c.c. Colic caeca. p.v. Cut root of portal vein.
d. Duodenum. r.v. Rectal vein.
g. Glandular patch. s. Proventriculus.
l.l. Meckel's tract. y. Meckel's diverticulum, or
l.i. Hind-gut. Yolk-sac vestige.
have not yet sufficient exact knowledge of the gut in Pisces,
Batrachia and Reptilia to find amongst these with any
certainty the most probable survival from the ancestral
condition. The primitive gut must be supposed to have run
backwards from the stomach to the cloaca suspended from the
dorsal wall of the body-cavity by a dorsal mesentery. This
tract, in the course of phylogeny of the common ancestors
of birds and mammals, became longer than the straight length
between its extreme points and, consequendy, was thrown into
a series of folds. The mesentery grew out with these folds,
but the presence of adjacent organs, the disturbance due to
the outgrowth of the liver, and the secondary relations brought
about between different portions of the gut, as the out-growing
loops invaded each other's localities, disturbed the primitive
simplicity. Three definite regions of outgrowth, however,
became conspicuous and are to be recognized in the actual
disposition of the gut in existing birds and mammals. The
first of these is the duodenum. In the vast majority of
birds, and in some of the simpler mammals, the portion of
the gut immediately distal of the stomach grows out into a
long and narrow loop (fig. 4, d), the proximal and distal
ends of which are close together, whilst the loop itself may
remain long and narrow, or may develop minor loops on its
course. In mammals generally, however, the duodenum is complex
and is not so sharply marked off from the distal portion
of the gut as in birds. The second portion is Meckel's
tract. It consists of the part generally known as the small
intestines, the jejunum and ileum of human anatomy, and
Fig. 5,--Intestinal Tract of Canis vulpes. S, cut
end of duodenum; C, caecum; R, cut end of rectum.
stretches from the distal end of the duodenum to the caecum or
caeca. It is the chief absorbing portion of the gut, and in nearly
all birds and mammals is the longest portion. It represents,
however, only a very small part of the primitive straight
gut, corresponding to not more than two or three somites of the
embryo. This narrow portion grows out to form the greater part
of what is called the pendent loop in mammalian embryology.
Its anterior or proximal end lies close to the approximated
Fig. 6.--Intestinal Tract of Macropus bennetti. S,
cut end of duodenum; R, cut end of rectum; C, caecum;
C2, accessory caecum; C.L, colic loop of hind-gut.
proximal and distal ends of the duodenal loop, whilst its
distal end passes into the hind-gut at the colic caecum or
caeca. In the embryos of all birds and mammals, the median
point of Meckel's tract, the part of the loop which has
grown out farthest from the dorsal edge of the mesentery, is
marked by the diverticulum caecum vitelli, the primitive
connexion of the cavity of the gut with the narrowing stalk
of the yolk-sac (fig. 4, y.) Naturally, in birds where the
yolk-sac is of great functional importance this diverticulum
is large, and in a majority of the families of birds persists
throughout life, forming a convenient point of orientation. In
mammals, no doubt in association with the functional reduction
of the yolk-sac, this diverticulum, which is known as Meckel's
diverticulum, has less importance, and whilst it has been
observed in a small percentage of adult human subjects has not
been recognized in the adult condition of any lower Mammalia.
In birds, Meckel's tract falls into minor folds or loops,
the disposition of which forms a series of patterns
remarkably different in appearance and characteristic of
different groups. In fig. 4 an extremely primitive type is
represented. In mammals Meckel's tract remains much more
uniform; it may be short, or increase enormously in length,
but in either case it falls into a fairly symmetrical shape,
suspended at the circumference of a nearly circular expanse
of mesentery. Where it is short it is thrown into very
simple minor loops (figs. 5, 6 and 7); where it is long,
these minor loops form a convoluted mass (figs. 8 abd 9).
FIG. 7.--Intestinal Tract of Tapir. S, cut end of
duodenum; R, cut end of rectum; C, caecum; CL, colon.
The third portion of the gut should be termed the hind-gut and
lies between the caecum or caeca and the anus, corresponding to
the large intestines, colon and rectum of human anatomy. It is
formed from a much larger portion of the primitive straight gut
than the duodenum and Meckel's tract together, and its proximal
portion, in consequence, lies very close to the origin of the
duodenum. In the vast majority of birds, the hind-gut in the
adult is relatively extremely short, often being only from
Fig. 8.--Intestinal Tract of Giraffe. S, cut end of duodenum;
R, cut end of rectum; C, caecum; P.C.L, post-caecal
loop; S.P, spiral loop; SF, third loop of hind-gut.
one-eighth to one-thirtieth of the whole length of the
gut. A certain number of primitive birds, however, have
retained a relatively long condition of the hind-gut (fig.
4), the greatest relative length occurring in struthious
birds, and particularly in the ostrich, where the hind-gut
exceeds in length the duodenum and Meckel's tract together.
Mammals may be contrasted with birds as a group in which
the hind-gut is always relatively long, sometimes extremely
long, and in which, moreover, there is a strong tendency to
differentiation of the hind-gut into regions the characters
of which are of systematic importance. The first region is
the colon, which forms a very simple expansion in mammals
such as Carnivora (fig. 5), where the whole hind-gut is
relatively short, or a series of simple loops in mammals
in which the whole gut has a primitive disposition (e.g.
Marsupialia, fig. 6). In the odd-toed Ungulata, the colon
(fig. 7) forms an enormously long loop, the two limbs of which
are closely approximated and the calibre of which is very
large. In Ruminantia (fig. 8) the colon is still more
highly differentiated, displaying first a simple wide loop,
then a complicated watchspring-like coil, and finally a very
long, irregular portion. In the higher Primates (fig. 9)
it forms one enormous very wide loop, corresponding to the
ascending, transverse and descending colons of human anatomy,
and a shorter distal loop, the omega loop of human anatomy.
Other striking patterns are displayed in other mammalian groups.
The second region of the hind-gut is usually known as the rectum.
and although it is sometimes lengthened it is typically little longer
than the portion of the primitive straight gut that it represents.
FIG. 9.--Intestinal Tract of Gorilla. S, cut end of
duodenum; R, cut end of rectum; C, vermiform appendix of
caecum; X, X2, X3, cut ends of factors of the portal vein.
Adaptations of the Intestinal Tract to Function.--The chief
business of the gut is to provide a vascular surface to which
the prepared food is applied so that the nutritive material
may be absorbed into the system. Overlying and sometimes
obscuring the morphological patterns of the gut, are many
modifications correlated with the nature of the food and
producing homoplastic resemblances independent of genetic
affinity. Thus in birds and mammals alike there is a direct
association of herbivorous habit with great relative length of
gut. The explanation of this, no doubt, is simply that
the vegetable matter which such creatures devour is in a
form which requires not only prolonged digestive action,
but, from the intimate admixture of indigestible material,
a very large absorbing surface. In piscivorous birds and
mammals, the gut is very long, with a thick wall and a
relatively small calibre, whilst there is a general tendency
for the regions of the gut to be slightly or not at all
defined. Fish, as it is eaten by wild animals, contains a
large bulk of indigestible matter, and so requires an extended
absorbing surface; the thick wall and relatively small
calibre are protections against wounding by fish bones. In
frugivorous birds the gut is strikingly short, wide and simple,
whilst a similar change has not taken place in frugivorous
mammals. Carnivorous birds and mammals have a relatively short
gut. In birds, generally, the relation of the length and
calibre of the gut to the size of the whole creature is
striking. If two birds of similar habit and of the same
group be compared, it will be found that the gut of the larger
bird is relatively longer rather than relatively wider.
The same general rule applies to Meckel's tract in mammals,
whereas in the case of the hind-gut increase of capacity is
given by increase of calibre rather than by increased length.
The Colic Caeca.--These organs lie at the junction of
the hind-gut with Meckel's tract and are homologous in
birds and mammals although it happens that their apparent
position differs in the majority of cases in the two
groups. In most birds, the hind-gut is relatively very
short, and the caecal position, accordingly, is at a very
short distance from the posterior end of the body. whereas
in most mammals the hind-gut is very long and the position of
the caecum or caeca is relatively very much farther from the
anus. Next, in most birds, the caeca when present are
paired, whereas in most mammals there is only a single
caecum. On the other hand, in certain birds (herons) as a
normal occurrence, and in many birds as an individual variation,
only a single caecum occurs. In some mammals, e.g. many
armadillos, in Hyrax and the manatee, the caeca are normally
paired; in many other (e.g. some rodents and marsupials)
in addition to the normal caecum there is a reduced second
caecum, whilst in quite a number of forms the relation of
the caecum, ileum and colon at their junction is readily
intelligible on the assumption that the caeca were originally
paired. The origin and many of the peculiarities of the
ileo-caecal valve find their best explanation on this hypothesis.
The caeca are hollow outgrowths of the wall of the gut, the
blind ends being directed forwards. The caecal wall is in
most cases highly glandular and contains masses of lymphoid
tissue. In birds and in mammals this tissue may be so
greatly increased as to transform the caecum into a solid
or nearly solid sac, the calibre of which is for the most
part smaller than that of the unmodified caecum. In some
birds, the whole area of the caecum may be modified in
this way; in mammals, it is generally the terminal portion,
which then becomes the vermiform appendix, familiar in
the anthropoid apes, in man and in some rodents. It is
difficult to see in this modification merely a degeneration;
not improbably it is the formation of a new glandular organ.
The caeca exhibit almost every gradation of development,
from relatively enormous size to complete absence, and there
is no definite, invariable connexion between the nature of
the food and the degree of their development. In the case
of birds, it may be said that on the whole the caeca are
generally large in herbivorous forms and generally small in
insectivorous, frugivorous, carnivorous and piscivorous
forms, but there are many exceptions. Thus, owls and falcons
have a diet that is closely similar, and yet owls have a
pair of very long caeca, whilst in the Falconidae these
organs are much reduced and apparently functionless. The
insectivorous and omnivorous rollers, motmots and bee-eaters
have a pair of large caeca, whilst in passerine birds of
similar habit the caeca are vestigial glandular nipples. It
is impossible to doubt that family history dominates in this
matter. Certain families tend to retain the caeca, others
to lose them, and direct adaptation to diet appears only to
accelerate or retard these inherited tendencies. So also
in mammals, no more than a general relation between diet
and caecal development can be shown to exist, although the
large size of the single caecum of mammals is more closely
associated with a herbivorous as opposed to a carnivorous,
frugivorous, piscivorous or omnivorous diet than is the case in
birds. There is no relationship between diet and the complete
or partial presence of both members of the primi-pair of caeca in
mammals, the occurrence of the pair being rather an ``accident''
of inheritance than in any direct relation to function.
LITERATURE.--T. W. Bridge, in The Cambridge Natural History
(vol. vii).; D. S. Jordan, A Guide to the Study of Fishes; R.
Owen, Anatomy of Vertebrates; M. Weber, Die Saugethiere;
W. H. Flower, The Organs of Digestien in Mammalia; R.
Wiedersheim, Lehrbuch der vergleichenden Anatomie der
Wirbelthiere; A. Oppel, Lehrbuch der vergleichenden
mikroskopischen Anatomie der Wirbelthiere; Chalmers Mitchell,
``The Intestinal Tract of Birds,'' Transactions of the
Linn. Soc. of London (vol. viii., 1901); and ``On the
Intestinal Tract of Mammals,'' Transactions of the Zool.
Soc. of London (vol. xvii., 1905). (In the two latter
memoirs a fuller list of literature is given.) (P. C. M.)
ALIMONY (from Lat. afere, to nourish), in law the
allowance for maintenance to which a wife is entitled out of
her husband's estate for her support on a decree for judicial
separation or for the dissolution of the marriage. Though,
as a rule, payable to a wife, it may, if the circumstances
of the case warrant it, be payable by the wife to the
husband. Alimony is of two kinds, (a) temporary (pendente
lite), and (b) permanent. Temporary alimony, or alimony
pending suit, is the provision made by the husband for the
wife in causes between them to enable her to live during the
progress of the suit, and is allowed whether the suit is by
or against the husband and whatever the nature of the suit may
be. The usual English practice is to allot as temporary
alimony about one-fifth of the husband's net income; where
it appears that the husband has no means or is in insolvent
circumstances, the court will refuse to allot temporary
alimony. So where the wife is supporting herself by her own
earnings, this fact will be taken into consideration. And
where the wife and husband have lived apart for many years
before the institution of the suit, and she has supported
herself during the separation, no alimony will be allotted. Nor
will the wife be entitled to alimony where she has sufficient
means of support independent of her husband. Permanent
alimony is that which is allotted to the wife after final
decree. By the Matrimonial Causes Act 1907, the court may,
if it think fit, on any decree for dissolution or nullity of
marriage, order that the husband shall, to the satisfaction
of the court, secure to the wife such a gross sum of money or
such annual sum of money for any term not exceeding her life,
as having regard to her fortune (if any), to the ability of
her husband, and to the conduct of the parties, it may deem
reasonable. The court may suspend the pronouncing of its
decree until a proper deed or instrument has been executed by
all necessary parties. The court may also make an order on the
husband for payment to the wife during their joint lives of a
reasonable monthly or weekly sum for her maintenance; the court
may also at any time discharge, modify, suspend or increase
the order according to the altered means of the husband; the
court has also power to make provision for children. Alimony
is paid direct to the wife or to a trustee or trustees on her
behalf, but the court may impose any restrictions which seem
expedient. We may also describe as a kind of alimony the
allowance of a reasonable weekly sum not exceeding L. 2 which
in England, under the Summary Jurisdiction (Married Women)
Act 1895, may be given to a married woman on applying to
a court of summary jurisdiction if she has been forced by
cruelty to leave her husband or has been deserted by him.
United States.--Alimony is granted by the courts of the
several states on much the same principle as in England, though
in many states the courts of equity as such may grant alimony
without divorce or separation proceedings independently of
any statute, on the ground that it is just that the husband
should support his wife when she lives apart from him for his
fault, and since the courts of common law provide no remedy
the courts of equity will. This is so in Alabama (Brady v.
Brady, 1905, 39 So. Rep. 237), Kentucky, North Carolina, Iowa,
California, Ohio, Virginia, South Dakota and the District of
Columbia. In other states alimony without such proceedings
is allowed by statute, and such alimony is now very general
throughout the United States. The usual grounds for the
allowance of it are desertion and such conduct as would amount
to legal cruelty. After divorce a vinculo, alimony or
separate maintenance is sometimes granted on good reason.
The marriage must be proven as a fact, but a ``common law''
marriage, i.e. one established by cohabitation and repute, is
sufficient. In several states alimony or maintenance is by
statute allowed to the husband in certain cases out of the wife's
property. This is so in Massachusetts, Virginia, Rhode Island and
Iowa. In Oregon he is entitled to one-third of his wife's
real estate in addition to maintenance on divorce for her
fault. The amount of alimony depends upon the circumstances of
each case as in England. Permanent alimony is generally more
than when pendenite lite, and usually one-third the husband's
income. It may generally be changed from time to time as the
circumstances of the parties change. Judgment for alimony is
considered a judgment in personam and not in rem, and can
only be enforced outside the state where rendered in case the
husband has been personally served with process within that
state. The remarriage of the man is not sufficient ground for
reducing the alimony (Smith v. Smith, 1905, 102 N.W. Rep.
631), but on remarriage of a woman to one able to support
her, her former husband being in poor circumstances, it will
be reduced (Kiralfy v. Kiralfy, 1901, 36 Wisc. N.S. 407).
ALIN, OSCAR JOSEF (1846--1900), Swedish historian and
politician, was born at Falun on the 22nd of December 1846.
In 1872 he became docent, and in 1882 professor of political
economy at Upsala, of which university he was afterwards
rector. In September 1888 he was elected a member of the
first chamber of the Riksdag, where he attached himself to
the conservative protectionist party, over which, from the
first, he exercised great authority. But it is as a historian
that Alin is most remarkable. Among his numerous works
the following are especially worthy of note: Bidrag till
svenska radets historia under. medeltiden (Upsala, 1872);
Sveriges Historia, 1511-1611 (Stockholm, 1878); Bidrag
till svenska statsrickets historia (Stockholm, 1884-1887);
Den svensk-norsk Unionen (Stockholm, 1889-1891), the best
book on the Norwego-Swedish Union question from the Swedish
point of view; Fjerde Artiklen af Fredstraktaten i Kiel
(Stockholm, 1899); Carl Johan och Sveriges yttre politik,
1810-1815 (Stockholm, 1899); Carl XIV. och Rikets Stander,
1840-1841 (Stockholm, 1893). He also edited Sveniska
Riksdagsakter, 1521-1554 (Stockholm, 1887), in conjunction
with E. Hildebrand, and Sveriges Grundlagar (Stockholm,
1892). He died at Upsala on the 31st of December 1900.
Obituary notice in Sv. Hist. Tidssk. (1901). (R. N. B.)
ALIPUR, a suburb of Calcutta, containing Belvedere
House, the official residence of the lieutenant-governor of
Bengal, and a number of handsome mansions. It lies within
the limits of the south suburban municipality, and is a
cantonment of native troops. On the Calcutta maidan,
opposite Alipur Bridge, stood two trees under which
duels were fought. It was here that the meeting in 1780
between Warren Hastings and Sir Philip Francis took place.
ALIQUOT (a Lat. word meaning ``some,'' ``so many''),
a term generally occurring in the phrase ``aliquot
part,'' and meaning that one quantity is exactly
divisible into another; thus 3 is an aliquot part of 6.
ALIRAJPUR, a native state of India, under the Bhopawar agency
in Central India. It lies in Malwa, near the frontier of
Bombay. It has an area of 836 sq. m.; and a population (1901) of
50,185. The country is hilly, and many of the inhabitants are
aboriginal Bhils. It has from time to time been under British
administration. The chief, whose title is Rana, is a Rahtor
Rajput. He has an estimated revenue of L. 8700, and pays
a tribute of L. 700. The Victoria bridge at Alirajpur
was built to commemorate the Diamond Jubilee of 1897.
ALISMACEAE (from the Gr. alisma, a water-plant mentioned by
Dioscorides), in botany, a natural order of monocotyledons belonging
to the series Helobieae, and represented in Britain by the water
plantain, Alisma Plantago, the arrow-head, Sagittaria,
the star-fruit, Damasonium, and flowering rush, Butomus
(from the Gr. bous, ox, temnein, to cut, in allusion to
leaves cutting the tongues of oxen feeding on them). They are
marsh- or water-plants with generally a stout stem (rhizome)
creeping in the mud, radical leaves and a large, much branched
inflorescence. The leaves show a great variety in shape, often
FIG. 1.--Flowering Rush (Butomus umbellatus.) 1, Flower in
vertical section; 2, horizontal plan of arrangement of flower.
the same plant, according to their position in, on or above the
water. The submerged leaves are long and grass- like, the
floating leaves oblong or rounded, while the aerial leaves
are borne on long, thin stalks above the water, and are often
heart- or arrow-shaped at the base. The flower-bearing stem
is tall; the flowers are borne in whorls on the axis as in
arrow-head, on whorled branchlets as in water plantain or in
an umbel as in Butomus (fig. 1). The flowers are regular
and rather showy, generally with three greenish sepals,
followed in regular succession by three white or purplish
petals, six to indefinite stamens and six to indefinite free
carpels. The floral arrangement thus recalls that of a
buttercup, a resemblance which extends to the fruit, which is
a head of achenes or follicles. The flowers contain honey,
and attract flies, short-lipped bees or other small insects
by the agency of which pollination is effected. The fruit
of Butomus is of interest in having the seeds borne over
the inner face of the wall of the leathery pod (follicle).
Damasonium derives its popular name, star-fruit, from the
fruits spreading when ripe in the form of a star. It is a western
FIG. 2.--Water Plantain (Alisma Plantago.) Plant
about 3 ft. high. 1, Flower; 2, same in vertical
section; 3, horizontal plan of flower; 4, mature fruit.
Mediterranean plant which spreads to the south of England,
where it is sometimes found in gravelly ditches and pools.
The order contains about fifty species in fourteen genera, and
is widely distributed in temperate and warm zones. Alisma
Plantago (fig. 2), a common plant in Britain (except in the
north) in ditches and edges of streams, is widely distributed
in the north temperate zone, and is found in the Himalayas,
on the mountains of tropical Africa and in Australia.
ALISON, ARCHIBALD (1757-1839), Scottish author, son of
Patrick Alison, provost of Edinburgh, was born on the 13th of
November 1757 at Edinburgh. After studying at the university
of Glasgow and at Balliol College, Oxford, he took orders in
the Church of England, and was appointed in 1778 to the curacy
of Brancepeth, near Durham. In 1784 he married Dorothea,
youngest daughter of Professor Gregory of Edinburgh. The next
twenty years of his life were spent in Shropshire, where he
held in succession the livings of High Ercall, Roddington and
Kenley. In 1800 he removed to Edinburgh, having been appointed
senior incumbent of St Paul's Chapel in the Cowgate. For
thirty-four years he filled this position with much ability,
his preaching attracting so many hearers that a new and
larger church was built for him. His last years were spent at
Colinton, near Edinburgh, where he died on the 17th of May
1839. Alison published, besides a Life of Lord Woodhouselee,
a volume of sermons, which passed through several editions,
and a work entitled Essays on the Nature and Principles of
Taste (1790), based on the principle of association (see under
AESTHETICS, p. 288). His elder son, Dr Wilham Pulteney Alison
(1790-1859), was a distinguished Edinburgh medical professor.
SIR ARCHIBALD ALISON, Bart. (1792-1867), the historian,
was the younger son, and was born at Kenley, Shropshire, on
the 29th of December 1792. He studied at the university of
Edinburgh, distinguishing himself especially in Greek and
mathematics. In 1814 he passed at the Scottish bar, but he
did not at once practise. The close of the war had opened
up the continent, and Alison set out in the autumn of 1814
for a lengthened tour in France. It was during this period
that the idea of writing his history first occurred to him.
A more immediate result of the tour was his first literary
work of any importance, Travels in France during the Years
1814-1815, written in collaboration with his brother and A. F.
Tytler, which appeared in the latter year. On his return to
Edinburgh he practised at the bar for some years with very fair
success. In 1822 he became one of the four advocates-depute
for Scotland. As a result of the experience gained in this
office, which he held until 1830, he wrote his Principles of
the Criminal Law of Scotland (1832) and Practice of the
Criminal Law of Scotland (1833), which in 1834 led to his
appointment by Sir Robert Peel to the office of sheriff of
Lanarkshire, which ranks next to a judgeship in the supreme
court. The office, though by no means a sinecure, gave him
time not only to make frequent contributions to periodical
literature, but also to write the long-projected History
of Europe, for which he had been collecting materials for
more than fifteen years. The history of the period from the
beginning of the French Revolution till the restoration of
the Bourbons in 1815 was completed in ten volumes in 1842,
and met with a success almost unexampled in works of its
class. Within a few years it ran through ten editions, and
was translated into many of the languages of Europe, as well
as into Arabic and Hindustani. At the time of the author's
death it was stated that 108,000 volumes of the library
edition and 439,000 volumes of the popular edition had been
sold. A popularity so widespread must have had some basis of
merit, and the good qualities of Alison's work lie upon the
surface. It brought together, though not always in a
well-arranged form, an immense amount of information that
had before been practically inaccessible to the general
public. It at least made an attempt to show the organic
connexion in the policy and progress of the different nations
of Europe; and its descriptions of what may be called external
history--of battles, sieges and state pageants--are spirited and
interesting. On the other hand the faults of the work are
numerous and glaring. The general style is prolix, involved
and vicious; mistakes of fact and false deductions are to be
found in almost every page; and the constant repetition of
trite moral reflections and egotistical references seriously
detracts from its dignity. A more grave defect resulted from
the author's strong political partisanship, which entirely
unfitted him for dealing with the problems of history in
a philosophical spirit. His unbending Toryism made it
impossible for him to give any satisfactory explanation of
so complex a fact as the French Revolution, or accurately to
estimate the forces that were to shape the Europe of the 19th
century. A continuation of the History, embracing the period
from 1815 to 1852, which was completed in four volumes in
1856, did not meet with the same success as the earlier
work. The period being so near as to be almost contemporary,
there was a stronger temptation, which he seems to have found
it impossible to resist, to yield to political prejudice, while
the materials necessary for a clear knowledge of the influences
shaping European affairs were not as yet accessible. The book
is now almost wholly out of date. In 1845 Alison was chosen
rector of Marischal College, Aberdeen, and in 1851 of Glasgow
University. In 1852 a baronetcy was conferred upon him, and
in the following year he was made a D.C.L. of Oxford. His
literary activity continued till within a short time of his
death, the chief works he published in addition to his History
being the Principles of Population (1840), in answer to
Malthus; a Life of Marlborough (1847, 2nd edition greatly
enlarged, 1852); and the Lives of Lord Castlereagh and Sir C.
Stewart (1861.) This latter, based on MS. material preserved at
Wynyard Park, is still of value, not only as the only available
biography, but more especially because Alison's Tory sympathies
enabled him to give a juster appreciation of the character
and work of Castlereagh than the Liberal writers by whom for
many years he was misjudged and condemned (see LONDONDERRY,
Robert Stewart, 2nd marquess of). Three volumes of Alison's
political, historical and miscellaneous essays were reprinted in
1850. He died at Possil House, Glaagow, on the 23rd of May
1867. His autobiography, Some Account of my Li/e and
Writings, edited by his daughter-in-law, Lady Alison, was
published in 1883 at Edinburgh. Sir Archibald Alison married
in 1825 Elizabeth Glencairn, daughter of Colonel Tytler, by
whom he had three children, Archibald, Frederick and Eliza
Frances Catherine. Both sons became distinguished officers.
SIR ARCHIBALD ALISON, Bart. (1826-1907), the elder of the
sons, entered the 72nd Highlanders in 1846. He served
at the siege of Sevastopol; and during the Indian Mutiny
he was military secretary to Sir Colin Campbell and was
severely wounded at the relief of Lucknow, losing an
arm. From 1862 to 1873 he was assistant adjutant-general at
headquarters, Portsmouth and Aldershot. He was second in
command of the Ashanti expedition 1873-1874, and was made a
K.C.B. For three years Alison was deputy adjutant-general in
Ireland, and then, for a few months, commandant of the Staff
College. He was promoted to be major-general in 1877,
and was head of the intelligence branch of the war office
(1878-1882). He commanded the troops at Alexandria in 1882
until the arrival of Sir Garnet Wolseley, led the Highland
brigade at the battle of Tel-el-Kebir, and remained in command
of the army of occupation until 1883. He commanded at Aldershot
1883-1888, was for some months adjutant-general to the forces
during Lord Wolseley's absence in Egypt, was made G.C.B. in
1887, was promoted general, and became a military member of the
Council of India in 1889. He retired in 1893 and died in 1907.
ALIWAL, a village of British India, in the Ludhiana district
of the Punjab, situated on the left bank of the Sutlej, and
famous as the scene of one of the great battles of the 1st Sikh
War. Late in January 1846 it was held by Ranjur Singh, who had
crossed the river in force and threatened Ludhiana. On the 28th
Sir Harry Smith, with a view to clearing the left or British
bank, attacked him, and after a desperate struggle thrice pierced
the Sikh troops with his cavalry, and pushed them into the
river, where large numbers perished, leaving 67 guns to the
victors. The consequence of the victory was the submission
of the whole territory east of the Sutlej to the British.
ALIWAL NORTH, a town of South Africa, on the south bank
of the Orange River, 4300 ft. above the sea, and 282 m. by
rail N.W. by N. of the port of East London. Pop. (1904)
5566, of whom 1758 were whites. The town, a trading and
agricultural centre for the N.E. part of the Cape and the
neighbouring regions of Basutoland and Orange Free State,
presents a pleasing appearance. It contains many fine stone
buildings. The streets are lined with trees, and water from
the neighbouring sulphur springs flows along them in open
channels. The river, here the boundary between the Cape province
and Orange Free State, is crossed by a stone bridge 860 ft.
long. The sulphur springs, 1 m. from the town, which yield
over 500,000 gallons daily, are resorted to for the cure
of rheumatism and skin diseases. By reason of its dry and
bracing climate, Aliwal North is also a favourite residence
of sufferers from chest complaints. In the neighbourhood are
stone quarries. Aliwal North is the capital of a division
of the province of the same name, with an area of 1330 sq.
m. and a pop. (1904) of 14,857, of whom 40% are whites.
Aliwal North was so called to distinguish it from Aliwal
South, now Mossel Bay, the seaport of the pastoral Grasveld
district, on the west side of Mossel Bay. Both places were
named in honour of Sir Harry Smith, governor of Cape Colony
1847-1852, Aliwal (see above) being the village in the Punjab
where in 1846 he gained a great Victory over the Sikhs.
Crossing the Orange River at this spot in September 1848, Sir
Harry noted that it was ``a beautiful site for a town,'' and
in the May following the town was founded. In the early months
of the Boer War of 1899-1902 Aliwal North was held by the
Boers. It was reoccupied by the British in March 1900.
ALIZARIN, or 1.2 DIOXYANTHRAQUINONE,
/CO\
C6H4 C6H2(OH)2[1.2],
\CO/
a vegetable dyestuff formerly prepared from madder root (Rubia
tinctorum) which contains a glucoside ruberythric acid
(C26H28O14). This glucoside is readily hydrolysed by
acids or ferments, breaking up into alizarin and glucose:
C26H28O14 + 2H2O = 2C6H12O6 + C14H8O4
Ruberythric acid = Glucose + Alizarin.
Alizarin was known to the ancients, and until 1868 was obtained
entirely from madder root. The first step in the synthetical
production of alizarin was the discovery in 1868 of C. Graebe
and C. Liebermann that on heating with zinc dust, alizarin
was converted into anthracene. In order to synthesize
alizarin, they converted anthracene into anthraquinone and
then brominated the quinone. The dibrominated product so
obtained was then fused with caustic potash, the melt dissolved
in water, and on the addition of hydrochloric acid to the
solution, alizarin was precipitated. This process, owing
to its expensive nature, was not in use very long, being
superseded by another, discovered simultaneously by the
above-named chemists and by Sir W. H. Perkin; the method being
to sulphonate anthraquinone, and then to convert the sulphonic
acid into its sodium salt and fuse this with caustic soda.
In practice, the crude anthracene is purified by solution
in the higher pyridine bases, after which treatment it is
frequently sublimed. It is then oxidized to anthraquinone
by means of sodium dichromate and sulphuric acid in leaden
vats, steam heated so that the mixture can be brought to the
boil. When oxidation is complete the crude anthraquinone
is separated in filter presses and heated with an excess
of commercial oil of vitriol to 120 deg. C., the various
impurities present in the crude material being sulphonated
and rendered soluble in water, whilst the anthraquinone is
unaffected; it is then washed, to remove impurities, and
dried. The anthraquinone so obtained is then heated for
some hours at about 150-160 deg. C. with fuming sulphuric acid
(containing about 40-50% SO3), and by this treatment is
converted into anthraquinone-b-monosulphonic acid. The
solution is poured into water and sodium carbonate is added
to neutralize the excess of acid, when the sodium salt of
the monosulphonic acid (known as silver salt) separates out
This is filtered, washed, and then fused with caustic soda,
when the sulpho-group is replaced by a hydroxyl group, and a
second hydroxyl group is simultaneously formed; in order to
render the formation of this second group easier, a little
potassium chlorate or sodium nitrate is added to the reaction
mixture. The melt is dissolved in water and the dyestuff is
liberated from the sodium salt by hydrochloric or sulphuric
acid, or is converted into the calcium salt by digestion with hot
milk of lime, then filtered and the calcium salt decomposed by
acid. The precipitated alizarin is then well washed and made
into a paste with water, in which form it is put on to the market.
K. Lagodzinski (Berichte, 1895, 28, p. 1427) has synthesized
alizarin by condensing hemipinic acid [(CH3O)2C6H2(COOH)2]
with benzene in the presence of aluminium chloride. The
product on acidification gives a compound C15H12O5.H2O
which is probably an oxy-methoxy-benzoyl benzoic acid. This
is dissolved in cold concentrated sulphuric acid, in which
it forms a yellowish red solution, but on heating to 100 deg.
C. the colour changes to red and violet, and on pouring out
upon ice, the monomethyl ether of alizarin is precipitated.
This compound is hydrolysed by hydriodic acid and alizarin is
obtained. It can also be synthesized by heating catechol
with phthalic anhydride and sulphuric acid at 150 deg. C.
/CO\ /CO\
C6H4 O + C6H4(OH)2[1.2] = H2O + C6H4 C6H2(OH)2.
\CO/ \CO/
Pure alizarin crystallizes in red prisms melting at 200 deg.
C. It is insoluble in water, and not very soluble in
alcohol. It dissolves readily in caustic alkalis on account
of its phenolic character, and it forms a yellow-coloured
di-acetate. Its value as a dyestuff depends on its power of
forming insoluble compounds (lakes) with metallic oxides. It
has no affinity for vegetable fibres, and consequently cotton
goods must be mordanted before dyeing with it (see DYEING.)
Numerous derivatives of alizarin are known. On solution in
glacial acetic acid and addition of nitric acid, b-nitroalizarin
OH
|
(alizarin orange) / \ /CO\ / \OH
| | | |
\ / \CO/ \ /NO2
is produced, and this on heating with sulphuric
acid and glycerin is converted into alizarin blue.
The trioxyanthraquinones--purpurin, anthrapurpurin, anthragallol
and flavopurpurin---are also very valuable dyestuffs. These
compounds may be represented by the following formulae:
OH OH OH OH
| | | |
/ \ /CO\ / \OH HO/ \ /CO\ / \OH / \ /CO\ / \OH / \ /CO\ / \OH
| | | | | | | | | | | | | | | |
\ / \CO/ \ / \ / \CO/ \ / HO\ / \CO/ \ / \ / \CO/ \ /OH
|
OH
Purpurin. Anthrapurpurin. Flavopurpurin. Anthragallol.
Purpurin (1.2.4 trioxyanthraquinone) is found with
alizarin in madder root; it is now prepared synthetically
by oxidizing alizarin with manganese dioxide and sulphuric
acid. After the separation of the silver salt (see above)
obtained on sulphonating anthraquinone, the remaining acid
liquid gives on treatment with calcium carbonate the calcium
salt of anthraquinone 2.6 disulphonic acid (anthraquinone-
a-disulphonic acid). This is converted into the sodium salt
by means of sodium carbonate, and on alkali fusion yields
fiavopurpurin. In a similar manner anthrapurpurin is
prepared by alkali fusion of anthraquinone 2.8 disulphonic
acid. Anthragallol is synthetically prepared by the
condensation of benzoic and gallic acids with sulphuric acid
OH OH
| |
/ \COOH / \OH / \ /CO\ / \OH
| | + | | = 2 H2O + | | | |
\ / HOOC\ /OH \ / \CO/ \ /OH
or from pyrogallol and phthalic anhydride in
the presence of sulphuric acid or zinc chloride.
A. Baeyer in 1890, by heating alizarin with fuming sulphuric
acid for 24-48 hours at 35-40 deg. C., obtained a product, which
after treatment with caustic soda gave a sulphuric acid ester
of quinalizarin, and this after acidification and boiling was
converted into quinalizarin (Alizarin Bordeaux) or 1.2.6.9
tetra-oxyanthraquinone. Penta-oxyanthraquinones have been
obtained from purpurin and anthrapurpurin, while a hexa-
oxyanthraquinone has been obtained from 1.5 dinitro- anthraquinone.
ALKAHEST (a pseudo-Arabic word believed to have been invented by
Paracelsus), a liquid, much sought after by the alchemists, having
the power of dissolving gold and every other substance, which
it was supposed would possess invaluable medicinal qualities.
ALKALI, an Arabic term originally applied to the ashes of
plants, from which by lixiviation carbonate of soda was obtained
in the case of sea-plants and carbonate of potash in that of
land-plants. The method of making these ``mild'' alkalis into
``caustic'' alkalis by treatment with lime was practised in
the time of Pliny in connexion with the manufacture of soap,
and it was also known that the ashes of shore-plants yielded
a hard soap and those of land-plants a soft one. But the
two substances were generally confounded as ``fixed alkali''
(carbonate of ammonia being ``volatile alkali''), till Duhamel
du Monceau in 1736 established the fact that common salt and
the ashes of sea-plants contain the same base as is found in
natural deposits of soda salts (``mineral alkali''), and that
this body is different from the ``vegetable alkali'' obtained
by incinerating land- plants or wood (pot-ashes). Later,
Martin Heinrich Klaproth, finding vegetable alkali in certain
minerals, such as leucite, proposed to distinguish it as
potash, and at the same time assigned to the mineral alkali the
name natron, which survives in the symbol, Na, now used for
sodium. The word alkali supplied the symbol for potassium,
K (kalium.) In modern chemistry alkali is a general term
used for compounds which have the property of neutralizing
acids, and is applied more particularly to the highly soluble
hydrates of sodium and potassium and of the three rarer ``alkali
metals,'' caesium, rubidium and lithium, also to aqueous
ammonia. In a smaller degree these alkaline properties are
shared by the less soluble hydrates of the ``metals of the
alkaline earths,'' calcium, barium and strontium, and by thallium
hydrate. An alkali is distinguished from an acid or neutral
substance by its action on litmus, turmeric and other indicators.
ALKALI MANUFACTURE. The word ``alkali'' denotes both soda and
potash, but by ``alkali manufacture'' we understand merely
the manufacture of sodium sulphate, carbonate and hydrate.
The corresponding potash compounds are not manufactured in
the United Kingdom, but exclusively in Germany (from potassium
chloride and from the mother-liquor of the strontia process
in the manufacture of beetroot sugar) and in France (from
vinasse) . The term alkali is employed in a technical sense
for the carbonate and hydrate (of sodium), but since in the
Leblanc process the manufacture of sodium sulphate necessarily
precedes that of the carbonate, we include this as well as
the manufacture of hydrochloric acid which is inseparable from
it. We also treat of the utilization of hydrochloric acid
for the manufacture of chlorine and its derivatives, which
are usually comprised within the meaning of the term ``alkali
manufacture.'' A great many processes have been proposed
for the manufacture of alkali from various materials, but
none of these has become of any practical importance except
those which start from sodium chloride (common salt); and
among the latter again only three classes of processes
are actually employed for manufacturing purposes, viz. the
Leblanc, the ammonia-soda, and the electrolytic processes.
I. THE LEBLANC PROCESS
The Leblanc process, which was invented by Nicolas
Leblanc (q.v.) about 1790, begins with the decomposition
of sodium chloride by sulphuric acid, by which sodium
sulphate and hydrochloric acid are produced. The sodium
sulphate is afterwards fluxed with calcium carbonate and
coal, and a mixture is thus obtained from which sodium
carbonate can be extracted by exhausting it with water.
Leblanc himself for a time carried out his process on a
manufacturing scale, but he was ruined in the political troubles
of the time and died by his own hand in 1806. His invention
was, however, at once utilized by others in France; and in
Great Britain, after a few previous attempts on a small scale,
it was definitely introduced by James Muspratt (q.v.) in
1823. From that time onward the Leblanc process spread more and
more, and for a considerable period nearly all the alkali of
commerce was made by it. The rise of the ammonia-soda process
(since 1870) gradually told upon the Leblanc process, which
in consequence has been greatly restricted in Great Britain
and Germany, and has become practically extinct in all other
countries, except as far as its first part, the manufacture
of sodium sulphate and hydrochloric acid, is concerned.
The production of alkali in Great Britain, soon after the
introduction of the Leblanc process, became the most extensive
in the world, and outstripped that of all other countries put
together. With the rise of the ammonia-soda process, for
which the economic conditions are nearly as favourable in other
countries, the predominance of Great Britain in that domain
has become less, but even now that country produces more alkali
than any other single country. Most of the British alkali
works are situated in South Lancashire and the adjoining part of
Cheshire, near the mouth of the Tyne and in the West of Scotland.
Various industries are carried on in Leblanc alkali works, as follows:--
1. Manufacture of sodium sulphate.
2. Manufacture of hydrochloric acid.
3. Preparation of chlorine.
4. Employment of chlorine for the manufacture
of bleaching- powder and of chlorates.
5. Manufacture of ordinary alkali from sulphate of soda.
6. Manufacture of caustic soda.
7. Manufacture of soda crystals.
8. Recovery of sulphur from alkali waste.
1. Manufacture of Sodium Sulphate.--This is commercially
known as salt-cake, and is made by decomposing common
salt with sulphuric acid of about 80%, the reaction being
2NaCl + H2SO4 = Na2SO4 + 2HCl. This reaction proceeds
in two stages. At first principally acid sodium sulphate,
NaHSO4, is formed together with some normal sulphate;
later, when the temperature has risen, the NaHSO4 acts
with more NaCl so that nearly all of it is converted into
Na2SO4. The gaseous hydrochloric acid evolved during
all this time must be absorbed in water, unless it is
directly converted into chlorine (see below, 2 and 3).
The process is carried out either in hand-wrought furnaces, or
mechanical furnaces, both called ``decomposing'' or ``salt-cake
furnaces.'' In the former case, the first reaction is produced
in cast- iron pans or ``pots,'' very heavy castings of circular
section, fired from below, either directly or by the waste
heat from the muffle- furnace. The reaction is completed
in a ``roasting- furnace.'' The latter was formerly often
constructed as a revereratory funace, which is easy to build
and to work, but the hydrochloric acid given off here, being
mixed with the products of the combustion of fuel, cannot
be condensed to strong acid and is partly, if not entirely,
wasted. It is, therefore, decidedly preferable to employ
``muffle-furnaces'' in which the heating is performed from
without, the fire-gases passing first over the arch and
then under the bottom of the muffle. This requires more
time and fuel than the work in ``open'' furnaces, but in
the muffles the gaseous hydrochloric acid is separated
from the fire-gases, just like that evolved in the pot, and
can therefore be condensed into strong hydrochloric acid,
like the pot-acid. This roaster-acid is, however, of less
value than the pot-acid, as it contains more impurities.
It is not easy to keep the muffles permanently tight, and as soon
as any leakages occur, either hydrochloric acid must escape into
the fire-flue, or some fire-gases must enter into the muffle.
The former is decidedly more objectionable than the latter, as
it means that uncondensed hydrochloric acid is sent into the
air. This drawback has been overcome by the construction of
``plus-pressure'' furnaces (figs. 1 and 2), where the fire-grate
is placed 11 ft. below the top of the muffle. In consequence
the fire-gases, when arriving there by the chimney shaft
(a), have already a good upward draught, and when circulatung
round the muffle are at a lower pressure than the gases within
the muffle, so that in case of any cracks being formed, no
hydrochloric acid escapes into the fire-flues, but vice versa.
Since the work with ordinary hand-wrought salt-cake furnaces
is disagreeable and costly, many attempts have been made
to construct mechanical salt-cake furnaces. Of these J.
Mactear's furnaces (fig. 3) have met with the greatest
success. They consist of a horizontal pan, 17 ft. wide,
which is made up of a central pan (e), and a series
of concentric compartments (C1), (C2), (C3), and
which is supported on a frame (d d), revolving round a
perpendicular axis on the wheels (n n). It is with an
arch and heated on the top from one side (l), either by an
ordinary coal-grate or by a gas-producer. A set of stirring
blades carried in the frame (b b), and driven by gearing,
FIGS. 1. and 2.--Salt-cake Furnace. (Sectional Elevation and Plan.) Scale
Figs. 1-9 from Lunge's Handbuch der Soda-Industrie,
by permission of Friedr. Vieweg u. Sohn.
passes through a gap in the arch in such a manner that the gases
cannot escape outwards. The salt is conveyed to the furnace
by a chain of buckets running on the pulley (g), and passing
into the hopper (h), and through the pipe (i) is mixed
with the proper amount of acid supplied by the pipe ( f.)
The mixture is fed in continuously to the central pan (e.)
whence it overflows into the compartments (c1), (c2), (c3)
successively until it reaches the circumference, where it is
discharged continously by o and p into the collecting-box
(q), being now converted into salt-cake. This furnace acts
very well, and has been widely introduced both in Great Britain
and in other countries, but it has one great drawback, apart
from its high cost, viz. that all the hydrochloric acid gas
gets mixed with fire-gases, and consequently is condensed
in a weaker and less pure form than from ordinary pots and
muffles. This has led some factories which had introduced
such furnaces to revert to hand-wrought muffle-furnaces.
Much was expected at one time from the.``direct salt-cake
process'' of Hargreaves and Robinson, in which common salt
is subjected in a series of large cast-iron cylinders to
the action of pyrites-burner gases and steam at a low red
heat. The reaction going on here is: 2NaCl + SO2 + O
+ H2O = Na2SO4 + 2HCl. This means that the previous
manufacture of sulphuric acid in the vitriol-chambers is
done away with, but this apparently great simplification is
balanced by the great cost of the Hargreaves plant, and by
the fact that the whole of the hydrochloric acid is mixed
with nine or ten times its volume of inert gases. Owing to
this, it is practically impossible to condense the gaseous
hydrochloric acid into the commercial acid, although this
acid may be obtained sufficiently strong to be worked up in
the Weldon chlorine process (see below, 3). Therefore the
Hargreaves process has been introduced only in a few places.
Although the consumption of salt-cake for the manufacture of
alkali is now much less than formerly, since the Leblanc alkali
process has been greatly restricted, yet it is largely made and
will continue to be made for the use of glassmakers, who use it
for the ordinary description of glass in the place of soda-ash.
Nor must it be overlooked that salt-cake must be made as long
FIG. 3.--Mechanical Salt-cake Furnace. (Sectional Elevation.) Scale
as there is a sale for hydrochloric acid, or a
consumption of the latter for the manufacture of chlorine.
2. Manufacture of Hydrochloric Acid (commercially also
known as ``muriatic acid''). This unavoidable gaseous
bye-product of the manufacture of salt-cake was, during
the first part of the 19th century, simply sent into the
air. When its deleterious effects upon vegetation, building
materials, &c., became better known, and when at the same
time an outlet had been found for moderate quantities of
hydrochloric acid, most factories made more or less successful
attempts to ``condense'' the gas by absorption in water. But
this was hardly anywhere done to the fullest possible extent,
and in those districts where a number of alkali works were
located at no great distance from one another, their aggregate
escapes of hydrochloric and other acids created an intolerable
nuisance. This was most notably the case in South Lancashire,
and it led to the passing of Lord Derby's ``Alkali Act,'' in
1863, supplemented by further legislation in 1874, 1881 and
later. There is hardly another example in the annals of
legislative efforts equal to this, in respect of the real
benefit conferred by it both on the general public and
on the manufacturers themselves. This is principally the
consequence of the exemplary way in which the duties of
inspector under these acts were carried out by Dr R. Angus
Smith (1817-1884) and his successors, who directed their
efforts not merely to their primary duty of preventing
nuisance, but quite as much to showing manufacturers how to
make the most of the acid formerly wasted in one shape or
another. Not merely Great Britain but all mankind has been
immensely benefited by the labours of the British alkali
inspectors, which were, of course, supplemented by the work of
technical men in all the countries concerned. The scientific
and technical principles of the condensation of hydrochloric
acid are now thoroughly well understood, and it is possible
to recover nearly the whole of it in the state of strong
commercial acid, containing from 32 to 36% of pure hydrochloric
acid, although probably the majority of the manufacturers are
still content to obtain part of the acid in a weaker state,
merely to satisfy the requirements of the law prescribing the
prevention of nuisance. The principles of the condensation,
that is of converting the gaseous hydrochloric acid given
off during the decomposition of common salt into a strong
solution of this gas in water, can be summarized in a few
words. The hydrochloric acid gas, which is always diluted
with air, sometimes to a very great extent, must be brought
into the most intimate contact possible with water, which
greedily absorbs it, forming ordinary hydrochloric acid,
and this process must be carried so far that scarcely any
hydrochloric acid remains in the escaping gases. The maximum
escape allowed by thc Alkali Acts, viz. 5 % of the total
hydrochloric acid, is far above that which is now practically
attained. For a proper utilization of the condensed acid it
is nearly always imperative that it should be as strong as
possible, and this forms a second important consideration
in the construction of the condensing apparatus. Since the
solubility of hydrochloric acid in water decreases with the
increase of the temperature, it is necessary to keep the
latter down--a task which is rendered somewhat difficult
both by the original heat retained by the gases on their
escape from the decomposing apparatus, and by the heat given
off through the reaction of hydrochloric acid upon water.
Very different methods have been employed to effect all the
above purposes. In Great Britain Gay-Lussac's coke-towers,
adapted by W. Gossage to the condensation of hydrochloric
acid, are still nearly everywhere in use, frequently combined
with a number of stone tanks through which the gas from
the furnaces travels before entering the towers, meeting
on its way the acid condensed in the tower. This process
is excellent for effecting a complete condensation of the
hydrochloric acid as prescribed by the Alkali Acts, and for
recovering the bulk of the acid in a tolerably strong state,
but less so for recovering nearly the whole of it in the
most concentrated state, although even this is occasionally
attained. On the continent of Europe, where the last-named
requirement has been for a long time more urgent than in Great
Britain, another system has been generally preferred, namely,
passing the gas through a long series of stoneware receivers,
and ultimately through a small tower packed with stoneware or
coke, making the acid flow in the opposite direction to the
gas. Great success has also been obtained by ``plate-towers''
made of stoneware, which allow both the coke-towers and
most of the stoneware receivers to be dispensed with.
3. Preparation of Chlorine.--In this place we speak only
of the preparation of chlorine from hydrochloric acid by
chemical processes; the electrolytic processes will be treated
hereafter. It is clear that free chlorine must be prepared
from hydrochloric acid by oxidizing the hydrogen. This can
be done most easily by ``active'' oxygen, such as is present
in the peroxides, in chromic or permanganic acid. Practically
the only agent employed in this way, and that already by C. W.
Scheele, the discoverer of chlorine, in 1774, is the peroxide
of manganese (manganese dioxide), found in considerable
quantities in nature as ``manganese ore'' (the purest of which
is called pyrolusite), and also artificially regenerated from
the waste liquors of a former operation. Even now, where
chlorine is required for immediate use in some other chemical
operations on a comparatively small scale, it is obtained by
the action of hydrochloric acid on native manganese dioxide,
according to the equation: Mno2 + 4HCl = MnCl2 + Cl2 +
2H2O. This action must be promoted by heating the mixture,
but even then nothing like all of the hydrochloric acid
employed is made to act as above, because the attack on the
manganese ore requires a certain minimum concentration of the
acid. Formerly, instead of free hydrochloric acid a mixture
of common salt and sulphuric acid was sometimes employed, but
this is never done on a manufacturing scale now. Owing to
the impossibility of employing any metal in contact with the
acid, the ``chlorine stills,'' where the above reaction is
carried out, must be made of acid-proof stones or ``chemical''
stoneware. This process is very costly, as much of the
acid and all of the manganese is wasted. Moreover it is
of a most disagreeable kind, as the waste ``still-liquor,''
containing very much free hydrochloric acid and even some free
chlorine, forms a most deleterious impurity when finding its
way into drains or water- courses, apart from the intolerable
nuisance caused by the escapes of chlorine from the stills
and otherwise, which cannot be at all times avoided.
Many endeavours were made to avoid the loss of the
manganese in this operation, but with only partial or no
success. The difficulty was only overcome by the Weldon
process, being the inventions of Walter Weldon from 1866
onwards, and his process up to this day furnishes the greater
proportion of chlorine manufactured in the world. It begins
with ``still-liquor,'' obtained in the old way from native
manganese ore and hydrochloric acid. This liquor is first
treated with carbonate of lime (ground chalk or limestone)
in a ``neutralizing-well,'' made of acid-proof material and
provided with wooden stirring-gear. Here the free hydrochloric
acid is converted into calcium chloride, and at the same time
any ferric chloride present is converted into insoluble ferric
hydroxide: 2FeCl3 + 3CaCO3 + 3 H2O = 2Fe(OH)3 + 3CaCl2 +
3CO2. The sulphuric acid present is mostly precipitated as
calcium sulphate. The mud thus formed is settled out, and
the clear liquor, which is now quite neutral and contains
both manganese and calcium chlorides, is mixed with cream of
lime and treated by a strong current of air, produced by a
blowing-engine. This is done in a tall iron cylinder, say
9 ft. wide and 30 ft. high, called the ``oxidizer.'' The
air-pipe goes right to the bottom of the cylinder and there
branches out into perforated side-pipes, so that the mass
is thoroughly stirred up all the time. The first action of
the lime is to convert the manganese chloride into manganous
hydrate (Mn(OH)2) and calcium chloride; then more lime
is added which greatly promotes and hastens the oxidizing
process. The object of the latter is to convert the
manganous hydroxide by the atmospheric oxygen into manganese
dioxide, but this would take place much too slowly if there
was not an excess of lime present ready to combine with the
manganese dioxide to form a calcium manganite. Only so much
lime is used that an acid manganite is formed corresponding
to one molecule of calcium oxide to two of manganous
oxide. This additional lime, which is called the ``basis,''
certainly takes up hydrochloric acid in the next stage of
the process, but that causes no more waste of acid than
the incomplete action on native manganese ore, mentioned
before. The product obtained, called ``Weldon mud,'' is of
such fine texture that it acts immediately with hydrochloric
acid when mixed with it in the ``Weldon stills'' (fig.
4), and that this acid can be almost entirely neutralized
thereby. The new still liquor formed in this manner is treated
as above, so that the manganese does its work over and over
again. There is only a slight mechanical loss, which
is reduced in the best managed works to about 2 parts of
manganese dioxide to 100 of bleaching- powder. There are
also other advantages of this process which explain its wide
extension, in spite of the fact that only from 30 to 35
parts of the hydrochloric acid employed is converted into
chlorine, the remainder ultimately leaving the factory in the
shape of a harmless but useless solution of calcium chloride.
Weldon's later attempts at superseding his classical process
by other inventions which utilize a larger proportion
of the chlorine, introduced as hydrochloric acid, have
not been successful in the long run, although some of
them were aided by the great technical skill of A. R.
Pechiney. But the Deacon process, the invention of Henry
Deacon (who was greatly aided by his chemist Dr Ferdinand
Hurter), carried out since 1868, has attained to better,
although nothing like complete, success in that direction.
The Deacon process, like the Weldon process, effects its object
by the oxidizing action of atmospheric air, but in a very
different manner. Weldon retained the principle of the Scheele
FIG. 4.--Weldon Chlorine Still. (Sectional Elevation.) Scale
C, Stone steam column resting in stone socket K.
process by employing the active oxygen of manganese dioxide
to convert hydrochloric acid into free chlorine, and he
employed the atmospheric oxygen only indirectly, for the
recovery of manganese dioxide from the manganese chloride
formed. But Deacon worked on the direct reaction: 2HCl +
O = H2O + Cl2. This reaction in ordinary circumstances
is so slow as to be practically useless. If, however, a
``contact-substance'' is employed and that at the proper
temperature, the process goes on at an immensely quickened
rate and can even be carried out as a continuous operation.
The only substance which possesses sufficiently strong
catalytic properties for the reaction is cupric chloride.
If pieces of porous clay are soaked in a solution of this
salt and dried and kept at a temperature of 450 deg. C. (in
practice it is necessary to go to a rather higher temperature),
it is possible continuously to convert a united stream of
hydrochloric acid and atmospheric air, passed through the
contact- substance in a ``decomposer'' (fig. 5), to a larger
extent into chlorine and water, of course mixed with the excess
of oxygen and all the nitrogen of the air. On a small scale
it is possible to push the decomposition as far as 90% of the
hydrochloric acid, but on the large scale only at most 60% is
reached. The mixture of hydrochloric acid and air is taken
directly from the ``decomposing-pan'' of an ordinary salt-cake
furnace, is first cooled down in pipes sufficiently to
condense most of the moisture present (together with about
8% of the hydrochloric acid), and then passed through a
cast-iron superheater and from this into the ``decomposer.''
The gaseous mixture, issuing from the latter, is washed with
water in the usual condensing apparatus, to remove the 40 or
50 parts of hydrochloric acid left unchanged, and can then be
immediately employed for the manufacture of chlorate of potash.
Where (as is the more usual case) the chlorine has to serve for
the manufacture of bleaching-powder, it must first be deprived
of the great amount of moisture which it contains, by means of
FIG. 5.--Deacon ``Decomposer.'' (Sectional Elevation.)
Scale 1/40. a,a, Upright cast-iron cylinders; b,b,
brick jacket; c,c, flues; d,e, iron plates arranged
like venetian blinds, between which the contact-substance
is contained; f, charging hole; g, discharging hole;
h, entrance pipe for gas; i, exit pipe for gas.
coke-towers fed with moderately strong sulphuric acid. As
the gas issuing from these contains only about 5 volumes % of
hydrochloric acid, it cannot be made to act upon lime in the
ordinary bleaching-powder chambers, but specially constructed
chambers must be provided (see fig. 4). The movement of
the gases through all this complicated set of apparatus is
produced by a Root's blower placed at the end of it all.
The Deacon process makes cheaper chlorine than the Weldon
process, but the plant is complicated and costly and the
working requires a great deal of attention. In skilled
hands it has been proved to yield excellent results.
The hydrochloric acid from the calcining-furnaces or
``roasters'' cannot be employed immediately for the Deacon
process, as the sulphuric acid always contained in the roaster
gases soon ``poisons'' the contact-substance and renders it
inoperative. This acid must, therefore, be condensed in the
ordinary way into liquid hydrochloric acid and formerly could
be worked up only by the Weldon process. R. Hasenclever
has overcome this drawback by running this impure acid into
moderately strong sulphuric acid (140 deg. Twaddell), blowing in
air at the same time. This produces a mixed current of pure
hydrochloric acid gas and air, which is carried into a Deacon
decomposer where it acts in the usual manner. The sulphuric
acid, of which 6 or 7 parts are used to one of impure liquid
hydrochloric acid, is always reserved for use in the same
process, by driving off the excess of water in a lead pan,
fired from the top, so that the principal expense of the
process is that of the fuel required for the last operation.
4. Applications of Chlorine.--Some of the chlorine manufactured
(practically only such as is obtained by the electrolysis
of chlorides) is condensed by cold and pressure into liquid
chlorine. If this is anhydrous, as it must be in any case for
this purpose, it does not act upon the metal of the compressors,
nor upon the iron bottles in which it is sent out. It may
even be sent out in tank wagons, similar to those which are
employed for carrying sulphuric acid, holding 10 tons each.
Sometimes the chlorine is employed directly for bleaching
purposes, especially for some kinds of paper. A number of
organic chlorinated products are also produced on a large
scale. But most of the chlorine is utilized for the production
of bleaching- powder, of bleach-liquor, and of chlorate of potash.
Bleaching-powder is a compound obtained by the action
of free chlorine on hydrated lime, containing a slight
excess of water at ordinary temperatures or slightly above
these. Its composition approaches the formula CaOCl2,
and it is regarded as a double salt of calcium chloride and
hypochlorite, which by the action of water splits up into
a mixture of these salts. It always contains a certain
quantity of chemically combined water and also an excess of
lime. Usually this lime is regarded only as mechanically
mixed with the bleaching-compound, CaOCl2, but some chemists
adopt formulae in which this lime is equally represented.
For the manufacture of bleaching-powder, limestone of high
degree of purity (especially free from magnesia and iron) is
carefully burned so as to drive out nearly all the carbon dioxide
without overheating the lime. The quick-lime is then slaked
with the requisite quantity of water; the product is passed
through a fine-meshed wire sieve and is spread in layers of 2
or 3 in. at the bottom of large boxes, the ``bleaching-powder
chambers,'' made of lead, or sometimes of cast-iron protected by
paint, of slate or even of tarred wood. Chlorine, generated
in an ordinary or a Weldon still, is passed in and is rapidly
absorbed. When the absorption becomes slow, the gas is cut
off and the chamber is left to itself for twelve hours or more,
when it will be found that all the chlorine has been taken
up. Now the door of the chamber is opened, the powder lying
at the bottom is turned over and the treatment with gas is
repeated. Sometimes a third treatment is necessary in order
to get the product up to the strength required in commerce,
viz. 35% of ``available'' chlorine. The finished product is
packed into wooden casks lined with brown paper. The work of
packing is a most disagreeable and unhealthy operation which
is best relieved by erecting the chambers at a higher level
and placing the casks underneath, communication being made by
means of traps in the chamber-bottom. so that the packers can
do their work outside the chambers. The bleaching-powder casks
must be kept in a dry place, as cool as possible, and never
exposed to the direct rays of the sun, in order to prevent a
decomposition which now and then has even led to explosions.
The weak chlorine from the Deacon process cannot be treated in
this manner, as chambers of impossibly large dimensions would be
required. Originally the absorption of the Deacon chlorine took
place in a set of chambers, constructed of large slabs of stone,
containing a great many horizontal shelves superposed over one
another. About sixteen such chambers were combined in such
manner that the fresh gas passed into that chamber which had
been the longest time at work and in which the bleaching-powder
was nearly finished, and so forth until the gas, now all but
entirely exhausted, reached the last-filled chamber in which
it met with fresh lime and there gave up the last of the
chlorine. These ``Deacon chambers'' occupied a large space,
besides being expensive to build and difficult to keep in repair.
They are now mostly replaced by an apparatus, the invention of R.
Hasenclever, consisting of four horizontal cast-iron cylinders
with internal stirring-gear. The fresh lime is continually
charged into the top cylinder, is gradually moved towards the
other end, falls down into the next lower cylinder and thus
gradually makes its way to the lowest cylinder. The weak chlorine
gas from the Deacon apparatus travels precisely the opposite
way, from the bottom upwards, the result being that finished
bleaching- powder is continually discharged at the bottom
and air free from chlorine leaves the apparatus at the top.
Bleaching-powder is manufactured to the extent of several
hundred thousands of tons annually, almost entirely for the
use of papermakers and cotton bleachers. Smaller quantities
are used for disinfection and other purposes. It is usually
sold in ``tierces,'' that is, casks containing about 10 cwt.
Bleach-liquors.--If the chlorine is made to act on cream of
lime, care being taken that the temperature does not rise
above 35 deg. and that the chlorine is not in excess, a solution
is obtained containing a mixture of calcium chloride and
hypochlorite which is a very convenient agent for bleachers,
but which does not bear the expense of carriage over long
distances. Similar liquids are obtained with a basis of sodium
(``eau de Javel''), by passing chlorine into solutions of sodium
carbonate. The former kind of bleach-liquor is mostly used
in the industry of cotton, the latter in that of linen.
Chlorate of Potash.--Formerly all chlorate of potash, as
some is still, was obtained by passing chlorine into milk
of lime, allowing the temperature to rise almost to the
boiling-point, and continuing until the bleaching-solution,
originally formed, is converted into a mixture of calcium
chlorate and chloride, the final reaction being 6Ca(OH)2
+ 6Cl2 = 5Cacl2 + Ca(ClO3)2 + 6H2O. On adding to this
solution, after settling out the mud, a quantity of potassium
chloride equivalent to the calcium chlorate, the reaction
Ca(ClO3)2 + 2KCl = CaCl2 + 2KClO3 is produced, the ultimate
proportions thus being theoretically 2KClO3 to 6CaCl2, though
in reality there is rather more calcium chloride present.
When this solution is concentrated by evaporation and cooled
down, about five-sixths of the chlorate of potash crystallizes
out. It is purified by redissolving and crystallization, and
is sold either in the state of crystals or finely ground.
During these operations care must be taken lest a spark should
produce the inflammation of the chlorate on contact with any
organic substance. Large quantities of potassium chlorate
exposed to strong heat in contact with the wood of casks
or the timber of a roof have produced violent explosions.
Most of the chlorate of potash is now prepared by electrolysis
of potassium chloride (see below). It is employed for
fire-works, for some descriptions of explosives, for safety
matches and as an oxidizer in some operations, especially
in dyeing and tissue printing. For the last-named purpose
it is sometimes replaced by sodium chlorate. The chlorates
are usually sold in wooden kegs containing 1 cwt. each.
5. The Manufacture of Soda-ash from Salt-cake by the Leblanc
process.--This process consists in heating a mixture of commercial
FIG. 6.--Black-ash Furnace and Boiling-down Pan. Scale
[14051]
sulphate of soda (salt-cake) with about the same weight of
crushed limestone and half its weight of coal, until the
materials are fluxed and a reaction has taken place, the
principal phase of which is expressed by the equation Na2SO4
+ CaC03 + 2C = 2CO2 + Na2CO3 + CaS. A number of secondary
reactions, however, occur, owing partly to the excess of
calcium carbonate and coal and partly to the impurities
present, so that the solid product of the process, which is
called ``black-ash,'' has a somewhat complicated composition.
Its principal constituents are always sodium carbonate
and calcium sulphide, which are separated by the action of
water, the former being soluble and the latter insoluble.
The furnace in which the reaction takes place is shown in
fig. 6 in a sectional plan. It is called a ``black-ash''
furnace, and belongs to the class of reverberatory furnaces.
A large fire-grate (ab), having a cave (c) to facilitate
stoking and stepped back at (d), is bounded on one side by a
fire-bridge (e); on the other side of this, separated by an
air-channel (g), there is first the proper fluxing bed (h),
and behind this the ``back-bed'' (i) for pre-heating the
charge. The flame issuing from the furnace by (o) is always
further utilized for boiling down the liquors obtained in
a later stage, either in a pan (p) fired from the top and
supported on pillars (qq) as shown in the drawing, or in
pans heated from below. The charge of salt-cake (generally
3 cwt.), limestone and coal is roughly mixed and put upon
the back-bed; when the front- bed has become empty it is
drawn forward and exposed to the full heat of the fire,
with frequent stirring. After about three- quarters of an
hour the substances are so far fluxed or softened that the
reaction now sets in fully, as shown by the copious escape of
gas. This is at first colourless carbon dioxide, but later
on inflammable gases come out of the mass, which at this stage
has turned into a thicker, pasty condition, showing that the
end of the reaction is near. The inflammable gas is carbon
monoxide, which, however, does not burn with its proper purple
flame, but with a flame tinged bright yellow by the sodium
present. This carbon monoxide is formed by the action of
coal on the lime formed at this stage from the original
limestone. When the ``candles'' of carbon monoxide appear,
the pasty mass is quickly drawn out of the furnace into iron
``bogies,'' where it solidifies into a grey, porous mass, the
``black-ash.'' Care must be taken to heat it no longer than
necessary, as it otherwise turns red and yields bad soda.
The hand-wrought black-ash furnace has been mostly superseded
in the large factories by the revolving black-ash furnace,
shown in fig. 7. These furnaces possess a large cylindrical
shell (e), lined with fire-bricks, and made to revolve
round its horizontal axis by means of a toothed wheel fixed
on its exterior; (ff) are tire-seats holding tires (gg),
which work in friction rollers (h). The flame of a fixed
fireplace (a) enters through an ``eye'' (b) in the centre
of the front end of the cylinder and issues in the centre of
FIG. 7.--Revolving Black-ash Furnace. (Elevation.) Scale
the back end, first into a large dust-chamber (m.) and
then over or under boiling-down pans (p.) These mechanical
furnaces do the work of from four to ten ordinary furnaces
according to their size. with comparatively very little
expense for labour, but they must be very carefully managed
and the black-ash from them is more difficult to lixiviate
than that from hand-wrought furnaces, because it is less
porous. The lixiviation of the black- ash requires great
care, as the calcium sulphide is liable to be changed into
soluble calcium compounds, which immediately react with sodium
carbonate and destroy a corresponding quantity of the latter,
rendering the soda weaker and impure. This change of the
calcium sulphide may be brought about either by the oxidizing
action of the air or by ``hydrolysis,'' produced by prolonged
contact with hot water, the use of which, on the other hand,
cannot be avoided in order to extract the sodium carbonate
itself. The apparatus which has been found most suitable
for the purpose was devised by Professor H. Buff of Giessen,
and first practically carried out by Charles Dunlop at St
Rollox. It consists of a number of tanks or ``vats,'' placed
at the same level and connected by pipes which reach nearly to
the bottom of one tank and open out at the top into the next
tank. The vats are also provided with false bottoms, outlet
cocks, steam pipes and so forth. Tepid water is run in at one
end of the series, where nearly exhausted black-ash is present;
the weak liquor takes up more soda from the intermediate tanks
and at last gets up to full strength in the last tank, charged
with fresh black-ash and kept at a higher temperature, viz.
60 deg. C. When the first tank has been quite exhausted, the
water is turned on to the next, the first tank is emptied by
discharging the ``alkali- waste,'' and is filled with fresh
black-ash, whereupon it becomes the last of the series. In
spite of all precautions a certain quantity of impurities is
always formed, but this should be kept down as much as possible
by strictly watching the temperature in the vats and by taking
care that the black-ash in the wet state is never exposed to the
air. The unavoidable contamination with muddy particles
of vat-waste is removed by allowing the vat- liquor to rest
for some hours in a separate tank and settling out the mud.
The clear vat-liquor, if allowed to cool down to ordinary
temperature, would separate out part of the sodium carbonate
in the shape of decahydrated crystals. As these do not
come out sufficiently pure, they would not be marketable and
therefore they are not allowed to be formed, but the liquid,
while still hot, is either run into the boiling-down pans, or
submitted to one of the purifying operations to be described
below. If it is boiled down without further purification,
the resulting soda-ash is not of the first quality, but it is
sufficiently pure for many purposes. The boiling down is most
economically performed by means of large iron pans covered
with a brick arch and heated from the top by the waste flame
issuing from the black-ash furnaces (see figs. 6 and 7). It
is continued until the contents of the pan have been converted
into a thick paste of small crystals of monohydrated sodium
carbonate, permeated by a mother-liquor which is removed by
draining on perforated plates or by a centrifugal machine,
and is always returned to the pans. The drained crystals are
dried and heated to redness in a reverberatory furnace; when
``finished,'' the mass is of an impure white or light yellow
colour and is sold as ordinary ``soda-ash.'' It is not easy
to make it stronger than 92% of sodium carbonate, which is
technically expressed as ``52 degrees of available soda'' (see next
page). If purer and stronger soda-ash is wanted, the boiling
down must be carried out in pans fired from below, and the
crystals of monohydrated sodium carbonate ``fished'' out as
they are formed, but this is mostly done after submitting the
liquor to the purifying operations which we shall now describe.
The dried or ``finished'' soda-ash is ground to a pretty fine
powder and is packed into wooden casks or ``tierces,'' holding from
10 to about 20 cwt. each, according to the way of filling them.
The principal impurities of crude vat-liquor are sodium
hydrate and sulphide, the latter of which always leads to
the formation of soluble double sulphur salts of sodium and
iron. The other impurities are of minor importance.
The sulphides can be removed by ``oxidizing'' them into
thiosulphates by means of atmospheric air, with or without
the assistance of other agents, such as manganese peroxide;
or by ``carbonating'' them with lime-kiln or other gases
containing carbon dioxide; or by precipitating them with
lead or zinc oxide. The last mentioned is the best but
costliest method, and is employed only in the manufacture
of the highest strengths of caustic soda. The most usual
process, where soda-ash is to be made, is the ``carbonating.''
This is usually effected either by forcing lime-kiln gas
through the liquor, contained in a closed iron vessel, or by
passing the gases through an iron tower filled with coke or
other materials, suitable for subdividing the stream of the
gases and that of the vat-liquor which trickles down in the
tower. The same apparatus is used for ``oxidizing'' by means
of atmospheric air passed through by means of an injector;
sometimes both air and carbon dioxide are passed in at the same
time. The operation is finished when all the sodium sulphide
has been converted into normal sodium carbonate, partly also
into acid sodium carbonate (bicarbonate) NaHCO3; at the
same time a precipitate is formed, consisting of ferrous
sulphide, alumina and silica, which is removed by another
settling tank, and the clear liquor is now ready either
for boiling down in a ``fishing-pan'' for the manufacture
of white soda-ash, or for the process of causticizing.
Soda-ash (as well as caustic soda) is sold by degrees of
``available soda.'' This means that portion which neutralizes the
acid employed for testing, and the degrees mean the percentage
of Na2O thus found, whether it be present as Na2CO3, NaOH,
or sodium aluminate or silicate. The purest soda-ash, equal
to 100% Na2CO3, would be 58 1/2 degrees of available soda. The
ordinary commercial strength of Leblanc soda-ash is from 52 to
54 degrees (in former times much was sold in the state of 48%).
6. Manufacture of Caustic Soda.--Most of the Leblanc liquor
is nowadays converted into caustic soda, as white soda-ash
is more easily and cheaply made by the ammonia-soda process.
We shall therefore in this place describe the manufacture
of caustic soda. This is always made from the carbonate by
the action of slaked lime: Na2CO3 + Ca(OH)2 = CaCO3 +
2NaOH. The calcium carbonate, being insoluble, is easily
separated from the caustic liquor by filtration. But as
this reaction is reversible, we must observe the conditions
necessary for directing it in the right sense. These are:
diluting with water so as not to exceed 10% of sodium carbonate
to 90% of water; boiling this mixture; and keeping it well
agitated. At the best about 92% of the sodium carbonate
can be converted into caustic soda, 8% remaining unchanged.
The operation is performed in iron cylinders, provided
with an agitating arrangement. This may consist of a steam
injector by means of which air is made to bubble through the
liquid, which produces both the required agitation and the
heating, and at the same time oxidizes at least part of the
sulphides; but this method of agitation causes a great waste
of steam and at the same time a further dilution of the
liquor. Many, therefore, prefer mechanical stirring by means
of paddles, fixed either to a vertical or to a horizontal
shaft, and inject only sufficient steam to keep the mass
at the proper temperature. Some heat is also gained by
the slaking of the caustic lime within the liquor. After
from half an hour to a whole hour the conversion of sodium
carbonate into sodium hydrate is brought about as far as is
practicable. The whole mass is now run into the filters,
which are always constructed on the vacuum principle. They
are iron boxes, in which a bed is made of bricks, above
them gravel, and over this sand, covered on the top by iron
grids. The space below the sieve thus formed is connected
by means of an outlet tap with a closed tank, and this again
communicates with a vacuum pump. By this means the filtration
is quickened by the atmospheric pressure, and goes on very
rapidly, as also does the subsequent washing. The filtered
caustic liquor passes to the concentration plants; the
washings are employed for diluting fresh vat-liquor for the
next operation, or for dissolving solid soda-ash for the same
purpose. The washed-out calcium carbonate, which always contains
much calcium hydrate and 2 or 3% of soda in various forms,
usually goes back to the black-ash furnaces, but it cannot be
always used up in this way, and what remains is thrown upon a
heap outside the works. Attempts have been made to use it in
the manufacture of Portland cement, but without much success.
The clear caustic soda liquor must be concentrated in such
a way that the caustic soda cannot to any great extent be
reconverted into sodium carbonate, and that the ``salts''
which it contains, sodium carbonate, sulphate, chloride, &c.,
can be. separated during the process. Formerly the most usual
concentrating apparatus was the ``boat-pan'' (fig. 8). This is an
FIG. 8.--Caustic Soda Concentration Boat-pan. (Sectional Elevation.) Scale
oblong iron pan, the bottom of which slopes from both sides
to a narrow channel. The latter rests on a brick pillar;
the remaining part of the sloping bottom is heated, either
by the waste fire from a black-ash furnace or by a special
fireplace. This arrangement has the effect that the salts, as
they separate out, slide down the sloping part and arrive in
the central channel, which is not exposed to the fire-gases,
so that they quietly settle there, without caking to the pan,
until they are fished out by means of perforated ladles. These
boat-pans were for many years almost everywhere employed, and
did their work quite well, but rather expensively. At many works
they have been replaced by either Thelen pans or vacuum pans.
The ``Thelen pan'' (thus named from its inventor, a foreman
at the Rhenania works near Aachen) is a mechanically worked
fishing-pan, which requires considerably less labour and
coal than ordinary boat-pans. It is a long trough, of nearly
semicircular section, the whole bottom being exposed to the
fire- gases. A horizontal shaft runs length-ways through the
trough, and is provided with stirring blades, arranged in
such a manner that they constantly scrape the bottom, so that
the salts cannot burn fast upon it, and are at the same time
moved forward towards one of the ends of the trough where
they are automatically removed by means of a chain of buckets.
The most efficient evaporating apparatus, as far as economy
of fuel is concerned, is the vacuum-pan, of which from two to
five are combined to form a set, but it has the drawback that
the removal of the salts is much more difficult than with the
older pans, described above. In this apparatus only the first
of the pans is heated directly, usually by means of ordinary
boiler- steam circulating round a number of pipes, containing
the liquid to be concentrated. The steam rising from the latter
is passed into a similar pan, in which it circulates round
another set of pipes, but as it could not bring the liquid in
the latter to boil under ordinary conditions, the second pan
is connected with a vacuum-pump so that the boiling-point of
the liquid in this pan is lowered. This pan may be followed by
a third pan, in which a stronger vacuum is maintained, and so
forth. By this means the latent heat of the steam, issuing
from all pans but the last, is utilized for evaporating
purposes, and from half to three-fourths of the fuel is saved.
After being concentrated up to a certain point, and after
the separation of nearly all the salts, the caustic liquor
is transferred to cast-iron ``finishing-pots'' (fig. 9),
holding from ten to twenty tons. Here it is further boiled
down until the greater part or nearly all of the water
has been removed, and until the salts on cooling would
set to a solid mass. This requires ultimately a good red
heat. Before the mass has reached that point the sulphides
still present have been destroyed, either by the addition of
solid nitrate of soda or by blowing air through the red-hot
melt. Before finishing, the molten mass must be kept at a quiet
FIG. 9.--Caustic Soda ``Finishing-pot.'' (Sectional Elevation.) Scale
heat for some hours in order to settle out the ferric oxide which
it always contains, and which becomes insoluble (through the
destruction of the sodium ferrite) only at high temperatures.
When it has completely cleared, the liquid caustic is ladled
or pumped out into sheet-iron drums, holding about 6 cwt. each,
where it solidifies and forms the caustic soda known to commerce.
The best caustic soda tests from 75 to 76 degrees of
``available soda''; this is only a few per cent removed
from the composition of pure NaOH, which would be = 77.5
degrees Na2O. Most of the caustic soda is sold at a
strength of 70 degrees, sometimes as low as 60 degrees.
Caustic soda is used in very large quantities in the
manufacture of soap, paper, textile fabrics, alizarin
and other colouring matters, and for many other purposes.
7. Soda-Crystals.--Another product made in alkali works is
soda-crystals. Their formula in Na2CO3, 10H2O, corresponding
to 37% of dry sodium carbonate. They are made by dissolving
ordinary soda-ash in hot water, adding a small quantity of
chloride of lime for the destruction of colouring matter and the
oxidation of any ferrous salts present, carefully settling the
solution, without allowing its temperature to fall below the
point of maximum solubility (34 deg. C.), and running the clarified
liquid into cast-iron crystallizers or ``cones,'' where, on
cooling down, most of the sodium carbonate is separated in
large crystals of the decahydrated form. This process lasts
about a week in winter, and up to a fortnight in summer. In
France the crystallization of soda is performed not in large
tanks but in sheet-iron dishes holding only about 1/4 cwt.,
and requires only from 27 to 48 hours in the cool season; it
is not carried on at all in warmer climates during the summer
months. The mother-liquor, drained from the soda-crystals, on
boiling down to dryness yields a very white, but low-strength
soda-ash, as the soluble impurities of the original soda-ash
are nearly all collected here; it is called ``mother-alkali.''
Although the soda-crystals contain the alkali combined
with such a large quantity of water, they are made in large
quantities, because their form, together with their complete
freedom from caustic soda, makes them very suitable for domestic
purposes. Hence they are best known as ``washing-soda.''
Sometimes they are made, not from soda-ash, but from Leblanc
soda-liquor before ``finishing'' the ash, or from the crude
bicarbonate of the ammonia-soda process by prolonged boiling,
until nearly half of the carbonic acid has been expelled.
Formerly bicarbonate of soda was made from Leblanc soda-
crystals by the action of carbonic acid, but this article
is now almost exclusively made in the ammonia-soda process.
8. The Recovery of Sulphur from Alkali-waste.--For many
years all the sulphur used in the Leblanc process in the
shape of sodium sulphate, and originally imported into the
manufacture in the shape of brimstone or pyrites, was wasted
in the crude calcium sulphide remaining from the lixiviation of
black-ash. This ``alkali-waste,'' also called tank-waste or
vat- waste, was thrown into heaps where the calcium sulphide
was gradually acted upon by the moisture and the oxygen of the
air. The sulphur was by these converted partly into gaseous
sulphuretted hydrogen, partly into soluble polysulphides,
thiosulphates and other soluble compounds, and in all shapes
caused a nuisance which became more and more intolerable as
the number and size of alkali works increased. Both the air
and the water in their neighbourhood were contaminated thereby.
Both this nuisance and the loss of the sulphur (whose cost
sometimes amounted to more than half of the total cost of the
soda-ash) led to many attempts at extracting the sulphur from the
alkali-waste. This was first done with a certain amount of
success by the processes of M. Schaffner (1861) and L. Mond
(1862), but as these required the use of hydrochloric acid,
and as they only recovered about half of the sulphur, they
were superseded by another--a process which had been originally
proposed by W. Gossage in 1837, but has been made practicable
only by the inventions of C. F. Claus, in 1883, and from 1887
onward by the technical skill of Messrs Chance Brothers, of
Oldbury. The Claus-Chance process, as it is called, comprises
the following operations. The wet alkali-waste as it comes
from the lixiviating vats, is transferred into upright
iron cylinders in which it is systematically treated with
lime-kiln gases until the whole of the calcium sulphide has
been converted into calcium carbonate, the carbon dioxide of
the lime-kiln gases being entirely exhausted. The sulphur
issues as sulphuretted hydrogen, mixed with the nitrogen of the
air. It is mixed with fresh air containing sufficient oxygen
for the combustion of the hydrogen, and the mixture is passed
through red-hot iron oxide (burnt pyrites) which by its
catalytic action causes the reaction H2S + O = H2O + S to take
place. By cooling the vapours the sulphur is condensed in a
very pure form, and about 85% of the whole of it is recovered,
the remaining 15% escaping in the shape of sulphur dioxide
(SO2) and H2S. Unfortunately it has been hitherto found
impossible to deal with these gases in any profitable way.
It should be noted that this ``recovered sulphur,'' which is equal
in purity to the ``refined brimstone'' of commerce, has a far
higher value than the sulphur contained in the originally employed
pyrites, so that the recovery is a paying process, in spite of
the somewhat considerable cost of the plant and of the working
operations. It has been introduced at most large Leblanc alkali
works, and has, so to say, given them a new lease of life.
II. THE AMMONIA-SODA PROCESS
In spite of the great improvements effected during recent
times the Leblanc process cannot economically compete with
the ammonia-soda process, principally for two reasons. The
sodium in the latter costs next to nothing, being obtained
from natural or artificial brine in which the sodium chloride
possesses an extremely slight value. The fuel required is less
than half the amount used in the Leblanc process. Moreover,
the ammonia process has been gradually elaborated into a very
complicated but perfectly regularly working scheme, in which
the cost of labour and the loss of ammonia are reduced to a
minimum. The only way in which the Leblanc process could still
hold its own was by being turned in the direction of making
caustic soda, to which it lends itself more easily than the
ammonia-soda process; but the latter has invaded even this
field. One advantage, however, still remained to the Leblanc
process. All endeavours to obtain either hydrochloric acid
or free chlorine in the ammonia- soda process have proved
commercial failures, all the chlorine of the sodium chloride
being ultimately lost in the shape of worthless calcium
chloride. The Leblanc process thus remained the sole
purveyor of chlorine in its active forms, and in this way
the fact is accounted for that, at least in Great Britain,
the Leblanc process still furnishes nearly half of all the
alkali made, though in other countries its proportional
share is very much less. The profit made upon the chlorine
produced has to make up for the loss on the alkali.
The ammonia-soda process was first patented in 1838 by H. G.
Dyar and J. Hemming, who carried it out on an experimental
scale in Whitechapel. Many attempts were soon after made
in the same direction, both in England and on the continent
of Europe, the most remarkable of which was the ingenious
combination of apparatus devised by J. J. T. Schloesing and E.
Rolland. But a really economical solution of the problem
was first definitely found in 1872 by Ernest Solvay,
as the result of investigations begun about ten years
previously. The greater portion of all the soda-ash of
commerce is now made by Solvay's apparatus, which alone we
shall describe in this place, although it should be borne
in mind that the principles laid down by Dyar and Hemming
have been and are still successfully carried out in a number
of factories by an entirely different kind of apparatus.
The leading reaction of this process is the mutual decomposition
of ammonium bicarbonate and sodium chloride: NaCl + NH4HCO3
= NaHCO3 + NH4Cl. It begins, however, not with ready-made
ammonium bicarbonate, but with the substances from which
it is formed--ammonia, water and carbon dioxide--which are
made to act on sodium chloride. In practice the process
is carried out as follows. A nearly saturated solution of
sodium chloride is obtained by purifying natural or artificial
brine, i.e. an impure solution of common salt, especially
removing the alkaline earths and so forth by addition of
sodium or ammonium carbonate and settling out the precipitate
formed. This solution is saturated with ammonia, produced
in the recovery plant (see below), in vessels provided with
mechanical agitators and strongly cooled by coils of pipes through
which cold water is made to flow. These vessels, as well as
all others which are used in the process, are not open to the
air, but communicate with it through washers in which fresh
salt solution is employed for retaining any escaping vapours of
ammonia. The ammoniacal salt solution is now saturated with
carbon dioxide. This is employed in the shape of lime-kiln
gases, obtained in a comparatively pure and strong form (up
to 33% CO2), in very large kilns, charged with limestone and
coke. The kilns are closed at the top, and the gases are drawn
out by powerful air-pumps, washers being interposed between the
kilns and the pumps for the purpose of purifying and cooling the
gas. The heat evolved by the compression in the air-pumps
(which rises to four atmospheres or upwards) is again removed
by cooling, and the gas is now passed upwards in the ``Solvay
tower'' (fig. 10). This is a tall iron erection, built up from
superposed cylinders, which are separated from one another by
perforated horizontal diaphragms, constructed in such a way
that the gases are over and over again subdivided into many
smaller streams and are thus thoroughly brought into contact
with the ammoniacal salt solution with which the tower is about
two-thirds filled. There the reaction mentioned above takes
place, and owing to the concentration of the liquid the sodium
bicarbonate formed is to a great extent precipitated in the
shape of small crystals, forming with the mother-liquor a thin
magma. This takes place with considerable evolution of heat
which is removed by internal and external cooling with water.
The temperature must not be allowed to rise beyond a certain
point, for the reaction NaCl + NH4HCO3 = NaHCO3 + NH4Cl is
reversible, and at a temperature of about 60 deg. or 70 deg. C. it
is in fact practically going the wrong way, viz. from right to
left. On the other hand the cooling must not be carried too
far, for in this case the crystals of sodium bicarbonate
become so fine that the muddy mass is very difficult to
filter. The best temperature seems to be about 30 deg. C.
Either at certain intervals, or continuously, a portion of
the contents of the tower is withdrawn and fresh ammoniacal
salt solution is introduced higher up. The muddy liquid
running out is passed on to the vacuum filters (Z, fig.
10). Here a separation takes place between the crystals
of sodium bicarbonate and the mother-liquor. The former
are washed with water until the chlorides are nearly
removed, and are then carried into the drying apparatus.
From Thorpe's Dictionary of Applied Chemistry,
by permission of Longmans, Green & Co.
FIG. 10.--Ammonia - soda Carbonating Towers and Filters.
(Sectional Elevation.) Scale 1/100. AA, Tower; B, ammoniacal brine
main; E, gas-inlet; Z, vacuum filter; V, pipe to air-pump.
This must be constructed in such a manner that the bicarbonate,
which always contains some ammonium salts, is first freed
from these by moderate heating (of course taking care that the
ammonia is completely recovered), and later on, by raising the
temperature, it is decomposed into solid sodium carbonate and
gaseous carbon dioxide. The former needs only grinding to
constitute the final product, ammonia- soda ash; the latter is
again employed in the process of treating the ammoniacal salt
solution with carbon dioxide. Various forms of apparatus are
employed for this treatment of the crude bicarbonate--sometimes
semi-circular troughs with mechanical agitators on the
principle of the Thelen pan (see above)--all acting on the
principle that the escaping ammonia and carbon dioxide must
be fully utilized over again. The soda-ash obtained in the
end is of a high degree of purity, testing from 98 to 99%
Na2CO3, the remaining 1 or 2% consisting principally of NaCl.
A very important part of the process has still to be described,
viz. the recovery of the ammonia from the mother-liquor
coming from the vacuum filters and various washing liquors.
Unless this recovery is carried out in the most efficient
manner, the process cannot possibly pay; but so much progress
has been made in this direction that the loss of ammonia
is very slight indeed, merely a fraction per cent. The
ammonia is for the major part found in the mother-liquor as
ammonium chloride. A smaller but still considerable portion
exists here and in the washings in the shape of ammonium
carbonates. These compounds differ in their behaviour to
heat. The ammonium carbonates are driven out from their
solutions by mere prolonged boiling, being thereby decomposed
into ammonia, carbon dioxide and water, but the ammonium
chloride is not volatile under these conditions, and must
be decomposed by milk of lime: 2NH4Cl + Ca(OH)2 = 2NH3
+ CaCl2 + 2H2O. The solution of calcium chloride is run
to waste, the ammonia is re-introduced into the process.
Both these reactions are carried out in tall cylindrical columns
or ``stills,'' Consisting of a number of superposed cylinders,
having perforated horizontal partitions, and provided with
a steam-heating arrangement in the enlarged bottom portion.
The milk of lime is introduced at a certain distance from the
bottom. The steam causes the action of the lime on the
ammonium chloride to take place in this lower portion of the
still, from which the steam, mixed with all the liberated
ammonia, rises into the upper portion of the column where its
heat serves to drive out the volatile ammonium carbonate. Just
below the top there is a cooling arrangement, so that nearly
all the water is condensed and runs back into the column, while
the ammonia, with the carbon dioxide formerly combined with
part of it, passes on first through an outside cooler where
the remaining water is condensed, and afterwards into the
vessels, already described, where the ammonia is absorbed by
a solution of salt and thus again introduced into the process.
The reversible character of the principal reaction has
the consequence that a considerable portion of the sodium
chloride (up to 33%) is lost, being contained in the waste
calcium chloride solution which issues from the ammonia
stills. This is, however, not of much importance, as it
had been introduced in the shape of a brine where its value
is very slight (6d. per ton of NaCl). It is true that all
the chlorine combined with the sodium is lost partly as NaCl
and partly as CaCl2; none of the innumerable attempts at
recovering the chlorine from the waste liquor has been made to
pay, and success is less likely than ever since the perfection
of the electrolytic processes. (See CHLORINE.) For all
that, especially in consequence of the small amount of fuel
required, and the total absence of the necessity of employing
sulphur compounds as an intermediary, the ammonia-soda process
has supplanted the Leblanc process almost entirely on the
continent of Europe and to a great extent in Great Britain.
III. ELECTROLITIC ALKALI MANUFACTURE
In theory by far the simplest process for making alkalis together
with free chlorine is the electrolysis of sodium (or potassium)
chloride. When this takes place in an aqueous solution, the
alkaline metal at once reacts with the water, so that a solution
of an alkaline hydrate is formed while hydrogen escapes. The
reactions are therefore (we shall in this case speak only of the
sodium compounds): (1) NaCl = Na + Cl, (2) Na + H2O = NaOH + H.
The chlorine escapes at the anode, the hydrogen at the
cathode. If the chlorine and the sodiun hydrate can act upon
each other within the liquid, bleach-liquors are formed: 2NaOH
+ Cl2 = NaOCl + NaOH + H2O. The production of these for the
use of papermakers and bleachers of textile fabrics has become
an important industry, but does not enter into our province.
If, however, the action of the chlorine on the sodium hydrate is
prevented, which can be done in various ways, they can both be
collected in the isolated state and utilized as has been previously
described, viz. the chlorine can be used for the manufacture of
liquid chlorine, bleaching-powder or other bleaching compounds,
or chlorates, and the solution of sodium hydrate can be sold
as such, or converted into solid caustic soda. Precisely the
same can be done in the electrolysis of potassium chloride.
There is a third way of conducting the action, viz. so that
the chlorine can act upon the caustic soda or potash at a
higher concentration and temperature, in which case chlorates
are directly formed in the liquid: KCl + 8H2O = KClO3 +
8H2. This has indeed become the principal, because it is the
cheapest, process for the manufacture of potassium and sodium
chlorate. Perchlorates can also be made in this way.
In all these cases the chlorine, or the products made from
it, really play a greater part than the alkali. From 58.5
parts by weight of NaCl we obtain theoretically 23Na = 40NaOH =
53Na2CO3, together with 35.5 Cl, or 100 bleaching-powder.
As the weight of bleaching-powder consumed in the world is at
most one-fifth of that of alkali, calculated as Na2CO3, it
follows that only about one-tenth of all the alkali required
could be made by electrolysis, even supposing the Leblanc process
to be entirely abolished. The remaining nine-tenths of alkali
must be supplied from other sources, chiefly the ammonia-soda
process. As long as the operation of the Leblanc process is
continued, it will supply a certain share of both kinds of
products. Trustworthy statistics on this point cannot be
obtained, because most firms withhold any information
as to the extent of their production from the public.
The first patents for the electrolysis of alkaline chlorides
were taken out in 1851 and several others later on; but
commercial success was utterly impossible until the invention
of the dynamo machine allowed the production of the electric
current at a sufficiently cheap rate. The first application
of this machine for the present purpose seems to have been
made in 1875 and the number of patents soon rapidly increased;
but although a large amount of capital was invested and
many very ingenious inventions made their appearance, it
took nearly another twenty years before the manufacture of
alkali in this way was carried out in a continuous way on a
large scale and with profitable results. A little earlier
the manufacture of potassium chlorate (on the large scale
since 1890) had been brought to a definite success by H.
Gall and the Vicomte A. de Montlaur; a few years later the
processes worked out at the Griesheim alkali works (near
Frankfort) for the manufacture of caustic potash and chlorine
established definitely the success of electrolysis in the
field of potash, but even then none of the various processes
working with sodium chloride had emerged from the experimental
stage. Only more recently the manufacture of caustic soda
by electrolysis has also been established as a permanent and
paying industry, but as the greatest secrecy is maintained
in everything belonging to this domain, and as neither patent
specifications nor the sanguine assertions and anticipations
of interested persons throw much real light on the actual
facts of the case, nothing certain can be said either in
regard to the date at which the profitable manufacture
of caustic soda was first carried out by electrolysis, or
as to what extent this is the case at the present moment.
We shall here give merely an outline of those more important processes
which are known to be at present working profitably on a large scale.
(1) The Diaphragm process is probably the only one employed
at present for the decomposition of potassium chloride, and
it is also used for sodium chloride. A hot, concentrated
solution of the alkaline chloride is treated by the electric
current in large iron tanks which at the same time serve as
cathodes. The anodes are made of retort-carbon or other
chlorine-resisting material, and they are mounted in cells
which serve as diaphragms. The material of these cells
is usually cement, mixed with certain soluble salts which
impart sufficient porosity to the material. The electrolysis
is carried on until about a quarter of the chloride has
been transformed; it must be stopped at this stage lest
the formation of hypochlorite and chlorate should set
in. The alkaline liquid is now transferred to vacuum pans,
constructed in such a manner that the unchanged chloride,
which ``salts out'' during the concentration, can be removed
without disturbing the vacuum, and here at last a concentrated
pure solution of KOH or NaOH is obtained which is sold in
this state, or ``finished'' as solid caustic in the manner
described in the section treating of the Leblanc soda.
(2) The Castner-Kellner process employs no diaphragm, but a
mercurial cathode. The electrolysis takes place in the central
compartment of a tripartite trough which can be made to rock
slightly either to one side or the other. The bottom of the
trough is covered with mercury. The sodium as it is formed
at the cathode at once dissolves in the mercury which protects
it against the action of the water as long as the percentage
of sodium in the mercury does not exceed, say, 0.02%. When
this percentage has been reached, the cell is rocked to the
other side, so that the amalgam flows into one of the outer
compartments where the sodium is converted by water into sodium
hydrate. At the same time fresh mercury, from which the
sodium had been previously extracted, flows from the other
outside compartment into the central one. After a certain time
the whole is rocked towards the other side, and the process
is continued until the outer compartments contain a strong
solution of caustic soda, free from chloride and hypochlorite.
(3) Aussig process.--Here the anode is fixed in a bell,
mounted in a larger iron tank where the cathodes are
placed. The whole is filled with a solution of common
salt. As the electrolysis goes on, NaOH is formed at the
cathodes and remains at the bottom. The intermediate layer
of the salt solution, floating over the caustic soda solution,
plays the part of a diaphragm, by preventing the chlorine
evolved in the bell from acting on the sodium hydrate formed
outside, and this solution offers much less resistance to
the electric current than the ordinary diaphragms. This
process therefore consumes less power than most others.
(4) The Acker-Douglas process electrolyses sodium chloride
in the molten state, employing a cathode consisting of molten
lead. The latter dissolves the sodium as it is formed and
carries it to an outer compartment where by the action of
water the sodium is converted into caustic soda, while the
lead returns to the inner compartment. This process is carried
on at Niagara Falls, but it is uncertain to what extent.
(5) The Hargreaves-Bird process avoids certain drawbacks
attached to other processes, by employing a wire diaphragm
and converting the caustic soda as it issues on the other
side of this, by means of carbon dioxide, into a mixture
of sodium carbonate and bicarbonate, which separates out
in the solid state. This process is but little used.
It stands to reason that the electrolytic processes have
been principally developed in localities where the electric
current can be produced in the cheapest possible manner by
means of water power, but this is not the only condition
to be considered, as the question of freight to a centre of
consumption and other circumstances may also play an important
part. Where coal is very cheap indeed and the other
conditions are favourable, it is possible to establish such
an industry with a prospect of commercial success, even when
the electric current is produced by means of steam-engines.
Natural Soda.--This is the term applied to certain
deposits of alkaline salts, or their solutions, which occur,
sometimes in very large quantities, in various parts of the
world. The oldest and best known of these are the Natron
lakes in Lower Egypt. The largest occurrence of natural soda
hitherto known is that in Owen's Lake and other salt lakes
situated in eastern California. The soda in all of these
is present as ``sesquicarbonate,'' in reality 4/3 carbonate:
NaHCO3.Na2CO3.2H2O, and is always mixed with large
quantities of chloride and sulphate, which makes its extraction
more difficult than would appear from the outset. Hence,
although for many centuries (up to Leblanc's invention)
hardly any soda was available except from this source, and
although we now know that millions of tons of it exist,
especially in the west of the United States, there is as yet
very little of it practically employed, and that only locally.
REFERENCES.--The principal work on the manufacture of alkali
is G. Lunge's Sulphuric Acid anid Alkali (2nd ed., vols. ii.
and iii., 1895-1896). This work has also appeared in a German
and a French edition. The same author wrote the articles
on the manufacture of sodium and potassium compounds and on
chlorine in Thorpe's Dictionary of applied Chemistry (3
vols., 1890-1893). The subject is also treated, very much
more briefly, in Sorel's Industrie chimique minerale
(1902), and of course in every other general treatise on
chemical technology. A special treatise on the manufaciure
of ammonia soda ash has been published in German by H.
Schreib. Consult also the official Annual reports on Alkali,
&c., and, from 1864 onwards, Journal of the Society of
Chemical Industry, Fischers Jahresberichte der chemischen
Technologie, and Zeitschrift fur angewandte Chemie. (G. L.)