In pursuance of this plan he went to Bal_Encyclopaedia Britannica, 11th Edition, "G" to "Gaskell, Elizabeth" Volume 11, Slice 4

and thenceforth the _Genius_ was published weekly, under the joint

editorship of the two men. It was understood, however, that Garrison

would do most of the editorial work, while Lundy would spend most of his

time in lecturing and procuring subscribers. On one point the two

editors differed radically, Lundy being the advocate of gradual and

Garrison of immediate emancipation. The former was possessed with the

idea that the negroes, on being emancipated, must be colonized somewhere

beyond the limits of the United States; the latter held that they should

be emancipated on the soil of the country, with all the rights of

freemen. In view of this difference it was agreed that each should speak

on his own individual responsibility in the paper, appending his initial

to each of his articles for the information of the reader. It deserves

mention here that Garrison was then in utter ignorance of the change

previously wrought in the opinions of English abolitionists by Elizabeth

Heyrick's pamphlet in favour of immediate, in distinction from gradual

emancipation. The sinfulness of slavery being admitted, the duty of

immediate emancipation to his clear ethical instinct was perfectly

manifest. He saw that it would be idle to expose and denounce the evils

of slavery, while responsibility for the system was placed upon former

generations, and the duty of abolishing it transferred to an indefinite

future. His demand for immediate emancipation fell like a tocsin upon

the ears of slaveholders. For general talk about the evils of slavery

they cared little, but this assertion that every slave was entitled to

instant freedom filled them with alarm and roused them to anger, for

they saw that, if the conscience of the nation were to respond to the

proposition, the system must inevitably fall. The _Genius_, now that it

had become a vehicle for this dangerous doctrine, was a paper to be

feared and intensely hated. Baltimore was then one of the centres of the

domestic slave trade, and upon this traffic Garrison heaped the

strongest denunciations. A vessel owned in Newburyport having taken a

cargo of slaves from Baltimore to New Orleans, he characterized the

transaction as an act of "domestic piracy," and avowed his purpose to

"cover with thick infamy" those engaged therein. He was thereupon

prosecuted for libel by the owner of the vessel, fined $50, mulcted in

costs, and, in default of payment, committed to gaol. His imprisonment

created much excitement, and in some quarters, in spite of the

pro-slavery spirit of the time, was a subject of indignant comment in

public as well as private. The excitement was fed by the publication of

two or three striking sonnets, instinct with the spirit of liberty,

which Garrison inscribed on the walls of his cell. One of these,

_Freedom of Mind_, is remarkable for freshness of thought and terseness

of expression.

John G. Whittier, the Quaker poet, interceded with Henry Clay to pay

Garrison's fine and thus release him from prison. To the credit of the

slaveholding statesman it must be said that he responded favourably, but

before he had time for the requisite preliminaries Arthur Tappan, a

philanthropic merchant of New York, contributed the necessary sum and

set the prisoner free after an incarceration of seven weeks. The

partnership between Garrison and Lundy was then dissolved by mutual

consent, and the former resolved to establish a paper of his own, in

which, upon his sole responsibility, he could advocate the doctrine of

immediate emancipation and oppose the scheme of African colonization. He

was sure, after his experiences at Baltimore, that a movement against

slavery resting upon any less radical foundation than this would be

ineffectual. He first proposed to establish his paper at Washington, in

the midst of slavery, but on returning to New England and observing the

state of public opinion there, he came to the conclusion that little

could be done at the South while the non-slaveholding North was lending

her influence, through political, commercial, religious and social

channels, for the sustenance of slavery. He determined, therefore, to

publish his paper in Boston, and, having issued his prospectus, set

himself to the task of awakening an interest in the subject by means of

lectures in some of the principal cities and towns of the North. It was

an up-hill work. Contempt for the negro and indifference to his wrongs

were almost universal. In Boston, then a great cotton mart, he tried in

vain to procure a church or vestry for the delivery of his lectures, and

thereupon announced in one of the daily journals that if some suitable

place was not promptly offered he would speak on the common. A body of

infidels under the leadership of Abner Kneeland (1774-1844), who had

previously been in turn a Baptist minister and the editor of a

Universalist magazine, proffered him the use of their small hall; and,

no other place being accessible, he accepted it gratefully, and

delivered therein (in October 1830) three lectures, in which he unfolded

his principles and plans. He visited privately many of the leading

citizens of the city, statesmen, divines and merchants, and besought

them to take the lead in a national movement against slavery; but they

all with one consent made excuse, some of them listening to his plea

with manifest impatience. He was disappointed, but not disheartened. His

conviction of the righteousness of his cause, of the evils and dangers

of slavery, and of the absolute necessity of the contemplated movement,

was intensified by opposition, and he resolved to go forward, trusting

in God for success.

On the 1st of January 1831, without a dollar of capital, and without a

single subscriber, he and his partner Isaac Knapp (1804-1843) issued the

first number of the _Liberator_, avowing their "determination to print

it as long as they could subsist on bread and water, or their hands

obtain employment." Its motto was, "Our country is the world--our

countrymen are mankind"; and the editor, in his address to the public,

uttered the words which have become memorable as embodying the whole

purpose and spirit of his life: "I am in earnest--I will not

equivocate--I will not excuse--I will not retreat a single inch--and I

will be heard." Help came but slowly. For many months Garrison and his

brave partner, who died long before the end of the conflict, made their

bed on the floor of the room, "dark, unfurnished and mean," in which

they printed their paper, and where Mayor Harrison Gray Otis of Boston,

in compliance with the request of Governor Robert Y. Hayne of South

Carolina, "ferreted them out" in "an obscure hole," "their only visible

auxiliary a negro boy." But the paper founded under such inauspicious

circumstances exerted a mighty influence, and lived to record not only

President Lincoln's proclamation of emancipation, but the adoption of an

amendment to the constitution of the United States for ever prohibiting

slavery. It was the beginning and the nucleus of an agitation that

eventually pervaded and filled every part of the country. Other

newspapers were afterwards established upon the same principles;

anti-slavery societies, founded upon the doctrine of immediate

emancipation, sprang up on every hand; the agitation was carried into

political parties, into the press, and into legislative and

ecclesiastical assemblies; until in 1861 the Southern states, taking

alarm from the election of a president known to be at heart opposed to

slavery though pledged to enforce all the constitutional safeguards of

the system, seceded from the Union and set up a separate government.

Garrison sought the abolition of slavery by moral means alone. He knew

that the national government had no power over the system in any state,

though it could abolish it at the national capital, and prohibit it in

the territories. He thought it should bring its moral influence to bear

in favour of abolition; but neither he nor his associates ever asked

Congress to exercise any unconstitutional power. His idea was to combine

the moral influence of the North, and pour it through every open channel

upon the South. To this end he made his appeal to the Northern churches

and pulpits, beseeching them to bring the power of Christianity to bear

against the slave system, and to advocate the rights of the slaves to

immediate and unconditional freedom. He was a man of peace, hating war

not less than he did slavery; but he warned his countrymen that if they

refused to abolish slavery by moral power a retributive war must sooner

or later ensue. The conflict was irrepressible. Slavery must be

overthrown, if not by peaceful means, then in blood. The first society

organized under Garrison's auspices, and in accordance with his

principles, was the New England Anti-Slavery Society, which adopted its

constitution in January 1832. In the spring of this year Garrison issued

his _Thoughts on African Colonization_, in which he showed by ample

citations from official documents that the American Colonization Society

was organized in the interest of slavery, and that in offering itself to

the people of the North as a practical remedy for that system it was

guilty of deception. His book, aided by others taking substantially the

same view, smote the society with a paralysis from which it never

recovered. Agents of the American Colonization Society in England having

succeeded in deceiving leading Abolitionists there as to its character

and tendency, Garrison was deputed by the New England Anti-Slavery

Society to visit England for the purpose of counteracting their

influence. He went in the spring of 1833, when he was but twenty-seven

years of age, and was received with great cordiality by British

Abolitionists, some of whom had heard of his bold assaults upon American

slavery, and had seen a few numbers of the _Liberator_. The struggle for

emancipation in the West Indies was then at the point of culmination;

the leaders of the cause, from all parts of the kingdom, were assembled

in London, and Garrison was at once admitted to their councils and

treated with distinguished consideration. He took home with him a

"protest" against the American Colonization Society, signed by

Wilberforce, Zachary Macaulay, Samuel Gurney, William Evans, S.

Lushington, T. Fowell Buxton, James Cropper, Daniel O'Connell and

others, in which they declared their deliberate judgment that "its

precepts were delusive," and "its real effects of the most dangerous

nature." He also received assurances of the cordial sympathy of British

Abolitionists with him in his efforts to abolish American slavery. He

gained a hearing before a large popular assembly in London, and won the

confidence of those whom he addressed by his evident earnestness,

sincerity and ability.

Garrison's visit to England enraged the pro-slavery people and press of

the United States at the outset, and when he returned home in September

with the "protest" against the Colonization Society, and announced that

he had engaged the services of George Thompson as a lecturer against

American slavery, there were fresh outbursts of rage on every hand. The

American Anti-Slavery Society was organized in December of that year

(1833), putting forth a masterly declaration of its principles and

purposes from the pen of Garrison. This added fresh fuel to the public

excitement, and when Thompson came over in the next spring, the

hostility to the cause began to manifest itself in mobs organized to

suppress the discussion of the slavery question. Now began what Harriet

Martineau called "the martyr age in America." In the autumn of 1835

Thompson was compelled, in order to save his life, to embark secretly

for England. Just before his departure the announcement that he would

address the Woman's Anti-Slavery Society of Boston created "a mob of

gentlemen of property and standing," from which, if he had been present,

he could hardly have escaped with his life. The whole city was in an

uproar. Garrison, almost denuded of his clothing, was dragged through

the streets with a rope by infuriated men. He was rescued with great

difficulty, and consigned to the gaol for safety, until he could be

secretly removed from the city.

Anti-slavery societies were greatly multiplied throughout the North, and

many men of influence, both in the church and in the state, were won to

the cause. Garrison, true to his original purpose, never faltered or

turned back. The Abolitionists of the United States were a united body

until 1839-1840, when divisions sprang up among them. Garrison

countenanced the activity of women in the cause, even to the extent of

allowing them to vote and speak in the anti-slavery societies, and

appointing them as lecturing agents; moreover, he believed in the

political equality of the sexes, to which a strong party was opposed

upon social and religious grounds. Then there were some who thought

Garrison dealt too severely with the churches and pulpits for their

complicity with slavery, and who accused him of a want of religious

orthodoxy; indeed, according to the standards of his time he was

decidedly heterodox, though he had an intensely religious nature and was

far from being an infidel, as he was often charged with being. He was,

moreover, not only a non-resistant but also an opponent of all political

systems based on force. "As to the governments of this world," he said,

"whatever their titles or forms we shall endeavour to prove that in

their essential elements, as at present administered, they are all

anti-Christ; that they can never by human wisdom be brought into

conformity with the will of God; that they cannot be maintained except

by naval and military power to carry them into effect; that all their

penal enactments, being a dead letter without any army to carry them

into effect, are virtually written in human blood; and that the

followers of Jesus should instinctively shun their stations of honor,

power, and emolument--at the same time 'submitting to every ordinance of

man for the Lord's sake' and offering no physical resistance to any of

their mandates, however unjust or tyrannical." These views were very

distasteful to many, who, moreover, felt that Garrison greatly injured

abolitionism by causing it to be associated in men's minds with these

unpopular views on other subjects. The dissentients from his opinions

determined to form an anti-slavery political party, while he believed in

working by moral rather than political party instrumentalities. These

differences led to the organization of a new National Anti-Slavery

Society in 1840, and to the formation of the "Liberty Party" (q.v.) in

politics. (See BIRNEY, JAMES G.) The two societies sent their delegates

to the World's Anti-Slavery Convention in London in 1840, and Garrison

refused to take his seat in that body, because the women delegates from

the United States were excluded. The discussions of the next few years

served to make clearer than before the practical workings of the

constitution of the United States as a shield and support of slavery;

and Garrison, after a long and painful reflection, came to the

conclusion that its pro-slavery clauses were immoral, and that it was

therefore wrong to take an oath for its support. The Southern states had

greatly enlarged representation in Congress on account of their slaves,

and the national government was constitutionally bound to assist in the

capture of fugitive slaves, and to suppress every attempt on their part

to gain their freedom by force. In view of these provisions, Garrison,

adopting a bold scriptural figure of speech, denounced the constitution

as "a covenant with death and an agreement with hell," and chose as his

motto, "No union with slaveholders."

One class of Abolitionists sought to evade the difficulty by strained

interpretations of the clauses referred to, while others, admitting that

they were immoral, felt themselves obliged, notwithstanding, to support

the constitution in order to avoid what they thought would be still

greater evils. The American Anti-Slavery Society, of which Garrison was

the president from 1843 to the day of emancipation, was during all this

period the nucleus of an intense and powerful moral agitation, which was

greatly valued by many of the most faithful workers in the field of

politics, who respected Garrison for his fidelity to his convictions. On

the other hand, he always had the highest respect for every earnest and

faithful opponent of slavery, however far their special views might

differ. When in 1861 the Southern states seceded from the Union and took

up arms against it, he saw clearly that slavery would perish in the

struggle, that the constitution would be purged of its pro-slavery

clauses, and that the Union henceforth would rest upon the sure

foundations of liberty, justice and equality to all men. He therefore

ceased from that hour to advocate disunion, and devoted himself to the

task of preparing the way for and hastening on the inevitable event. His

services at this period were recognized and honoured by President

Lincoln and others in authority, and the whole country knew that the

agitation which made the abolition of slavery feasible and necessary was

largely due to his uncompromising spirit and indomitable courage.

In 1865 at the close of the war, he declared that, slavery being

abolished, his career as an abolitionist was ended. He counselled a

dissolution of the American Anti-Slavery Society, insisting that it had

become _functus officiis_, and that whatever needed to be done for the

protection of the freedmen could best be accomplished by new

associations formed for that purpose. The _Liberator_ was discontinued

at the end of the same year, after an existence of thirty-five years. He

visited England for the second time in 1846, and again in 1867, when he

was received with distinguished honours, public as well as private. In

1877, when he was there for the last time, he declined every form of

public recognition. He died in New York on the 24th of May 1879, in the

seventy-fourth year of his age, and was buried in Boston, after a most

impressive funeral service, four days later. In 1843 a small volume of

his _Sonnets and other Poems_ was published, and in 1852 appeared a

volume of _Selections from his Writings and Speeches_. His wife, Helen

Eliza Benson, died in 1876. Four sons and one daughter survived them.

Garrison's son, WILLIAM LLOYD GARRISON (1838-1909), was a prominent

advocate of the single tax, free trade, woman's suffrage, and of the

repeal of the Chinese Exclusion Act, and an opponent of imperialism;

another son, WENDELL PHILLIPS GARRISON (1840-1907), was literary editor

of the New York _Nation_ from 1865 to 1906.

The above article, with certain modifications, reproduces the account

given in the 9th edition of this work by Oliver Johnson (reprinted

from his _Garrison: an Outline of his Life_, New York, 1879). The

writer (1809-1889) was a prominent Abolitionist, editor, and an

intimate friend of Garrison; he edited the _Liberator_ during

Garrison's absence in England in 1833, and later was an editor or an

associate editor of various journals, including, after the Civil War,

the New York _Tribune_ and the New York _Evening Post_. He also

published an excellent brief biography in _William Lloyd Garrison and

his Times_ (Boston, 1880).

The great authority on the life of Garrison is the thorough and candid

work of his sons, W.P. and F.J. Garrison, _William Lloyd Garrison

1805-1879: The Story of his Life told by his Children_ (4 vols., New

York, 1885-1889), which is indispensable for the student of the

anti-slavery struggle in America. Goldwin Smith's _The Moral Crusader:

a Biographical Essay on William Lloyd Garrison_ (New York, 1892) is a

brilliant sketch.

GARRISON, originally a term for stores or supplies, also a defence or

protection, now confined in meaning to a body of troops stationed in a

town or fortress for the purpose of defence. In form the word is derived

from O. Fr. _garison_, modern _guerison_, from _guerir_, to furnish with

stores, to preserve, but in its later meaning it has been confused with

the Fr. _garnison_, the regular word for troops stationed for purposes

of defence. In English "garnison" was used till the 16th century, when

"garrison" took its place. In the British army "garrison troops,"

especially "garrison artillery," are troops trained and employed for

garrison work as distinct from field operations.

GARROTE (Spanish for "cudgel"), an appliance used in Spain and Portugal

for the execution of criminals condemned to death. The criminal is

conducted to the place of execution (which is public) on horseback or in

a cart, wearing a black tunic, and is attended by a procession of

priests, &c. He is seated on a scaffold fastened to an upright post by

an iron collar (the garrote), and a knob worked by a screw or lever

dislocates his spinal column, or a small blade severs the spinal column

at the base of the brain. (See CAPITAL PUNISHMENT.) Originally a stout

cord or bandage was tied round the neck of the criminal, who was seated

in a chair fixed to a post. Between the cord and the neck a stick was

inserted (hence the name) and twisted till strangulation ensued.

"Garrotting" is the name given in England to a form of robbery with

violence which became rather common in the winter of 1862-1863. The

thief came up behind his victim, threw a cord over his head, and

tightened it nearly to strangulation point, while robbing him. An act of

1863, imposing the penalty of flogging in addition to penal servitude

for this offence, had the effect of stopping garrotting almost entirely.

At any rate, the practice was checked; and, though the opponents of any

sort of flogging refuse to admit that this was due to the penalty, that

view has always been taken by the English judges who had experience of

such cases.

GARRUCHA, a seaport of south-eastern Spain, in the province of Almeria;

on the Mediterranean Sea and on the right bank of the river Antas. Pop.

(1900) 4461. The harbour of Garrucha, which is defended by an ancient

castle, affords shelter to large ships, and is the natural outlet for

the commerce of a thriving agricultural and mining district. Despite its

small size and the want of railway communication, Garrucha has thus a

considerable trade in lead, silver, copper, iron, esparto grass, fruit,

&c. Besides sea-going ships, many small coasters enter in ballast, and

clear with valuable cargoes. In 1902, 135 vessels of 390,000 tons

entered the harbour, the majority being British or Spanish; and in the

same year the value of the exports reached L478,000, and that of the

imports L128,000. Both imports and exports trebled their value in the

ten years 1892-1902.

GARSTON, a seaport in the Widnes parliamentary division of Lancashire,

England, on the Mersey, 6 m. S.E. of Liverpool. Pop. (1891) 13,444;

(1901) 17,289. The docks, belonging to the London & North Western

railway company, employ most of the working population. There is about a

mile of quayage, with special machinery for the shipping of coal, which

forms the chief article of export.

GARTH, SIR SAMUEL (1661-1719), English physician and poet, was born of a

good Yorkshire family in 1661. He entered Peterhouse, Cambridge, in

1676, graduating B.A. in 1679 and M.A. in 1684. He took his M.D. and

became a member of the College of Physicians in 1691. In 1697 he

delivered the Harveian oration, in which he advocated a scheme dating

from some ten years back for providing dispensaries for the relief of

the sick poor, as a protection against the greed of the apothecaries. In

1699 he published a mock-heroic poem, _The Dispensary_, in six cantos,

which had an instant success, passing through three editions within a

year. In this he ridiculed the apothecaries and their allies among the

physicians. The poem has little interest at the present day, except as a

proof that the heroic couplet was written with smoothness and polish

before the days of Pope. Garth was a member of the Kit-Kat Club, and

became the leading physician of the Whigs, as Radcliffe was of the

Tories. In 1714 he was knighted by George I. and he died on the 18th of

January 1719. He wrote little besides his best-known work _The

Dispensary_ and _Claremont_, a moral epistle in verse. He made a Latin

oration (1700) in praise of Dryden and translated the _Life of Otho_ in

the fifth volume of Dryden's Plutarch. In 1717 he edited a translation

of Ovid's _Metamorphoses_, himself supplying the fourteenth and part of

the fifteenth book.

GARTOK, a trade-market of Tibet, situated on the bank of the Indus on

the road between Shigatse and Leh, to the east of Simla. In accordance

with the Tibet treaty of 1904, Gartok, together with Yatung and Gyantse,

was thrown open to British trade. On the return of the column from Lhasa

in that year Gartok was visited by a party under Captain Ryder, who

found only a few dozen people in winter quarters, their houses being in

the midst of a bare plain. In summer, however, all the trade between

Tibet and Ladakh passes through this place.

GARY, a city of Lake county, Indiana, U.S.A., at the southern end of

Lake Michigan, about 25 m. S.E. of Chicago, Ill. Pop. (1910 census)

16,802. Gary is served by the Baltimore & Ohio, the Lake Shore &

Michigan Southern, the Michigan Central, the Pennsylvania, the Wabash,

and (for freight only) the Chicago, Lake Shore & Eastern, and the

Indiana Harbor Belt railways, and by several steamship lines plying the

Great Lakes. There are about 21 sq. m. within the municipal limits, but

the city lies chiefly within a tract of about 8000 acres composed at the

time of its settlement mainly of sand dunes and swamps intersected from

east to west by the Grand Calumet and the Little Calumet rivers, small

streams respectively about 1 and 3 m. S. of the lake shore. In 1906 the

United States Steel Corporation bought this tract to establish on it a

great industrial community, as direct water connexion with the Lake

Superior ore region was possible, and it was comparatively accessible to

West Virginia coal and Michigan limestone, with unusual railroad

facilities. The Steel Corporation began the actual building of the town

in June 1906, the first step being the installation of an elaborate

system of sewers, and of mains and conduits, for the distribution of

water, gas and electricity. The water-supply is taken from the lake at a

point 2 m. offshore by means of a tunnel. These public utilities the

Steel Corporation controls, and it has built about 500 dwellings, two

hotels, a bank, and its own plant. A small patch of land, now within the

limits of the city, has been from the beginning in the hands of private

owners, but the remainder of the lots (except those already sold) are

owned by the Steel Corporation, and are sold under certain restrictions

intended to prevent real estate speculation, to guarantee bona fide

improvement of the property, and to restrict the sale of intoxicating

drinks. Between the Grand Calumet river (which has been dredged out into

a canal) and the lake lies the plant of the Steel Corporation, covering

about 1200 acres. All the machinery in this great plant is driven by

electricity from generators whose motive power is supplied by the

combustion of gases from the blast furnaces. From the same sources is

also supplied the electricity for lighting the city. The rail mill is

operated by three-phase induction motors of from 2000 to 6000

horse-power capacity. The city was chartered in 1906 and was named in

honour of Elbert Henry Gary (b. 1846), chairman of the board of

directors and chairman of the finance committee of the United States

Steel Corporation.

GAS, a general term for one of the three states of aggregation of

matter; also more specifically applied to coal-gas, the gaseous product

formed in the destructive distillation of coal or other carbonaceous

matter (see below, section _Gas Manufacture_; for gas engines see the

separate heading GAS ENGINE).

_The Gaseous State._--Matter is studied under three physical

phases--solids, liquids and gases, the latter two being sometimes

grouped as "fluids." The study of the physical properties of fluids in

general constitutes the science of hydromechanics, and their

applications in the arts is termed hydraulics; the special science

dealing with the physical properties of gases is named pneumatics.

The gaseous fluid with which we have chiefly to do is our atmosphere.

Though practically invisible, it appeals in its properties to other of

our senses, so that the evidences of its presence are manifold. Thus we

feel it in its motion as wind, and observe the dynamical effects of this

motion in the quiver of the leaf or the motion of a sailing ship. It

offers resistance to the passage of bodies through it, destroying their

motion and transforming their energy--as is betrayed to our hearing in

the whiz of the rifle bullet, to our sight in the flash of the meteor.

The practically obvious distinction between solids and fluids may be

stated in dynamical language thus:--solids can sustain a longitudinal

pressure without being supported by a lateral pressure; fluids cannot.

Hence any region of space enclosed by a rigid boundary can be easily

filled with a fluid, which then takes the form of the bounding surface

at every point of it. But here we distinguish between fluids according

as they are gases or liquids. The gas will always completely fill the

region, however small the quantity put in. Remove any portion and the

remainder will expand so as to fill the whole space again. On the other

hand, it requires a definite quantity of liquid to fill the region.

Remove any portion and a part of the space will be left unoccupied by

liquid. Part of the liquid surface is then otherwise conditioned than by

the form of the wall or bounding surface of the region; and if the

portion of the wall not in contact with the liquid is removed the form

and quantity of the liquid are in no way affected. Hence a liquid can be

kept in an open vessel; a gas cannot so be. To quote the differentia of

Sir Oliver Lodge: "A solid has volume and shape; a liquid has volume,

but no shape; a gas has neither volume nor shape."

It is necessary to distinguish between a gas and a "vapour." The latter

possesses the physical property stated above which distinguishes a gas

from a fluid, but it differs from a gas by being readily condensible to

a liquid, either by lowering the temperature or moderately increasing

the pressure. The study of the effects of pressure and temperature on

many gases led to the introduction of the term "permanent gases" to

denote gases which were apparently not liquefiable. The list included

hydrogen, nitrogen and oxygen; but with improved methods these gases

have been liquefied and even solidified, thus rendering the term

meaningless (see LIQUID GASES). The term "perfect gas" is applied to an

imaginary substance in which there is no frictional retardation of

molecular motion; or, in other words, the time during which any molecule

is influenced by other molecules is infinitesimally small compared with

the time during which it traverses its mean free path. It serves as a

means of research, more particularly in mathematical investigations, the

simple laws thus deduced being subsequently modified by introducing

assumptions in order to co-ordinate actual experiences.

The gaseous state was well known to the ancients; for instance, in Greek

cosmology, "air" ([Greek: pneuma]) was one of the fundamental elements.

The alchemists used such terms as _spiritus_, _flatus_, _halitus_,

_aura_, _emanatio nubila_, &c., words implying a "wind" or "breath." The

word "gas" was invented by J.B. van Helmont in his _Ortus medicinae_,

posthumously published in 1648, in the course of his description of the

gas now known as carbon dioxide. He found that charcoal on burning

yielded a "spirit," which he named _spiritus sylvestris_ on account of

its supposed untamable nature ("Gas sylvestre sive incoercibile, quod in

corpus cogi non potest visibile"); and he invented the word "gas" in the

expression: "... this spirit, hitherto unknown, ... I call by a new name

_gas_" ("hunc spiritum, incognitum hactenus, novo nomine _gas_ voco").

The word was suggested by the Gr. [Greek: chaos], chaos, for he also

writes: "I have called this spirit _gas_, it being scarcely

distinguishable from the Chaos of the ancients" ("halitum illum _Gas_

vocavi, non longe a Chao veterum secretum"). The view that the word was

suggested by the Dutch _geest_, spirit, is consequently erroneous. Until

the end of the 18th century the word "air," qualified by certain

adjectives, was in common use for most of the gases known--a custom due

in considerable measure to the important part which common air played in

chemical and physical investigations.

The study of gases may be divided into two main branches: the physical

and the chemical. The former investigates essentially general

properties, such as the weight and density, the relation between

pressure, volume and temperature (piezometric and thermometric

properties), calorimetric properties, diffusion, viscosity, electrical

and thermal conductivity, &c., and generally properties independent of

composition. These subjects are discussed in the articles DENSITY;

THERMOMETRY; CALORIMETRY; DIFFUSION; CONDUCTION OF HEAT; and

CONDENSATION OF GASES. The latter has for its province the preparation,

collection and identification of gases, and the volume relations in

which they combine; in general it deals with specific properties. The

historical development of the chemistry of gases--pneumatic

chemistry--is treated in the article CHEMISTRY; the technical analysis

of gaseous mixtures is treated below under _Gas Analysis_. Connecting

the experimental study of the physical and chemical properties is the

immense theoretical edifice termed the kinetic theory of gases. This

subject, which is discussed in the article MOLECULE, has for its purpose

(1) the derivation of a physical structure of a gas which will agree

with the experimental observations of the diverse physical properties,

and (2) a correlation of the physical properties and chemical

composition.

_Gas Analysis._--The term "gas analysis" is given to that branch of

analytical chemistry which has for its object the quantitative

determination of the components of a gaseous mixture. The chief

applications are found in the analysis of flue gases (in which much

information is gained as to the completeness and efficiency of

combustion), and of coal gas (where it is necessary to have a product of

a definite composition within certain limits). There are, in addition,

many other branches of chemical technology in which the methods are

employed. In general, volumetric methods are used, i.e. a component is

absorbed by a suitable reagent and the diminution in volume noted, or it

is absorbed in water and the amount determined by titration with a

standard solution. Exact analysis is difficult and tedious, and

consequently the laboratory methods are not employed in technology,

where time is an important factor and moderate accuracy is all that is

necessary. In this article an outline of the technical practice will be

given.

The apparatus consists of (1) a measuring vessel, and (2) a series of

absorption pipettes. A convenient form of measuring vessel is that

devised by W. Hempel. It consists of two vertical tubes provided with

feet and connected at the bottom by flexible rubber tubing. One tube,

called the "measuring tube," is provided with a capillary stopcock at

the top and graduated downwards; the other tube, called the "level

tube," is plain and open. To use the apparatus, the measuring tube is

completely filled with water by pouring water into both tubes, raising

the level tube until water overflows at the stopcock, which is then

turned. The test gas is brought to the stopcock, by means of a fine tube

which has been previously filled with water or in which the air has been

displaced by running the gas through. By opening the stopcock and

lowering the level tube any desired quantity of the gas can be aspirated

over. In cases where a large quantity of gas, i.e. sufficient for

several tests, is to be collected, the measuring tube is replaced by a

large bottle.

[Illustration: (By permission of Messrs Baird & Tatlock.)

FIG. 1.

FIG. 2.]

The volume of the gas in the measuring tube is determined by bringing

the water in both tubes to the same level, and reading the graduation on

the tube, avoiding parallax and the other errors associated with

recording the coincidence of a graduation with a meniscus. The

temperature and atmospheric pressure are simultaneously noted. If the

tests be carried out rapidly, the temperature and pressure may be

assumed to be constant, and any diminution in volume due to the

absorption of a constituent may be readily expressed as a percentage.

If, however, the temperature and pressure vary, the volumes are reduced

to 0 deg. and 760 mm. by means of the formula V0 = V(P-p)/(1 +

.00366t)760, in which V is the observed volume, P the barometric

pressure, p the vapour tension of water at the temperature t of the

experiment. This reduction is facilitated by the use of tables.

Some common forms of absorption pipettes are shown in figs. 1 and 2. The

simpler form consists of two bulbs connected at the bottom by a wide

tube. The lower bulb is provided with a smaller bulb bearing a capillary

through which the gas is led to the apparatus, the higher bulb has a

wider outlet tube. The arrangement is mounted vertically on a stand.

Sometimes the small bulb on the left is omitted. The form of the pipette

varies with the nature of the absorbing material. For solutions which

remain permanent in air the two-bulbed form suffices; in other cases a

composite pipette (fig. 2) is employed, in which the absorbent is

protected by a second pipette containing water. In the case of solid

reagents, e.g. phosphorus, the absorbing bulb has a tubulure at the

bottom. To use a pipette, the absorbing liquid is brought to the outlet

of the capillary by tilting or by squeezing a rubber ball fixed to the

wide end, and the liquid is maintained there by closing with a clip. The

capillary is connected with the measuring tube by a fine tube previously

filled with water. The clip is removed, the stopcock opened, and the

level tube of the measuring apparatus raised, so that the gas passes

into the first bulb. There it is allowed to remain, the pipette being

shaken from time to time. It is then run back into the measuring tube by

lowering the level tube, the stopcock is closed, and the volume noted.

The operation is repeated until there is no further absorption.

The choice of absorbents and the order in which the gases are to be

estimated is strictly limited. Confining ourselves to cases where

titration methods are not employed, the general order is as follows:

carbon dioxide, olefines, oxygen, carbon monoxide, hydrogen, methane and

nitrogen (by difference). This scheme is particularly applicable to

coal-gas. Carbon dioxide is absorbed by a potash solution containing one

part of potash to between two and three of water; the stronger solution

absorbs about 40 volumes of the gas. The olefines--ethylene, &c.--are

generally absorbed by a very strong sulphuric acid prepared by adding

sulphur trioxide to sulphuric acid to form a mixture which solidifies

when slightly cooled. Bromine water is also employed. Oxygen is absorbed

by stick phosphorus contained in a tubulated pipette filled with water.

The temperature must be above 18 deg.; and the absorption is prevented by

ammonia, olefines, alcohol, and some other substances. An alkaline

solution of pyrogallol is also used; this solution rapidly absorbs

oxygen, becoming black in colour, and it is necessary to prepare the

solution immediately before use. Carbon monoxide is absorbed by a

solution of cuprous chloride in hydrochloric acid or, better, in

ammonia. When small in amount, it is better to estimate as carbon

dioxide by burning with oxygen and absorbing in potash; when large in

amount, the bulk is absorbed in ammoniacal cuprous chloride and the

residue burned. Hydrogen may be estimated by absorption by heated

palladium contained in a capillary through which the gas is passed, or

by exploding (under reduced pressure) with an excess of oxygen, and

measuring the diminution in volume, two-thirds of which is the volume of

hydrogen. The explosion method is unsatisfactory when the gas is

contained over water, and is improved by using mercury. Methane cannot

be burnt in this way even when there is much hydrogen present, and

several other methods have been proposed, such as mixing with air and

aspirating over copper oxide heated to redness, or mixing with oxygen

and burning in a platinum tube heated to redness, the carbon dioxide

formed being estimated by absorption in potash. Gases soluble in water,

such as ammonia, hydrochloric acid, sulphuretted hydrogen, sulphur

dioxide, &c., are estimated by passing a known volume of the gas through

water and titrating the solution with a standard solution. Many types of

absorption vessel are in use, and the standard solutions are generally

such that 1 c.c. of the solution corresponds to 1 c.c. of the gas under

normal conditions.

[Illustration: (By permission of Messrs Baird & Tatlock.)

FIG. 3.]

Many forms of composite gas-apparatus are in use. One of the commonest

is the Orsat shown in fig. 3. The gas is measured in the graduated

cylinder on the right, which is surrounded by a water jacket and

provided with a levelling bottle. At the top it is connected by a

capillary tube bent at right angles to a series of absorbing vessels,

the connexion being effected by stopcocks. These vessels consist of two

vertical cylinders joined at the bottom by a short tube. The cylinder in

direct communication with the capillary is filled with glass tubes so as

to expose a larger surface of the absorbing solution to the gas. The

other cylinder is open to the air and serves to hold the liquid ejected

from the absorbing cylinder. Any number of bulbs can be attached to the

horizontal capillary; in the form illustrated there are four, the last

being a hydrogen pipette in which the palladium is heated in a

horizontal tube by a spirit lamp. At the end of the horizontal tube

there is a three-way cock connecting with the air or an aspirator. To

use the apparatus, the measuring tube is completely filled with water by

raising the levelling bottle. The absorbing vessels are then about half

filled with the absorbents, and, by opening the cocks and aspirating,

the liquid is brought so as completely to fill the bulbs nearer the

capillary. The cocks are then closed. By opening the three-way cock to

the supply of the test gas and lowering the levelling bottle, any

desired amount can be drawn into the measuring tube. The absorption is

effected by opening the cock of an absorbing vessel and raising the

levelling bottle. The same order of absorption and general directions

pertaining to the use of Hempel pipettes have to be adopted.

Although the earliest attempts at gas analysis were made by Scheele,

Priestley, Cavendish, Lavoisier, Dalton, Gay-Lussac and others, the

methods were first systematized by R. Bunsen, who began his researches

in 1838. He embodied his results in his classical _Gasometrische

Methoden_ (1857, second edition 1877), a work translated into English

by H. Roscoe. Clemens Winkler contributed two works, _Anleitung zur

chemischen Untersuchung der Industriegase_ (1876-1877) and _Lehrbuch

der technischen Gasanalyse_ (2nd ed., 1892), both of which are very

valuable for the commercial applications of the methods. W. Hempel's

researches are given in his _Neue Methode zur Analyse der Gase_ (1880)

and _Gasanalytische Methoden_ (1890, 3rd ed. 1900).

GAS MANUFACTURE

Historical.

1. _Illuminating Gas._--The first practical application of gas distilled

from coal as an illuminating agent is generally ascribed to William

Murdoch, who between the years of 1792 and 1802 demonstrated the

possibility of making gas from coal and using it as a lighting agent on

a large scale. Prior to 1691, however, Dr John Clayton, dean of Kildare,

filled bladders with inflammable gas obtained by the distillation of

coal, and showed that on pricking the bladders and applying a light to

the escaping gas it burnt with a luminous flame, and in 1726 Stephen

Hales published the fact that by the distillation of 158 grains of

Newcastle coal, 180 cub. in. of inflammable air would be obtained. Jean

Pierre Minckelers, professor of natural philosophy in the university of

Louvain, and later of chemistry and physics at Maestricht, made

experiments on distilling gas from coal with the view of obtaining a

permanent gas sufficiently light for filling balloons, and in 1785

experimentally lighted his lecture room with gas so obtained as a

demonstration to his students, but no commercial application was made of

the fact. Lord Dundonald, in 1787, whilst distilling coal for the

production of tar and oil, noticed the formation of inflammable gas, and

even used it for lighting the hall of Culross Abbey. It is clear from

these facts that, prior to Murdoch's experiments, it was known that

illuminating gas could be obtained by the destructive distillation of

coal, but the experiments which he began at Redruth in 1792, and which

culminated in the lighting of Messrs Boulton, Watt & Co.'s engine works

at Soho, near Birmingham, in 1802, undoubtedly demonstrated the

practical possibility of making the gas on a large scale, and burning it

in such a way as to make coal-gas the most important of the artificial

illuminants. An impression exists in Cornwall, where Murdoch's early

experiments were made, that it was a millwright named Hornblower who

first suggested the process of making gas to Murdoch, but, as has been

shown, the fact that illuminating gas could be obtained from coal by

distillation was known a century before Murdoch made his experiments,

and the most that can be claimed for him is that he made the first

successful application of it on a practical scale.

In 1799 a Frenchman named Philippe Lebon took out a patent in Paris for

making an illuminating gas from wood, and gave an exhibition of it in

1802, which excited a considerable amount of attention on the European

continent. It was seen by a German, F.A. Winsor, who made Lebon an offer

for his secret process for Germany. This offer was, however, declined,

and Winsor returned to Frankfort determined to find out how the gas

could be made. Having quickly succeeded in discovering this, he in 1803

exhibited before the reigning duke of Brunswick a series of experiments

with lighting gas made from wood and from coal. Looking upon London as a

promising field for enterprise, he came over to England, and at the

commencement of 1804 took the Lyceum theatre, where he gave

demonstrations of his process. He then proceeded to float a company,

and in 1807 the first public street gas lighting took place in Pall

Mall, whilst in 1809 he applied to parliament to incorporate the

National Heat and Light Company with a capital of half a million

sterling. This application was opposed by Murdoch on the ground of his

priority in invention, and the bill was thrown out, but coming to

parliament for a second time in 1810, Winsor succeeded in getting it

passed in a very much curtailed form, and, a charter being granted later

in 1812, the company was called the Chartered Gas Light and Coke

Company, and was the direct forerunner of the present London Gas Light

and Coke Company. During this period Frederick C. Accum (1769-1838), Dr

W. Henry and S. Clegg did so much by their writings and by the

improvements they introduced in the manufacture, distribution and

burning of coal gas, that their names have become inseparably connected

with the subject.

The growth of gas lighting.

In 1813 Westminster Bridge, and in the following year the streets of

Westminster, were lighted with gas, and in 1816 it became common in

London. After this so rapid was the progress of this new mode of

illumination that in the course of a few years it was adopted by all the

principal towns in the United Kingdom for lighting streets as well as

shops and public edifices. In private houses it found its way more

slowly, partly from an apprehension of danger attending its use, and

partly from the discomfort which was experienced in many cases through

the gas being distributed without purification, and to the careless and

imperfect manner in which the service pipes were first fitted. It was

during the last four decades of the 19th century that the greatest

advance was made, this period having been marked not only by many

improvements in the manufacture of illuminating gas, but by a complete

revolution in the methods of utilizing it for the production of light.

In 1875 the London Argand, giving a duty of 3.2 candles illuminating

power per cubic foot of ordinary 16 candle gas, was looked upon as the

most perfect burner of the day, and little hope was entertained that any

burner capable of universal adoption would surpass it in its power of

developing light from the combustion of coal gas; but the close of the

century found the incandescent mantle and the atmospheric burner

yielding six times the light that was given by the Argand for the

consumption of an equal volume of gas, and to-day, by supplying gas at

an increased pressure, a light of ten times the power may be obtained.

Since the advent of the incandescent mantle, the efficiency of which is

dependent upon the heating power of the gas more than on its

illuminating power, the manufacture of coal gas has undergone

considerable modifications.

Coals used for gas-making.

Coal, the raw material from which the gas is produced by a process of

destructive distillation, varies very widely in composition (see

COAL), and it is only the class of coals rich in hydrogen, known as

bituminous coal, that can with advantage be utilized in gas

manufacture. Coals of this character are obtained in England from the

Newcastle and Durham field, South Yorkshire, Derbyshire and Barnsley

districts, and an idea of their ultimate composition may be derived

from the following table:--

+--------------------------+-------+------+--------+------+-------+------+------+

| | | gen. | | gen. | | | ure. |

+--------------------------+-------+------+--------+------+-------+------+------+

| Newcastle gas coal | 82.16 | 4.83 | 1.00 | 1.23 | 6.82 | 3.20 | 0.76 |

| Durham gas coal | 84.34 | 5.30 | 0.73 | 1.73 | 4.29 | 2.42 | 1.14 |

| South Yorkshire silkstone| 80.46 | 5.09 | 1.66 | 1.67 | 6.79 | 3.30 | 1.03 |

| Derbyshire silkstone | 76.96 | 5.04 | 2.39 | 1.77 | 6.92 | 3.28 | 3.64 |

| Barnsley gas coal | 75.64 | 4.94 | 2.84 | 1.65 | 7.25 | 4.28 | 3.40 |

+--------------------------+-------+------+--------+------+-------+------+------+

Our knowledge of the composition of coal is limited to the total

amount of carbon, hydrogen, nitrogen, oxygen and foreign materials

which it contains; and at present we know practically but little of

the way in which these bodies are combined. This being so, the

ordinary analysis of a coal affords but little indication of its value

for gas-making purposes, which can only be really satisfactorily

arrived at by extended use on a practical scale. Bituminous coal,

however, may be looked upon as containing carbon and also simple

hydrocarbons, such as some of the higher members of the paraffin

series, and likewise organic bodies containing carbon, hydrogen,

nitrogen, oxygen and sulphur.

Destructive distillation of coal.

On submitting a complex substance of this character to destructive

distillation, it will be found that the yield and quality of the

products will vary very considerably with the temperature existing in

the retorts, with the size of the charge of coal used, with its

distribution in the retort, with the length of time the distillation

has been going on, and with an infinity of other factors of a more or

less complex nature. If bituminous coal is distilled at a low

temperature, the tar is found to contain considerable quantities of

light paraffin oils; and there is no doubt that paraffin hydrocarbons

are present in the original coal. These paraffins, under the influence

of heat, split up into simpler members of the same series and into

olefines; and if we imagine the action in its simplest form, we should

have the gases, as they were evolved, consisting of (say) ethane and

ethylene. These have now to pass down the heated retort on their way

to the ascension pipe, and the contact with the heated sides of the

retort, and the baking from the radiant heat in the retort, set up an

infinity of changes. Ethane, when heated to this degree, splits up

into ethylene and hydrogen, whilst ethylene decomposes to methane and

acetylene, and the acetylene at once polymerizes to benzene,

styrolene, retene, &c. A portion also condenses, and at the same time

loses some hydrogen, becoming naphthalene; and the compounds so formed

by interactions amongst themselves build up the remainder of the

hydrocarbons present in the coal tar, whilst the organic substances

containing oxygen in the coal break down, and cause the formation of

the phenols in the tar.

There is very little doubt that the general course of the

decompositions follows these lines; but any such simple explanation of

the actions taking place is rendered impossible by the fact that,

instead of the breaking-down of the hydrocarbons being completed in

the coal, and only secondary reactions taking place in the retort, in

practice the hydrocarbons to a great extent leave the coal as the

vapours of condensible hydrocarbons, and the breaking down of these to

such simple gaseous compounds as ethylene is proceeding in the retort

at the same time as the breaking up of the ethylene already formed

into acetylene and methane, and the polymerization of the former into

higher compounds. Starting with a solid hydrocarbon of definite

composition, it would be theoretically possible to decompose it

entirely into carbon, hydrogen, ethylene and methane, and, by rapidly

removing these from the heating zone before any secondary actions took

place, to prevent formation of tar. But any such ideal is hopeless in

practice, as the coal is not a definite compound, and it is impossible

to subject it to a fixed temperature.

Effect of temperature in the retort.

If the retorts are at a temperature of 1000 deg. C. when the charge of

coal is put in, the temperature of the distillation will vary from

about 800 deg. C. close to the walls, to about 400 deg. C. in the

centre of the coal; and in the same way, in the space above the coal,

the products which come in contact with the sides of the retort are

heated to 1000 deg. C., whilst the gas near the coal is probably

heated to only 600 deg. C. Moreover, the gases and vapours in the

retort are subjected to a period of heating which varies widely with

the distance from the mouth of the retort of the coal that is

undergoing carbonization. The gas developed by the coal near the mouth

of the retort is quickly washed out into the ascension pipe by the

push of the gas behind, and the period for which it has been exposed

to the radiant heat from the walls of the retort is practically nil;

whilst the gas evolved in the portion of the retort farthest from the

mouthpiece has only its own rate of evolution to drive it forward, and

has to traverse the longest run possible in the retort, exposed during

the whole of that period to radiant heat and to contact with the

highly heated surface of the retort itself. Hence we find that the tar

is formed of two distinct sets of products, the first due to

incomplete decomposition and the second to secondary reactions due to

the products of the decomposition being kept too long in the zone of

heat.

Of the first class, the light paraffin oils and pitch may be taken as

examples; whilst benzene, naphthalene and retort carbon represent the

second. The formation of the second class of bodies is a great loss to

the gas manufacturer, as, with the exception of the trace of benzene

carried with the gas as vapour, these products are not only useless in

the gas, but one of them, naphthalene, is a serious trouble, because

any trace carried forward by the gas condenses with sudden changes of

temperature, and causes obstructions in the service pipes, whilst

their presence in the tar means the loss of a very large proportion of

the illuminating constituents of the gas. Moreover, these secondary

products cannot be successfully reduced, by further heating, to

simpler hydrocarbons of any high illuminating value, and such bodies

as naphthalene and anthracene have so great a stability that, when

once formed, they resist any efforts again to decompose them by heat,

short of the temperature which breaks them up into methane, carbon and

hydrogen.

The ammonia is derived from the nitrogen present in the coal combining

with hydrogen during destructive distillation, the nitrogen becoming

distributed amongst all three classes of products. The following table

will give an approximate idea of the proportions which go to each:--

Per cent.

Nitrogen as ammonia 14.50

" as cyanogen 1.56

" free in gas and combined in tar 35.26

" remaining in coke 48.68

------

100.00

The effect produced by alteration in the temperature of the retort

upon the composition of both gas and tar is very marked. As the

temperature is raised, the yield of gas from a given weight of coal

increases; but with the increase of volume there is a marked decrease

in the illuminating value of the gas evolved. Lewis T. Wright found,

in a series of experiments, that, when four portions of the same coal

were distilled at temperatures ranging from a dull red heat to the

highest temperature attainable in an iron retort, he obtained the

following results as to yield and illuminating power:--

+-----------------+-------------+------------+---------+

+-----------------+-------------+------------+---------+

| 1. Dull red | 8,250 | 20.5 | 33.950 |

| 2. Hotter | 9,693 | 17.8 | 34.510 |

| 3. " | 10,821 | 16.7 | 36.140 |

| 4. Bright orange| 12,006 | 15.6 | 37.460 |

+-----------------+-------------+------------+---------+

_Composition of the Gas._

+-----------------+-----------+-----------+-----------+

| | 1. | 2. | 4. |

+-----------------+-----------+-----------+-----------+

| Hydrogen | 38.09 | 43.77 | 48.02 |

| Marsh gas | 42.72 | 34.50 | 30.70 |

| Olefines | 7.55 | 5.83 | 4.51 |

| Carbon monoxide | 8.72 | 12.50 | 13.96 |

| Nitrogen | 2.92 | 3.40 | 2.81 |

| +-----------+-----------+-----------+

| | 100.00 | 100.00 | 100.00 |

+-----------------+-----------+-----------+-----------+

The gas analysis of No. 3 was lost, but the illuminating power shows

that it was intermediate in composition between Nos. 2 and 4. From

this it will be seen that, with the increase of temperature, the

hydrocarbons--the olefines and marsh gas series--gradually break up,

depositing carbon in the crown of the retort, and liberating hydrogen,

the percentage of which steadily increases with the rise of

temperature.

The tar formed is affected to an even greater extent than the gas by

alterations in the temperature at which the destructive distillation

takes place. The lower the temperature, the smaller will be the volume

of gas produced, and the lighter the specific gravity of the tar,

whilst with increase of temperature, the volume of gas rapidly rises,

and so does the specific gravity of the tar. Working with a caking

coal Wright obtained the following results:--

+--------------+------------------+

| Yield of Gas | Specific Gravity |

| per ton, | of Tar. |

| Cub. ft. | |

+--------------+------------------+

| 6,600 | 1.086 |

| 7,200 | 1.120 |

| 8,900 | 1.140 |

| 10,162 | 1.154 |

| 11,700 | 1.206 |

+--------------+------------------+

Analysis of the tar showed that the increase of the specific gravity

was due to the increase in the quantity of pitch, which rose from

28.89 to 64.08% in the residuals; whilst the ammonia, naphtha and

light oils steadily fell in quantity, the creosote and anthracene oils

doing the same, but to a smaller extent. Naphthalene also begins to

show in quantity in the tar as soon as the yield of gas reaches 10,000

cub. ft. per ton of coal carbonized.

In spite of these variations, however, the products in their main

characteristics will remain the same. They may be divided into--(a)

Solids, such as the coke and retort carbon; (b) liquids, consisting of

the tar and ammoniacal liquor; and (c) gases, consisting of the

unpurified coal gas. The proportions in which the products are

approximately obtained from a ton of gas coal have been given as

follows:--

10,000 cub. ft. of gas = 380 lb. = 17.0 per cent.

10 gallons of tar = 115 " = 5.1 "

Gas liquor[1] = 177 " = 7.9 "

Coke = 1568 " = 70.0 "

---- -----

2240 100.0

Solid products.

The chief solid residue, coke, is not absolutely pure carbon, as it

contains the mineral non-volatile constituents which remain behind as

ash when the original coal is burnt, and which, to a great extent,

existed in the sap that filled the cells of the plant from which the

coal was formed. The retort carbon formed as a dense deposit on the

crown of the retort by the action of the high temperature on the

hydrocarbons is, however, carbon in a very pure form, and, on account

of its density, is largely used for electrical purposes.

Liquid products.

The liquid products of the destructive distillation of coal are tar

and ammoniacal liquor. Tar derived from ordinary bituminous coal is a

black, somewhat viscid liquid, varying in specific gravity from 1.1 to

1.2. The ultimate composition of tar made in the London Gas Works is

approximately as follows:--

Carbon 77.53

Hydrogen 6.33

Nitrogen 1.03

Sulphur 0.61

Oxygen 14.50

------

100.00

These elements in tar are built up into an enormous number of

compounds (see COAL TAR), and its value as a by-product may be

gathered from the fact that on fractional distillation it yields--(1)

benzene and its homologues, from which aniline, the source of most of

the coal-tar colours, can be derived; (2) carbolic acid, from which

picric acid, used as a dye, a powerful explosive, and to give the

bitter flavour to some kinds of beer, is made, also many most valuable

disinfectants; (3) naphthalene, used for disinfecting, and also as the

"Albo-carbon" employed in an enriching burner for gas; (4) pitch,

extensively used in path-making, from which such bodies as anthracene

and saccharin can be extracted.

The second liquid product of the destructive distillation of coal is

the ammoniacal or gas liquor, which consists of water containing

ammonia salts in solution, partly condensed from the hot gas, and

partly added to wash the gas in the scrubbers. It contains, as its

principal constituents, ammonia, partly combined with carbonic acid

and sulphuretted hydrogen to form compounds which are decomposed on

boiling, with evolution of ammonia gas, and partly combined with

stronger acids to form compounds which require to be acted upon by a

strong alkali before the ammonia contained in them can be liberated.

The ammonia in the first class of compounds is technically spoken of

as "free"; that present in the latter as "fixed." The following

analysis by L.T. Wright will give an idea of the relative quantities

in which these compounds exist in the liquor:--

Grammes per litre.

/ Ammonium sulphide 3.03

Free < Ammonium carbonate 39.16

\ Ammonium chloride 14.23

/ Ammonium thiocyanate 1.80

Fixed < Ammonium sulphate 0.19

| Ammonium thiosulphate 2.80

\ Ammonium ferrocyanide 0.41

From a scientific point of view, the term "free" is absolutely

incorrect, and in using it the fact must be clearly borne in mind that

in this case it merely stands for ammonia, which can be liberated on

simply boiling the liquor.

Gaseous products.

The gas which is obtained by the destructive distillation of coal, and

which we employ as our chief illuminant, is not a definite compound,

but a mechanical mixture of several gases, some of which are reduced

to the lowest limit, in order to develop as fully as possible the

light-giving properties of the most important constituents of the gas.

The following analysis gives a fair idea of the composition of an

average sample of gas made from coal, purified but without

enrichment:--

Hydrogen 52.22

Unsaturated hydrocarbons 3.47

Saturated hydrocarbons 34.76

Carbon monoxide 4.23

Carbon dioxide 0.60

Nitrogen 4.23

Oxygen 0.49

------

100.00

These constituents may be divided into--(a) light-yielding

hydrocarbons, (b) combustible diluents and (c) impurities. The

hydrocarbons, upon which the luminosity of the flame entirely depends,

are divided in the analysis into two groups, saturated and

unsaturated, according to their behaviour with a solution of bromine

in potassium bromide, which has the power of absorbing those termed

"unsaturated," but does not affect in diffused daylight the gaseous

members of the "saturated" series of hydrocarbons. They may be

separated in a similar way by concentrated sulphuric acid, which has

the same absorbent effect on the one class, and not on the other. The

chief unsaturated hydrocarbons present in coal gas are: ethylene,

C2H4, butylene, C4H8, acetylene, C2H2, benzene, C6H6, and naphthalene,

C10H8, and the saturated hydrocarbons consist chiefly of methane, CH4,

and ethane, C2H6.

The light-giving power of coal gas is undoubtedly entirely due to the

hydrocarbons. The idea held up to about 1890 was that the illuminating

value depended upon the amount of ethylene present. This, however, is

manifestly incorrect, as, if it were true, 4% of ethylene mixed with

96% of a combustible diluent such as hydrogen should give 16- to

17-candle gas, whereas a mixture of 10% of ethylene and 90% of

hydrogen is devoid of luminosity. In 1876 M.P.E. Berthelot came to

the conclusion that the illuminating value of the Paris coal gas was

almost entirely due to benzene vapour. But here again another mistaken

idea arose, owing to a faulty method of estimating the benzene, and

there is no doubt that methane is one of the most important of the

hydrocarbons present, when the gas is burnt in such a way as to evolve

from it the proper illuminating power, whilst the benzene vapour,

small as the quantity is, comes next in importance and the ethylene

last. It is the combined action of the hydrocarbons which gives the

effect, not any one of them acting alone.

The series of operations connected with the manufacture and

distribution of coal gas embraces the processes of distillation,

condensation, exhaustion, wet purification by washing and scrubbing,

dry purification, measuring, storing and distribution to the mains

whence the consumer's supply is drawn.

[Illustration: FIG. 4.--Plan of Works.]

Site of gas works.

The choice of a site for a gas works is necessarily governed by local

circumstances; but it is a necessity that there should be a ready

means of transport available, and for this reason the works should be

built upon the banks of a navigable river or canal, and should have a

convenient railway siding. By this means coal may be delivered direct

to the store or retort-house, and in the same way residual products

may be removed. The fact that considerable area is required and that

the works do not improve the neighbourhood are important conditions,

and although economy of space should be considered, arrangements

should be such as to allow of extension. In the case of a works whose

daily make of gas exceeds four to five million cub. ft., it is usual

to divide the works into units, there being an efficiency limit to the

size of apparatus employed. Under these conditions the gas is dealt

with in separate streams, which mix when the holder is reached. From

the accompanying ground plan of a works (fig. 4) it will be possible

to gain an idea of the order in which the operations in gas

manufacture are carried out and the arrangement of the plant.

[Illustration: FIG. 5.--Cross Section of Retorts.]

Retorts.

The retorts in which the coal is carbonized are almost universally

made of fire-clay, and in all but small country works the old

single-ended retort, which was about 9 ft. in length, has given way to

a more economical construction known as doubles, double-ended, or

"through" retorts. These are from 18 to 22 ft. long, and as it is

found inconvenient to produce this length in one piece, they are

manufactured in three sections, the jointing together of which demands

great care. The two outer pieces are swelled at one end to take an

iron mouthpiece. The cross sections generally employed for retorts are

known as "D-shaped," "oval" and "round" (fig. 5). The "D" form is

mostly adopted owing to its power of retaining its shape after long

exposure to heat, and the large amount of heating surface it presents

at its base. The life of this retort is about thirty working months. A

cast iron mouthpiece and lid is bolted to the exterior end of each

retort, the mouthpiece carrying a socket end to receive the ascension

pipe, through which the gas passes on leaving the retort. The retorts

are heated externally and are set in an arch, the construction

depending upon the number of retorts, which varies from three to

twelve. The arch and its retorts is termed a bed or setting, and a row

of beds constitutes a bench. It is usual to have a separate furnace

for each setting, the retorts resting upon walls built transversely in

the furnace.

The heating of the retorts is carried out either by the "direct

firing" or by the "regenerative" system, the latter affording marked

advantages over the former method, which is now becoming extinct. In

the regenerative system of firing, a mixture of carbon monoxide and

nitrogen is produced by passing air through incandescent gas coke in a

generator placed below the bench of retorts, and the heating value of

the gases so produced is increased in most cases by the admixture of a

small proportion of steam with the primary air supply, the steam being

decomposed by contact with the red-hot coke in the generator into

water gas, a mixture of carbon monoxide and hydrogen (see FUEL:

_Gaseous_). The gases so formed vary in proportion with the

temperature of the generator and the amount of steam, but generally

contain 32 to 38% of combustible gas, the remainder being the residual

nitrogen of the air and carbon dioxide. These gases enter the

combustion chamber around the retorts at a high temperature, and are

there supplied with sufficient air to complete their combustion, this

secondary air supply being heated by the hot products of combustion on

their way to the exit flue. This method of firing results in the

saving of about one-third the weight of coke used in the old form of

furnace per ton of coal carbonized, and enables higher temperatures to

be obtained, the heat being also more equally distributed.

[Illustration: FIG. 6.--Regenerative Setting.]

There are a great number of methods of applying the regenerative

principle which vary only in detail. Fig. 6 gives an idea of the

general arrangement. The furnace A is built of fire-brick, coke is

charged at the top through the iron door B, and near the bottom are

placed fire bars C, upon which the fuel lies. The primary air

necessary for the partial combustion of the coke to "producer" gas

enters between these bars. The gases are conducted from the furnace to

the combustion chamber E through the nostrils D D, and the secondary

air is admitted at the inlet F a little above, this air having been

already heated by traversing the setting. Complete combustion takes

place at this point with the production of intense heat, the gases on

rising are baffled in order to circulate them in every direction round

the retorts, and upon arriving at the top of the setting they are

conducted down a hollow chamber communicating with the main flue and

shaft. The amount of draft which is necessary to carry out the

circulation of the gases and to draw in the adequate amount of air is

regulated by dampers placed in the main flue. By analysis of the

"producer" and "spent" gases this amount can be readily gauged.

Retorts are set in either the horizontal, inclined or vertical

position, and the advantages of the one over the other is a question

upon which almost every gas engineer has his own views.

Charging and drawing.

The introduction of labour-saving appliances into gas works has

rendered the difficult work of charging and discharging horizontal

retorts comparatively simple. Formerly it was the practice to carry

out such operations entirely by hand, men charging the retorts either

by means of shovel or hand-scoop, and the coke produced being

withdrawn with hand rakes. Now, however, only the smaller gas works

adhere to this system, and this work is done by machinery driven by

either compressed air, hydraulic or electric power. In the first two

cases a scoop, filled with coal from an overhead hopper carried by the

travelling machine, is made to enter the retort and is turned over;

the operation is then repeated, but this time the scoop is turned over

in the opposite direction, the coal thus assuming such a position that

as much of its under surface as possible is exposed to the heated side

of the retort. With "through" retorts charging machines feed the

retorts at both ends, the scoop, which has a capacity of about 1-1/2

cwt., entering and discharging its contents twice at each end, so that

the total charge is about 6 cwt., which is allowed from four to six

hours to distil off according to the quality of the gas required. The

machines charge simultaneously at each end, so that the lids of the

retorts may be shut immediately the coal enters. The charging machines

travel on lines in front of the retort bench, and the power is

transmitted by connexions made with flexible hose. A device of more

recent introduction is an electrically-driven charging machine, in

which the centrifugal force created by a fly-wheel revolving at high

speed is applied to drive coal into the retort. If the velocity is

sufficiently high the coal may be carried the whole length of a 20-ft.

retort, the coal following banking up until an even layer is formed

throughout the length of the retort.

For the purpose of discharging the coke from the retort either

compressed air or hydraulic machinery is employed, a rake being made

to enter the retort and withdraw the coke on returning. With this

method it is necessary that the rake should enter and discharge

several times before the retort is clear, and thus the use of a

telescopic ram worked by hydraulic power, which pushes the coke before

it and discharges it at the other end, is an advantage. As much as

one-third on each ton of coal carbonized is saved by the use of

machinery in the retort-house. Taking into account the original cost

of such machines, and the unavoidable wear and tear upon the retorts

brought about by using labour-saving appliances, and the fact that the

coke-dust is very detrimental to the machinery, it is clear that the

suggestion of setting the retorts at an incline in order to facilitate

the work presented great inducements to the gas manager. The object

aimed at in thus setting retorts is to allow gravity to play the part

of charging and discharging the coal and coke, the retorts being

inclined at an angle to suit the slip of the class of coal used; this

angle is between 28 deg. and 34 deg. The coal, previously elevated to

hoppers, is dropped into the feeding chambers, which are so arranged

that they can travel from end to end of the retort-house and feed the

coal into the retorts. When the retort is to be charged, an iron stop

or barrier is placed in the lower mouthpiece, and the door closed. The

shoot is placed in the upper mouthpiece, and the stop or door, which

retains the coal in the chamber, is released; the coal is then

discharged into the retort, and rushing down the incline, is arrested

by the barrier, and banks up, forming a continuous backing to the coal

following. By experience with the class of coal used and the

adjustment of the stops in the shoot, the charge can be run into the

retort to form an even layer of any desired depth. For the withdrawal

of the residual coke at the end of the carbonization, the lower

mouthpiece door is opened, the barrier removed and the coke in the

lower part of the retort is "tickled" or gently stirred with an iron

rod to overcome a slight adhesion to the retort; the entire mass then

readily discharges itself. Guides are placed in front of the retort to

direct its course to the coke hoppers or conveyer below, and to

prevent scattering of the hot material. This system shows a greater

economy in the cost of carbonizing the coal, but the large outlay and

the wear and tear of the mechanical appliances involved have so far

prevented its very general adoption.

The vertical retort was one of the first forms experimented with by

Murdoch, but owing to the difficulty of withdrawing the coke, the low

illuminating power of the gas made in it, and the damage to the retort

itself, due to the swelling of the charge during distillation, it was

quickly abandoned. About the beginning of the 20th century, however,

the experiments of Messrs Settle and Padfield at Exeter, Messrs

Woodall and Duckham at Bournemouth, and Dr Bueb in Germany showed such

encouraging results that the idea of the vertical retort again came to

the front, and several systems were proposed and tried. The cause of

the failure of Murdoch's original vertical retort was undoubtedly that

it was completely filled with coal during charging, with the result

that the gas liberated from the lower portions of the retort had to

pass through a deep bed of red-hot coke, which, by over-baking the

gas, destroyed the illuminating hydrocarbons. There is no doubt that

the question of rapidly removing the gas, as soon as it is properly

formed, from the influence of the highly-heated walls of the retort

and residual coke, is one of the most important in gas manufacture.

In the case of horizontal retorts the space between the top of the

coal and the retort is of necessity considerable in order to permit

the introduction of the scoop and rake; the gas has therefore a free

channel to travel along, but has too much contact with the highly

heated surface of the retort before it leaves the mouthpiece. In the

case of inclined retorts this disadvantage is somewhat reduced, but

with vertical retorts the ideal conditions can be more nearly

approached. The heating as well as the illuminating value of the gas

per unit volume is lowered by over-baking, and Dr Bueb gives the

following figures as to the heating value of gas obtained from the

same coal but by different methods of carbonization:--

Vertical Retorts, 604 British thermal units per cub. ft.

Inclined " 584 " " "

Horizontal " 570 " " "

Of the existing forms of vertical retort it remains a matter to be

decided whether the coal should be charged in bulk to the retort or

whether it should be introduced in small quantities at regular and

short intervals; by this latter means (the characteristic feature of

the Settle-Padfield process) a continuous layer of coal is in process

of carbonization on the top, whilst the gas escapes without contact

with the mass of red-hot coke, a considerable increase in volume and

value in the gas and a much denser coke being the result.

Hydraulic main.

From the retort the gas passes by the ascension pipe to the hydraulic

main (fig. 7). This is a long reservoir placed in a horizontal

position and supported by columns upon the top of the retort stack,

and through it is maintained a slow but constant flow of water, the

level of which is kept uniform. The ascension pipe dips about 2 in.

into the liquid, and so makes a seal that allows of any retort being

charged singly without the risk of the gas produced from the other

retorts in the bench escaping through the open retort. Coal gas,

being a mixture of gases and vapours of liquids having very varying

boiling points, must necessarily undergo physical changes when the

temperature is lowered. Vapours of liquids of high boiling point will

be condensed more quickly than those having lower boiling points, but

condensation of each vapour will take place in a definite ratio with

the decrease of temperature, the rate being dependent upon the boiling

point of the liquid from which it is formed. The result is that from

the time the gaseous mixture leaves the retort it begins to deposit

condensation products owing to the decrease in temperature.

Condensation takes place in the ascension pipe, in the arch piece

leading to the hydraulic main, and to a still greater extent in the

hydraulic main itself where the gas has to pass through water.

[Illustration: FIG. 7.--Hydraulic Main.]

Ascension pipes give trouble unless they are frequently cleared by an

instrument called an "auger," whilst the arch pipe is fitted with hand

holes through which it may be easily cleared in case of stoppage. The

most soluble of the constituents of crude coal gas is ammonia, 780

volumes of which are soluble in one volume of water at normal

temperature and pressure, and the water in the hydraulic main absorbs

a considerable quantity of this compound from the gas and helps to

form the ammoniacal liquor, whilst, although the liquor is well

agitated by the gas bubbling through it, a partial separation of tar

from liquor is effected by gravitation. The liquor is run off at a

constant rate from the hydraulic main to the store tank, and the gas

passes from the top of the hydraulic main to the foul main.

Condensation.

The gas as it leaves the hydraulic main is still at a temperature of

from 130 deg. to 150 deg. F., and should now be reduced as nearly as

possible to the temperature of the surrounding atmosphere. The

operation of efficient condensing is not by any means as simple as

might be supposed. The tar and liquor when condensed have a dissolving

action on various valuable light-giving constituents of the gas, which

in the ordinary way would not be deposited by the lowering of

temperature, and for this reason the heavy tar, and especially that

produced in the hydraulic main, should come in contact with the gas as

little as possible, and condensation should take place slowly.

The main difficulty which the condenser ought to overcome and upon

which its efficiency should depend is the removal of naphthalene: this

compound, which is present in the gas, condenses on cooling to a solid

which crystallizes out in the form of white flakes, and the trouble

caused by pipe stoppages in the works as well as in the district

supplied is very considerable. The higher the heat of carbonization

the more naphthalene appears to be produced, and gas managers of

to-day find the removal of naphthalene from the gas a difficult

problem to solve. It was for some time debated as to whether

naphthalene added materially to the illuminating value of the gas, and

whether an endeavour should be made to carry it to the point of

combustion; but it is now acknowledged that it is a troublesome

impurity, and that the sooner it is extracted the better. Gas leaves

the retorts saturated with naphthalene, and its capacity for holding

that impurity seems to be augmented by the presence of water vapour.

The condenser, by effecting the condensation of water vapour, also

brings about the deposition of solid naphthalene, apart from that

which naturally condenses owing to reduction of temperature.

Condensers are either air-cooled or water-cooled, or both. In the

former case the gas traverses pipes exposed to the atmosphere and so

placed that the resulting products of condensation may be collected at

the lowest point. Water is a more efficient cooling medium than air,

owing to its high specific heat, and the degree of cooling may be more

easily regulated by its use. In water-cooled condensers it is usual to

arrange that the water passes through a large number of small pipes

contained in a larger one through which the gas flows, and as it

constantly happened that condenser pipes became choked by naphthalene,

the so-called reversible condenser, in which the stream of gas may be

altered from time to time and the walls of the pipes cleaned by

pumping tar over them, is a decided advance.

The solubility of naphthalene by various oils has led some engineers

to put in naphthalene washers, in which gas is brought into contact

with a heavy tar oil or certain fractions distilled from it, the

latter being previously mixed with some volatile hydrocarbon to

replace in the gas those illuminating vapours which the oil dissolves

out; and by fractional distillation of the washing oil the naphthalene

and volatile hydrocarbons are afterwards recovered.

Exhauster.

The exhauster is practically a rotary gas pump which serves the

purpose of drawing the gas from the hydraulic main through the

condensers, and then forcing it through the purifying vessels to the

holder. Moreover, by putting the retorts under a slight vacuum, the

amount of gas produced is increased by about 12%, and is of better

quality, owing to its leaving the heated retort more quickly. A

horizontal compound steam-engine is usually employed to drive the

exhauster.

At this point in the manufacturing process the gas has already

undergone some important changes in its composition, but there yet

remain impurities which must be removed, these being ammonia,

sulphuretted hydrogen, carbon disulphide and carbon dioxide. Ammonia

is of considerable marketable value, and even in places where the

local Gas Act does not prescribe that it shall be removed, it is

extracted. Sulphuretted hydrogen is a noxious impurity, and its

complete removal from the gas is usually imposed by parliament. As

nearly as possible all the carbon dioxide is extracted, but most gas

companies are now exempt from having to purify the gas from sulphur

compounds other than sulphuretted hydrogen. Cyanogen compounds also

are present in the gas, and in large works, where the total quantity

is sufficient, their extraction is effected for the production of

either prussiate or cyanide of soda.

Atkinson Butterfield gives the composition of the gas at this point to

be about

per cent. by vol.

Hydrogen from 42 to 53

Methane " 32 " 39

Carbon monoxide " 3 " 10

Hydrocarbons--

Gases " 2.5 " 4.5

Light condensable

vapours " 0.5 " 1.2

Carbon dioxide " 1.1 " 1.8

Nitrogen " 1.0 " 5.0

Sulphuretted hydrogen " 1.0 " 2.0

Ammonia " 0.5 " 0.95

Cyanogen " 0.05 " 0.12

Carbon disulphide " 0.02 " 0.035

Naphthalene " 0.005 " 0.015

Washers.

It happens that ammonia, being a strong base, will effect the

extraction of a certain proportion of such compounds as sulphuretted

hydrogen, carbon dioxide and hydrocyanic acid, and the gas is now

washed with water and ammoniacal liquor. The process is termed washing

or scrubbing, and is carried out in various forms of apparatus, the

efficiency of which is dependent upon the amount of contact the

apparatus allows between the finely divided gas and water in a unit

area and the facility with which it may be cleared out. The "Livesey"

washer, a well-known type, is a rectangular cast iron vessel. The gas

enters in the centre, and to make its escape again it has to pass into

long wrought iron inverted troughs through perforations one-twentieth

of an inch in diameter. A constant flow of liquor is regulated through

the washer, and the gas, in order to pass through the perforations,

drives the liquor up into the troughs. The liquor foams up owing to

agitation by the finely divided streams of gas, and is brought into

close contact with it. Two or three of these washers are connected in

series according to the quantity of gas to be dealt with.

Scrubbers.

The final washing for ammonia is effected in an apparatus termed a

"scrubber," which is a cylindrical tower packed with boards 1/4 in.

thick by 11 in. broad, placed on end and close together; water is

caused to flow down over the surface of these boards, the object being

to break up the gas as much as possible and bring it into close

contact with the water. In this wet purifying apparatus the gas is

almost wholly freed from ammonia and from part of the sulphuretted

hydrogen, whilst carbon dioxide and carbon disulphide are also

partially extracted.

[Illustration: FIG. 8.--Purifier.]

Purifiers.

The final purification is carried out in rectangular vessels, known as

"dry purifiers" (fig. 8). Internally, each purifier is filled with

ranges of wooden trays or sieves A, made in the form of grids (fig.

9), and covered with the purifying material B to a depth of about 6

in., the number of tiers and size of purifier boxes being proportional

to the quantity of gas to be purified. The gas enters at the bottom by

the pipe C, the inlet being protected from any falling material by the

cover D; it forces its way upwards through all the trays until,

reaching the lid or cover E, it descends by the exit tube F, which

leads to the next purifier. The edges of the lid dip into an external

water seal or lute G, whereby the gas is prevented from escaping.

[Illustration: FIG. 9.--Purifier Grid.]

When the gas had to be purified from carbon disulphide as well as from

sulphuretted hydrogen, slaked lime was employed for the removal of

carbon dioxide and the greater quantity of the sulphur compounds,

whilst a catch box or purifier of oxide of iron served to remove the

last traces of sulphuretted hydrogen. Not fewer than four lime

purifiers were employed, and as the one which was first in the series

became exhausted, i.e. began to show signs of allowing carbon dioxide

to pass through it unabsorbed, it was filled with fresh slaked lime

and made the last of the series, the one which was second becoming

first, and this procedure went on continuously. This operation was

necessitated by the fact that carbon dioxide has the power of breaking

up the sulphur compounds formed by the lime, so that until all carbon

dioxide is absorbed with the formation of calcium carbonate, the

withdrawal of sulphuretted hydrogen cannot proceed, whilst since it is

calcium sulphide formed by the absorption of sulphuretted hydrogen by

the slaked lime that absorbs the vapour of carbon disulphide,

purification from the latter can only be accomplished after the

necessary calcium sulphide has been formed. The foul gas leaving the

scrubbers contains, as a general average, 30 grains of sulphuretted

hydrogen, 40 grains of carbon disulphide and 200 grains of carbon

dioxide per 100 cub. ft. On entering the first purifier, which

contains calcium thiocarbonate and other combinations of calcium and

sulphur in small quantity, the sulphuretted hydrogen and disulphide

vapour have practically no action upon the material, but the carbon

dioxide immediately attacks the calcium thiocarbonate, forming calcium

carbonate with the production of carbon disulphide vapour, which is

carried over with the gas into the second box. In the connexion

between the first and the second box the gas is found to contain 500

grains of sulphuretted hydrogen and 80 grains of carbon disulphide per

100 cub. ft., but no trace of carbon dioxide. In the second box the

formation of calcium thiocarbonate takes place by the action of carbon

disulphide upon the calcium sulphide with the liberation of

sulphuretted hydrogen, which is carried over to the third purifier.

The gas in the connecting pipe between the second and third purifier

will be found to contain 400 grains of sulphuretted hydrogen and 20

grains of carbon disulphide. The contents of the third box, being

mostly composed of slaked lime, take up sulphuretted hydrogen forming

calcium sulphide, and practically remove the remaining impurities, the

outlet gas showing 20 grains of sulphuretted hydrogen and 8 grains of

carbon disulphide per 100 cub. ft., whilst the catch box of oxide of

iron then removes all traces of sulphuretted hydrogen. It will be

noticed that in the earlier stages the quantity of sulphur impurities

is actually increased between the purifiers--in fact, the greater

amount of sulphiding procures the ready removal of the carbon

disulphide,--but it is the carbon dioxide in the gas that is the

disturbing element, inasmuch as it decomposes the combinations of

sulphur and calcium; consequently it is a paramount object in this

system to prevent this latter impurity finding its way through the

first box of the series. The finding of any traces of carbon dioxide

in the gas between the first two boxes is generally the signal for a

new clean purifier being put into action, and the first one shut off,

emptied and recharged with fresh lime, the impregnated material being

sometimes sold for dressing certain soils.

The action of oxide of iron, which has now partly replaced the lime

purification, depends on its power of combining with sulphuretted

hydrogen to form sulphide of iron. Such is the affinity of the oxide

for this impurity that it may contain from 50 to 60% by weight of free

sulphur after revivification and still remain active. Upon removing

the material from the vessel and exposing it to the atmosphere the

sulphide of iron undergoes a revivifying process, the oxygen of the

air displacing the sulphur from the sulphide as free sulphur, and with

moisture converting the iron into hydrated oxide of iron. This

revivification can be carried on a number of times until the material

when dry contains about 50% of free sulphur and even occasionally 60%

and over; it is then sold to manufacturers of sulphuric acid to be

used in the sulphur kilns instead of pyrites (see SULPHURIC ACID).

Apart from the by-products coke, coke-breeze, tar and retort carbon,

which are sold direct, gas companies are now in many cases preparing

from their spent purifying material pure chemical products which are

in great demand. The most important of these is sulphate of ammonia,

which is used for agricultural purposes as a manure, and is obtained

by passing ammonia into sulphuric acid and crystallizing out the

ammonium sulphate produced. To do this, saturated ammoniacal liquor is

decomposed by lime in the presence of steam, and the freed ammonia is

passed into strong sulphuric acid, the saturated solution of ammonium

sulphate being carefully crystallized. The market value of the salt

varies, but an average figure is L12 per ton, whilst the average yield

is about 24 lb. of salt per ton of coal carbonized. In large works the

sulphuric acid is usually manufactured on the spot from the spent

oxide, so that the sulphuretted hydrogen, which in the gas is

considered an undesirable impurity, plays a valuable part in the

manufacture of an important by-product.

Cyanogen compounds are extracted either direct from the gas, from the

spent oxide or from ammoniacal liquor, and some large gas works now

produce sodium cyanide, this being one of the latest developments in

the gas chemical industry.

[Illustration: FIG. 10.--Gasholder.]

[Illustration: FIG. 11.--Cup and Grip.]

Gasholder.

The purified gas now passes to a gasholder (sometimes known as a

gasometer), which may be either single lift, i.e. a simple bell

inverted in a tank of water, or may be constructed on the telescopic

principle, in which case much ground space is saved, as a holder of

much greater capacity can be contained in the same-sized tank. The

tank for the gasholder is usually made by excavating a circular

reservoir somewhat larger in diameter than the proposed holder. A

banking is allowed to remain in the centre, as shown in fig. 10, which

is known as the "dumpling," this arrangement not only saving work and

water, but acting as a support for the king post of a trussed holder

when the holder is empty. The tank must be water-tight, and the

precaution necessary to be taken in order to ensure this is dependent

upon the nature of the soil; it is usual, however, for the tanks to be

lined with concrete. Where the conditions of soil are very bad, steel

tanks are built above ground, but the cost of these is much greater.

The holder is made of sheet iron riveted together, the thickness

depending upon the size of the holder. The telescopic form consists of

two or more lifts which slide in one another, and may be described as

a single lift holder encircled by other cylinders of slightly larger

diameter, but of about the same length. Fig. 10 shows the general

construction. Gas on entering at A causes the top lift to rise; the

bottom of this lift being turned up all round to form a cup, whilst

the top of the next lift is turned down to form a so-called grip, the

two interlock (see fig. 11), forming what is known as the hydraulic

cup. Under these conditions the cup will necessarily be filled with

water, and a seal will be formed, preventing the escape of gas. A

guide framing is built round the holder, and guide rollers are fixed

at various intervals round the grips of each lift, whilst at the

bottom of the cup guide rollers are also fixed (fig. 11). In the year

1892 the largest existing gasholder was built at the East Greenwich

works of the South Metropolitan Gas Company; it has six lifts, its

diameter is 293 ft., and when filled with gas stands 180 ft. high. The

capacity for gas is 12 million cub. ft.

Governor.

The governor consists usually of a bell floating in a cast iron tank

partially filled with water, and is in fact a small gasholder, from

the centre of which is suspended a conical valve controlling the gas

inlet and closing it as the bell fills. Any deviation in pressure will

cause the floating bell to be lifted or lowered, and the size of the

inlet will be decreased or increased, thus regulating the flow.

Enrichment.

The fact that coal gas of an illuminating power of from 14 to 16

candles can be made from the ordinary gas coal at a fairly low rate,

while every candle power added to the gas increases the cost in an

enormous and rapidly growing ratio, has, from the earliest days of

the gas industry, caused the attention of inventors to be turned to

the enrichment of coal gas. Formerly cannel coal was used for

producing a very rich gas which could be mixed with the ordinary gas,

thereby enriching it, but as the supply became limited and the price

prohibitive, other methods were from time to time advocated to replace

its use in the enrichment of illuminating gas. These may be classified

as follows:--

1. Enriching the gas by vapours and permanent gases obtained by

decomposing the tar formed at the same time as the gas.

2. Mixing with the coal gas oil gas, obtained by decomposing crude

oils by heat.

3. The carburetting of low-power gas by impregnating it with the

vapours of volatile hydrocarbons.

4. Mixing the coal gas with water gas, which has been highly

carburetted by passing it with the vapours of various hydrocarbons

through superheaters in order to give permanency to the hydrocarbon

gases.

Enrichment by tar.

Very many attempts have been made to utilize tar for the production

and enrichment of gas, and to do this two methods may be adopted:--

(a) Condensing the tar in the ordinary way, and afterwards using the

whole or portions of it for cracking into a permanent gas.

(b) Cracking the tar vapours before condensation by passing the gas

and vapours through superheaters.

If the first method be adopted, the trouble which presents itself is

that the tar contains a high percentage of pitch, which tends rapidly

to choke and clog up all the pipes. A partly successful attempt to

make use of certain portions of the liquid products of distillation of

coal before condensation by the second method was the Dinsmore

process, in which the coal gas and vapours which, if allowed to cool,

would form tar, were made to pass through a heated chamber, and a

certain proportion of otherwise condensible hydrocarbons was thus

converted into permanent gases. Even with a poor class of coal it was

claimed that 9800 cub. ft. of 20- to 21-candle gas could be made by

this process, whereas by the ordinary process 9000 cub. ft. of

15-candle gas would have been produced. This process, although

strongly advocated by the gas engineer who experimented with it, was

never a commercial success. The final solution of the question of

enrichment of gas by hydrocarbons derived from tar may be arrived at

by a process which prevents the formation of part of the tar during

the carbonization of the coal, or by the process devised by C.B. Tully

and now in use at Truro, in which tar is injected into the

incandescent fuel in a water-gas generator and enriches the water gas

with methane and other hydrocarbons, the resulting pitch and carbon

being filtered off by the column of coke through which the gas passes.

Enrichment by oil gas.

The earliest attempts at enrichment by oil gas consisted in spraying

oil upon the red hot mass in the retort during carbonization; but

experience soon showed that this was not an economical method of

working, and that it was far better to decompose the liquid

hydrocarbon in the presence of the diluents which are to mingle with

it and act as its carrier, since, if this were done, a higher

temperature could be employed and more of the heavier portions of the

oil converted into gas, without at the same time breaking down the

gaseous hydrocarbons too much. In carburetting poor coal gas with

hydrocarbons from mineral oil it must be borne in mind that, as coal

is undergoing distillation, a rich gas is given off in the earlier

stages, but towards the end of the operation the gas is very poor in

illuminants, the methane disappearing with the other hydrocarbons, and

the increase in hydrogen being very marked. Lewis T. Wright employed a

coal requiring six hours for its distillation, and took samples of the

gas at different periods of the time. On analysis these yielded the

following results:--

_Time after beginning Distillation._

+------------------------+----------+------------+------------+------------+

+------------------------+----------+------------+------------+------------+

| Sulphuretted hydrogen | 1.30 | 1.42 | 0.49 | 0.11 |

| Carbon dioxide | 2.21 | 2.09 | 1.49 | 1.50 |

| Hydrogen | 20.10 | 38.33 | 52.68 | 67.12 |

| Carbon monoxide | 6.19 | 5.66 | 6.21 | 6.12 |

| Saturated hydrocarbons | 57.38 | 44.03 | 33.54 | 22.58 |

| Unsaturated " | 10.62 | 5.98 | 3.04 | 1.79 |

| Nitrogen | 2.20 | 2.47 | 2.55 | 0.78 |

+------------------------+----------+------------+------------+------------+

Encyclopaedia Britannica, 11th Edition, "G" to "Gaskell, Elizabeth" Volume 11, Slice 4 · 第 7 / 8 章

In pursuance of this plan he went to Baltimore in the autumn of 1829,