
2K Fe(CN), + (NH,),8,0,

= 2K,Fe(CN), + 2(NH,)KSO,

The potassium ferrocyanide, which is dissolved
in water (1:1), is oxidized with ammonium per-
sulphate at 60° C., 270 parts by weight of ammo-

POTASSIUM FERRICYANIDE 143

nium persulphate being required to every 1000 of
ferrocyanide. In consequence of the heat generated
by the reaction, the solution must be well cooled.
When the decomposition is complete, the salts are
separated by fractional crystallization, the ammo-
nium-potassium sulphate, as the least soluble salt,
crystallizing out first.

When sodium persulphate is used as the oxidiz-
ing agent, a ferrocyanide solution of 1: 1-5 is taken,
282 parts of the persulphate being added per 1000
of ferrocyanide. The reaction is conducted at 50° C.,
and the resulting salts are separated by fractional
crystallization.

CHAPTER XI.
THE CYANOGEN PIGMENTS.

THE cyanogen pigments consist of complex com-
pounds of iron salts and hydroferri- or hydroferro-
cyanic acid. The chief representatives of the series,
which are met with in commerce as Prussian blue,
Berlin blue, and Puris blue, have the formula,
Fe (CN)...

Chemically speaking, they are identical, differing
only in their degree of purity. Paris blue is the
purest form. It has an intensely blue colour and
a peculiar coppery metallic lustre. The other
members: Prussian blue, Berlin blue and mineral
blue, are prepared from less pure salts and, in
addition to containing such impurities as gypsum
and carbonate, are adulterated with variable pro-
portions of alumina, chalk, starch and even heavy
spar. These substances naturally render the colour
correspondingly paler, and also impair the bronze
lustre.

There are two methods of making Paris blue. In
the one, a solution of pure potassium ferrocyanide
is treated with ferric salts, thus forming a precipitate
of pure Paris blue; whilst in the other, the pre-

(144)

THE CYANOGEN. PIGMENTS 145

cipitation is effected with ferrous salts, which are
cheaper, and the pale blue to dirty green precipitate
is oxidized afterwards. The former method naturally
furnishes the purer product.

A solution of ferric nitrate is added to one of
potassium ferrocyanide until a sample no longer
gives any further precipitate with the nitrate
solution. The ferri-ferrocyanide thus formed se-
parates as a completely insoluble substance and
settles down. The supernatant liquid is siphoned
off, and the precipitate is washed with water, by
decantation, until all the potassium chloride has
been extracted. It is next pressed, while still moist,
cut up into cubes and dried. The first stage of
drying is conducted at air temperature or up to
30° C. (86° F.), and it is only when the product
is air-dry that the drying is finished off at 100° C.
(212° F.), whereupon the copper-red (‘‘ bronze ’’)
metallic lustre, characteristic of the pure article,
develops.

In the preparation with ferrous salts, followed by
oxidation, ferrous sulphate is employed in practice.
The following may be given as the most suitable
proportions: ferrous sulphate 9 parts by weight;
sulphuric acid (60° Bé.) 15 parts (dissolved in 100
parts of water); potassium ferrocyanide (yellow prus-
siate), 10 parts, dissolved in 100 parts of water.

The addition of sulphuric acid is intended to
prevent the precipitation of iron carbonate by the
carbonic acid in the water. The two solutions are
poured into a wooden vat, only a slight excess of

146 COAL GAS BY-PRODUCTS

the ferrous salt being present. The liquid should
be kept constantly stirred during the pouring
process. The resulting white precipitate, which
always has a slight bluish tint due to small quanti=
ties of ferric salt, is oxidized with 20 parts of nitric
acid (1-3298) added in small quantities at a time,
steam being admitted simultaneously. The heating
is continued until“no more nitrous fumes can be
observed. In this way the precipitate is oxidized
- Ina very short time. The Paris blue is allowed to
subside and, after the clear supernatant liquid has
been drawn off, is washed with water. The sub-
sequent treatment of the precipitate is identical with
that described above.

Hochstitter employs bleaching powder and hydro-
chloric acid as the oxidizing agent. In _ these
circumstances he has to start with ferrous chloride,
and dispense with the use of sulphuric acid, since
otherwise the finished product would be contamin-
ated with gypsum. Any oxidizing agent can be
used for turning the white precipitate blue, man-
ganese chloride being a highly suitable means.
After separation from the solution, the precipitate
is treated with a solution of manganese chloride in
excess; and as soon as the colour of the product
attains its maximum oe the oxidation is
complete.

Berlin blue differs from Paris blue solely by
reason of impurities, in consequence of which it is
inferior in “bronze”. Instead of working with
pure salts, a crude salt, such as that obtained in

THE CYANOGEN PIGMENT 147

making potassium ferrocyanide, is used. This
contains considerable quantities of potassium carbon-
ate and sulphate. Alum is generally added to the
ferrous sulphate solution used for precipitating the
blue, the object being to neutralize the carbonate
and, at the same time, to increase the volume of
the precipitate, the carbonate reacting with the
alum and forming a precipitate of alumina. Oxida-
tion in an acid solution would cause the precipitate
of alumina to redissolve, and therefore the oxidation
must be carried out with atmospheric oxygen. A
better plan is to oxidize the ferrous sulphate before-
hand. In other respects the manufacture of Berlin
blue does not differ essentially from that of its purer
congener, Paris blue. The depth of colour di-
minishes in accordance with the proportion of
impurities present, which in ‘‘ mineral’’ blue attain as
much as 80 per cent. Mineral blue is made from
the inferior crude liquors from the potassium ferro-
cyanide process. The cyanogen pigments are met
with in commerce in the form of cubes, powder and
paste. Their shade depends on the quantity of
added substances and the method of precipitation
employed. |

Berlin blue is also put on the market in soluble
form, and is now largely used for injecting
anatomical preparations. At one time it was also
used as a colouring matter for ink, but has now
been entirely superseded by the aniline dyes.

In its preparation, the ferrocyanide must be
present in large excess in the solution, the following

148 COAL GAS BY-PRODUCTS

proportions being given by Briicke: Potassium
ferrocyanide 2170 parts, dissolved in 11,000 parts
of water and treated gradually with a solution of
100 parts of ferric chloride in 1000 of water.
The iron solution is mixed with twice its volume of
a saturated solution of Glauber salt (sodium sul-
phate). The resulting precipitate is filtered off, and
is washed with water so long as the washings
exhibit a bluish tinge. The residue is then dried,
-and is sold in the form of powder. This blue,
which is. chemically the same as Berlin blue, is
completely soluble in water.

Guignet utilizes the solubility of Berlin blue in
oxalic acid, for preparing a soluble blue. A satur-
ated solution of oxalic acid is shaken up witha large
excess of Berlin blue in paste form, and filtered,
the solution being then left to itself for two months,
during which interval the dissolved Berlin blue
gradually settles down, leaving the solution as clear
as water. The blue obtained in this way is also
soluble in water. In addition to oxalic acid, tartaric
acid and molybdic acid have the faculty of dissolving
Berlin blue.

Apart from Berlin blue and its varieties, men-
tion may be made of the copper salt of potassium
ferrocyanide, which is of a brown colour, and is met
with in commerce as Hatchet brown. It is pre-
pared by precipitating a solution of potassium ferro-
cyanide with copper sulphate, the shade of the
product varying in accordance with the excess of
copper sulphate used.

CHAPTER XII.
SULPHUR AND SULPHURIC ACID.

IF it be desired to recover sulphur, as such, from
the spent gas-purifying materials, this is preferably
effected before the said materials are treated for the
preparation of cyanogen compounds. The manner
of extracting the sulphur has already been dealt
with, carbon disulphide being the only solvent used.
The process is exactly similar to that used in the
extraction of fat from bones, and there is therefore
no need to go into further details.

In the main, the sulphur from spent purifying
material is transformed into sulphuric acid by
roasting, the material treated in this way being, of
course, such as has previously been freed from the
other valuable constituents. The lixiviated and
dissociated material chiefly contains ferric hydroxide
or oxide, ferrous hydroxide, sulphur and lime (from
the dissociation treatment), in addition to the sub-
stances (sawdust, etc.) required for loosening the
material and facilitating the passage of the gas to be
purified. In the roasting process, the ferric oxide
remains behind, and the sulphur is liberated as
sulphur dioxide. The roasting furnaces do not

(149)

150 COAL GAS BY-PRODUCTS

differ essentially from those used for pyrites and
other sulphur ores. The entire process of making
sulphuric acid from spent gas-purifying materials
does not entail the use of any typical special
appliances, and therefore it is sufficient here merely
to mention that sulphuric acid, also, is one of the
by-products of the manufacture of coal gas.

FInIs.

INDEX

Actp receiver, sulphate plant, 92,
94.

Ahrens & Senger on sampling
tar, 36.

Allner on testing gas tar, 37, 42.

Ammonia, aqueous, 81-8.

— determination of,
liquor, 54, 55.

distilling from gas liquor, 57-
74.

from gas liquor, 71.

in coal gas, 3.

— — crude gas, 15.

— cyanogen sludge, 18.

— — gas liquor, 6-9.

liquefied, 89-90.

preparation of, 81-90.

— separation of, 4-6.

Ammonium carbonate
liquor, 6-9.

chloride in gas liquor, 7-9.

chloride, precipitating waste
liquor with, 133, 134.

ferrocyanide in gas liquor, 6-9.

— — recovery of, 128,129.

stable salts of in gas liquor,
7, 9.

sulphate in gas liquor, 6-9.

— See also Sulphate of Am-

monia.)

sulphide in gas liquor, 7, 9.

sulphydrate in gas liquor, 6.

thiocyanate in gas liquor, 6-9.

— recovery of, 121.

— treatment of, 137, 138. -

— thiosulphate in gas liquor, 6-9.

in gas

—

in gas

Anthracene in gas tar, 35, 44, 51.

— oil in gas tar, 35, 43, 44, 51.

Ash content of coke, 23.

— determination of, in gas tar,
39.

— percentage of, in coal, 3.

Asphaltum in gas tar, 35.

Brecx’s ferricyanide process, 142,
143.
Benzol in coal tar, 34.
Berlin-Anhalt Co.’s
plant, 84-6.
— — — carbon dioxide separator,
68-71.
— — — gas liquor still, 62-4.
Berlin blue, 144, 146-8.
Bertelmann on absorption of car-
bon dioxide by gas liquor,
70.
— — gas purification, 10.
Béckelmann & Sachse’s tar dis-
tilling process, 52. ~
Bohemian coals, yield of tar, 34.
Béssner on treating spent purifying
material, 124, 125.
British Cyanides Co.’s gas purify-
ing process, 20.
Brucke’s Berlin blue process, 148.
Buéb method of treating cyanogen
sludge, 128, 129.
— process of cyanogen recovery,
15-8.
Bunte on yield of gas tar, 34.
Burkheiser sulphate of ammonia
process, 98-102.

ammonia

(151)

152

Burmeister & Wain on separating
water from gas tar, 40.

Caucrum ferrocyanide, 122, 125,
129, 134-6.

Calorimeter, 24, 25.

Cannel coal, yield of tar, 34.

Carbon, in coal, 3.

— — coke, 23.
— determination of, in gas tar,
37-9.
— dioxide, absorption of, by gas
liquor, 70.
— — eliminating in ammonia

manufacture, 86-8.

from gas liquor, 71.

in water gas, 29.

separator, 68-72, 77-9.

monoxide in water gas, 29.

Carbonaceous matter in gas tar, 35.

Carpenter’s gas purifying process,
20.

Chlorine for oxidizing ferrocyan-
ide, 139.

Coals, chemical composition of, 3.

Coke, 23-9.

— breaker, 26, 27.

breeze, 26.

chemical composition of, 23.

fragility of, 23.

heating value of, 23-5.

physical properties of, 23.

— yield of, from coal, 3.

Column stills for gas liquor, 60-
6

Condenser (atmospheric),
liquor from, 7.

— ceilular, 79, 80.

— reflux, 66, 67.

Copper-potassium
ide, 148.

Copper reagent for determining
ferrocyanogen, 109.

Creosote oils in gas tar, 44, 49.

Cuprous thiocyanate, treatment
of, 137, 138.

gas

ferrocyan-

COAL GAS BY-PRODUCTS

Cyanogen in coal gas, 38.

— compounds, preparing from
spent purifying materials,
114-97 -

removal of, 7-21.

sludge, 15-8.

— treating, 128-9.

— — recovery of, 116, 122-6.
— pigments, 144-8.

—_—

DevutscHE Continental Gas Gesell-
schaft method of separating
water from gas tar, 39, 40.

— Gold & Silberscheide Anstalt
ferricyanide process, 142.

Distillation plant, experimental, 2.

— temperature of coal, 2.

Donat & Ornstein’s Prussian blue

process, 115.
Dérrite stone from gas tar, 42.
Drehschmidt on determination of
ferrocyanogen, 110, 111.
Dulong’s calorific value formula,
24.

Evectropes, retort graphite, 31,
32.

Electrolytic preparation of ferri-
cyanide, 141, 142.

English coals, composition of, 3.

— — gas tar from, 35, 43.

Frwp’s gas purification process, 19,

20.
— sulphate of ammonia process,
102-4.
Feldmann-Pintsch ammonia plant,
86-8.
— — gas liquor separator, 71, 74,
77-9.

Ferric oxide as gas purifier, 9, 10,
13.

Ferrocyanides, recovery of, 114-
29, 141, 142.

Ferrocyanogen, determination of,
105-13.

INDEX

Ferrous chloride as gas purifier,
14.

— salts as gas purifiers, 19.

— sulphate as purifying agent,
16, 17.

Foulis method of treating cyan-
ogen sludge, 128.

—-process of hydrocyanic acid
recovery, 13, 14.

Franke’s gas liquor still, 58, 59.

Gas, crude, composition of, 15.

illuminating, from gas tar, 42.

liquor, 53, 104. -

— absorption of carbon dioxide

by, 70.

ammonia in, 54, 55.

composition of, 6-9, 53.

concentrated, 74-81.

concentrating, 56, 57.

distillation of, 57-74.

from retorts, composition

of, 7:83

preheater for, 65.

separators for, 74-81.

testing, 54-5.

yield of, 3.

purification of, 4-21. -

purifying agents, sulphuric acid
from, 140, 150. See
also Purifying Materials.

— treatment of, 105-27.

— value of spent, 113.

tar, 33-52.

artificial stone from, 42.

as paint, 41.

composition of, 34, 36.

distilling, 43-52.

fractionating, 39.

illuminating gas from, 42.

influence of retorts on, 35,

—

oils in, 35, 36, 43.

pitch in, 35, 43, 44.
physical properties, 34, 35.
sampling, 36.

153

Gas tar, separating water from, 39-
41.

— — specific gravity of, 38.

— testing, 36-39.

yield from gas tar, 35.

— per ton of coal, 3.

Graphite, retort, 30-2.

Griineberg, Tieftrunk & Buhe’s
ammonia plant, 84-6.

Guignet’s soluble blue, 148.

—

HatcuHet brown, 148.

Heating value of coke, 23-5.

— — — gas tar, 37.

— — — water gas, 29.

Hirzel’s gas tar still, 50, 51.

Hochstiatter’s Paris blue process,
146.

Hydraulic main, 4.

— — gas, liquor from, 7.

Hydrocyanic acid in crude gas, 15.

— — removal of, 7-21.

Hydrogen, in coal, 3.

— — coke, 23.

— — water gas, 29.

Iron salts, treating waste liquor
with, 131, 132.

— thionate process for sulphate of
ammonia, 103.

|Kassner’s process for oxidizing

| ferrocyanide, 141.

-Kloénne method of separating
water from gas tar, 40.

Knoblauch process of cyanogen re-

| covery, 12, 13.

_— — — determining ferrocyano-

gen, 107.

Kohler on testing gas tar, 38, 39.

Koningh, De, process for determin-
ing ferrocyanogen, 106.

Kopper’s gas liquor still, 64-6.

Kramer & Spilker on testing gas

_ tar, 39.

‘ Krey’s tar distillation process, 50,

-10*

154

Kunheim & Zimmermann’s ferro-
cyanide process, 114,
115.

— — process for treating waste
liquor, 132.

Lamine’s purifying material, 9.

Lennard’s tar distilling process,
51, 52.

Leybold & Moldenhauer process
for determining ferrocyanogen,
106.

Lime, milk of, in treating gas

liquor, 57, 58, 60-5, 72, 73.

— for purifying gas, 8, 9.

— testing, 55.

— washer for ainmonia plant, 84,

85.

Liquor, waste treatment of, 130-

Lixiviation plant for spent purify-
ing materials, 118, 121.

Maenesium salts as gas purifiers,
20.

Marrasses’ thiocyanogen process,
116.

NAPHTHALENE in coal tar, 34, 43.
Nitrogen in coal, 3.

— — coke, 23.

— — water gas, 29.

Oru in gas tar, 35, 36, 43.

— heavy in gas tar, 35, 43.
— light in gas tar, 35, 43.

— medium in gas tar, 35, 43.
Opitz & Klotz gas tar still, 49.
‘Oxygen, in coal, 3.

— — coke, 23.

— — water gas, 29.

Patnt, gas tar, 41.

Paris blue, 144-6.

Peroxides for oxidizing ferrocyan-
ide, 140, 141.

COAL GAS BY-PRODUCTS

Persulphates for oxidizing ferro-
cyanide, 142.
Phenol in coal tar, 34, 43.
Pintsch concentrator for gas liquor,
74-81.
— process for liquefied ammonia,

— sulphate of ammonia plant, 92-

Pitch in gas tar, 35, 43, 44.
Polysulphides as gas purifiers, 20.
Polythionate process for sulphate
of ammonia, 103-4.
Potassium ferricyanide, prepara-
tion of, 139-43.
ferrocyanide, converting into
ferricyanide, 139-143.
— recovery of, 114, 115, 125,
126, 134, 136.

— salts, treating waste liqour
with, 134-6.

— thiocyanate, preparation of,
138.

Prussian blue, 107, 109, 110, 144-
8

— in cyanogen sludge, 15.

— preparation of, 131, 132.

— recovery of, 115.

green, 140.

Purification, gas, 4-21.

— — dry process, 5-12.

— — wet process, 4-8.

Purifying boxes, 5.

— materials, 9-21.

— — absorbent capagity of, 11.

— — regenerating, 5/9. See also
Gas Purifying Agents.

Pyridin in coal tar, 34.

—

Resprer’s gas tar still, 47.

Rispler on distilling gas tar, 48.

Roofing felt, gas tar, 41, 42.

Rosenkranz ammonia absorber,
96.

Riitgerswerke method of separat-
ing water from gas tar, 41.

INDEX

Rutten on hydrocyanic acid re-
covery, 14, 15.

Saar coals, tar from, 34, 43.

Schénbein’s process for oxidizing
ferrocyanide, 140.

Scotch gas tar stills, 46.

Scrubbers, 4, 5.

Silesian coals, composition of, 3.

Smith, Gidde, Salomon & Al-
bright’s gas purifying proc2ss,
20.

Sodium ferrocyanide, 132.

Stills for gas liquor, 58-66.

— — — tar, 44-52.

Stone, artificial, from gas tar, 42.

Sulphate of ammonia, preparation
of, 90-104, 121.

— — — recovery, 56.

— — — solubility of, 97.

—_ — — See also Ammonium
Sulphate.

Sulphite of ammonia in sulphate,

99-102.
Sulphuretted hydrogen in crude
gas, 15.

-— — from gas liquor, 71.

— — removal in ammonia manu-
facture, 86-8.

— — — of, 6, 8-10.

Sulphuric acid from spent purify-

ing materials, 149-50.

— — in treating gas liquor, 56.

Sulphur in coal gas, 3.

— — coke, 23.

— determination of, in spent puri-

fying materials, 113.

155

Sulphur eliminating from spent
purifying materials, 117.

— percentage of, in coal, 3.

— recovering, 149, 150.

Tar, separation of, 4.

— yield of, from coal, 3. See also
Gas Tar.

Thiocyanogen, recovery of, 116.

Turnbull’s blue, 139.

VALENTINE’S ferrocyanide process,
LE 5

WasHER, gas liquor from, 7.
— Zimpel, 96, 97.
Water, determination of, in gas
tar, 37.
— gas, 26-9.
— in gas tar, 35-38, 43.
— separating from gas tar, 39-41,
47, 48.
Weil method of separating water
from gas tar, 41.
Wernecke’s tar distilling process,
52.
Westphalian coal, tar from, 34.
— coals, composition of, 3.
Witzek method of determining fer-
rocyanogen, 112, 113.

ZimPEL bell washer, 96, 97.
Zulkowsky method of determining
ferrocyanogen, 105, 106.
Zwickau coals, tar from,

43,

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Ozone, Industrial Use of.
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PAGE
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Staining Marble, and Bone =
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Textile Fibres sis owe 14
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Timber 5 tet. BO
Toilet Soapmaking | wear 2
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Vegetable Fats and Oils |. 6
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F.C.S. Third Revised and Enlarged Edition. Seventy-four
Illustrations. 384 pp. Demy 8vo. Price 10s. 6d. net. (Post
free, lls. home; 11s. 34. abroad.)

TECHNOLOGY OF PETROLEUM : Oil Fields of the
World—Their History, Geography and Geology—Annual Pro-
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HENRY NEUBERGER and HENRY Noaunat. Translated from the
French by J. G. McINTosH. 550 pp. 153 Illustrations. 26 Plates,
Super Royal 8vo. Price 21s. net. (Post free, 21s. 9d. home;
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MINERAL WAXES: Their Preparation and Uses. By
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home; 6s. 6d. abroad.)

THE PRACTICAL COMPOUNDING OF OILS,
TALLOW AND GREASE FOR LUBRICA-

TION, ETC. By An Expert O1L Reriner. Second
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THE MANUFACTURE OF LUBRICANTS, SHOE
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RICHARD BRUNNER. Translated from the Sixth German Edition
by Cuas. SALTER. 10 Illustrations. Crown 8vo. 170pp. Price
7s. 6d. net. (Post free, 7s. 10d. home; 8s. abroad.)

THE OIL MERCHANTS’ MANUAL AND OIL
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Demy 8vo. 214 pp. With Two Sheets of Tables. Price 7s. 6d.
net. (Post free, 7s. 10d. home; 8s. 3d. abroad.)

ANIMAL FATS AND OILS: Their Practical Pro-

duction, Purification and Uses for a great Variety of Purposes.
Their Properties, Falsification and Examination. Translated
from the German of Louis EpGar ANDES. Sixty-two Illustrations.
240 pp. Second Edition, Revised and Enlarged. Demy 8vo.
Price 10s. 6d. net. (Post free, 10s. 10d. home; 11s. 3d. abroad.)

VEGETABLE FATS AND OILS: Their Practical
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trations. 340 pp. Second Edition. Demy 8vo. Price 10s. 6d.
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EDIBLE FATS AND OILS: Their Composition, Manu-
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C. A. MiTcHELL, B.A. (Oxon.). Demy 8vo. 150 pp. Price
7s. 6d. net. (Post free, 7s. 10d. home; 8s. abroad.)

(Glycerine.)
GLYCERINE. By T. W. Kopps. Translated from the

German. [In the Press.

(Essential Oils and Perfumes.)

THE CHEMISTRY OF ESSENTIAL OILS AND
ARTIFICIAL PERFUMES. By Ervyesr J. Parry,
B.Sc. (Lond.), F.I.C., F.C.S. Second Edition, Revised and

Enlarged. 552 pp. 20 Illustrations. Demy 8vo. Price 12s. 6d.
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(Soap Manufacture. )

SOAPS. A Practical Manual of the Manufacture of
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2nd edition. 390 pp. 66 Illustrations. Demy 8vo. Price 12s. 6d.
net. (Post free, 13s. home; 13s. 6d. abroad.)

TEXTILE SOAPS AND OILS. Handbook on the
Preparation, Properties and Analysis of the Soaps and Oils used
in Textile Manufacturing, Dyeing and Printing. By GEORGE
H. Hurst, F.C.S. Second Edition, Revised and partly re-
written by W. H. Simmons, B.Sc. (Lond.). Demy 8vo. 200 pp.
11 Illustrations. Price 7s. 6d. net. (Post free, 7s. 10d. home;
8s. abroad.) :

THE HANDBOOK OF SOAP MANUFACTURE.
By WM. H. Simmons, B.Sc. (Lond.), F.C.S.,and H. A. APPLETON.

Demy 8vo. 160 pp. 27 Illustrations. Price 8s. 6d. net. (Post
free, 8s. 10d. home; 9s. abroad.)

MANUAL OF TOILET SOAPMAKING, including
Medicated Soaps, Stain-removing Soaps, Metal Polishing Soaps,
Soap Powders and Detergents. Translated from the German

of Dr. C. DeireE. Demy 4to. 150 pages. 79 Illustrations.
Price 12s. 6d. net. (Post free, 13s. home; 13s. 6d. abroad.)

(Cosmetical Preparations.)

COSMETICS: MANUFACTURE, EMPLOYMENT
AND TESTING OF ALL COSMETIC
MATERIALS AND COSMETIC SPECIALITIES.

Translated from the German of Dr. THEODOR KOLLER. Crown
8vo. 262 pp. Price 5s. net. (Post free, 5s. 4d. home; 5s. 6d.

ee Cg RA UM

(Glue, Bone Products and Manures.)

GLUE AND GLUE TESTING. By Samue. Ripeat,
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8vo. 196 pp. 14 Illustrations. Price 10s. 6d. net. (Post free,
10s. 10d. home ; 11s. abroad.) [Ffust published.

BONE PRODUCTS AND MANURES: An Account
of the most recent Improvements in the Manufacture of Fat,
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LAMBERT, Technical and Consulting Chemist. Second Revised
Edition. Demy 8vo. 172 pages. 17 Illustrations. Price 7s. 6d.
net. (Post free, 7s. 10d. home; 8s. abroad.)

(See also Chemical Manures, p. 9.)

(Chemicals, Waste Products, etc.)

REISSUE OF CHEMICAL ESSAYS OF C. W.
SCHEELE. First Published in English in 1786.
Translated from the Academy of Sciences at Stockholm, with
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home; 5s. 9d. abroad.)

THE MANUFACTURE OF ALUM AND THE SUL-
PHATES AND OTHER SALTS OF ALUMINA

AND IRON. Their Uses and Applications as Mordants
in Dyeing and Calico Printing, and their other Applications in
the Arts, Manufactures, Sanitary Engineering, Agriculture and
Horticulture. Translated from the French of LucrEN GEscu-
WIND. 195 Illustrations. 400 pp. Royal 8vo. Price 12s. 6d.
net. (Post free, 13s. home; 13s. 6d. abroad.)

AMMONIA AND ITS COMPOUNDS: Their Manu-
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Central School of Arts and Manufactures, Paris. Translated
from the French by M. J. SALTER. Royal 8vo. 114 pp. Thirty-
two Illustrations. Price 5s. net. (Post free, 5s. 4d. home;
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CHEMICAL WORKS: Their Design, Erection, and
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220 pp. With 9 Folding Plates and £0 Illustrations. Price 21s.

_ met. (Post free, 21s. 6d. home; 22s. abroad.)

MANUAL OF CHEMICAL ANALYSIS, as applied to
the Assay of Fuels, Ores, Metals, Alloys, Salts and other Mineral
Products. By E. Prost, D.Sc. Translated by J. CRUICKSHANK
SmiTH, B.Sc. Royal 8vo. 300 pages. 44 Illustrations. Price
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TESTING OF CHEMICAL REAGENTS FOR

PURITY. Translated from the German of Dr. C.
KravucH. Royal 8vo. 350 pages. Price 12s. 6d. net. (Post free,
13s. home ; 13s. 6d. abroad.)

Bor rontents of these hooks. sce Lict TJ.

9
SHALE OILS AND TARS and their Products. By

Dr. W. SCHEITHAUER. Translated from the German. Demy 8vo.
190 pages. 70 Illustrations and 4 Diagrams. Price 8s. 6d. net.
(Post free, 8s. 10d. home; 9s. abroad).

THE BY-PRODUCTS OF COAL-GAS MANUFAC-
TURE. By K.R.Lance. Translated from the German.

Crown 8vo. 164 pages. 13 Illustrations. Price 5s. net. (Post
free, 5s. 4d. home; 5s. 6d. abroad.) [Fust published.

INDUSTRIAL ALCOHOL. A Practical Manual on the
Production and Use of Alcohol for Industrial Purposes and for
Use as a Heating Agent, as an Illuminant and as a Source of
Motive Power. By J. G. McIntosu, Lecturer on Manufacture
and Applications of Industrial Alcohol at The Polytechnic,
Regent Street, London. Demy 8vo. 1907. 250 pp. With 75
Illustrations and 25 Tables. Price 7s. 6d. net. (Post free, 7s. 10d.
home; 8s. 3d. abroad.)

THE UTILISATION OF WASTE PRODUCTS. A
Treatise on the Rational Utilisation, Recovery and Treatment of
Waste Products of all kinds. By Dr. THEODOR KOLLER. Trans-
lated from the Second Revised German Edition. Second English
Revised Edition. Demy 8vo. 336 pp. 22 Illustrations. Price
7s. 6d. net. (Post free, 8s. home; 8s. 6d. abroad.)

[Fust published.

ANALYSIS OF RESINS AND BALSAMS. Trans-
lated from the German of Dr. KARL DIETERICH. Demy 8vo. 340
pp. Price 7s. 6d. net. (Post free, 7s. 10d. home; 8s. 3d. abroad.)

DISTILLATION OF RESINS, RESINATE LAKES
AND PIGMENTS, CARBON PIGMENTS AND
PIGMENTS FOR TYPEWRITING MACHINES,
MANIFOLDERS, ETC. By Victor ScHWEIZER.

Demy 8vo. 185 pages. 68 Illustrations. Price 7s. 6d. net. (Post
free, 8s. home; 8s. 3d. abroad.)

DISINFECTION AND DISINFECTANTS. By M.

CHRISTIAN. Translated from the German. Crown 8vo. 112
pages. 18 Illustrations. Price 5s. net. (Post free, 5s. 3d. home ;
5s. 6d. abroad.)

(Agricultural Chemistry and Manures.)
MANUAL OF AGRICULTURAL CHEMISTRY. By

HERBERT INGLE, F.1.C., Late Lecturer on Agricultural Chemistry,
the Leeds University ; Lecturer in the Victoria University.
Third and Revised Edition. 400 pp. 16 Illustrations. Demy
8vo. Price 7s. 6d. net. (Post free, 8s. home; 8s. 6d. abroad.)

CHEMICAL MANURES. Translated from the French
of J. FRITSCH. Demy 8vo. Illustrated. 340 pp. Price 10s. 6d.
net. (Post free, 1ls. home; 11s. 6d. abroad.)

(See also Bone Products and Manures, p. 8.)

(Writing Inks and Sealing Waxes.)

INK MANUFACTURE: Including Writing, Copying,
Lithographic, Marking, Stamping and Laundry Inks. By
SIGMUND LEHNER. Translated from the German of the Fifth |
Edition. Second Revised and Enlarged English Edition.
Crown 8vo. 180 pages. Three Illustrations. Price 5s. net. (Post
free, 5s. 3d. home ; 5s. 6d. abroad.)

SEALING-WAXES, WAFERS AND- OTHER
ADHESIVES FOR THE HOUSEHOLD, OFFICE,

WORKSHOP AND FACTORY. By H.C. Sranpace.

Crown 8vo. 96 pp. Price 5s. net. (Post free, 5s. 3d. home ;
5s. 4d. abroad.)

(Lead Ores and Lead Compounds.)

LEAD AND ITS COMPOUNDS. By Tuos. LAMBeErt,

Technical and Consulting Chemist. Demy 8vo. 226 pp. Forty
Illustrations. Price 7s. 6d. net. (Post free, 7s. 10d. home;
8s. 3d. abroad.)

NOTES ON LEAD ORES: Their Distribution and Pro-
perties. By Jas. Farriz, F.G.S. Crown 8vo. 64 pages. Price
Is. net. (Post free, 1s. 3d. home; 1s. 4d. abroad.) ;

(White Lead and Zinc White Paints, see p. 5.)

(Industrial Hygiene. )

THE RISKS AND DANGERS TO HEALTH OF
VARIOUS OCCUPATIONS AND THEIR PRE-
VENTION. By Leonarp A. Parry, M.D., B.Sc.

(Lond.). 196 pp. Demy 8vo. Price 7s. 6d. net. (Post free,
7s. 10d. home ; 8s. abroad.)

(Industrial Uses of Air, Steam and
Water.) |
DRYING BY MEANS OF AIR AND STEAM. Ex-

planations, Formulz, and Tables for Use in Practice. Trans-
lated from the German of E. HAusBRAND. Second Revised
English Edition. Two folding Diagrams, Thirteen Tables, and
Two Illustrations. Crown 8vo. 76 pp. Price 5s. net. (Post
free, 5s. 3d. home; 5s. 6d. abroad.)

(See also “ Evaporating, Condensing and Cooling Apparatus,” p. 18.)
PURE AIR, OZONE AND WATER. A Practical.

Treatise of their Utilisation and Value in Oil, Grease, Soap, Paint,
Glue and other Industries. By W. B. CowELu. Twelve Illus-
trations. Crown 8vo. 85 pp. Price 5s. net. (Post free, 5s. 3d.
home; 5s. 6d. abroad.)

For contents of these books, see List III.

THE INDUSTRIAL USES OF WATER. COMPOSI-
- TION—EFFECTS—-TROUBLES— REMEDIES —
RESIDUARY WATERS — PURIFICATION—AN-
ALYSIS. By H. pe ta Coux.: Royal 8vo. .Trans-
lated from the French and Revised by ARTHUR Morris. 364 pp.
135 Illustrations. Price 10s. 6d. net. (Post free, 11s. home;
11s. 6d. abroad.)
(See Books on Smoke Prevention, Engineering and Metallurgy, p. 18.)

(X Rays.)

PRACTICAL X RAY WORK. By Franx T. Appyman,
B.Sc. (Lond.), F.1.C., Member of the Roentgen Society of London ;
Radiographer to St. George’s Hospital; Demonstrator of Physics
and Chemistry, and Teacher of Radiography in St. George’s
Hospital Medical School. Demy 8vo. Twelve Plates from
Photographs of X-Ray Work. Fi.ty-two Illustrations. 200 pp.
Price 10s. 6d. net. (Post free, 10s. 10d. home; 11s. 3d. abroad.)

(India-Rubber and Gutta Percha.)

INDIA-RUBBER AND GUTTA PERCHA. Second
English Edition, Revised and Enlarged. Based on the French
work of T. SEELIGMANN, G. LAMy TORRILHON and H. FALCONNET
by JoHN GEDDES McINTosH. Royal 8vo. 100 Illustrations. 400
pages. Price 12s. 6d. net. (Post free, 13s. home; 13s. 6d.
abroad.)

(Leather Trades.)
THE LEATHER WORKER'S MANUAL. Being a

Compendium of Practical Recipes and Working Formule for
Curriers, Bootmakers, Leather Dressers, Blacking Manufac-
turers, Saddlers, Fancy Leather Workers. By H. C. STANDAGE.
Demy 8vo. 165 pp. Price 7s. 6d. net. (Post free, 7s. 10d. home ;
8s. abroad.)

(See also Manufacture of Shoe Polishes, Leather Dressings, etc., p. 6.)

(Pottery, Bricks, Tiles, Glass, etc.)

MODERN BRICKMAKING. By Atrrep B. SEARLE,
Royal 8vo. 440 pages. 260 Illustrations. Price 12s. 6d. net.
(Post free, 13s. home; 13s. 6d. abroad.)

THE MANUAL OF PRACTICAL POTTING. Com-
piled by Experts, and Edited by Cuas. F. Binns. Fourth Edition,
Revised and Enlarged. 200 pp. Demy 8vo. Price 17s. 6d. net.
(Post free, 17s. 10d. home; 18s. 3d. abroad.)

POTTERY DECORATING. A Description of all the Pro-
cesses for Decorating Pottery and Porcelain. By R. HAINBACH.
Translated from the German. Crown 8vo. 250 pp. Twenty-
two Illustrations. Price 7s. 6d. net. (Post free, 7s. 10d. home ;
8s. abroad.)

A TREATISE ON CERAMIC INDUSTRIES. A

Complete Manual for Pottery, Tile, and Brick Manufacturers. By
EMILE Bourry. A Revised Translation from the French, with
some Critical Notes by ALFRED B. SEARLE. Demy 8vo. 308
Illustrations. 460 pp. Price 12s.6d. net. (Post free, 13s. home;
13s. 6d. abroad.)

ARCHITECTURAL POTTERY. Bricks, Tiles, Pipes,

Enamelled Terra-cottas, Ordinary and Incrusted Quarries, Stone-
ware Mosaics, Faiences and Architectural Stoneware. By I.EON
LEFEVRE. Translated from the French by K. H. Birp, M.A.,
and W. Moore BINNS. With Five Plates. 950 Illustrations in
the Text, and numerous estimates. 500 pp. Royal 8vo. Price
15s. net. (Post free, 15s. 6d. home; 16s. 6d. abroad.)

THE ART OF RIVETING GLASS, CHINA AND
EARTHENWARE. By J. Howorrtu. Second
Edition. Paper Cover. Price ls. net. (By post, home or abroad,
Is. 1d.)

NOTES ON POTTERY CLAYS. The Distribution,
Properties, Uses and Analyses of Ball Clays, China Clayg and
China Stone. By Jas. Fatrige, F.G.S. 132 pp. Crown 8vo.
Price 3s. 6d. net. (Post free, 3s. 9d. home; 3s. 10d. abroad.)

HOW TO ANALYSE CLAY. By H. M. Asupy, Demy

8vo. 72 pp. 20 Illustrations. Price 3s. 6d. net. (Post free,
3s. 9d. home; 3s. 10d. abroad.)

A Reissue of

THE HISTORY OF THE STAFFORDSHIRE POT-
TERIES; AND THE RISE AND PROGRESS
OF THE MANUFACTURE OF POTTERY AND
PORCELAIN. With References to Genuine Specimens,
and Notices of Eminent Potters. By SIMEON SHAW. (Originally

published in 1829.) 265 pp. Demy 8vo. Price 5s. net. (Post
free, 5s. 4d. home; 5s. 9d. abroad.)

A Reissue of

THE CHEMISTRY OF THE SEVERAL NATURAL
AND ARTIFICIAL HETEROGENEOUS COM-
POUNDS USED IN MANUFACTURING POR-
CELAIN, GLASS AND POTTERY. By Simeon
SHaw. (Originally published in 1837.) 750 pp. Royal 8vo.
Price 10s. net. (Post free, 10s. 6d. home; 12s. abroad.)

BRITISH POTTERY MARKS. By G. WooLLiscrort

RHEAD. Demy 8vo. 310 pp. With over Twelve-hundred Illus-
trations of Marks. Price 7s. 6d. net. (Post free, 8s. home;
8s. 3d. abroad.)

For contents of these books, see List III.

(Glassware, Glass Staining and Painting.)

RECIPES FOR FLINT GLASS MAKING. By a
British Glass Master and Mixer. Sixty Recipes. Being Leaves
from the Mixing Book of several experts in the Flint Glass Trade,
containing up-to-date recipes and valuable information as to
Crystal, Demi-crystal and Coloured Glass in its many varieties.
It contains the recipes for cheap metal suited to pressing, blow-
ing, etc., as well as the most costly crystal and ruby. Second
Edition. Crown 8vo. Price 10s. 6d. net. (Post free, 10s. 9d.
home; 10s. 10d. abroad.)

A TREATISE ON THE ART OF GLASS PAINT-
ING. Prefaced with a Review of Ancient Glass. By
ERNEST R. SUFFLING. With One Coloured Plate and Thirty-
seven Illustrations. Demy 8vo. 140 pp. Price 7s. 6d. net.
(Post free, 7s. 10d. home; 8s. abroad.)

(Paper Making and Testing.)

THE PAPER MILL CHEMIST. By Henry P. STEvEns,
M.A., Ph.D., F.L.C. Royal 12mo. 60 Illustrations. 300 pp.
Price 7s. 6d. net. (Post free, 7s. 9d. home; 7s. 10d. abroad.)

THE TREATMENT OF PAPER FOR SPECIAL
PURPOSES. By L.E. Anpé&s. Translated from the
German. Crown 8vo. 48 Illustrations. 250 pp. Price 6s. net.
(Post free, 6s. 4d. home; 6s. 6d. abroad.)

(Enamelling on Metal.)
ENAMELS AND ENAMELLING. For Enamel

Makers, Workers in Gold and Silver, and Manufacturers of
Objects of Art. By Paut Ranpau. Second and Revised
Edition. Translated from the German. With 16 Illustrations.
Demy 8vo. 200 pp. Price 10s. 6d. net. (Post free, 10s. 10d.
home; 11s. abroad.)

THE ART OF ENAMELLING ON METAL. By
W. Norman Brown. Second Edition, Revised. Crown 8vo.

60 pp. Price 3s. 6d. net. (Post free, 3s. 9d. home; 3s. 10d.
abroad.)

(Textile and Dyeing Subjects.)
THE FINISHING OF TEXTILE FABRICS (Woollen,

Worsted, Union, and other Cloths). By RoBertTs BEAUMONT.
With 150 Illustrations of Fibres, Yarns and Fabrics, also Sectional
and other Drawings of Finishing Machinery. Demy 8vo. 260 pp.
Price 10s. 6d. net. (Post free, 10s. 10d. home; 11s, 3d. abroad.)

STANDARD CLOTHS. By Roserts BEAumont.
[In the Press.

FIBRES USED IN TEXTILE AND ALLIED IN-
DUSTRIES. By C. ArnswortH MircHe.u, B.A.
(Oxon.), F.I.C., and R. M. PripEaux, F.I.C. With 66 IIlustra-
tions specially drawn direct from the Fibres. Demy 8vo.
200 pp. Price 7s. 6d. net. (Post free, 7s. 10d. home ; 8s. abroad.)

DRESSINGS AND FINISHINGS FOR TEXTILE
FABRICS AND THEIR APPLICATION. De-
scription of all the Materials used in Dressing Textiles: Their
Special Properties, the preparation of Dressings and their em-
ployment in Finishing Linen, Cotton, Woollen and Silk Fabrics.
Fireproof and Waterproof Dressings, together with the principal
machinery employed. Translated from the Third German
Edition of FRIEDRICH POLLEYN. Demy 8vo. 280 pp. Sixty
Illustrations. Price 7s. 6d. net. (Post free, 7s. 10d. home ;
8s. abroad.)

THE CHEMICAL TECHNOLOGY OF TEXTILE
FIBRES: Their Origin, Structure, Preparation, Wash-
ing, Bleaching, Dyeing, Printing and Dressing. By Dr. GEorG
VON GEORGIEvicS. Translated from the German by CHARLES
SALTER. 320 pp. Forty-seven Illustrations. Royal 8vo. Price
10s. 6d. net. (Post free, 11s. home; 11s. 3d. abroad.)

POWER-LOOM WEAVING AND YARN NUMBER-

ING, According to Various Systems, with Conversion
Tables. Translated from the German of ANTHON GRUNER. With
Twenty-six Diagrams in Colours. 150 pp. Crown 8vo. Price
7s. 6d. net. (Post free, 7s. 9d. home; 8s. abroad.)

TEXTILE RAW MATERIALS AND THEIR CON-.-
VERSION INTO YARNS. (The Study of the Raw
Materials and the Technology of the Spinning Process.) By
JULIUS ZIPSER. Translated from German by CHARLES SALTER.
302 Illustrations. 500 pp. Demy 8vo. Price 10s. 6d. net.

(Post free, 1Is. home; 11s. 6d. abroad.)

GRAMMAR OF TEXTILE DESIGN. By H. Nisset,
Weaving and Designing Master, Bolton Municipal Téchnical
School. Demy 8vo. 280 pp. 490 Illustrations and Diagrams.
Price 6s. net. (Post free, 6s. 4d. home; 6s. 6d. abroad.)

ART NEEDLEWORK AND DESIGN. POINT

LACE. A Manual of Applied Art for Secondary Schools
and Continuation Classes. By M. E. Witkinson. Oblong
quarto.’ With 22 Plates. Bound in Art Linen. Price 3s. 6d.
net. (Post free, 3s. 10d. home; 4s. abroad.)

HOME LACE-MAKING. A Handbook for Teachers and
Pupils. By M. E. W. MiLroy. Crown 8vo. 64 pp. With 3
Plates and 9 Diagrams. Price 1s. net. (Post free, ls. 3d, home ;
1s. 4d. abroad.)

For contents of these books, see List II.

15
THE CHEMISTRY OF HAT MANUFACTURING.

Lectures delivered before the Hat Manufacturers’ Association.
By Watson SmitH, F.CS., F.1.C. Revised and Edited by
ALBERT SHONK. Crown 8vo. 132 pp. 16 Illustrations. Price
7s. 6d. net.’ (Post free, 7s. 9d. home ; 7s. 10d. abroad.)

THE TECHNICAL TESTING OF YARNS AND
TEXTILE FABRICS. With Reference to Official
Specifications Translated from the German of Dr. J. HERZFELD.
Second Edition. Sixty-nine Illustrations. 200 pp. Demy 8vo
Price 10s. 6d net. (Post free, 10s. 10d. home; 11s. abroad.)

DECORATIVE AND FANCY TEXTILE FABRICS.
By R. T, Lorp. For Manufacturers and Designers of Carpets,
Damask, Dress and all Textile Fabrics. 200 pp. Demy 8vo.
132 Designs and Illustrations. Price 7s. 6d. net. (Post free,
7s. 10d. home; 8s. abroad.)

THEORY AND PRACTICE OF DAMASK WEAV-
ING. By H. Kinzer and K. Watter. Royal 8vo.
Eighteen Folding Plates. Six Illustrations. Translated from

the German. 110 pp. Price 8s. 6d. net. (Post free, 9s. home ;
9s. 6d. abroad.)

FAULTS IN THE MANUFACTURE OF WOOLLEN
GOODS AND THEIR PREVENTION. By
Nicotas REISER. Translated from the Second German Edition.
Crown 8vo. Sixty-three Illustrations. 170 pp. Price 5s. net.
(Post free, 5s. 4d. home; 5s. 6d. abroad.)

SPINNING AND WEAVING CALCULATIONS,

especially relating to Woollens. From the German of N.

REISER. Thirty-four Illustrations. Tables. 160 pp. Demy

S8vo. 1904. Price 10s. 6d. net. (Post free, 10s. 10d. home; IIs.
abroad.)

WORSTED SPINNERS’ HANDBOOK. By UH.
TURNER. Crown 8vo. About 176 pages. [In the Press.

ANALYSIS OF WOVEN FABRICS. ByA. FP. Barker,
M.Sc., and E. MipcGLtey. Demy 8vo. 316 pp. Numerous Tables,
Examples and 82 Illustrations. Price 7s. 6d. net. (Post free,
7s. 10d. home ; 8s. abroad.)

WATERPROOFING OF FABRICS. By Dr. S. Mir-
ZINSKI. Second Edition, Revised and Enlarged. Crown 8vo.
140 pp. 29 Illus. Price 5s. net. (Post free, 5s. 4d. home;
5s. 6d. abroad.)

HOW TO MAKE A WOOLLEN MILL PAY. By

JOHN Mackie. Crown 8vo. 76 pp. Price 3s. 6d. net. (Post
free, 3s. 9d. home; 3s. 10d. abroad.)

YARN AND WARP SIZING IN ALL ITS
BRANCHES. Translated from the German of CARL

KRETSCHMAR. Royal 8vo. 123 Illustrations. 150 pp. Price
10s. 6d. net. (Post free, 10s. 10d. home; 11s. abroad.)

(For “ Textile Soaps and Oils” see p. 7.)

(Dyeing, Colour Printing, Matching
and Dye=stuffs.)
THE COLOUR PRINTING OF CARPET YARNS.

Manual for Colour Chemists and Textile Printers. By Davip
PaTERSON, F.C.S. Seventeen Illustrations. 136 pp. Demy
8vo. Price 7s. 6d. net. (Post free, 7s. 10d. home; 8s. abroad.)

TEXTILE COLOUR MIXING. By Davin Paterson.

Formerly published under title of ‘“‘ Science of Colour Mixing ”’.

Second Revised Edition. Demy 8vo. 140 pp. 41 Illustrations,

with 5 Coloured Plates and 4 Plates showing Dyed Specimens.
Price 7s. 6d. net. ,(Post free, 7s. 10d. home; 8s. abroad.)

[Fust published.

DYERS’ MATERIALS : An Introduction to the Examina-

ve tion, Evaluation and Application of the most important Sub-

=i stances used in Dyeing, Printing, Bleaching and Finishing. B

~ Paut HEERMAN, Ph.D. Translated from the German by A. C.

«2»’WRrIGHT, M.A. (Oxon)., B.Sc. (Lond.). Twenty-four Illustrations.

via Crown 8vo. 150 pp. Price 5s. net. (Post free, 5s. 4d. home;
5s. 6d. abroad.)

COLOUR MATCHING ON TEXTILES. A Manual
intended for the use of Students of Colour Chemistry, Dyeing and
Textile Printing. By Davip PaTERSON, F.C.S. Coloured Frontis-
piece. Twenty-nine Illustrations and Fourteen Specimens of
Dyed Fabrics. Demy 8vo. 132 pp. Price 7s. 6d. net. (Post
free, 7s. 10d. home; 8s. abroad.)

COLOUR: A HANDBOOK OF THE THEORY OF
COLOUR. By Georce H. Hurst, F.C.S. With Ten
Coloured Plates and Seventy-two Illustrations. 160 pp. Demy
8vo. Price 7s. 6d. net. (Post free, 7s. 10d. home ; 8s. abroad.)

Reissue of

THE ART OF DYEING WOOL, SILK AND
COTTON. Translated from the French of M. HELtort,
M. MacgueEr and M. LE PILEUR D’APLIGNY. First Published in
English in 1789. Six Plates. Demy 8vo. 446 pp. Price 5s. net.
(Post free, 5s. 6d. home; 6s. abroad.)

THE CHEMISTRY OF DYE-STUFFS. By Dr. GEore
Von GEORGIEVICS. Translated from the Second German Edition.
412 pp. Demy 8vo. Price 10s. 6d. net. (Post free, 11s. home;
11s. 6d. abroad.)

THE DYEING OF COTTON FABRICS: A Practical
Handbook for the Dyer and Student. By FRANKLIN BEECH,
Practical Colourist and Chemist. 272 pp. Forty-four Illus-
trations of Bleaching and Dyeing Machinery. Demy 8vo. Price
7s. 6d. net. (Post free, 7s. 10d. home; 8s. abroad.)

THE DYEING OF WOOLLEN FABRICS. By
FRANKLIN BEECH, Practical Colourist and Chemist. Thirty-
three Illustrations. Demy 8vo. 228 pp. Price 7s. 6d. net.
(Post free, 7s. 10d. home; 8s, abroad.)

For contents of these books, see List II.

(Silk Manufacture. )

SILK THROWING AND WASTE SILK SPIN-
NING. By Ho tuws Rayner. Demy 8vo. 170 pp.
117 Illus. Price 5s. net. (Post free, 5s. 4d. home; 5s. 6d. abroad.)

(Bleaching and Bleaching Agents.)

A PRACTICAL TREATISE ON THE BLEACHING
OF LINEN AND COTTON YARN AND FABRICS.
By L. TatLFer, Chemical and Mechanical Engineer. Trans-
lated from the French by JoHN GeDDES McINTOSH. Demy 8vo.
303 pp. Twenty Illus. Price 12s. 6d. net. (Post free, 13s.
home; 13s. 6d. abroad.)

MODERN BLEACHING AGENTS AND DETER-
GENTS. By Professor Max BorrLer. Translated
from the German. Crown 8vo. 16 Illustrations. 160 pages.
Price 5s, net. (Post free, 5s. 3d. home; 5s. 6d. abroad.)

(Cotton Spinning, Cotton Waste and
Cotton Combing.)

COTTON SPINNING (First Year). By THomas
THORNLEY, Spinning Master, Bolton Technical School. 160 pp.
84 Illustrations. Crown 8vo. Second Impression. Price 3s.
net. (Post free, 3s. 4d. home; 3s. 6d. abroad.)

COTTON SPINNING (Intermediate, or Second Year).
By T.THORNLEY. 2nd. Impression. 180pp. 70 Illus. Crown 8vo.
Price 5s. net. (Post free, 5s. 4d. home; 5s. 6d. abroad.)

COTTON SPINNING (Honours, or Third Year). By
T. THORNLEY. 216 pp. 74 Illustrations. Crown 8vo. Second
Edition. Price 5s. net. (Post free, 5s. 4d. home; 5s. 6d. abroad.)

COTTON COMBING MACHINES. By Tuos. THorn-
LEY, Spinning Master, Technical School, Bolton. Demy 8vo.
117 Illustrations. 300 pp. Price 7s. 6d. net. (Post free, 8s.
home; 8s. 6d. abroad.)

COTTON WASTE: Its Production, Characteristics,
Regulation, Opening, Carding, Spinning and Weaving. By THOMAS
THORNLEY. Demy 8vo. 286 pages. 60 Illustrations. Price 7s. 6d.
net. (Post free, 7s. 10d. home; 8s. abroad.)

THE RING SPINNING FRAME: GUIDE FOR
OVERLOOKERS AND STUDENTS. By N. Bootn.
Crown 8vo. 76 pages. Price 3s.net. (Post free, 3s. 3d. home;
3s. 6d. abroad.)

(Flax, Hemp and Jute Spinning.)
MODERN FLAX, HEMP AND JUTE SPINNING

AND TWISTING. A Practical'Handbook for the use
of Flax, Hemp and Jute Spinners, Thread, Twine and Rope
Makers. By HERBERT R. CarTER, Mill Manager, Textile Expert

and Engineer, Examiner in Flax Spinning to the City and Guilds
nf: tT natn Peetetista Diawwew Ren 10609: Wiek @9 Tiltietratinne.

(Collieries and Mines.)
RECOVERY WORK AFTER PIT FIRES. By Rosert

LAMPRECHT, Mining Engineer and Manager. Translated from
the German. Illustrated by Six large Plates, containing Seventy-
six Illustrations. 175 pp. Demy 8vo. Price 10s. 6d. net. (Post
free, 10s. 10d. home; 11s. abroad.)

VENTILATION IN MINES. By Roserr Wasner,
Mining Engineer. Translated from the German. Royal 8vo.
Thirty Plates and Twenty-two Illustrations. 240 pp. Price
10s. 6d. net. (Post free, 1ls. home; 11s. 3d. abroad.)

THE ELECTRICAL EQUIPMENT OF COLLIERIES.
By W. GaLLoway DuNGCAN and Davip PENMAN. Demy 8vo.
310 pp. 155 Illustrations and Diagrams. Price 10s. 6d. net.
(Post free, 11s. home; 11s. 3d. abroad.)

(Dental Metallurgy.)

DENTAL METALLURGY: MANUAL FOR STU-
DENTS AND DENTISTS. By A. B. Grirrirtus,

Ph.D. Demy 8vo. Thirty-six Illustrations. 200 pp. Price
7s. 6d. net. (Post free, 7s. 10d. home; 8s. abroad.)

(Engineering, Smoke Prevention and
Metallurgy.)

THE PREVENTION OF SMOKE. Combined with
the Economical Combustion of Fuel. By W. C. PopPLEWELL,
M.Sc., A.M. Inst., C.E., Consulting Engineer. Forty-six Illus-
trations. 190 pp. Demy 8vo. Price 7s. 6d. net. (Post free,
7s. 10d. home; 8s. 3d. abroad.)

GAS AND COAL DUST FIRING. A Critical Review
of the Various Appliances Patented in Germany for this purpose
since 1885. By ALBERT Pdtscu. 130 pp. Demy 8vo. Trans-
lated from the German. With 103 Illustrations. Price 5s. net.
(Post free, 5s. 4d. home; 5s. 6d. abroad.)

THE HARDENING AND TEMPERING OF STEEL
IN THEORY AND PRACTICE. By FRripo.tin
REISER. Translated from the German of the Third Edition.
Crown 8vo. 120 pp. Price 5s. net. (Post free, 5s. 3d. home;
5s. 4d. abroad.)

SIDEROLOGY: THE SCIENCE OF IRON (The

Constitution of Iron Alloys and Slags). Translated from

- German of HANNS FREIHERR V. JUPTNER. 350 pp. Demy 8vo.
Eleven Plates and Ten Illustrations. Price 10s. 6d. net. (Post
free, lls. home; 11s. 6d. abroad.

)
EVAPORATING, CONDENSING AND COOLING
APPARATUS. Explanations, Formule and Tables
for Use in Practice. By E. HAUSBRAND, Engineer. Translated
by A. C. WricuT, M.A. (Oxon.), B.Sc. (Lond.). With Twenty-
one Illustrations and Seventy-six Tables. 400 pp. Demy 8vo.
Price 10s. 6d. net. (Post free, 1ls. home; 11s. 6d, abroad.)

(The ‘‘Broadway’’ Series of Engineering
Handbooks. )

Uniform in Size: Narrow Crown 8vo. (Pocket Size.)

VOLUME |.-ELEMENTARY PRINCIPLES OF RE-

INFORCED CONCRETE CONSTRUCTION. By
Ewart S. ANDREWS, B.Sc. Eng. (Lond.). 200 pages. With 57
Illustrations. Numerous Tables and Worked Examples, Price
3s. net. (Post free, 3s. 3d. home; 3s. 6d. abroad.)

Votume I1—GAS AND OIL ENGINES. By A.

KirRSCHKE. Translated and Revised from the German, and
adapted to British practice. 160 pages. 55 Illustrations.
Price 3s. net. (Post free, 3s. 3d. home; 3s. 6d. abroad.)

Votume Il].— IRON AND STEEL CONSTRUC-
TIONAL WORK. By K. Scuinpier. Translated
and Revised from the German, and adapted to British practice.
140 pages. 115 Illustrations. Price 3s. 6d. net. (Post iree,
3s. 9d. home; 4s. abroad.)

Vo.tume 1V.—TOOTHED GEARING. ByG.T. Wuire,
B.Sc. (Lond.). 220 pages. 136 Illustrations. Price 3s. 6d. net.
(Post free, 3s. 9d. home ; 4s. abrcad.)

Votume V.—STEAM TURBINES: Their Theory and
Construction. By H. Wiutpa. Translated from the German ;
Revised and adapted to British practice. 200 pages. 104 IIlus-
trations. Price 3s.6d. net. (Post free, 3s. 9d. home; 4s. abroad.)

Votume VI._CRANES AND HOISTS. Their Con-

struction and Calculation. By H. WiLpa. Translated from the
German; revised and adapted to British practice. 168 pages.
399 Hlustrations. Price 3s. 6d. net. (Post free, 3s. 9d. home;
4s. abroad.)

Vo_umE VII.—FOUNDRY MACHINERY. By E.
TREIBER. Translated from the German; revised and adapted to
British practice. 148 pages. 51 Illustrations, Price 3s. 6d. net.
(Post free, 3s. 9d. home ; 4s. abroad.)

Votume VIII.—MOTOR CAR MECHANISM.’ By
W. E. Dommetr. 200 pages. 102 Illustrations. Price 3s. 6d.
net. (Postfree, 3s. 9d. home; 4s. abroad.)

VotumeE I[X.— ELEMENTARY PRINCIPLES OF
ILLUMINATION AND ARTIFICIAL LIGHTING.
By A. Buox, B.Sc. 240 pages. 124 Illustrations and Diagrams
and 1 Folding Plate. Price 3s. 6d. net. (Post free, 3s. 9d.
home; 4s. abroad.)

Vo_ume X.-HYDRAULICS. By E, H. Spracuz, 190
pages. With Worked Examples and 89 Illustrations. Price
3s. 6d. net. (Post free, 3s. 9d. home ; 4s. abroad.)

VotumeE XI.— ELEMENTARY PRINCIPLES OF

SURVEYING. By M. T. M. Ormspy. 244 pages.
With Worked Examples and 135 Illustrations and Diagrams, in-
cluding 4 Folding Plates. Price 4s. net. (Post free, 4s.3d. home ;
4s. 6d. abroad.)

Vo.LumE XII_—THE SCIENCE OF WORKS MANAGE.-
MENT. By Joun Batey. 232 pages. Price 4s. net.
(Post free, 4s. 3d. home ; 4s. 6d. abroad.)

VoLume XII].—THE CALCULUS FOR ENGINEERS.
By Ewart S. ANpRews, B.Sc.Eng. (Lond.), and H. Bryon
Heywoonp, D.Sc. (Paris), B.Sc. (Lond.). 284 pages. 102 Illustra-
tions. With Tables and Worked Examples. Price 4s. net. (Post
free, 4s. 3d. home; 4s. 6d. abroad.)

VoLumeE XIV.—LATHES: Their Construction and
Operation. By G. W. Buruey. 244 pages. 200 Illustrations.
Price 3s. 6d. net. (Post free, 3s. 9d. home; 4s. abroad.)

[Ffust published.

Votume XV.—STEAM BOILERS AND COMBUS-

TION. By Joun Batey. 220 pages. 18 Diagrams.
Price 4s. net. (Post free, 4s. 3d. home; 4s. 6d. abroad.)
[Fust published.

VoLumME XVI.— REINFORCED CONCRETE IN

PRACTICE. By A. Artspan H. Scorr. 190 pages.
130 Illustrations and Diagrams and 2 Folding Plates. | Price
4s. net. (Post free, 4s. 3d. home; 4s. 6d. abroad.)

[Fust published.

[IN PREPARATION.]
PORTLAND CEMENT. Its Properties and Manu-
facture. By P. C. H. WEst, F.C.S.
TESTING OF MACHINE TOOLS. By G. W. Burtey.
BRIDGE FOUNDATIONS. By W. Bornsipg, M.I.C.E.
CALCULATIONS FOR A STEEL FRAME viene monies
ING. By W. C. Cockine, M.C.I.
GEAR GUTTING. By G. W. Burtey.

MOVING LOADS BY INFLUENCE LINES AND
OTHER METHODS. By E. H. Spracug, A.M.I.C.E.

THE STABILITY OF ARCHES. By E. H. Spracug,
A.M.1.C.E.

DRAWING OFFICE PRACTICE. By W. CLecc.
ESTIMATING STEELWORK FOR BUILDINGS. By

B, P. F. GLEED and S. BYLANDER.
THE THEORY OF THE CENTRIFUGAL AND
TURBO PUMP. By J. WELLS.

STRENGTH OF SHIPS. By James Bertram THOMAS.
STABILITY OF MASONRY. By E. H. Spracue.
MACHINE SHOP PRACTICE. By G. W. Bortey.

For contents of these books, see List III.

(Sanitary Plumbing, Metal Work, etc.)

EXTERNAL PLUMBING WORK. A Treatise on
Lead Work for Roofs. By JoHN W. Hart, R.P.C. 180 Illustra-
tions. 272 pp. Demy 8vo. Second Edition Revised. Price
7s. 6d. net. (Post free, 7s. 10d. home; 8s. abroad.)

HINTS TO PLUMBERS ON JOINT WIPING, PIPE
BENDING AND LEAD BURNING. Third Edition,
Revised and Corrected. By JoHN W. Hart, R.P.C. 184 Illus-
trations. 313 pp. Demy 8vo. Price 7s. 6d. net. (Post free,
8s. home; 8s. €d. abroad.)

SANITARY PLUMBING AND DRAINAGE. By
JoHN W. Hart. Demy 8vo. With 208 Illustrations. 250 pp.
1904. Price 7s. 6d. net. (Post free, 7s. 10d. home; 8s. abroad.)

THE PRINCIPLES AND PRACTICE OF DIPPING,
BURNISHING, LACQUERING AND BRONZ-
ING BRASS WARE. By W. Norman Brown. 48 pp.

Crown 8vo. Price 3s. net. (Post free, 3s. 3d. home and abroad.)

A HANDBOOK ON JAPANNING. For I[ronware,
Tinware, and Wood, etc. By WiLtiaAmM NorMAN Brown.
Second Edition. 70 pages. 13 Illustrations. Crown 8vo. Price
3s. 6d. net. (Post free, 3s. 9d. home: 4s. abroad.)

THE PRINCIPLES OF HOT WATER SUPPLY. By
JOHN W. Hart, R.P.C. With 129 Illustrations. 177 pp. Demy
8vo. Price 7s. 6d. net. (Post free, 7s. 10d. home; 8s. abroad.)

SHEET METAL WORKING. Cutting, Punching,
Bending, Folding, Pressing, Drawing and Embossing Metals,
with Machinery for same. By F. Georcr and A. SCHUBERT.
Translated from the German. Demy 8vo. 160 pages. 125 Draw-
ings and Illustrations. 2 Folding Plates. Price 7s. 6d. net.
(Post free, 7s. 10d. home; 8s. abroad.) [Fust published.

(Electric Wiring, etc.)

THE DEVELOPMENT OF THE INCANDESCENT

ELECTRIC LAMP. By G. Basiz Barnan, A.M.I.E.E.
Demy 8vo. 200 pages. 2 Plates, 25 Illustrations and 10 Tables.
Price 5s. net. (Post free, 5s. 4d. home; 5s. 6d. abroad.)

WIRING CALCULATIONS FOR ELECTRIC
LIGHT AND POWER INSTALLATIONS. A
Practical Handbook containing Wiring Tables, Rules, and
Formulz for the Use of Architects, Engineers, Mining Engineers,
and Electricians, Wiring Contractors and Wiremen, etc. By G.
W. Lummis PaTERSON. Crown 8vo. 96 pages. 35 Tables.
Price 5s. net. (Post free, 5s. 3d. home ; 5s. 6d. abroad.)

ELECTRIC WIRING AND FITTING. By Sypney F.
WALKER, R.N., M.I.E.E., M.I.Min.E., A.M.Inst.C.E., etc., etc.
Crown 8vo. 150 pp. With Illustrations and Tables. Price 5s.
net. (Post free, 5s. 3d. home; 5s. 6d..abroad.) ~.

(Brewing and Botanical.)

HOPS IN THEIR BOTANICAL, AGRICULTURAL
AND TECHNICAL ASPECT, AND AS AN
ARTICLE OF COMMERCE. By EmmanueEt Gross.
Translated from the German. 78 Illus. 340 pp. Demy 8vo. Price
10s. 6d. net. (Post free, 1ls. home ; 11s 6d. abroad.)

INSECTICIDES, FUNGICIDES AND WEED-
KILLERS. By E. Bourcart, D.Sc. Translated from
the French. Revised and Adapted to British Standards and
Practice. Demy 8vo. 450 pages, 83 Tables, and 12 Illustrations,
Price 12s. 6d. net. (Post free, 13s home; 13s. 6d. abroad.)

(For Agricultural Chemistry, see p. 9.)

(Wood Products, Timber and Wood Waste. )

WOOD PRODUCTS: DISTILLATES AND EX-
TRACTS. By P. Dumesny, Chemical Engineer,

Expert before the Lyons Commercial Tribunal, Member of the
International Association of Leather Chemists; and J. NoyvEer.
Translated from the French by DONALD GRANT. Royal 8vo.
320 pp. 103 Illustrations and Numerous Tables. Price 10s. 6d.
net. (Post free, 11s. home; 11s. 6d. abroad )

TIMBER: A Comprehensive Study of Wood in all its
Aspects (Commercial and Botanical), showing the different
Applications and Uses of Timber in Various Trades, etc. Trans-
lated from the French of PAUL CHARPENTIER. Royal 8vo. 437
pp. 178 Illustrations. Price 12s. 6d. net. (Post free, 13s.
home; 14s. abroad.)

THE UTILISATION OF WOOD WASTE. Trans-
lated from the German of ERNST HUBBARD. Crown 8vo. 192 pp.
50 Illus. Price 5s. net. (Post free, 5s.4d. home; 5s. 6d. abroad.)

(See also Utilisation of Waste Products, p. 9.)

(Building and Architecture.)

ORNAMENTAL CEMENT WORK. By OLIVER
WHEATLEY. Demy 8vo. 83 Illustrations. 128 pp. Price 5s.
net. (Post free, 5s. 4d. home; 5s. 6d. abroad.)

THE PREVENTION OF DAMPNESS IN BUILD-
INGS; with Remarks on the Causes, Nature and
Effects of Saline, Efflorescences and Dry-rot, for Architects,
Builders, Overseers, Plasterers, Painters and House Owners.
By ADOLF WILHELM KEIM. ‘Translated from the German of the
second revised Edition by M. J. SALTER, F.I1.C., F.C S. Eight
oo. Pal Plates and Thirteen Illustrations. Crown 8vo. 115

p. Price 5s, net. (Post free, 5s. 3d. home; 5s. 4d. abroad.)

HANDBOOK OF TECHNICAL TERMS USED IN
ARCHITECTURE AND BUILDING, AND THEIR
ALLIED TRADES AND SUBJECTS. By Avucus-

TINE C. PASSMORE. Demy 8vo. 380 pp. Price 7s. €d. net.
(Post free, 8s. home; 8s. 6d. abroad.)

For contents of these books, se: List III.

(Foods, Drugs and Sweetmeats.)

FOOD AND DRUGS. ByE.J. Parry, B.Sc., F.1.C.,F.C.S.
Volume |. The Analysis of Food and Drugs (Chemical and
Microscopical). Royal 8vo. 724 pp. Price 21s. net. (Post
free, 21s. 6d. home; 22s. 6d. British Colonies; 23s. 3d. other
Foreign Countries.)
Volume Il. The Sale of Food and Drugs Acts, 1875-1907.
Royal 8vo. 184 pp. Price 7s. 6d. net. (Post free, 7s. 10d.
home; 8s, abroad.)

THE MANUFACTURE OF PRESERVED FOODS
AND SWEETMEATS. By A. Hausner. With
Twenty-eight Illustrations. Translated from the German of the
third enlarged Edition. Second English Edition. Crown 8vo. 225
pp. Price 7s. 6d. net. (Post free, 7s. 9d. home; 7s. 10d. abroad.)

RECIPES FOR THE PRESERVING OF FRUIT,
VEGETABLES AND MEAT. By E. Wacne_r.

Translated from the German. Crown 8vo. 125 pp. With 14
Illustrations. Price 5s. net. (Post free, 5s. 3d. home; 5s. 4d.
abroad.)

(Dyeing Fancy Goods.)

THE ART OF DYEING AND STAINING MARBLE,
ARTIFICIAL STONE, BONE, HORN, IVORY
AND WOOD, AND OF IMITATING ALLSORTS
OF WOOD. A Practical Handbock for the Use of
Joiners, Turners, Manufacturers of Fancy Goods, Stick and
Umbrella Makers, Comb Makers, etc. Translated from the
German of D. H. SoxHLet, Technical Chemist. Crown 8vo.
168 pp. Price 5s. net. (Post free, 5s. 3d. home; 5s. 4d. abroad.)

(Celluloid. )
CELLULOID: Its Raw Material, Manufacture, Properties

and Uses. A Handbook for Manufacturers of Celluloid and
Celluloid Articles, and all Industries using Celluloid; also for
Dentists and Teeth Specialists. By Dr. Fr. BOcCKMANN, Tech-
nical Chemist. Translated from the Third Revised German
Edition. Crown 8vo. 120 pp. With 49 Illustrations. Price 5s.
net. (Post free, 5s. 3d. home; 5s. 4d. abroad.)

(Lithography, Printing and
Engraving. )
ART OF LITHOGRAPHY. By H. J. Ruopes. Demy
8vo. 344 pages. 120 Illustrations, 2 Folding Plates. Copious

combined Index and Glossary. Price 10s. 6d. net. (Post free,
lls. home ; 11s. 3d. abroad.)

PRINTERS’ AND STATIONERS READY
RECKONER AND COMPENDIUM. Compiled by

VICTOR GRAHAM. Crown 8vo. 112 pp. 1904. Price 3s. 6d. net.
(Post free, 3s. 9d. home; 3s. 10d. abroad.)
ENGRAVING FOR ILLUSTRATION. HISTORI-

CAL AND PRACTICAL NOTES. By J. Kirxsripe.
72 pp. Two Plates and 6 Illustrations. Crown 8vo. Price
2s. 6d. net. (Post free, 2s. 9d. home; 2s. 10d. abroad.)
(For Printing Inks, see p. 4.)

(Bookbinding. )

PRACTICAL BOOKBINDING. By Paut. ApaAm.

Translated from the German. Crown 8vo. 180 pp. 127 Illus-
trations. Price 5s. net. (Post free, 5s. 4d. home; 5s. 6d. abroad.

(Sugar Refining.)

THE TECHNOLOGY OF SUGAR: Practical Treatise
on the Mcdern Methods of Manufacture of Sugar from the Sugar
Cane and Sugar Beet. By JoHN GepDES McINTosnH. Third Re-
vised and Enlarged Edition. Demy 8vo. [New Edition in the Press.

(See “‘ Evaporating, Condensing, etc., Apparatus,” p. 18.)

(Emery.) |
EMERY AND THE EMERY INDUSTRY. Trans-

lated from the German of A. HaENiIG. Crown 8vo. 45 Illus.
104 pp. Price 5s. net. (Post free, 5s. 3d. home; 5s. 6d. abroad.)

(Bibliography. )

CLASSIFIED GUIDE TO TECHNICAL AND COM-
MERCIAL BOOKS. Compiled by Epcar GREEN-
woop. Demy 8vo. 224pp. 1904. Being a Subject-list of the
Principal British and American Books in Print; giving Title,
Author, Size, Date, Publisher and Price. Price 5s. net. (Post
free, 5s. 4d. home; 5s. 6d. abroad.)

HANDBOOK TO THE TECHNICAL AND ART
SCHOOLS AND COLLEGES OF THE UNITED

KINGDOM. Containing particulars of nearly 1,000
Technical, Commercial and Art Schools throughout the United
Kingdom. With full particulars of the courses of instruction,
names of principals, secretaries, etc. Demy 8vo. 150pp.. Price
3s. 6d. net. (Post free, 3s. 10d. home; 4s. abroad.)

SCOTT, GREENWOOD. &. SON,

TECHNICAL BOOK AND TRADE JOURNAL PUBLISHERS,
8 BROADWAY, LUDGATE, LONDON, E.C.

Telegraphic Address, ‘‘ Printeries, Cent., London ”. April, 1915.

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Full text of "The by-products of coal-gas manufacture"

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