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AMERICAN
SULPHtJRIC ACID PRACTICE

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rUBllSUtRS OF »OOKS FOR^

Coat Age « Electric Railway Journal
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AMERICAN

SULPHURIC ACID

PRACTICE

PHILIP DbWOLF

AND

E. L. LARISON

AxtooHsA CoFnts MiHiHa CoHrAiti

WITH A SPECIAL CHAPTER

W. M. LbCLEAR

FtR9T Edition

McGEAW-HILL BOOK COMPANY, IHC.

NEW YORK: 370 SEVENTH AVENUE

LONDON: A a BOUVEBIE BT., E. C. 4

1921

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COFTBIOHT, 1921, BY THl

McGraw-Hill Boos Coupant, Inc.

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During a period of several years in close contact with the
manufacture of Sulphuric Acid the writers have a great many
times been asked to recommend Bome published work upon the
subject from which a knowledge of the practical essentials of
modern American acid making could be obtained. This inquiry
has come from men working in association with, and under the
supervision of, the writers, and also from men in allied lines who
wished to acquaint themselves quickly with this information.

So far as the writers know, such a work in English does not
exist. Lunge's "Sulphuric Acid and Alkali" is admirable in
many ways, and certainly every one permanently connected with
the manufacture of acid should have it for reference: it does not,
however, cover modern American practice, nor is it suitable to
present to a new chamber operator as a source of information.
Besides Lunge, there are several books which include a few
chapters on sulphuric acid, but none is satisfying.

The writers' purpose in preparing this volume has been to
provide some fundamental information for the man with little
preliminary knowledge of the subject. It does not in any way
pretend to cover acid manufacture with the thoroughness of
Lunge. History, chemical and physical theory, and many other
things are treated from the technical, not the scientific, view-point,
in an effort to avoid the error, so common in "Handbooks," of
not devoting much time to Why, while very thoroughly covering
How.

Note. — "Sullivan's Handbook" so thoroughly covers the
laboratory end that we have not included laboratory practice,
and recommend his methods.

The writers are much indebted to several manufacturers of
acid plant equipment for photographs and drawings of machinery
and apparatus.

Philip DbWolp.
E. L. Larison.

Anaconda, Montana,
April, 1921.

381911 , ,

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CONTENTS

Preface '. . . . v

I. AiiCHEtn, HisTORT, Development, Status 1

IL Elementary Cheuibtrz of Suli>buric Acid 7

III. Cbaracteristicb and Uses ' 16.

IV. Raw Materiau 44

t Prodcction OF SO, 49

iTI. A Brief Debcriftion OF THB Chaubbr Process 82

VII. IhjsT Settlimo Apparatus 86

VIII. The Glover Tower 94

IX. The Chambers 101

X. Gat Ldssac Towers 113

XI. Acid Circdlation 118

XII. Introduction OF NiTEB 136

XIII. Draft 159

XrV. Tbbtino 166

XV. Operation 180

^VI. Concentration 189

(^XVII. Odtlinb or the Contact Process 207

XVIII. Purification op Gases 217

XIX. CONVEETINO 228

XX. Abbobbtion 238

XXI. Convbhteb Mas8 243

XXII. AccocNTiNa 247

Appendix 260

Indse 265

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AMERICAN
SULPHURIC ACID PRACTICE

CHAPTER I
ALCHEMY, HISTORY, DEVELOPMENT, STATUS

When the old and bewhiskered alchemist mentally planned bis
transmutations from lead to gold, he no doubt considered his
reagent "spiritus vitroli" second only to his trusty Philosopher's
Stone in power and usefulness; for we read of sulphuric acid back
through Alchemical times, but the name of the true discoverer
will probably always remain unknown.

The Arabian, Geber (A.D. 960), was formerly thoi^ht to
have been the first to describe the "spirit of alum" and its
solvent powers, in the mythical literature of the time, but there
is a question now whether this did not creep in during the Latin
"translations" of the same. The Persian Alchemist, Abn-Bekr-
Alrhases (A.D. 930), and also DeBeauvais (A.D. 1240) are con-
ceeded probable discovers, but direct evidence is woefully lacking.

Basil Valentine (A.D. 1425), in that landmark of Alchemical
lore, "The Triumphal Car of Antimony," is the first- to refer to
any method of manufacture, and therein describes the burning
of sulphur with saltpeter in glass vessels. This method was
adopted by the apothecaries of the time, for the manufacture of
sulphuric acid on a small scale for pharmaceutical use. From
the apothecaries' laboratory to an industrial installation was the
logical sequence, and about 1746, at Richmond, near London, we
find what was then considered a large plant, operated by a quack
doctor named Ward.

From this point the manufacture branches off from alchemy
and quackery, and its development is aloi^ scientific and me-
chanical lines. The development and introduction of lead
chambers instead of glass, took place about 1746, when Dr.
Roebuck, and later a Mr. Garbet, erected plants with lead
chambers six feet square. Later factories were built at Worces-
tershire, London, and Glasgow.

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2 AMERICAN SULPHURIC ACID PRACTICE

FIRST AMBKICAN ACID PLAITT

The house now known as HarriBon Btds. & Co., Inc. was
founded in 1793 by Mr. John Harrison of Philadelphia. Mr.
Harrison received his early education in Philadelphia, and then
spent two years in Europe inveatigating the arts and processes
of the manufacture of chemicals and in studying under the
celebrated chemist, Dr. Joseph Priestley, Mr. Harrison became
deeply impressed with the belief that many staples were imported
which coiUd be produced to advantage in the United States,
thereby rendering the citizens independent of foreign producers
and aiding the industrial development of the youthful Republic.
Following this thought, in 1793 he began in Philadelphia the
manufacture of chemicals, notably Sulphuric Acid, of which he
was the first maker in the United States.

In that year, he had a lead chamber capable of producing 300
carboys per annum. The competition of foreign makers was so
overwhelming at first, that his enterprise was confined to manu-
facturing for his own use and filling orders on a small but very
remunerative scale for a few of his patrons, his investment at the
start not exceeding (5,000. In 1807 he built what was for that
time quite a large lead chamber; it was 50 ft. long, 18 ft. wide and
18 ft. high and capable of making nearly half a million pounds of
Sulphuric Acid annually, the price of the staple being then aa '
high as 15c. per pound. According to a letter addressed by Mr.
Harrison to President Jefferson, dated November 1, 180S, and
now in the archives of the State Department at Washington, it is
learned that he bad then developed his Sulphuric Acid Plant to
such an extent as to have a possible annual output of 3,500
carboys and he had also extended the line of products in his
laboratory by adding the various preparations of mercury,
antimony, copper, etc., used in the arts and medicines at an
investment of some $40,000. This waa at his establishment on
Green Street, west of Third.

As is well known, acid produced in lead chambers is not the
Oil of Vitriol of commerce and the only method known at that
time to concentrate it to the required strength was by boilii^; it
in glass retorts — a very precarious and dangerous process. The
constant breakage of the ^as largely increased the cost of the
concentrated acid and the dangers of the work. To obviate this
great trouble Mr. Harrison, in 1814, introduced the use of Plati-

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ALCHEMY, HISTORY, DEVELOPMENT, STATUS 3

num for the manufacture of Sulphuric Acid, for the first time, at
least in this country. In the previous year, 1813, Dr. Eiic
BoUman, a Dane, had come to Philadelphia. Dr. Bollman was
familiar with the metallurgy of platinum and a highly scientific
man. He brought with him from France Dr. Wollaston's
method for converting the crude grains of platinum into bars
and sheets. About the first use that Dr. Bollman made of these
platinum sheets was the construction, early in 1814, of a still for
the concentration of Sulphuric Acid for the Harrison Works. It
weighed 700 oz., had a capacity of 25 gal., and was in continuous
use for 15 years. This early application of platinum for such
purposes was highly characteristic of the sagacity and ingenuity
of the American manufacturer. At the time the use of this rare
metal was a novelty in Europe and known only to a few persons
and certainly entirely unknown in this country. It follows,
therefore, that Mr. John Harrison was not only the earliest
successful manufacturer of Sulphuric Acid in America, but the
first in this country to concentrate it in platinum. Too great
praise cannot be given him for, as Liebig has said, " The quantity
of Sulphuric Acid made in a country is a sure index to its wealth
and prosperity."

In 1806, Mr. Harrison began the manufacture of white lead
and he and his successors have continuously marketed their
product since that date. In fact, with one exception, the "Harri-
son" lead is the oldest established brand of white lead in the
United States. In later years, he introduced into his works
apparatus for making pyroligneous and acetic acids and their
dependent products, white and brown sugar of lead, also oxides
of lead, colors, alum, coppers, iron liquors, etc. Mr. Harrison
may be credited with doing more to infiuence the establishment
and development of the chemical industries than almost any
man of his time.

The Green Street Works soon grew too small for such large
operations as Mr. Harrison had undertaken and an eligible loca-
tion was secured in Kensii^ton, now the Eighteenth Ward of
this city, where extensive buildings were erected and lai^ manu-
facturing facilities provided. In 1831 he admitted his sons to
partnership, under the title of John Harrison & Sons. He died
in 1333 and in that year the firm name was changed to Harrison
Brothers. In 1859, by the admission of the founder's grandsons,
John Harrison, George L. Harrison and Thomas 8. Harrison, the

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4 AMERICAN SULPHURIC ACID PRACTICE

finn name became Harrison Bros. & Company and in 18^ waa
incorporated. In 1917 the Greys Ferry plant was taken over
by the Du Font Company and is now known aa the Harrison
Works.

Holker, in 1766, introduced the firet lead chambers into France,
and at his Rouen plant the two important ideas of introducing
steam into the chambers during combustion, and continuous air
feed, were mechanically developed. In Germany the first lead
chambers were probably those at Ringkuhl, near Cassel. Dr.
Richard's plant near Dresden (1820) was one of the oldest, and
although it was erected some time after the idea of continuous
air feed had been perfected, it represented the old intermittent
type.

The last 150 years has seen little or no chai^ in the funda-
mental idea of the English, or chamber process. True, the
chambers have been increased tremendously in size, the genera-
tion of SOt has undei^ne marvelous mechanical development,
and the utilization of valuable waste products has become of
great importance; methods of handling the product have been
rendered many times more efficient: but for the original idea
we are indebted to the pseudo-Bcientists of the Alchemical period.

One of the promoters of the Contact Process once said, "The
alchemists and the early English chemists could hardly have
helped stumbling onto the discovery and manufacture of oil of
vitriol by the Chamber Process, but it remained for a nation of
real scientists to discover and develop the Contact Process." For
nowhere in the field of industrial chemistry can the chemical
engineer see so clearly the result of systematic, painstaking
research, experiment, and accurate interpretation of observation.

Up to the close of the e^hteenth century the little fuming acid
demanded by the arts had been produced almost exclusively by
the firm of Joseph Starck, in Bohemia, by the distillation of dry
ferrous sulphate and the absorption of the evolved S0| in a high
strength pan concentrated acid. From the place where it was
stored it was called Nordhausen acid.

About 1875, CI. Winkler, and later Squire and Wessel, showed
that SOg is easily formed by the interaction of SOj and Oi, in the
presence of a number of substances in a finely divided state, with
certain other requirements as to temperature, humidity, and
pressure. Although the oxides of iron and cobalt, and metallic
gold, iridium, and silicon produce this result, none of them

^dbvGooglc

ALCHEMY. HISTORY, DEVELOPMENT, STATUS .5

approach the efficiency of conversion obtained with small per-
centages of metallic platinum. The platinum itself is unacted
upon and termed a catalyzer, after the si^geBtion of Berzilius,
in 1835.

The commercialization of Winkler's idea has been rapid during
the last forty years, owing to the increased demands of the dye
makers and oil refiners, so that today the old distillation process
is obsolete.

About 1875, the promoters of the process that later became
known as the Hanish and Schroder, using Winkler's ideas,
secretly tried out the catalysis of SOg, using first pure SOj and
oxygen, and later dilute SOi from pyrites, with platinized asbestos
as the catalytic a^ent, and a heateU entrance gas, under a pressure
of three atmospheres.

But the great obstacles in the way of the development of the
process were the failure to get a dry and arsenic free entrance gas,
the false idea that SOj and oxygen must be present in stoichi-
ometrical proportions, and that nitrogen was detrimental. These
three difficulties alone must be considered the causes of the failures
of the pioneers, and the financial losses through semi-commercial
experiments were startling.

Through the disloyalty of a workman at the Badische works
CLudwigshaven) the important secrets of their process were ob-
tained by their competitors, and simultaneously, 1898, patents
were issued to three different companies: The Badische Anilin

DND SODAFABHIK OF LuDWIGBHAVEN; ThB FaRBEWERKE VOKM

Meistek, Ltrcitrs & Bruning, of Hochst; and The Vbbein
Cheuischer Fabriken of Manhbiu.

These three companies at once set about the commercial per-
fection of the process, as aecretely as possible, the only important
variation being in the catalytic agent. To trace the foreign
development would indeed be interestii^, but we are limited by
title to American practice,

American manufacturers, due to their lack of appreciation of
the results of organized research and experiment, refused to
finance any work Eilong these lines, and followed the usual course
of importing the developed process and trained men for install-
ations in this country. The Schroder process, employit^
platinized magnesium sulphate, and the Badische, with platinized
asbestos, have been the most favored in America.

An eminent chemical engineer has called sulphuric acid the

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6 AMERICAN SULPHURIC ACID PRACTICE

back bone of the chemical industry, for like soda, ita uses are eo
diversified and its production so great, that in any country it is
a true barometer of chemical and industrial progress. It finds
its greatest use in fertilizer manufacture (80 per cent), and is
indispensable in the manufacture of coal tar dye stuffs, petroleum
products, paper, stearine, oleine, sodium sulphate, soda; hydro-
chloric, nitric, citric, and tartaric acids; sulphates of iron and
copper; alums, shoe blackings, coke plant by-products, electro-
lytic refining of metals, mostly copper; it enters, directly or
indirectly, into almost every chemical procese. In some of the
more important branches of the chemical industry it is a raw
material costing millions. The amounts used in the manufacture
of explosives, during the late War, wereenormous. This huge war
increase was of course only temporary, and there are many plants,
paid for by the War, that should make very cheap acid.

While the Contact process has many advant^es over the
Chamber process, such as no bulky chambers of concentration
pans, it is very doubtful if it will ever completely replace the
chambers. It cannot make 50° and 60° B£. acids to compete,
and requires some method of producing weak acid to keep it
going. But on the production of higher strength acids it is
supreme, and statistics show that it is gaining in the United States
today. The cost of platinum for concentrating pans is excessive
and increasing, and that required for contact mass is negligible
in comparison. Both processes are being improved steadily,
and the patent rights are costing less each year, and in a few years
will become public property. Supervision, regulation and yield
are all better on the contact process, while depreciation and
maintainance are less.

In April, 1920, the Department of Commerce had no figures for
production since 1915. They show a 25 per cent increase in
production during 1915 over the previous year, and one war time
plant alone, completed in 1916, produced a qtiarter of a million
tons of fuming acid a year, against 49,000 tons for the whole
country in 1914.

A few figures on the world's production will give an idea of the
rate of development:

1880 1,850,000 tons

1892 2,818,000 tons

1902 4,450,000 tona

)9W 8,000,000 tons

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CHAPTER II
ELEMENTARY CHEMISTRY OF SULPHURIC ACH)

When Bulphur, either brimBtone or a metallic sulphide, is
burned in air, sulphur dioxide, SOa, is produced. This is the
starting point of the sulphuric acid industry.

SOi is a colorless gas of a suffocating odor, and will not bum
nor support combustion directly, under ordinaiy conditions. It
is very injurious to plants. It contains 50.05 per cent sulphur,
and 49.95 per cent oxygen. Molecular weight, 64.04 per cent.
Specific gravity, 2,2136. A liter of SOj at 0°C. and 760 mm.
pressure weighs 2.8608 g. Its heat of formation is given
(Richards) as 69,260 as a gas, or 77,600 in dilute solution.

Anhydrous sulphur dioxide will not act upon iron, up to 100°C.,
but the commercial product, containing up to the 1 per cent
HjO that it carries at saturation, does act slightly.

Owing to the catalytic action of the hot iron of the bumers,
some 8O3 is formed when brimstone is burned but not enough to
influence the process. With pyrites, however, the 8O3 formed is
considerable, as the catalytic action of the red hot iron oxides is very
marked; in fact the oxides of iron, copper and chromium are the
only catalytic (?) agents that have been seriously experimented
with, outside of platinum. The generally accepted theory for
the action of the metallic oxides is that they are more oxygen,
carriers than actual catalyzers: doing their work more as the
nitrogen oxides do theirs, than as platinum does its work.

The yields, when ferric oxide is used, are not high enough to
permit it to seriously compete with platinum as the catalytic
agent used in this industry, in the present state of our knowledge.

The reactions are probably two, both takii^ place at very
nearly the same temperature, viz. :

2FesOa + 30i + 6SO1 = 2Fes(SO0i

which splits up into

FeiOa + 3S0,

the FejOa being ready to repeat the cycle
7

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8 AMERICAN SULPHURIC ACID PRACTICE

*"** 3Fe,0, + 80, = 2Fe,04 + SO.

"^ 4Fe,04 + Oi - 6Fe,0,

when the FetOa is agato ready to repeat.

SOi is pretty soluble in water, one volume of water, at atmoB-
pheric preaeure, and 32''F., disai^!viug about 80 volumes SOj.
However, this does not appear to be a chemical compound,
HiSOi, sulphurous acid, because SOi evaporates trom it even at
ordinary temperatures.

Bunsen and Schonfeld published the following table, in 1905,
of the solubility of SOi in water, at 760 mm. pressure:

Tablb 1

TaiiriKATnKi, I litbb

79.8

6 57,5

10 56.6

Solutions of SOj slowly oxidize in the pr^ence of air.

Sulphuric acid is a compound, in varying proportions, of
sulphur trioxide and water. Several different compounds exist,
showing all the properties of definite chemical compounds. The
mono- and the duo-hydrates have been the most frequently
studied. Acid of a concentration of 98.3 per cent or better
seems to hold the 1.7 per cent or leas of water present chemically,
and this is the absolute limit to which a concentration by distilla-
tion can go. In practice, 98 per cent is rarely reached, however.

Sulphuric acid has a tremendous affinity for water, combining
with it violently, with evolution of great heat. Of the entire
molecular heat of formation, 192,200 calories, 100,300 calories,
or 53.5 per cent, results from the combination of the anhydrous
SO* with the water. A very common manifestation of this
affinity is the charring of carbo-hydrates by sulphuric acid, the
water in the combination being removed, leaving the carbon
behind.

Another familiar result of this affinity is the dense white
cloud that forms when SOj escapes into the air. Air at all times
contains moisture-humidity and the SOt combining with this
moisture forms H^SO* m minute particles. These particles are

=dbvCoi>Qlc1

ELEMENTARY CHEMISTRY OF SULPHURIC ACID 9

small enough tfl remain suspended in the air for a long time, form-
ing a white cloud, or "fume" not properly a fume at all, because
it is not a gas, but a mass of small liquid particles.

As there is always some moisture in the air we always have an
indicator as to whether S0| is going through our system and
beti^ lost out our stacks. While "fumes" come from other
causes, if there is no "fume" there is no SOj escaping.
• The moisture in the air has a very direct effect upon the contact
process in keeping down the strength of the acid that' can be
made. The air introduced into the system carries with it its
own share of humidity, which must be absorbed, and thus dilute
the acid made. In the Middle Atlantic States this will average
60 lb. of water per ton of 100 per cent acid made, or 3 per cent:
less in winter, and more in summer, for the saturation point of
air increases rapidly with the temperature. Consequently, if it
is desired to make very high concentration fumii^ the location
must be in the driest climate possible.

There are three distinct steps in the evolution of sulphur into
sulphuric acid, either naturally, or directed by man. They are
the burning of the sulphur to SOi, the oxidation of the dioxide
to the trioxide, and the hydrating of this trioxide.

In the chamber process the last two steps proceed simultane-
ously, the water acting both as an assistant to the catalyser,
various oxides of nitrogen, and as the hydrator. The oxidation
will not proceed at a commercially practicable rate unless water
is present in excess, consequently the acid produced is dilute,
and to make strong acid must be concentrated.

We know what results may be attained by different methods
of handling the process, but the intermediate changes that occur
are the subjects of very heated controversy. There b no doubt
that nitrososulphuric acid, SOi(OH)(ONO) is formed, which
breaks up into HiSO* and NO. The NO becomes oxidized to
N0«, NiOa, and N1O4, probably a mixture of all three, and HNOj,
derivii^ the oxygen from the excess of air present, and the HjSOj
immediately takes up an excess of water and condenses.

In a work of this character, written as an operating handbook,
not as a treatise, it would not serve any useful purpose to go into
the theories of Weber, Winkler, Raschig, and Lunge, regarding
changes withm the chambers.

The saving of the nitn^en oxides is of the uttermost import-
ance, as without this saving the process would not be corn-

ed byCooglc

10 AMERICAN SULPHURIC ACID PRACTICE

mercially practicable. The Gay-Lussac tower was the first
nitrate saver, and now, in conjunction with the Glover tower,
reduces the nitrate from 11 per cent to 4 per cent.

Strong sulphuric acid absorbs nitrous acid, forming nitroso-
sulphuric acid as follows:

2H^0« + NiOa = 2S0s(0H)(0N0) + H,0
it absorbs nitric pero}dde, forming nitrososulpburic acid and
nitric acid:

HiSO* + NiO* = SO,(OH)(ONO) + HNO,

Nitrososulpburic acid is decomposed by water alone, (1) or
by water and SOj, (2) :

(1) 2S0b(0H)(0NO) + H,0 = 2H,S04 + NjO,

(2) 2S0,(0H)(0N0) + SO, + 2H,0 = 3H,S0« + 2N0
and the nitric oxides are ready to repeat.

The recovery of the nitrogen gases is accomplished by taking
advantage of two of the reactions that proceed within the
chamber — the absorbtion of NjOj and N1O4, in the Gay-Lussac
tower, by strong sulphuric acid, and the decomposition of the
product, at a point where it is available, by burner gas, (S0»),
to H,SO, and NO.

NjOj and 'S^^0^ are absorbed by strong sulphuric acid, forming
nitrososulpburic acid, as shown in the reactions of the chamber.
This prevents the escape of the nitrogen gases into the atmos-
phere, with the attendant loss of nitre and the damage done, but
the nitrososulpburic acid is of little value, and must be made
into a useful product.

The Glover tower accomplishes this. As shown in the chamber
reactions, water and SO, decompose SO,(OH)(ONO) — nitroso-
sulpburic acid — to HjSO* aod NO, so by bringing the hot burner
gases, rich in SO2, in contact with the nitrososulpburic acid that
reaction is brought about, and in addition the heat present effects
a considerable concentration, the water from the concentrated
acid going on with the burner gas and the NO back to the
chambers, thus being used over and over again.

CONTACT PROCESS

In the contact process SOs is produced by the same means that

are employed to make it for chambers. The last two steps are

separate and distinct, however, and instead of an excess of water.

^dbvGooglc

ELEMENTARY CHEMISTRY OF SULPHURIC ACID 11

givii^ a dilute acid, there is an excess of SOt, producing fuming
acid.

Burner gaees must be cleaned of certain impurities, before
touchii^ the catalytic agent, which in this country is always
finely divided platinum, on either asbestos or roasted magnesium
sulphate.

The following is from a paper by Dr. Charles L. Reese, Journal
of the Society of Chemical Industry, March 31, 1906:

"Water — it was thought at one time to be essential that the gases
be dried by sulphuric acid not weaker than 60°B^., but this was found
to be an error, in that the gases could be saturated with moisture, by
passing them through water before introduction into the contact msss,
without affecting the conversion in any way. Fuming sulphuric add
was produced, but, of course, such a procedure could not be carried
out on a manufacturing scale, where it is necessary to use iron pipes.

"Carbon dioxide had no effect whatever, whenever introduced into
the gas, as was to be expected, but I was surprised to find that caihonic
oxide had no deleterious effect, in spite of its reducing qualities. On
one occasion the conversion in a certain plant ceased altogether, and
we were at a loss to know the cause. We, however, soon found that
some coal had got mixed with the pyrites in the burners. In this case
there was carbon dioxide, and possibly carbonic oxide, present, but
there was also evidently a lack of oxygen, and when the coal was con-
sumed, conversion began again.

"Sulphur will at times find its way through two or three scrubbing
towers, and, before the filtering system was adopted, it became neces-
sary te determine whether the presence of sulphur in the gas would
affect the catalytic action of the contact material. Experiments were
carried out to determine this point. It was desirable to introduce sul-
phur into the gas in as finely divided condition as possible. This was
accomplished by introducing hydrogen sulphide into the gas. When
hydrogen sulphide ia mixed with sulphur dioxide the reaction between
these two gases takes place, producing sulj^ur and water, and thus
sulphur was introduced into the mass. It was found, on discontinuing
the introduction of hydrogen sulphide, the conversion continued to be
normal, and the sulphur was simply carried through the tube. This
experiment waa repeated a number of times with the same result, show-
ing that the presence of sulphur does not affect the reaction. Of course,
hydrogen sulphide would affect it, in that it would reduce the sulphur
dioxide.

"The above substancesdo not aSect the reaction of the contect mass,
but hydrochloric acid, chlorine, silicon tetra-fiuoride, arsenic, and lead
do seem to affect it in two distinct ways: first, by their presence in

^dbvGooglc

12 AMERICAN SULPHURIC ACID PRACTICE

the gaa, and only when present in the gas; and second, affecting the
catalytic property of the contact material. In the fint case we have
hydrochloric acid, chlorine, and silicon tetra-fluoride. In the second we
have areenic and lead.

"When Hydrochloric Add gas is introduced, theeffect is instantaneous,
reducing the conversion from 98.5 per cent to 42 per cent, but when the
hydrochloric acid gas is discontiaued and air passed through fot a while
to displace it, the conversion becomes normal in a short time.

"The presence of Chlorine in the gas seems to have an effect similar
to that of hydrochloric acid, although not so intense. In both cases
the dry chlorine or the hydrochloric acid was introduced, until a mini-
mum yield was obtained, which in the case of HCl was about 42 per
cent, and that of the CI was 57 per cent. After discontinuing the HCl
and the CI, air was passed through and the operation was continued at
the same temperature. As will be seen by the curve the percentage
conversion gradually arose again to the normal. Although at one point
the gas showed a trace of HCl, the conversion amounted to 94 per cent.
"The introduction of a small quantity of silicon tetra-fluoride caused
the conversion to drop immediately, but on discontinuing, the conver-
sion rose in a few minutes to normal. In each case some silica was un-
doubtedly deposited upon the contact mass, but most of it passed
through the tube, as was made evident by the fact that the silica sepa-
rated out niien the gas came in contact with the water solution used in
testing the exit gas. Of course a minute quantity of silicon tetra-
fluoride in the gas would gradually deposit silica on the contact mass,
and would eventually cover the contact agent, so as to render it inactive;
but when contact mass is so affected it can be easily rendered active by
simply removing it from the converter and putting it back again. The
handUng will be sufficient to expose surfaces.

"The injurious effect of arsenic upon the contact mass is extremely
marked. Areenious acid was placed in the front end of the tube, heated,
and carried into the contact tube by the flow of gas. The effect of the
arsenic was to reduce the conversion absolutely to zero, owing to the
large amount introduced, but after 40 min. it rose again to 40 per cent.
At this time HCl was introduced for 50 min. to remove the arsenic, and
then air drawn through for 15 min. more. The process was then con-
tinued, and the conversion then rose to 96.6 per cent. Several attempts
were made to find a simple means of removing As from the contact
mass, and at firat CI was used for this purpose. The mass was placed
in a tube, heated, and CI passed throu^. This did remove some of
the As, but did not regenerate the mass sufficiently. A very interest-
ing observation was made, however, during this experiment. It was
found the CI carried over platinum to the exit end of the tube, and
deposited it in the form of a chloride. This was done at a temperature
of 400°-i50''C.

^dbvGooglc

ELBMENTARY CHEMISTRY OF SULPHURIC ACID 13

"It was found in attempting to regenerate or remove arsenic, that
HCI mixed with the reduced sulphurous gas was much more effectire,
as is shown by the curve referred to, ail arsenic having been removed.

"It is w^ known that when platinum is heated in the presence of
lead or lead salts, lead combines wiUi the platinum either to form an
alloy or a compound, and this oombination of lead with platinum un-
doubtedly destroys the catalytic property of the platinum. The effect
of lead, however, was not determined in the regular way, but can be
shown very readily by one or two experiments.

" It is well known that when a platinum spiral is heated in a gas flame,
tbe gas turned off for a few minutes, and on again, the spiral will reignite
tiie gaa. A small piece of contact mass will do the same, but if either
is moistened with a small quantity of lead acetate and then ignited, it
will lose this property of leigniting gaa, unless it is heated sufficiently
loi^ to volatilize the lead. A similar experiment will show in a tou^
way the effect of arsenic on contact mass or a platinum spiral."

The above quotation shows very clearly the necessity for
very careful scrubbing. The loss of sulphur, and consequently
of acid, from unconverted SO* that passes on out the stacks
is anywhere from 60 per cent to 80 per cent of the entire loss,
and anything that throws the mass off at all will enormously
increase that loss. The operation costs the same, with the
exception of the small item of handling the finished acid, with
a low as with a high conversion and the yield, and consequently
the income, is cut down in the proportion that the conversion falls
off.

Arsenic is by all odds the worst of the contact "poisons" with
which we have to deal.

Opl's theory is that the destruction t£ the activity of the
contact mass is caused by the deposition of a glass-Uke coating
over the platinum, thus mechanically preventing ita contact
with the gas. This coating is, he says, a deposition product of
AstOi and SOj, with a formula SAsgO*, 2S0a. Lunge says this
product has actually been loimd in dust chambers.

Dr. KrauBS holds that the arsenic is oxidized to a non-volatile
oxide, which combines with platinum.

In a plant on the Pacific coast, operating on the Schroeder-
GriUo process, using pyrites, it is necessary to regenerate the
mass about every four weeks, and an astonishing fact has been
noted — that while the platinum recovers its activity, the arsenic
remains in the mass. It appears to exist after the regeneration
in the form of Realgar, arsenic disulphide, AsiSt, and in that

^dbvGooglc

14 AMERICAN SULPHURIC ACID PRACTICE

form is apparently not a contact poison. I have been infonned
that after 3 years the quantity of arsenic in the mass is actually
greater than the amount of platinum, but the old arsenic seems
to be perfectly inert, having no effect, good or bad, and it is not
until fresh arsenic compoimds are introduced that the mass again
loses it« activity.

Of course there is a loss of the efficiency of the mass in regen-
erating, because the platinum becomes distributed through the
grains of magnesium sulphate, instead of all being on the outside,
thus reducing the area that can come in contact with the gas.
' The absorbtion system requires conditions proper for the
combination of SOi and HiO. The principal interferences with
these conditions are vapor pressures, as follows:

(a) Vapor pressure due to HjO,

(fc) Vapor pressure due to SO*, and

Heat increases vapor pressures, so temperature control is

The vapor pressure due to HjO exists when the strength of
the absorbii^ acid drops below 98.3 per cent HiSOt. Above
that ^;ure the HjO seems to be chemically combined with the
HiSOi and no water vapor exists. SOg coming in contact with
water vapor forms very small drops of sulphuric acid, almost
impossible to condense, and any SOi used in this way may be
considered as lost beyond any reasonable hope of recovery, aa
even a very long condensation and absorbtion apparatus will
catch very little of it.

The second vapor, that of SOs, is only met with in making
fimiii^ acid. A glance at the absorbtion curve will show how
rapidly the absorbtion drops, as the strength <A the absorbing
acid increases. But SOi passing through fuming acid unab-
sorbed is in no way changed, and is caught perfectly by the
close to 100 per cent acid in the back of the system.

The vapor pressure of foreign acids comes of course from
impure materials. Sometimes it is necessary to clean out the
system after foreign acids have gotten in; but frequently any
trouble of this character can be cured by letting the system get
as hot as possible and simply "boiling out" the foreign substance.
It is necessary to watch weak acid from chamber plants closely,
to prevent nitric acid getting in.

^dbvGooglc

ELEMENTARY CHEMISTRY OF SULPHURIC ACID 15

As fuming acid has h^h meltii^ points, the exact varying with
the strength, the temperature must be kept up sufficiently high
to prevent freezii^. In shipping fuming acid it is general
practice to add a little nitric, if the intended use will not be
interfered with by nitric acid. Five per cent of nitric aeid wUl
drop the freezing point of fuming acid to — 10.5°F.

^dbvGooglc

' CHAPTER III
CHARACTERISTICS AND USES

Sulphuric acid is a viscous, colorless (when pure) liquid,
composed, by weight, of 2.04 per cent hydrogen, 32.64 per cent
sulphur, and 65.28 per cent oxygen. It is very strongly acid.

Its most outstanding characteristic is its affinity for water,
either free or combined, and violent combination, with evolution
of much heat, with it.

The, sulphuric acid industry is a business barometer, as the
acid enters into most other industries, and general trade condi-
tions are very soon re&ected in both sales and prices.

Sulphuric acid forms sulphates with all the metals, replacing
any other acid radical, and freeing the other acid. Its affinity
for water makes it the most important desiccating agent known.
It readily forms bisulphates (acid sulphates) and double sul-
phates. Most of its combinations are characterized by extreme
stability. Below 65 per cent HtSOi it attacks iron vigorously;
above that, very little. Below 92 per cent HiSO« its action
upon lead is sl^ht — it increases fast with strength. Hot acid
acts more vigorously than cold. The water in sulphuric acid
of 98.3 per cent concentration seems to be, not a diluent, but an
actual part of the acid, exerting none of the characteristics of
water in the less high concentrations.

Upon these main characteristics depends the important place
of sijlphuric acid in modem life. A list of the industries using
it would be a catalogue of the industry of the world.

The LeBlanc process for soda ash, datii^ from the end of the
eighteenth century, took the manufacture of sulphuric acid out
of the drug business, and made it a major industry.

Common salt, treated with sulphuric acid, gives off hydrochloric
acid, with the formation of sodium sulphate, after the formula
2Naa + H^04 = 2Ha + NajSO*

The sodium sulphate, roasted with coal and slaked lime, gives
soda ash (sodium carbonate), oxide and sulphide of calcium, and
carbon dioxide.

There are other methods of making sodium carbonate from the
sulphate, with by-products of sulphur and hyposulphites, but
the LeBlanc process is still a tremendous producer.

Nitric acid is made from its natural sodium aait, Chile saltpeter,
16

iiz^dbvCoOglc

CHARACTERISTICS AND USES 17

by treatment with sulphuric acid, the result being nitric acid and
sodium sulphate, or salt cake. By the use of twice the theoretical
amount of sulphuric acid a bisulphite is formed, which is fusible,
and easily removed from the stills. This bi-, or acid, sulphate,
has many of the characteristics of the acid itself, and is fre^
quently used for pickling iron castings, its 31 per cent of free
HsSO* being sufficient to accomplish this purpose.

Petroleum refining consumes large quantities of sulphuric acid.

Without sulphuric acid and its product, nitric acid, the coal tar
dye industry could not exist.

The fertilizer industry depends upon sulphuric acid for its
sulphate of lime, or land plaster; and even more, as a means of
converting cheap phosphate rock into a soluble form, from which
phosphoric acid is made.

The medical profession uses it in many ways. The quinine we
are brought up on is the sulphate of that alkaloid. The manu-
facture of "sulphuric" ether from ethel alcohol uses sulphuric
acid as a catalytic agent.

In all nitrating processes, whether for celluloid, nitro-cellulose,
either for ammunition or some form of soluble cotton, the action
of sulphuric is a desiccating one, removii^, and holding fast to
the OH radical released, preventing its doing any harm.

Fuming Sulphuric Acid is a solution of SOt in HjSOi — it is

~ lai^y used in the manufacture of coal tar dye stuffs. Its most

important use is the "butting up" the 96 per cent to 97.5 per

cent acid of the best concentrators to the 100 per cent that is

needed in many industries.

The popularity of the sulphate method of pulping wood is

growing, and with it the use of HiSOi. It is not necessary to

' pick the wood so carefully, as in the sulphite or caustic methods,

as resinous parts, such as knot« or sappy wood, are pulped by

it to an extent impossible by any other method.

An extensive use for sulphuric acid is (was) in the preparation
of the mash for distilling.

The large number of alums, used especially in the textile
industry, are double sulphates. Originally sulphate of alumina
was invariably one of the sulphates, chromium, iron, sodium,
potassium and ammonium being the usual others, and from the
aluminum it took its name — but today other pairs of sulphates
go under the name of alum. Sulphate of alumina, free from
iron, is used as a mordant and dyeing agent, to escape the injurious
iron that alum frequently carries.

^dbvGooglc

AMERICAN SULPHURIC ACID PRACTICE

Both alum and sulphate of alumina have wide application for
clarifying drinking water, and in coagulating and settling sewage.

Sulphate of zinc is used as a drier for painta, a disinfectant, and
a mordant in dyeing.

Much erf the electroplating industry, including the electrolytic
refining of copper and other metals, uses the suphate of the metal
as the electrolyte.

Copper sulphate, or blue vitriol, and iron sulphate, or green vit-
riol, have large application in the dyeing industry, also in recovering
silver by the amalgamation process. Green vitriol, perhaps better
known as copperas, is very largely used in ink manufacturing.

The leaching of low grade copper ores with weak solutions of sul-
phuric acid has become a great industry within the last few years.

"Shoddy" wool is freed from cotton by "carbonizing" the
goods with sulphuric acid, which consists in lettii^ a solution of
acid dry on, when the cotton or other vegetable fibre gives up its
OH radical, only the carbon remaining, and that in the form of a
powder, which is easily shaken off.

.The foregoing is only a brief list of some of the most important
uses to which sulphuric acid may be put, and is not intended to
do more than show how dependent modem civilization is upon
this industry.

The Bureau of Mines BvlleHn No. 184 reports for the period
June to August, 1918, the following distribution of sulphuric
acid among the industries:

Table 2

tDdutTT

Too. Hdd <lHd

^^ariisr-

Per Bent of
toUUcid

140,000
111,000
35,000

38,600
36,500
S,200
6,300

15,200
3,800

2,700,000

2,130,000

671,000

740,000
700,000
100,000
104,000

202,000
73,000

36.0
28

4. Chemicals, drugs, aad ammonium

9.3
I 3

1.4

390,500

7,610,000

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CHARACTERISTICS AND USES

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AMERICAN SULPHURIC ACID PRACTICE

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AMERICAN SULPHURIC ACID PRACTICE

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^d by Google

28 AMERICAN SULPHURIC ACID PRACTICE

This table shows, eliminating the acid used for munitions and
explosives, and allowing about 10,000 tons per month for domestic
explosives, an indicated requirement for normal peace purposes
of possibly 260,000 tons per month (basis, 100 per cent HtSOt),
or about 5,000,000 tons per year (basis, 50°B4.}.

There is no question that the use of phosphate fertilizer will
increase all over the country for many years. And as acid is
expensive to transport, it will have to be made near the place it
is used.

Sulphur, the primary raw material, either as pjrrites or brim-
stone has recently been described by Drs. Raymond F. Bacoa
and Harold S. Davis before the American Institute of Chemical
Ei^neers. The following extracts have been taken from their
paper.*

America now dominates the sulphur industry and virtually all the
American sulphur is produced by three companies— viz., the Union
Sulphur Co., the Freeport Bulphur Co. and the Texas Gulf Sulphur Co.
These three companies produce not only virtually all the sulphur used
in the United States but also a considerable surplus vhioh is exported.
The only other sulidiur which normally enters the American market in
quantity cornea from Japan and its percentage calculated on the con-
sumption of the United States is small and is not likely to increase.
Riaii^ costs of living have meant much higher wages in Japan, as well
as in other parts of the world; in fact, the percentage increase has prob-
ably been greatest in Japan, due not only to world conditions affecting all
countries but to the rising standards of living of the Japanese. These
facte, together with present higher transportation costs, will make it
increasingly difficult for Japanese sulphur to compete on our Pacific
coast with the American product.

Expansion of Indostrt Ddeino War

During the World War, and especially after America's entry into it,
the demand for sulphur grew enormously. Some time previous to our
declaration of war consideration had been given by a certain group of
New York capitalists to the opening up of the sulphur deposit (known
as the "Big Dome") located near Matagorda, Tex. These plans were
hastened to realization by our Government's need and demand during
the war for the maximum production from every possible source of sul-
I^ur. The plana eventuated in the formation of the Texas Gulf Sul-
phur Co., which, however, did not get its plants into operation until
after the armistice. Production has been practically continuous since

Chem. & Met. Eng., January 12, 1921.

^dbvGooglc

CHARACTERISTICS AND USES

Fio. 1.— Views of lie Texas GuH Sulphur Co.
General Views Showing Topography, Figa. I, 2, S, 8.

n,i,io,n,Go(5glc

AMERICAN SULPHUI

Fio. 2.— Views of the 1
Houses, Pavilion and Hospital,
Method of Loading for Shipmet
Exterior and Interior Views ot !

i,io,n,Go(5glc

CHARACTERISTICS AND USES 31

the company first mined sulphur on March 19, 1919. The plant of
this company, which has been described elsewhere,' was designed to
have a capacity of 1,000 tons of sulphur per day, but for montiis at a
time during the past year it has produced on an average 2,000 tons per
day. The total production for the year 1920 exceeds 800,000 long tons,
while in all probability the production for 1921 will be the largest of
any sulphur company in the world. The possible daily production
with the present plant, under favorable conditions, could be forced to
3,000 or 4,000 tons per day. The deposit contoins upward of ten
million tons of sulphur; and a brief description of its character is a^
follows;

DESCBipnoN OF Bio Domb at Matagorda

The main deposit has a diameter of about 4,000 ft. and is situated
800 to 1,000 ft. below the surface of the ground. The sulphur occurs
in an almost flat stratum, whose general shape is like that of a flat-
topped umbrella. Above the sulphur stratum is an unconsolidated
sediment consisting of bands of shale, gumbo and boulders. Below is
a layer of salt and gypsum, and then a layer of salt of undetermined
but very considerable thickness. The sulj^ur content of the deposit
runs quite uniform with a slightly higher percentage of sulphur on one
side of the dome. The mining operations are carefully checked, and a
large-sized model of the deposit enables the engineers constantly to
visualize what is taking place underground.

Production and Stocks Exceed Post-war Normal Demand

At the time the Texas Gulf Sulphur Co. entered the market the situa-
tion was about as follows: The Union Sulphur Co. had on top of the
ground, in unsold stock of sulphur, upward of one miUion tons and the
Freeport Sul[4iur Co. had several hundred thousand tons. The normal
consumption of sulphur in the United States had been between four and
five hundred thousand tons per annum, which quantity could be readily
supplied by the two older companies.* A new sulphur company enter-
ing the market with a large production of sulphur was therefore com-
pelled to pursue one of two policies — either to attempt to obtain a share

Read before the American Institute of Chemical Engineeia, New Orleans,
December 6, 1920. By Ratuond F. Bacon and Harold S. Davis.

' Ckem. a- Met. Bng., vol. 20, No. 4, pp. 186-188. Eng. Min. J., vol. 107
(1919), pp. 555-557.

* It may be stated, in passing, that any economic data given regarding
either the Union Sulphur Co. or the Freeport Sulphur Co, are subject to
the usual statement on advertisements of bond sales; that is, "they are
gathered from sources we believe to be reliable, but are not guoruiteed by

^dbvGooglc

32 AMERICAN SULPHURIC ACID PRACTICE

of the buBiness by cuttiog prices or to place the sulphur in markets
which hsd not hitherto used sulphur; in other worde, to increase the
sulphur consumption of the country.

With reference to the first possibility, competition based on cut-
throat slashing of prices always has proved disastrous to the whole
industry. Moreover, the mining of sulphur by the Frnsch process, to
be carried out economically, must be conducted on a very large scale,
80 that even if a company under the conditions outlined above had
obtained a third of a possible 600,000-toa consumption, this would not
have insured profitable operation. The company has chosen what is
surely the wiser course, in attempting to place its sul|Aur by increaang
the total consumption in the industries.

It was possible to do this owing to the prevailing economic conditions.
The United States had in recent years consumed annually, for the manu-
facture of sulphuric acid, upward of 600,000 tons of sulfdiur in the form
of pyrites, most of which came from Spain. The older sulphur com-
panies, either because of some agreement with the pyrites iroportets or
because of a desire to hold the price of sulphur at a certain level, had
not attempted seriously in past years to substitute sulphur for pyrites
as the raw material of sulphuric acid manufacture. Importetion of
Spanish pyrites, due to war transportation conditions, fell off very
seriously during the war years. This caused many producers of sul-
phuric acid to discard the pyrites roasters and to install sulphur-burning
equipment, while new producers in this field erected plants which were
almost entirely so equipped. The new company was able to obtain its
fair proportion of the new business and the net result has been that
the total consumption of sulphur of the United States during the past
year has been upward of 1,000,000 tons, as compared with a normal
consumption in recent years of about half that figure.

Ptbiteb vebbus Sulphdr as a Sodrcb of so*

It is interesting, in this connection, to give just a little history, for if
the subject is examined it is found that in the early days of sulphuric
acid manufacture all the sulphuric 'add of Europe, excepting Nord-
bausen acid, was made from brimstone. This includes the period from
about 1750 to 1839, when pyrites first was used commercially for the
manufacture of sulphuric acid in England. This use of pyrites was
due to the fact that the Neapolitan Government in 1838 granted a
monopoly for the exportation of sulphur to Taix & Co., of Marseilles,
which film immediately raised the price of sulphur from $25 to $70 per
ton. By so doing, it killed the goose that laid the golden egg, for
I^tes was substituted immediately for sulphur in most European
countries and the era of high-priced sulphur was but short lived. The
loss of this market was a permanent setback to Sicilian sulphur.

^dbvGoot^lc

CHARACTERISTICS AND USES 33

The subsequent history of the sulphur industry is one of violent ups
and downs. If one considers this history up until some time after
FrBBch made America a factor in the business, it will be noted that it
has been characterized at all times by short periods of prosperity,
followed by a short-sighted, selfish, destructive competition on the part
of certain interests. Following this would come a period of such marked
depression as to threaten the life of the entire industry, and it would
be necessary for some governmental or other outside agency to exercise
pressure to get the producers together on a common-sense basis and
thus gradually put the industry again on its feet.' Since the time when
Fraach made possible America's sulphur industry the stabiUty of the
whole industry has been much greater. While at the present time there
is an extremely lively competition among the companies for business,
there is every reason to believe that American common sense, spirit of
fair play, and co-operation will prevent this competition going to the
extent of threatening the industry itself, as has happened many times
in the past. Present indications are that all the sulphur companies are
pursuing an enlightened policy, in that all are doing more or less research
and development work having aa its ultimate object the opening up of
broader markets for sulphur, of which sulphuric acid manufacture
affords but one.
Advantaobs op Sulphur over Ptoiteb

For sulphuric acid manufacture sulphur has many very marked ad-
vantages over pyrites. Using pyrites means handling into the works a
comparatively large quantity of material, its slow combustion in expen-
sive roasters, a certain inevitable dust nuisance and the disposal of a ,'
large tonnage of cinder. As against this, sulphur of less than one-half. V'^
the weight of pyrites for a given tonnage of acid produced is handled'
into the works, is humed cleanly in inexpensive equipment and leaves
no residues to be taken care of. Sulphur ia constant in composition,
and its freedom from arsenic and other impurities allows the production
of a purer acid. It is also claimed that, in practice, the burnii^ of
sulplfur means a higher rate of production for a given size of lead cham-
ber space.

These acknowledged advantages of the use of sulphur over pyrites
for sulphuric-acid manufacture have been demonstrated by the willing-
ness of acid producers to pay a higher price per unit for elementary
sulphur than for combined sulphur in the form of pyrites. An example
of this is the fact that one of our largest and best organized chemical
companies, in making a large contract, chose sulphur over pyrites for
Bulphuric acid manufacture, where the differential in offered prices was
8c. per unit of sulphur.

■ In this oonneetlon, see Frabch, Perkin Medal Address, Met. &■ Chtm.
Bng.. vol. XO, No. 2, pp. 73-82, and J. Ind. Eng. Chem., vol. 4 (1912), p. 139.

^dbvGoOgfc

34 AMERICAN SULPHURIC ACID PRACTICE

When one considers the present high prices of labor, the uncertainty
of the copper market and the fact that sulphur may be purchased in a
competing market, from concerns which have large stocks on hand, so
that delivery is certain, it would seem to be a vise business policy to
use sulphur rather than pyrites for Bul[^urtc acid manufacture even
with a very large differential in price. This is especially true when one
considers the other side of the situation — namely, that in buying im-
ported pyrites the consumer is putting himself at the mercy of one large
set of interests which, while it may at the present time ofFer pyrites at
low prices and even below actual cost, will almost certainly at some time
JD the future reap its profit by much higher prices. It is said that
imported pyrites has been offered for lai^ contracts in this country at
about 10c. per unit of sulphur, ex-vessel, Atlantic seaboard, while at the
same time pyrites was selling in England, much nearer the base of
supplies, at 20c. to 22c. per unit of sulphur. It reminds one somewhat
of the tactics of Standard Oil in the old days before "trust-busting"
became fashbnable with politicians; and everyone knows that those
who bou^it cheaply when the company was extii^uishii^ a competitor
never reaped any peimanent advantage, but later more than paid for
temporary reductions in price.

Sulphur is today one of the few substances which have not risen in
price since pre-war days. In fact, sulphur is cheaper today than at any
other time in the history of the industry. The price for large contracts
is about $20 per ton, Atlantic seaboard. Tbia makes sulphur one of
the cheapest raw materials available and should, it would seem, greatly
extend its usefulness. Sulphur as mined and sold by all three com-
panies is of remarkably high grade. In fact, many so-called C.F. chem-
icals do not possess the purity of crude sulphur, as sold by these
companies. The sulphur is free from arsenic, seleaium and tellurium,
and often for days at a time wells will yield a product running higher than
99.9 per cent sulphur, as calculated on b moisture-free basis; in fact,
sulphur companies selling the crude sulphur on contracts guarantee the
purity to be over 99 or 99H psr cent.

Effect of Tracbs op Petroleum on Combustion

One impurity occurring in traces in the sulphur of all three companies
is oil. liere is a dearth of information in the technical literature
respecting the subject of oil in sulphur. Since tlie effect of this im-
purity is very interesting, it is appropriate to discuss it here. The
peculiar effect of oil is its influence on the burning qualities and also on
the color and odor of sul[riiur. A priori, one would not assume that
mere traces of a combustible substance like petroleum oil could affect
adversely the combustion of another combustible substance like sulphur,
but such is indeed the case.

^dbvGooglc

CHARACTERISTICS AND USES 35

If one will make a simple experiment by attempting to bum two small
lots of sulphur, one being chemically pure and the other containing 0.2
per cent of petroleum oil, he will note the following phenomena: The
pure sulphur will bum quietly until it is b^tally consumed; the sulphur
containing the oil will bum for a very short time, when it will be ob-
served that a thin, elastic film is being formed over its surface. Very
soon combustion is taking place only in spots, and within an exceedingly
flhort time the flame goes out, although only a small percentage of the
sulphur has been consumed. The explanation is quite simple. Sulphur
and oil at a moderate temperature react together to form asphalt, and
if the reaction is carried to completion the final result is carbon.

In the burning of sulphur containing oil the oil reacts mth the sulphur
to form an asphaltic nmterial, which quickly spreads as a film over the
surface. The result, as combustion proceeds, is a film of carbon over
tlie surface of the sulphur. The ignition temperature of carbon, or of
the intermediate asphaltic material, is so much higher than that of
sulphur itself or than the temperature developed during the burning
of the sulphur that this film is not ignited and consequently the whole
flame is extii^^ished.

The remedy for burning such sulphur is also quite obvious. If the
devices for sulphur combustion are such as to agitate the surface of the
burning sulphur or in any other way break this film of asphaltic mate-
rial, no difficulty will be experienced. Acid manufacturere who use
mostly modem tyi)eB of sulphur burners, such as the rotary or cascade
type, which allow the sulphur to drop from one level to another, have
at^lutely no difliculty in burning sulphur containing 0.2 per cent of
oil, which figure represents more oil than any of the. commercial sul-
phurs contain at the present time. On the other hand, many of the
small paper-pulp manufacturers still adhere to types of burners in
which the burnii^; sulphur is more or less quiescent. With such a type
there is no agitation of the burning liquid surface, so that some of these
paper-pulp manufacturers have had difficulty in burning sulphur when
they happened to obtain a shipment comparatively high in oil.

The sulphur deposits of all three operatiug companies are located in
chwe proximity to oil fields. When a sulphur deposit is first opened
some of the product may be high in oil, running as much as 0.2 per cent,
but as production proceeds the oil becomes progressively lower until
finally, for days at a time, it may amount to only 0.04 per cent, which ia
totally negligible, even for bumers which provide no agitation of the
surface. We have assumed that hot water carried this small quantity
of oil from small crevices in the oil-sand formation to the sulphur below
when the well was first opened. After a region has become heated up
by the hot water, these traces of oil are pretty well watdied out ; conse-
quently, Buli^ur mined later in the same area is virtually free from it.
Examination of drill cores of native sulphur showed such in aitu sul-

^dbvGooglc

36 AMERICAN SULPHURIC ACID PRACTICE

phur to be oil-free. We are informed by ex-employeee of die UnioD
Sulphur Co. th&t this con«8pond8 with tiie experiences of that organ-
isation in heating up any new area of sulphur ground. The examina-
tion of a very lai^ number of samples of sulphur, representing the
production of all three companies, has shown quite positively that none
of their sulphur contains enou^ oil to cause any difficulty in its com-
bustion with rotary burners or other burpers which agitate the surface of -
the burning sulphur during combustion. It is only very exceptionally
that one will find a car of sulphur whose oil content is high enough to
make difficulties in its combustion in a stationary type of burner.
Properties and Uses of Sulphur

Sulphur is now and is likdy to be for some time one of our cheapest
raw materials, and accordingly should and undoubtedly will find a
much wider range of usefulness. It is by studying the physical and
chemical properties of a substance that one first obtains ideas as to
possible new uses therefor. The chief physical properties of sulphur
are tabulated in Table 4. The present tonnage uses of sulphur are
presented in the chart. Those properties which suggest certain possible
tonnage uses for sulphur are its very poor conductivity of heat and
electricity, its resistance to being wetted by water and its inertness
toward most acids, all of this combined with a, fair d^ree of physical
strength. These properties suggest heat-insulating materials, electrical
insulators of various types, water- and acid-proof cements, and acid-
proof construction materials.

As against the properties of sulphur which might make it very de«r-
able for certain construction purposes are certain objectionable ones,
such OS its brittlenesB and its flammability. The brittleness can be
overcome sufficiently for many purposes by making mixtures of sulphur
with other materials, such as sand, asbestos, or paper pulp, or by rein-
forcing with wire screen. In many cases the flammabiUty is not a
serious objection.

A survey of the literature, especially the patents, on the subject of
sulphur mixtures reveals that almost every conceivable thing has been
suggested as a perfective admixture for sulphur to obtain a material
which has all the air- and acid-resistant properties one could desire or
to get a completely resistant kind of concrete useful in building. We
have tested out most of the recipes which appeared to be promising and
find as usual that the claims have been much overstated. However,
the ordinary mixture of sand and sulphur which has been repeatedly
mentioned in the literature has merits which should make it better
known. The mixture which has seemed to us the best for most uses is
that of 40 of sulphur and 60 of sand (parts by weight). The tensile
strengths of sulphur-sand mixtures as measured in the usual manner for
testing cement were as follows:

^dbvGooglc

CHARACTBttlSTICS AND USES 37

Tabi^ 3. — Tensilh Strenoths of Sulphur-band MixTDBEa

100 ■ 250

We have also used other fillers which have given tensile strengths of
800 and even 1,100 lb. measured in the same manner and have to a
large extent overcome the brittlenesB of the sulphur in some of these
mixtures. Sulphur-sand briquets kept on hand for one year show no
deterioration in strength. It is evident that the 40:60 sulphur-sand
mixture can be used as an acid-resistant concrete, for making acid-
resistjng pipe, tanks, gutters, launders, etc. The manipulation of such
a mixture is much like that of pourii^ concrete and is as follows:

Practical M amputation. — It is evident that the sand should contain
no constituent which wilt be attacked by any material which is to come
in contact with the finished product; for instance. In the case of acid
tanks it should be free from limestone or other acid-soluble constituente.
If necessary, it should be washed and dried. The sulphur may be
melted in a kettle with constant stirring, and the sand, which has been
heated separately, poured into it while the stirring is continued. Un-
less the sand is heated, it will lump when poured into the sulj^ur.
When the material is thick enou^ (40 per cent sulphur and 60 per cent
sand) it is ladled into the molds.

Considerable flexibility is possible in handling this material. For
instance, a small tank was made which was 2 ft. square, IS in. deep,
and 2 in. thick. The mixture was poured into a wooden mold in twelve
different lots. Although several of these lots had solidified before the
next was poured upon them, nevertheless the resulting joints were
Btrong. Apparently the hot mixture melts sufficient of the solidified
part to form a sohd joint. There was no contraction of the tank ae a
whole and no tendency to split in the mold. This mixture can be
worked with a trowel, tike mortar. It can also be reinforced by wire
netting placed in the mold before it is poured. The specific gravity of
a sulphur^eand mixture (40 :60) was found te be 2.46.

Weight of! cu. ft 154 lb.

Weiglit of Bulphur required per aubic feet 62 lb.

Weight of Hulphur required per cubic yard — 1,670 lb.

Taking the value of sand as SI per cu. yd. and of sulphur as $20 per
ton, the price of the materials per cubic yard will be about $18. It may
be possible to decrease appreciably the amount of sulphur necessary and

^dbvGooglc

38 AMERICAN SULPHURIC ACID PRACTICE

hence the cost by imbedding latter pieces of crushed rock or some such
substance in the mass. Teets of the material in sea water are being
made, but it is too early to give results. It is apparently standing up
well to date.

Pipes cast of this sulphur-sand mixture show no deterioration aft«r
one year in 5 per cent hydrochloric or 5 per cent sulphuric acid. The
ordinary organic acids have no effect on such a mixture.

Tabu; 4. — -The Physicochemical PaoFERTiEa op Sdlphub

Vapor Presbcbe Curve'
Forms of sulphar:

CTyHtalline a». or.

(fl) Rhmlnc. Ordinary form stable below Oe'C. (205"?.) , . 2 . 07"

(6) Monodinic Stable above %&°C. (205°F.) 1 .96'

(c) MiUt o} SidfkvT. Formed, e.g., by action of diluted
acids on polysulphides. Generally called amorphous,
but shown by Smith and Brownlee to be crystalline.'
There are several other modifications of crystalline sul-
phur of scientific interest but not of general importance.

Liquid. At lia'C. (235°?.) 1.81»

Contains:

SvlpkuT (liquid, soluble), 8\.

S^dphuT (liquid, insoluble or amorphous), Sfi.

The proportion of S(i to 8\ increases with the temperature.
Ainorphotia. S(i (sohd) 1.89'

Flaatic Sutpkw. Formed by heating sulphur above viscous

stage, 162°C. or 324°F., and cooling quickly 1,88'

Elaatie S^dphur. Formed by heating sulphur above 400''C.
or 752°F. and pouring in a thin stream into liquid air.
Its elastic properties arc soon lost.

Blaek S^djAur, " When sulphur mixed with very Uttle oil is
thrown into a hot platinum dish, a black substance is
obtained which has been looked on as a modification
of sulphur. The product contains 55 per cent of
sulphur and 33 per cent carbonaceous material." —
Watts, Du^ionary of ChemiatTy.

^dbvGoogle

CHARACTERISTICS AND USES

a ranges of temperatuieB a.

Electrical CoNDUcxiviTr'
Moaeured aa reciprocal value of rcBistivity in ohms of 1 o:

22 72 IX 10-"

69 156 0.254 X 10-"

116 239 0.105 X 10-"

130 266 O.S X 10-"

430 806 0.1 X 10-"

Comp&re;

Foroelwn 1 X 10-"

Mica 1 X 10-'»

Ebonite 1.6 X 10-"

Feictional Elbi

When rubbed with practically any other aubstance, e.g., glass, fur, silk,
wool or hard rubber — sulphur becomes charged with negative electricity.

CiBPFiciENT OP Linear Expanbion'

Surface Tbnsioi

Temp.

Ex. ooeff.

Temp.

Surface tension,

mg./mm.

0-13

32-56

0. 000046

120

248.0

6.71

13-50

56-122

0.00007

131

267.8

6.12

50-78

122-173

0.00009

146

294-8

6.05

78-97

173-207

0.0002

195

383.0

6.62

97-110

207-230

0.001

idb,Go(5glc

AMERICAN SULPHURIC ACID PRACTICE

APPROXIMATE CURVE OF SURFACE TENSION
COMPEESSIBILtTX '

Average fractional change ot volume caused by 1 megabar change in
presaure between 100-500 megabara 0.0000125.

1 megabar ^ 0.987 atmoBphera

CoNDOCTiviTV OF Hbat'
Measured as the numbet of gram-caloFJes transmitted in 1 sec. throi^h
a plate 1 cm. thick and having surfacee 1 eq. cm. id area when opposite
faces differ in temperature by I'X?.

20°-100°C. (68''-2l2°F.) 0. 0006

Compare:

Ice 0.002

Copper 1 . 00

InteniBtional Atomic Weight, 1920 - 32.06
Vapor Denaity:
At boiling point corre^mnds ^)proximate]y to formula Sg".
At 1,000°C. (1,832°^) corresponds approximately to formula St.
EcoNouicB DP Natural Sclpevr
Until 1900, 96 per cent of world's supply from Sicily
Iq 1912, 60 per cent of world's supply from Sicily
In 1917, 14 per cent of world's supply from Sicily
In 1917, 80 per cent of world's supply from U. S. A.

United States f^ports and Imports

1909 exports 37, U2 long tons

1909 unports 30,589 long tons

1918 exports 131 ,092 long tons

191S imports 82 long tons

United States Production

1894 494 long tons 1909 303,000 long tons

1899 1,590 long tons 1914 347,491 long tons

1904 196,888 long tons

1919 Texas Gulf Sulphur Co.
Only 9 months production after start, 348,380 long tons.

Properties of Commercial Solphuk
Insoluble in Water
Insoluble in Most Acids
Tensile strength, 200 lb. per square inch (apprra.).
Heat conduotivity, low: H that of cork, ^ that of ice.

^dbvGooglc

CHARACTERISTICS AND USES 41

Electrical conductivity lower than that of practically any other solid sub-
stance.
Melting point, depending on conditions, 1I0.2°-119.26°C. (230.4°-24e.

rr.).

Ignition temperature, 248°C. (478^.).'
Boiling point, 444.6''C. {832.3°F.).*

Melting Point'

Temp. ■

Type of sulphur C. F.

Rhombic 112. 8 235

Monoclinic 109 , 25 246 . 7

Natural freezing point S\ and %i in equilibrium (96.3 per cent SX, 3.7
per cent S^), 110.2'C. (230.4°F.).

Specific Heat'

Temp. .

Type of sulphur C. F. Sp. ht

Rhombic 0-96° 32-203° 0. 1761

Liquid 160-201 320-393 0.279

201-233 393-451 0.331

Heat of Combuation'

G. cal. per g. S B.t.u. per Ih.

8 -I- Oi ^ SO, 2 , 200 3 ,960

8-. HiSO. (dilute) 2,450 4,410

S-. H.SO. (dilute) 4,460 8,010

Heat of Vaporization*

Temp. G. Cal. B.t.u.

C. F. per g. per lb.

444.6° 832.3'' 70 126

(Approx.)

Transition Temperature'
S Monoclinic ^ 8 Rhombic

I^esBure, Temp. ■

kg./eq. cm. Lb./in. C. F.

10.6 16 96° 204,8°

123 17B 100 212.2

1,350 1,920

TBIPLB POIHT
Sulphur
Uquld

♦ Monoclinfc.
ISZO 18TT ISI* S04*

.dby,QQ,Qgie

AMERICAN SULPHURIC ACID PRACTICE

Hbatb or Solution in CSi*
G. cal. per g.

Dilute solution -11,89

Saturated solution —11.65

Heats of FnaiON"

G. cal. per g.

Rhombic at lOO-C. (212°^) 14.9

Monoclinicat 100°C. (212°^) 11.5

To form pure liquid sulphur (Sx):

From rhombic 14.6

From monoolinio 11.1

B.t.u. per lb.
-21.4
-20.9

CHANGE IN VISCOSITY WITH TEMPERATURE'
Solubilities in Various Solvents"

Solubility,
G. in 100-g.
solution

Carbon dimilphide. .

Carbon tetrachloride

Chloroform

Coal-tar oil, sp. gr. 0.87

^dbvGooglc

CHARACTERISTICS AND USES

I^naeedoU

0.4

160

320

9.0

Olive oil (sp. gr.

130

266

Sulphur chloride

65.2

131.4

186.8

Phenol

175

346

26.7

Toluene

73.4

1. 48

Turpentme (oil of)

60.8

1.33

Chamgd or MsLTiNa Point With Pbebsukb*

References Cited
> liANDOLT-BoBNarKiN-RoTH's "Physikalisch-Chemische Tabellen" (4th
•d.).

• R. H. Brownlbb, J. Am. Chem. Soc., vol. 29, pp. 1032-1062 <1907).
' A. WiBOAND, Ann. Phynik, vol, 22, pp. 64-98 (1907).

*H. ZicKENDSAHT, Ann. Phj/nk, vol. 21, p. 141 (1906).

' T, W. Richards and others, Carnegie Inst. Pub. No. 76, May, 1907.

■ MuELLEB AND BnnoEsB, J. Am. Cbtm. Soc., vol. 41, pp. 745-63 (1919).
' J. R. Hill, Chem. News, vol. 95, p. 169 (1907).

■ Calculated from vapor pressure curve. See also J. W. RiCHABns,
"Metallurgical Calculations" (2d ed.).

• M. BBU.ATI AND L. FiNAzii, Aui. r. Intl. Veneto, vol, 72, II, pp.
1303-14 (1913).

'* Lkwib and Randall, J. Am. Chem. Soe., vol. 33, pp. 476-88 (1911).
>i Seioeli^ "Solubilities of Inorganic and Organic Compounds" (2d ed.J.
'* MorrEseiEB, Mem. Acad, de MontepeUier, vol. 6, p. 107 (1S64).
" Oiibi.in-Kbaut, "Handbuch der anorgonishen Chemie."

^dbvGooglc

CHAPTER IV
RAW MATERIALS

The raw materiala for Sulphuric Acid are sulphur, oxygen
(supplied from the air), and water. The oxides of nitrogen,
either as Chile saltpeter or nitric acid, might be called indirect
raw materials.

Wat^F and air need no introduction nor description, so this
chapter will be devoted to the description of the sources of
sulphur and the nitric oxides. The amount of acid produced by
distillation from natural sulphates is practically nothing, leaving
brimstone and the metallic sulphides as our commercial sources.

Sulphur occurs native, as brimstone, in all parte of the world,
particularly rich deposits existing in Iceland and Sicily; but the
enormous deposits of Calca^iou Parish, south-western Louisiana,
furnish the United States. A small amount is mined in Utah and
Wyoming for local use, and the Pacific Coast is supplied from
Japan.

The Louisiana beds, worked by the Frasch process, were
discovered in boring for oil, and a most interesting and ingenious
method of recovering the sulphur was devised by Herinan Frasch,
for which he was awarded the Perkin medal.

The sulphur ore, containing up to 90 per cent sulphur, occurs
450 ft. down, under quicksands that make usual mining methods
impossible. The Umit^ of the bed have never been determined,
although 40,000,000 tons have been locked out.

The Frasch process, described in United States patents,
No. 799,642 and No. 800,127, is as follows: A 13-in. hole is drilled
to a depth of 800 ft., cased, and inside, concentrically, a 10-in.,
a 3-in., and a 1-in. pipe is placed. Between the 3-in. and the
10-in,, and the 10-in. and the 13-in. pipes superheated water,
heated by superheated steam to a temperature where sulphur
begins to darken, is forced by its own expansive force, and by
steam pressing, into the deposit. The hot water, after melting
the sulphur, passes into the crevices of the rock, the molten
sulphur separating from the water by gravity, and being forced
up the inner pipe by steam pressure. The steam pressure is
kept less than the head of a column of molten sulphur reaching

^dbvGooglc

RAW MATERIALS 45

to the ground, and the sulphur is lifted the last part of the way
by compressed air.

The molten sulphur is run into huge spaces fenced in with
boards, where it solidifies and is then blasted down for shipment.
It will run over 99.6 per cent S, and praeticaHy no As.

Louisiana sulphur is shipped from Sabine Pass, Texas, to
supply all the eastern United States. It was quoted (1916) at
$22 a ton, and was reported to cost, f.o.b. mines, under $3.

The Japanese sulphur, greyish in color, comes in large blocks,
about 3 by 2 by 1 ft., wrapped in matting. It supplies the
Pacific coast demand.

PTRITES

Iron pyrites, FeSi, bisulphide of iron, is one of the most widely
distributed of ores, and has been, since about 1840, a material
of prime importance in the manufacture of sulphuric acid.

Pyrites crystallizes in the regular system, as a cube, octohedron,
and pyrihedron, and often as twin crystals. The crystals are
frequently well developed, and become very large. It is greenish
yellow in color, its popular name, "Fool's Gold," describing it
well. Small crystals show darker colors, and the powder is
greenish black. Fracture is concboidal or irregular. Hardness
6 to 6.55; Bp. gr., 4.83 to 5.2; it contains 46.58 per cent of iron,
and 53.42 per cent of sulphur.

Volcanic pyrites contains no water, while sedimentary deposits
do. Some of the pyrites containing water bursts upon roasting.

The principal North American deposits of pyrit^ are at
Tilt's Cove; New Foundland; Capleton, Quebec; Ely, Vermont;
and Pulaski, Virginia. Cuba is becoming a large producer.

Pyrrhotite, magnetic iron sulphide, FeySg, is not a practicable
source of sulphur: first, because of its low sidphur content
(39.5 per cent sulphur, 60.5 per cent iron), but even more impor-
tant, the sulphur that it does contain is not readily given up, the
lumps crusting with oxide of iron, and extinguishing whatever
flame is started. It has been successfuly roasted in powdered
form in a Herreshoff roaster. E. D. Peters speaks, in "Principles
of Copper Smelting" (p. 169), of $200,000 thrown away on an
acid from pyrrhotite proposition.

Copper-bearing pyrites, of the general form of chalcoperite,
CujS, Fe»S), is a valuable source of sulphur, either when the ore
is roasted and the SOi given off used for acid making, and the

^dbvGooglc

46 AMERICAN SULPHURIC ACID PRACTICE

cinder for copper; or aa at the Tennessee Copper Co., the gases
from semi-pyritic emelting are used direct to the chambers.

Zinc blende, ZnS, the principal ore of zinc, is an important raw
material, the SOi derived from its being roasted to ZnO being
used. Blende contains 32.9 per cent sulphur when pure — ores
usually contain some FbS and other impurities, so that the
sulphur content may drop as low as 20 per cent. Very little
arsenic occurs with blende, and the acid produced from it is in
demand for that reason.

The SOj produced by the roasting of zinc blende would prob-
ably never be used to make sulphuric acid if the gases were not
injurious to v^etation, for the gas from a material so low in
sulphur is very dilute. And in addition, sufficient air must be
introduced, not only to bum tlie sulphur, but to oxidize the zinc
as well:

2ZnS + 30, = 2ZnO + 2S0j.

As is shown, 50 per cent more oxygen than is required to bum
the sulphur is required, and the nitrt^n from that air serves to
dUute the gas formed. So sulphuric acid from blende is less
a by-product than a means of taking care of the hannful gases,
that otherwise, if let free, destroy all vegetation near the plant.
Consequently, while an important source of acid in this country,
the burning of blende is properiy a part of zinc metallurgy, and
for thorough treatment the reader is referred to works on that
subject.

Zinc ores must be well roasted, so 'the cinder should contain
under 0.75 per cent sulphur, either as ZnS or as ZnSOi- If the
furnace temperature is too low the sulphate will form, and that
must be specially treated to get it into the form of ZnO, for
distillation.

The muffle type of furnace, with a mechanical stirrer, is in use
in all modem works.

Lead ores are too low in sulphur to be used for a raw material
for sulphuric acid, pure galena only containing 13.4 per cent
sulphur.

I cannot find that spent oxide of iron is used in this country as
a raw material, although it is used abroad. Gas works remove
the HtS from gas by a mixture of hydrated iron oxide and
sawdust, according to the formula;

Fe,(OH) ,-|- 3H,S - 2FeS + 6H,0 + S,

^dbvCooglc

RAW MATERIALS 47

and upon exposure to the air precipitates more sulphur, as
follows:

4FeS + 30, + 6HtO = 2Fe,(0H), + 28,

This regeneration is repeated perhaps thirty times, before the
quantity of sulphur is sufficient to interfere with the use of the
oxide as a purifier. It contains as high as 60 per cent sulphur
then, and is used as acid material.

KITRATB OF SODA

Nitrate of Soda, usually called Nitre, or Chile saltpeter, has
been the source of practically all our nitric acid, and still accounts
for the largest part of it, although the various fixation processes
are making the nitrogen of the air available in ever increasing
quantities ,

Formula— NaNO,; hardness, IH to 2; sp. gr., 2.09 to 2.39;
the large crystals are colorless, transparent, and brilliant; small
crystals white and opaque; crystallizes in rhombohedra; has a
bitter, cooling taste; upon heating it first melts and then decom-
poses, at a red heat, into sodium nitrite and oxygen; fuses at
316°C.; and it dissolves very readily in water, with absorption of
heat.

There are many known deposits of nitre, but the world's
supply comes from northern Chile. There it is found under a
cap, up to 7 ft. thick, of "costra," a hard conglomerate. The
actual nitrate bearing ore, called "caliche," occurs in horizontal
beds, up to 5 ft. thick, containing 45 per cent to 85 per cent
of sodium nitrate, 20 per cent to 40 per cent sodium chloride,
and sodium, potassium, and magnesium nitrates, sulphates,
iodates, and chlorates, and guano. It is an old ocean bed.

The caliche is crushed and the soluble salts leached out; then
the sodium nitrate crystallized out in a very pure form, carrying
the chlorates and iodates, which are recovered during the nitric
acid manufacture. The mother liquor retains most of the sodium
chloride.

An average analysis of commercial Chile saltpeter is:

96.00 per cent NaNOj (including nitrate, iodate, etc.),
0.05 per cent NaCI,

0.75 per cent sulphates (calculated as NaaSO*),
2 , 75 per cent moisture.

^dbvGooglc

48 AMERICAN SULPHURIC ACID PRACTICE

The imports of this material into the United States have grown
steadily, from 125,000 tons in 1898, to 519,000 tons in 1910.
About 80 per cent of this goes into commercial fertilizers, the
remaining 20 per cent into our chemical industry.

Being deliquescent, the salt becomes damp and adheres to the
bags it is shipped in, not only causit^ loss of nitre, but danger of
fire, as the bags will ignite spontaneously. The bags are therefore
usually washed out with hot water, and dried, the saltpeter being
crystallized out of the water. The mother liquors from this
crystallization contain NaNOj, KNO„ I, Nal, KI, KCIO,, 20per
cent to 30 per cent insoluble, water, and small quantities of borates
and chromatea.

The mother liquor is run into a wooden vat, equipped with a
mechanical stirrer, and is slightly acidulated with sulphuric acid;
the result is NaHSOt and I, from the iodates — now NaNOj is
added, reacting as follows:

(1) NaNO, + H^O, = PNO, + NaHSO*,

(2) 2HN0, + 2HI = 21 + 2N0 f 2H,0,
Bubbling air through gives

(3) 2N0 + O, = N,0„
which reacts with HI m

(4) N»0» + 4HI = 41 + 2N0 + 2H,0,

and the reaction repeats.

Agitation is then stopped, and the liquor is allowed to settle
over night, decanted, filtered, and washed with soda-ash. The
product is a paste, running 75 per cent iodine and 25 per cent
water.

The decanted Uquor contains 0.02 per cent I, which is treated
with sodium sulphite, to fix the iodine, so it will not pass off as a
fume, and goes back to the bag house to be reconcentrated. The
proper amount of sulphite is known to have been added when the
color of the liquor changes from black to dark brown.

^dbvGooglc

CHAPTER V
PRODUCTION OF SO2

By far the largest part of the sulphuric made is from SOj pro-
duced especially for that purpose. A very considerable tonnage,
however, is made from gases which are by-products of certain
metallurgical operations.

High grade brimstone is the ideal material for niaking SO2 for
acid manufacture. The equipment for burning it is compara-
tively small and inexpensive, and as it ail bums, there is no ex-
pense for handling cinder. Moreover, a verj- rich and uniform
gas can be obtained. Several very satisfactory brimstone
burners are made and regularly marketed in the United States.
The two most used and perhaps best suited for burning large
quantities of sulphur, are the cet'i'^_tyi>s and the^^helf type.

The rotary type is shown in Fig. 3. This burner b sunilar in
appearance to the Bruckner or White-Howell roasters, except
that no fire box is required.

Brimstone melts at a temperature below its combustion point,
Bo whether it is in lumps or in powder or is run into the burner
molten, is not important to the actual burning, although the
condition in which it is to be fed will determine the nature of the
feeding apparatus if it be a mechanical one.

If a pile is made of lump sulphur and a fire started at the
bottom of the pile, the sulphur melting and running down will
smother the flame; so a small depression is made in the top of the
pile, a piece of oily waste lighted and thrown in, the sulphur
begins to melt and run down to the bottom of the cavity and to
take fire. The pool enlarges itself rapidly by melting down new
sulphur, and soon the entire mass is burning but all on the top.

The molten sulphur is sticky, and this property is taken advan-
tage of in rotary burners, of which the Glenn Falls Machine Co.
makes the best known. This burner is a plate iron cylinder with
east iron truncated cone-shaped ends, mounted upon trunnions,
horizontally, the sulphur and air going in at one end, the SOj
and partly comsumed air, with a little vaporized sulphur, passing
out at the other into a large fire-brick lined vertical cylindrical

^dbvGooglc

50 AMERICAN SULPHURIC ACID PRACTICE

combustion chamber. In the combustion chamber entrance
further air is admitted and the vapor of sulphur is completely
burned. (See Fig. 3.)

The advantage of the rotating burner is that the molten sulphur
sticks to the inside of the cylinder as it revolves and bums all
the way around, which, with the dripping sulphur adds in small
compass very largely to the combustion area and so increases the
capacity. The burner revolves slowly, being adjusted to have
the sticky film almost burned up when that portion of the side
of the cylinder dips into the molten sulphur again.

The labor of attending these furnaces is very light. One man
can easily feed two of them with a shovel in addition to looking
after oiling, adjusting dampers, and all other operation. If the
sulphur is supplied to the burners by mechanical means they
require very little attention. The sulphur may be fed, in either
the solid or molten state. If solid, the material is carried into
the burner from a small hopper by a short screw. If molten, an
iron tank containing a steam coil b placed somewhat above the
burner, the molten sulphur is carried to the burner through a
steam-heated pipe, and the flow controlled by a steam-jacketed
valve. Either method works well if properly handled.

^dbvGooglc

PRODUCTION OP 50, 51

Control of the quality of gas and its volume lies in the handling
of dampers at the feed end and the entrance to the combustion
chamber, and in the quantity of sulphur fed. The production
of gas of the grade most desirable for making sulphuric acid, i.e.,
not over 10 per cent SOi is not at all difficult. The chief trouble
which occurs in the operation of sulphur burners, especially in
producing high strei^h gas, is that if dampers are not properly
adjusted some sulphur vapor may go through the combustion
chamber without being burned. This sulphur on being cooled
in the flues or in the towers becomes soUd and chokes the

Rotary burners are regularly made in sizes with capacities
ranging from 200 to 300 lb., to 15 tons per 24 hours. Floor space
12 ft. by 40 ft. will accommodate even the largest size mentioned.
The power consumed in driving them is very small.

Rotary type burners have been Ukened to Bruckner roasters, and
the shelf type may properly be said to resemble the McDougall
roaster. It employs the superimposed tray or hearth construo-
tion. Of course a stirrii^ mechanism is unnecessary because the
sulphur is molten and simply overflows one tray and drops to the
nextandsoon. A burner of this type is shown in Fig. 4. It consists
essentially of a cylindrical cast-iron or steel, brick-lined chamber
containing severai cast-iron hearths or trays. At the top is a
chamber or reservoir into which the sulphur is chaiged and in
which it melta. A valve in the bottom of this chamber controls
the flow of molten sulphur into the burner proper.

In operation a charge of sulphur is put into the top reservoir, a
fire is started in the tray immediately below and allowed to burn
until the sulphur starts to melt. The valve is then opened and
the molten sulphur trickles in and ignites. Any part not burned
on the first tray overflows to the second, and so on. Most of the
ash and dirt is carried by the flow to the bottom pan. Doors
are provided however to give access to any hearth.

In capacity range these burners are regularly made to bum
up to 10 or 12 tons of sulphur per 24 hours. The manufacturers
point out the following advantages for this type of burner:

1. No moving parts or power required.

2. Small floor space. A 9-ft. diameter cyhnder burns 10 to 12
tons per 24 hours.

3. Better heat conservation than any other type.

As mentioned before, brimstone burning allows the production

^dbvGooglc

52 AMERICAN SULPHURIC ACID PRACTICE

of very rich and uniform gas. The percentage of SOi is limited
by the fact that for either chamber or contact- work a certain
minimum oxygen percentage must be maintained. This oxygen
percentage should be at least per cent -„ — t- i, since one volume

of SOi requires ^4 of one volume of oxygen to form SOj, and about
4 per cent excess is desirable. Since air contains about 20.8 per
cent oxygen, the sum of SOj and oxygen in the gas from the
burner will be 20.8 per cent. The maximum SOi then should

^dbyGoogle

PRODUCTION OF SO, 53

be, in ftccordance with the above proportion, 11.2 per cent and
oxygen 9.6 per cent.

BDRKING PYRITES

Iron pyrites, when pore, has the formula FeSi, and contains
46.7 per cent iron and 53.3 per cent sulphur. It is never obtained
entirely pure, although material containing over 50 per cent sul-
phur is sometimes found. The general range is from 40 per cent
to 50 per cent aulphur.

Sulphides of the metals burn in air, with the production of the
metallic oxides and SOi; and if the operation, called roasting, is
not complete, intermediate sulphates and bisulphates.

Iron pyrites when roasted gives off of its FeSi nearly one atom
of sulphur very easily. At comparatively low temperatures the
sulphur bums at once to S0» leaving behind FcySg. At higher
temperatures it is at first volatilized as a dense cloud of yellow
smoke, and then bums to SOt. At the second stage of the process
begins the oxidation of the iron in the ore along with that of the
remaining sulphur. This is much slower and less vigorous than
the burning of the primary atom of sulphur, and as the various
iron oxides formed are fairly active catalytic agents or "contact
Bubstances," a considerable quantity of SOg is formed at this
Btage. For purposes of calculation the net result of these
reactions may be written:

4FeSt + 110, = 2Fe,0j + 8S0,

Pyrites is obtained and burned in two different forms, viz.,
as lump pyrites and as fines. The former is material in pieces
from the size of the fist down to about 3^ in. Fines is material
under ^^ in. These two classes are burned in distinctly different
forms of burners.

The lump burners used in this country are quite simple. The
general scheme is similar to the burning of lump coal on grates
except that the bed of fire is carried much deeper, i.e., around 2
ft. Fines in any appreciable amount are not permissible as they
prevent free draught. In brief, a single burner consists of a
brick box up to 6 ft. long from front to back, and 4 or 5 ft. wide.
It is divided by a grate into an upper or burner compartment,
and a lower or ash pit compartment. A charging door is placed
at such a level above the grate as to allow a bed of ore about 2
ft. deep. A small door at the grate level allows the grates to be

^dbvGooglc

54 AMERICAN SULPHURIC ACID PRACTICE

shaken. A door in the ash pit provides for removal of dnder.
Orate bus made of cast iron, of square section about 2 in, on a
side are used. They are supported by cast^ron bearers at two
or three points. The bars are made with circular section at the
pointo of support in order that they may be turned. When
their diagonals are set vertical and horizontal a considerably
smaller space exists between them than when they are turned
with their diagonals 45° from horizontal. By turning the bars
from one position to the other with a wrench the lumps are
crushed and the shaking out of the spent cinder is accomplished.
F^ure 5 shows the general features of a lump burner and grates.
Most of the modem plants using the lump burner have im-
proved its details making it tighter and more convenient to
operate. Burners are now made practically encased in steel or

tB *

cast-iron plates. Door frames and doors are planed to give
tight joints without using putty. In scHne cases the ash pits
discharge into cars in a tunnel below the burner set. These
improvements have made labor less and gas more uniform, but
the nature of this form of burner demands a considerable amount
of hand labor which cannot well be eliminated.

The capacity of a burner depends somewhat upon the sulphur
tenor of the ore and its melting point. High grade pyrites con-
taining little copper can be burned to give much more SOi per
unit of grate area than low grade ore high in copper or which
contains pyrrhotite; in other words ore of low fusing point. We
cannot in any event expect to get much more than one ton of
QO" acid from one good sized burner. Driving a burner too fast
causes fusing and stickit^ and much hot laborious effort to clean.

It will be seen that to provide gas for a large set of chambers
the ground area and buildings required for lump burners is very
great. Lump burners are built in blocks back to back and
consisting of almost any number desired. Sets of 24 to 30 are

^dbvGoO^lc

PRODUCTION OF SO, 55

common, and some up to 40 are to be Been. To decrease ground
area the obvious thii^ to do would be to carry greater depth of
ore on the grates. This presents several difficulties however.
Heat would get too high if rate of burning per square foot were
increased. Shaking out cinder uniformly would be uncertain.
If fusing occurred, cleaning would be difficult. Burning of
lump pyrites is practiced almost entirely on acid unitB of not
over 50 tons OCBS. acid daily capacity.

mSTRnCTIOHS P0« STARTING LUMP BDRHERS

Be sure the brickwork is not too green upon starting. The
moisture should be dried out of the bricks by means of a very
light fire in the bottom before starting up.

Uniformity otsize of charge is important and money spent on
this will pay well.

First clean out the furnaces thoroughly; see that the top fiues
are clean; put in the grate bars. See that all doors are in place.
Manhole doors should have a thin joint of tar and fireclay.

The top buckstay rods should not be too tight, which is readily
seen by striking them with a hammer, so as to allow for expan-
sion as the furnace heats up. This must be watched carefully.

Before putting a fire in the ftu'nace provision should be made
for taking oS the smoke, wMch is best done by means of a tempo-
rary stack on the uptake to the Glover tower, over the opening
in one of the top plates. This stack should have a t^ht damper
in it so it will not be necessary to remove it when its use is dis-
continued.

The damper in the Glover fiue must be closed to prevent smoke
from gettii^ into the system. It is necessary to cover the grate
bars with something like pyrites cinder to protect them from
warping. If cinder is not to be had, broken stone or brick will
do. Spread out this protector a foot thick except in the corners,
where it should be 15 in. A wood fire is then started in each
furnace on top of the cinder. The fire is kept burning until the
whole interior is well warmed up and there is a bed of red ashes
over the entire area of the furnaces. The fire is then increased
until the interior of the furnaces is red hot, including the top of
the bed of cinders.

The best material for firing is oak or hickory as these make little
smoke. Broken coke and coal are used but as these make a very

^dbvGooglc

56 AMERICAN SULPHURIC ACID PRACTICE

hot fire, care must be taken that no clinkers are formed with
the cinder. If any are formed they must be removed before
changing ore.

As the ^ass of brickwork and iron is bound to expand as it
heats up, the buekstay rods must be loosened from time to time.
A tap with a hammer shows if they are too tight, a hard nietalhc
ring indicating that they should be slacked off. Do not loosen
tbera too much as it is hard to tighten them again owing to the
great pressure of the arches, which may crack in consequence.
Care must be taken that a furnace does not get hot too quickly.
Firii^ should take 30 to 36 hours for a new furnace, less time
being required for an old one being restarted.

After the final heating the wood should be burned ofE about the
same time in each furnace, leaving a bed of hot embers. Before
ore is charged withdraw any unbumed fuel, at the time making
sure there is no matte where the main fire was. Distribute the
hot embers evenly then charge sufficient pyrites to cover the
whole grate. The pyrites should be placed in front of the fur-
naces beforehand so that no time is lost in charging, for it is
very important that they go in quickly before the furnaces lose
heat. This is best done by having several men charging at the
same time. When the charges are in, the gas can be turned
into the system. When the first fharge is burning well, the
furnaces should receive a second charge so as to insure a suffi-
cient quantity of ore in the furnace to prevent any possibUity
of running low and losing its heat.

The gases leaving the furnace contain for a time some carbon
dioxide in addition to SOj, due to the residual fuel. It is highly
important to charge the furnaces with clock-like regularity. For
example, if there are 24 furnaces one will be charged every hour or
every half hour as desired. A regular schedule is followed in
any event. The charging time of each furnace should be marked
upon it.

FUTES BURNERS

Fines burners are by far the most used and most important
of the apparatus for producing SO3 for making sulphuric acid.
The main reasons for this are:

1. I^t^ capacity with small ground area.

2. Charging ore and dischai^ing cinder are continuous and are aoconi'
ptiahed without opening the furnace, and the gas ia in consequence uniform.

^dbvGooglc

PRODUCTION OF 50, 57

3. Handling of ore and cinder ore done by mooliiner}', practically elimi-
nating hand labor,

4. Several well-designod and satisfactory fumacfts are on the market and
can be bought practically from stock.

In the early days of acid making pyrites fines were bumed in
the crudest way. The favorite method was on a brick heaxtb,
the pyrites being fed by hand with shovels, and rabbled by hand.
ThiB method produced cinder high in sulphur and most untini-
form, besides being very costly in labor.

The first improvements over the hand method in rabbling
were along the line of mechanical rabbles in the form of plows
which were dragged through the furnace on a chain, pulling
the ore aloi^. with it and turning it over, giving a much better
roast with lower labor costs. But to get a complete roast the
temperature had to be high and maintenance costs were heavy.
Also the plows were heavy and the wear on the hearths consider-
able.

The next step was an annular furnace with arms branching
out from a revolving central axis, the arms carrying rakes for
stirring the ore). The roof of the furnace had to be supported
from the outside as the arms entered the furnace through a
slot in the inner wall. A great deal of air entered through this
slot so it was often covered by an iron apron revolving with
the arms.

In 1868, McDougall introduced his circular multiple hearth
furnace. The McDougall furnace consists essentially of a
cylindrical steel shell lined with about 9 in. of brick and
containing several self-supporting arched brick hearths. Through
the center of the furnace runs a vertical iron shaft or column.
To it are fastened horizontal iron arms, one, two, or even three
to each hearth, and these bear iron rabble teeth. This shaft
with its arms is supported on a bearing beneath the furnace
and in operation is revolved slowly. Alternate hearths have
drop-holes near the central column and near the outside waU.
The rabble teeth stir the burning ore and move it across the
hearths so that it passes uniformly down through the furnace,
crossing each hearth and falling to the one below.

The original McDougall furnaces did not include any provision
for keeping the shaft and arms and rabbles cool, and this was
probably the chief reason that the furnace gave trouble and was
not more widely used for many years. Mr. J. B. F. Herreshoff

^dbvGooglc

58 AMERICAN SULPHURIC ACID PRACTICE

of the Nichola Chemical Co. on investigating the problem built
a furnace with a hollow iron shaft and hollow armg, and blew
cold air throi^h them, in that way keeping the temperature of
the metal at such a point that ite strength was not impaired.
HerreshofF also arranged to admit controUed amounts of the heated
air issuing from the shaft and arms, into the hearths at any
desirable points. Frasch also applied water cooling to the hollow
shaft and arms.

Other improvements and refinements have been made on the
McDougall furnace and we find to-day that the name McDot^all
has largely disappeared, and these furnaces are known by the
names of those who have made the modifications.

The chief differences in the furnaces of this type now on the
market are in the shafts and arms, and the following claasification
is made on that basis :

1. Furnaces having water-cooled ghafta and anna.

2. Furnaces having airnjooled ahafta and arms.

3. &naU shaft fumacee, t.e., shafts into which a man cannot enter.

4. Large shaft furnacea, i.e., shafts large enough to allow a man to enter
and work.

In roasting any of the pyritic materials suitable for acid makii^
it should be understood that furnace temperatures, i.e., temperar-
tures of gas, ore, and brickwork, are influenced only to a small
extent by either the air or water which may be circulated through
the shaft and arms. This statement applies in greater degree
to large than to small furnaces. The prime function of the air or
the water is to regulate the temperature of the iron parts them-
selves. A rough heat balance sheet of a roaster burning a pyritic
ore of moderate sulphur tenor is interesting in showing the dis-
posal of the heat units.

As this balance is intended to show only the relative amounts
of heat going to the various products, etc., rather than acutal
heat units, only the iron sulphid is considered.

This ore contains 34.7 per cent S as FeSi.

The calcine contains 7.0 per cent S.

The calcine weight is 80 per cent of that of the ore from which it is made.

For each 100 parts of ore there is burned 34.7-80 per cent of 7 or 29.1
parts of sulphur

Assume that one half this is "volatile atom" and its dissociation heat
requirement is negligible. The heat evolvera are then:

^dbvGooglc

PRODUCTION OF SO^ 59

29.1 parta S to SO, @ 2,170 caloriea = 63,200

29.7 X 1.76 parts Fe to Fe,Oi @ 1,750 calories - 44,500
Total calories per 100 parts ore = 107,700

Heat is absorbed by dissociation of FeS.

40 FeS @ 273 calories - 10.920

Net calories evolved per 100 parta ore = 96,780

Assume that the furnace roasts 100 lb. ore per minute and that
the gas issuing from it contains 9 per cent SOi, 8 per cent
oxygen and 83 per cent nitrogen.

29.1 lb. S make 320.6 cu. ft. SOi. Total gas per minute then =
3,562 cu. ft. Assume the air enters the furnace at 20''C. and the
gas leaves it at 620''C. Then the heat carried away by the gas is :

SOi 09 X 3,562 (.0226 X 600 X .0000187; = 10.80

O OS X 3,662 (.0189 X 600 X .0000017) = 6.65

N .83 X 3,662 (.0189 X 600 X 0000017) - 59.80

Calories per degree 75 . 3

The ore enters the furnace at 20''C. and the calcine is discharged
at 420''C. Heat carried away by calcine is 80 (.1456 X 400 X
.000188) = 17.664 pound calories per degree. Calories for
400" = 7,066.

This furnace is assumed to be air cooled. There are 1,000
cu. ft. per minure of air at 20°C. blown in through the arms, and
this air issued at 220°C. Calories carried away by this air =
3,848.

RBCAPITUL4TION

Total heat envolved - 96,780 caloriea

Heat to gas 45,210

Heat to calcine 7,066

Heat to air ■. . 3,848

Total accounted tor 56,124

Balance for radiation 40,650

Badiation surface of the furnace, 2,200 sq. ft.

Loss per square foot per minute -> 18.4 lb. calories.

This calculation shows that the two chief ways in which the
heat is carried off from a roasting furnace are by the gas and by
iBdiation. The heat units carried away by the cooling medium
circulated through the shaft and arms, and by the calcine, are

^dbvGooglc

60 AMERICAN SULPHURIC ACID PRACTICE

ins^ificant. As the radiating capacity of a furnace once built
is not variable at will, it is apparent that control of furnace
temperature must lie in feed of ore and volume of air admitted.
When air cooling of the iron parts can properly be used it is to
be preferred over water cooling for several reasons. When water
is used for cooling, the temperature of the arms is so low that the
iron becomes sulphated and the rabbles soon become cemented to
the arms and can often be removed only by breaking. With
air cooling, the temperature of the metal is usually so h^h that
this sulpbating does not occur. Another advantage is that slight
leaks at joints or chaplet plugs do no harm if air cooling is em-
ployed, while with water even slight leaks cannot be tolerated.
Often a water-cooled arm must be removed on account of a
persistent small water leak where an air leak of the same size
would scarcely be noticed.

WatOT<ooled Arm Htedge Type Arm Eno
Fia. 6.

Air-cooled arms and shaft must have much larger p
them than necessary when water ia tised for cooling. Indeed the
success or failure of air cooling depends much upon whether or
not the passages are of ample area. The thickness of metal in
air-cooled arms is less than in water-cooled arms.

Figure 6 shows the essential features of an air-cooled arm with
Hanged end for bolting to shaft, and a water-cooled arm with
end-detail as used in the Wedge furnace.

The other major difference in the McDougall types is in the
large and small central columns. Until the advent of the Wedge
furnace all the McDougall furnaces had small central columns,
i.e., not above 18 or 20 in. diameter, and hence too small foraman
to enter. When, any thii^ became wrong with an arm which
necessitated replacing it, it was necessary to stop the furnace and

^dbvGooglc

PRODUCTION OF SOt 61

allow it to cool down enough to permit men to enter the hearth,
unfasten the bad arm from the shaft and fasten on a new one.
This always required several days and meant that the furnace
had to be restarted with fuel. Such a loss of time is a serious
thing to an acid plant, especially if a single furnace is being
depended upon.

Many attempts have been made to devise arrangements
whereby arms could be replaced without cooling and entering the
hearths. It is not difficult to do this if air cooling or no cooling
is sufficient. If water cooling is necessary and water-tight con-
nections have to be made it seems impossible unless one can get
at the inner end of the arm, which with the small column furnace
means getting into the hearth. While this feature of the small
shaft furnaces is disagreeable, it should not be overestimated.
Well made arms properly taken care of last for long periods, and
there are other things beside failure of arms which demand
cooling down a furnace at times, failure of brickwork for example.
It is often possible to get along with a sick arm for a time until a
genera! overhauling is desirable.

Small column furnaces of which the Herreshoff is an example
have their columns made up of cast-iron sections flanged together.
When water cooling is used a water supply pipe extends down
the middle. It is provided with a tee fitting corresponding to
each arm, into which is screwed a pipe which extends well out
toward the end of the arm. The water enters the arm through
this pipe and returns around it into the annular space in the
column. Usually the arm itself has a flanged end which is
bolted to a corresponding flange on the column casting. There
are variations in this method of fastening but the flange is most
used.

For air cooling a partitioned arm, as shown in Fig. 6, is used
and an interior column construction as shown in Fig, 5.

The Wedge furnace, shown in Fig. 6B, is the only furnace made
with the large column. This column is 4 or 5 ft, in internal
diameter, built of steel plates riveted together, and covered on
the fire side with fire brick and insulating material. The arms
project through the wall of this column and are fastened inside.
The air or water connections are hkewise inside the column.
It is a simple matter in case of the failure of an arm for a man to
enter the column immediately, disconnect the pipes, and loosen
the latch. The arm can then be pulled out and a new one in-

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62 AMERICAN SULPHURIC ACID PRACTICE

Fio. 6A,- — Herreahoff furnacoB.

idb,Go(5glc

PRODUCTION OF SOt

serted and connected. It is not a pleaeant job because the inside
of the column is decidedly warm, but it can be readily and safely
done by any men who are reasonably accustomed to furnace
work. There are certainly many more aevere tasks about metal-
lurgical furnaces. If proper arrangements are made an arm
may be removed and a new one inserted and connected ready to
go in 4 hours.

One feature of the large column which has given some trouble
u) the carrying of the great rotating weight in a satisfactory way.
The customary design for the larger sizes provides a set of six
large beveled rollers upon which the cast spider carrying the
column revolves. In the middle is a small guide bearing. The
trouble with this arrangement is in maintaining the shaft plumb,
and the load equally distributed upon the rollers. The side

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64 AMERICAN SULPHURIC ACID PRACTICE

thrust causes some wear of the rollers and their thrust bearings,
whidh is not equal all the way around. As soon as one roller ia
further away from the center than the others it ceases to carry its
proper share of the load, or else the shaft goes out of plumb.
This cannot be said to be a very serious fault, but it makes the
arrangement less satisfactory than the old step bearing.

In the 25-ft. furnaces of this type erected at Anaconda a few
years ago, the columns are supported on 9-in, step bearings of
very rugged construction. The coliunn is held plumb by a set
of vertical rollers beorii^ against a ring fastened around the- top
of the column.

Fines bumeis are started by bedding the upper floore with ore
then heating with wood, coal, oil, gas, or powdered coal, with the
mechanism stationery. When sufficiently heated the floors are
cleared and the mechanism started with a hght feed of ore. It
is usually necessary to use a Httle fuel for a time after starting
feed. The variables used in the control of a furnace are amount
of ore fed, and voliune of air admitted, also sometimes the rate
of revolution of the arms. The usual speed of revolution is from
1 to 2 R,P,M. The operation is watched through peep-holes.
A 15-ft (diameter) furnace requires one horse power.

BT-PRODUCT GAS FROM COPPER REDUCTION WORKS

About one-half million tons per year of acid is made from gases
evolved from the reduction of copper ore. The only two sources
of such gases at present are roasting furnaces and blast furnaces.
The roasting furnaces used at copper reduction works in con-
nection with acid making are all of theMcDougall type, and of
several different miJces, embracing all the types described above.
The materials roasted show wide range and are all materially
difEerent from the pyrites ores regularly bought for acid making.
However as the gas used is really a waste product and no chaige
for sulphur is made against the acid, these acid plants can well
afford to work with less favorable ores.

The chief difference between the materials available at copper
reduction works and the ordinary ores is that the former are
lower in sulphur and higher in copper, are of irregular analysis,
and are often exceedingly fine. While pyrites ores range from
40 per cent to 50 per cent sulphur afld contain little copper, the
ores and concentrates used at copper works rai^e from 25 per

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PRODUCTION OF SOt 65

cent to 40 per cent Bulphur, and contain up to 12 per cent or 15
per cent copper. Moreover at eome plants the sulphur content
of the material varies 5 tolO per cent from day to day.

The copper-iron sulfide, and the copper sulfide minerals fuse
at a considerably lower temperature than does straight pyrites,
so in roasting copper ores and concentrates accretions arc found
to form on the brickwork and on the shaft of the furnace much
more than they do when roasting pyrites. This fact makes it
necessary to watch the furnace temperatures carefully or serious
formations of matte may occur. A good deal of barring and
plowing of the hearths is necessary even with the most careful
attention.

As the cinder from the roasted copper ore is usually treated in
a reverberatory furnace to make a copper matte, some sulphur
should be left in the cinder. For example at Anaconda where
the copper content of the cinder is about 10 per cent, it is desirable
to leave about 7 per cent sulphur in the cinder to make matte.

THE BLAST FURNACE
The blast furnace is a very unusual source of SOi for acid mak-
ing. The only place in this country where it has been used is
at the reduction works of the Tennessee Copper Co. and the
Ducktown Sulphur, Copper, and Iron Co., in the Ducktown
district in southeastern Tennessee. There exists a peculiar set
of conditions there which will rarely be duplicated, but the ton-
nage of acid produced is so large, and the plants themselves
present so much of interest in their construction and operation,
that some description of the operations is in order.

The ore treated at these works is a heavy sulfide carrying
substantially :

Pbh cbkt

.Coppar 2.5

Iron 30.0

Sulphur 20.0

luBoluble 30.0

CaO, MgO 10.0

Zinc 3.0

Al,Oi 3.0

This ore is treated directly in blast furnaces with no prelimi-
nary dressing or concentration whatever. It is very near self-
fluxing when making a 15 per cent copper matte, and it can be
smelted with about 5 per cent coke. This permits the production

^dbvGooglc

66 AMERICAS SULPHURIC ACID PRACTICE

of a gas containing 7 per cent to 8 per cent SOi, 5 per cent to 6 per
cent COi, and about 3 per cent to 4 per cent oxygen.

At the time the first acid plants were built, about 1907, no
experience was available to say what could be done with such
gas. However it was neceesaTy to undertake the manufacture
of acid because the United States Supreme Court had enjoined
the smelteries from allowing to escape more SOi than the state
of Georgia deemed reasonable. The redeeming feature of the
situation lay in the fact that Ducktown basin ts in the heart of
that portion of the country which consumes the greater part of
all the acid phosphate fertilizer made in the United States, that
is to say there is an excellent market for sulphuric acid.

For some time after the completion of the plants troubles of
various kinds were experienced and many curious phenomena
arose. The chief differences between this blast furnace gas
and the gases usually used for making sulphuric acid are t-he
high CO] content and the low oxygen. It was necessary to
revise ideas about the oxygen content of exit gases, or else if
the customary 6 per cent were maintained there, to take a gas
entering at about 2 per cent to 3 per cent SOi. One solution of
this devised at the Ducktown plant, was to adjust the gas enter-
ing to contain about 3 per cent oxygen, and to introduce air into
each chamber sufficient to maintain 3 to 4 per cent oxygen at all
stages of the process. Working without this arrangement the
best way seemed to keep the oxygen in the exit gases above 2 per
cent and get as good SOi entering as that would allow.

It should perhaps be explained that in near-pyritic smelting
the gases issuing from the cbat^ contain almost no oxygen and
if the furnace top and flues are tight the gas entering the acid
plant contains only such oxygen as may be voluntarily admitted.

The high percentage of COi in this gas along with the unusually
low oxygen makes the reactions in the chambers very sluggish.
In order to get reasonable tonnage from the plant is is necessary
to use much more than the normal nitre circulation and this in
turn tends to make high nitre loss.

A very serious feature of the blast furnace work is the irregu-
larity of the gas due to the mode of operating the furnace. It
is necessary to open the furnace top several times an hour to
charge and barring and cleaning are necessary every day. If
the fines are dampered so as to cause some pressure at the
furnace top, the working conditions on the charge floor are

^dbvGooglc

PRODUCTION OF SOt 67

almost impossible. If Buction is maintained, every time the
furnace is opened false air rushes in and dilutes the gas. In
spite of these difficult conditions these acid plants must be
considered very successful both technically and financially.

COPPER CONVERTERS

It has many times been au^ested that the gases from copper
converters m^;ht be used for making acid, but as yet this has
not been attempted.

Taken without modification the gas from a single converter
ranges in a period of a few hours from almost no SOj to perhaps
20 per cent. As a reasonable approach to uniformity is a neces-
sity in the chamber process, such a gas would not do. It may
be possible with a battery of several converters working on a
schedule and equipped with tight hoods and dampers to get a
workable gas. It must be said that the converter is not an
attractive source of gas for acid making, although perhaps a not
impossible one.

SO) FROM ROASTmO ZINC ORES

In the reduction of the sulfide ores of zinc it is necessary to
roast off sulphur, and the gas so produced is utilized in making
sulphuric acid. The zinc reduction works in this country are
usually BO located geographically that the sulphuric acid produced
is readily marketed.

In roastii^ zinc sulfide ores preliminary to distillation for
metal it is necessary to convert, as nearly as possible, all the
zinc to zinc oxide. In order to do this certain temperature and
oxygen percentage figures must be observed which make the
roasting operation more difficult and the gas less favorable for
acid making than in roasting pyrites.

The essentials of this are that in roasting zinc sulfide some
sulphates of zinc form; these are not broken up completely at
temperatures much below 900°C.; after the sulphur content of
the roasting ore is down to about 8 per cent it no longer burns
with sufficient vigor to maintain a roasting temperature, much
less a temperature sufficient to break up the sulphates. It is
therefore necessary at the later stages of the roast to add heat by
means of the hot gases from burning carbonaceous fuel. As
this fire gas would be a serious diluent of the roaster gases going
to the chambers, it is kept separate from the latter.

^dbvGooglc

68 AMERICAN SULPHURIC ACID PRACTICE

The roasting furnace most used in this country for zinc roastii^
in connection mth acid chambers, is the Hegler furnace, first
used at the Matthieeson and Hegler works, LaSalle, 111. The
Hegler furnace is a multiple hearth, rectangular furnace, with
the lower hearths of muffle construction. The ore is moved
longitudinally over each hearth falling to the one below. The
rabbles mounted on frames of steel shapes are drawn through
the hearths by means of long rods. After each passage through,
the rabbles are drawn clear out of the furnace and allowed to
cool for a short time. Their temperature therefore never
becomes high enough to impair their strength and rigidity.
The latest Hegler furnaces have seven hearths, and producer
gas is used to heat the muffled hearths in the lower parts of the
furnace.

In order to properly roast zinc ores a plentiful supply of air
must be allowed to pass over the roasting ore, i.e. the oxygen
percentile must be kept well up. Observing this requirement
then, the gas going to the chambers contains only 4 to 5 per cent
SOi. There is of course some dilution due to rabbles entering
and leaving the furnace and to the doors leaking air.

BURNING P7RITE CINDER

Even with the most careful handling some where about 2 to
3 per cent of sulphur will remain in the cinder from roasting
pyrites. This causes two losses, that of the sulphur, and that of
the market for the cinder as iron blast furnace material, as
with so high a sulphur content good iron is an impossibihty, and
many acid plants have a potential market for their iron "ore."
The Dwight & Lloyd sintering machine, as sold by the American
Ore Reclamation Co., 71 Broadway, New York City, overcomes
the twin difflculties of high sulphur content and fineness, and is
best described by the company as follows :

"Sintering is a comparatively recent art in the iron industry. It is
the process of agglomerating fine ore material into a mass that is suit-
able for blast furnace use. Sintering may be illustrated aa the making
of flour into biscuits. With the use of the fine ores from the Mesaba
Range in Minnesota and the resulting makii^ of flue dust at blast
furnaces, many attempts were made to recover the valuable iron in the
flue dust by briquetting. This means of treatment has not proven very
satisfactory, since, to secure a firm bond, the proeess is expensive, and
when the bond is fickle the briquettes quickly return to dust.

^dbvGooglc

PRODUCTION OF 50, 69

"The briquette is a porous mass and the spaces are filled witli air, bo
that the mass must be heated first to expel the air to allow the reducing
mass of the furnace to Come in contact with the ore particles, which
delays the reduction and the mass is easily disintegrated into dust.
Sinter made by the continuous down draft process is cellular in struo-
ture, providing an open and large area of contact between ore and reduc-
ing gases; and as the cell walls are quickly heated to the temperature
required for reduction, an economy in coke consumption results from
the use of sinter.

"To quote Shinz's law (in his "Action of the Blast Furnace"): 'A
chemical action can only take place between two bodies, however great
then- affinity, if they are in intimate contact with each other and the
rapidity of this action will be much greater the more numerous the
points of contact are.' The material which provides the greatest area
of contact is more readily and economically reduced in the furnace.

"The iron-bearing materials treated by sinterii^ include blast-furnace
flue dust, roll-^cale, magnetite concentrates, magnetic sands, high sul-
phur ore, pyrites cinder, etc. Any finely divided ore or ores, containing
high sulphur or high moisture and combined water, can be converted
into ideal material for use in the blast furnace. Flue dust sludge from
blast-furnace gas washers may be sintered by adding the sludge to a
dry sintering mixture instead of moistening the charge with water.

"Sintering was first applied in the iron industry to the reclamation
of flue dust, but it has since widened out into other fields and demon-
strated its adaptability for treating pyrites cinder, magnetic ore con-
centrates, and other fine ores or hydrated ores.

"A plant installation is made up of two main parts, the sintering
machine proper, and the raw materials plant, both forming a unit, of
which the former is more or less standardized, but the latter made to
conform to local conditions and materials. The following is a descrip-
tion of a typical plant.

"The materials to be sintered are delivered to a peries of bins, the
number and size of which depend on the kind and quantity of materials
to be treated ; or the raw materials may be dumped from the cars into
a pit and transferred to the bins by a grab bucket.

"In the case of fine dust the screening of it is necessary, and a con-
siderable quantity of coke is recovered for furnace use.

"The bins are fitted with feeders of a special type which are driven
as a group in synchronism with the sintering machine. The required
composition of the sintering mixture is made up by adjustii^ the feeder
gates and the total amount of sinterii^ mixture delivered by the feeders
is adjusted to suit the needs of the sintering machine at various speeds.
The sintering mixture is carried to, and thoroughly mixed and moistened
in, a pug miU or other mixing device, and is delivered onto the grates of
the sintering machine in a continuous layer of desired thickness and

^dbvGooglc

AMERICAN SULPHURIC ACID PRACTICE

unifonn penneability. This contiouous layer is moved under an igni-
tion burner where the fue! in the upper surface of the layer is ignited
and the charge then continues its movement over a wind bos connected
to a auction fan which draws air down through all parts of the charge
and the sintering action is progressive through the whole depth of the
layer down to the grates. At the end of the sintering machine the
sinter is discharged over a grizzly screem which thorouhly separates
all fines from the sintered material and the fine sinter is returned to the
siQtering machine to increase the permeability and thereby the rate of
sintering is increased."

The whole operation of regulating the feeding of material and
speed of sintering ie controlled by a sinj^e lever.
SINTERING MACHINBS

Capacities of the three machines made by the Dwight & Lloyd
people are as follows, all in tons per 24 hours:

Material

Type A

1>peB

TypeC
(two strand)

Elue dust

126-160
150-176
175-200

260-310
300-375
350-400

Pvritea cinder

Pyrites cinder and high sulphur ores are sintered and desul-
phurized in one operation. The cinder contains from 1.5 per
cent to 5 per cent sulphur, and is reduced to 0.10 per cent to
0.15 per cent in the sintered product. About 8 to 10 per cent
fuel is required.

CoHTiHTS PrniTca cihdbr, Sintib,

Iron 56.28 61.00

Sulphur 4.41 0.07

Mktuke of Pthites Cindee and Floe Ddbt

Contents

Pyrites
ciader,
per cent

Hue dust,
per cent

Average
mixture,
per cent

Smter

56.28
4.41

33,00
0.18
24.00

46.97
2.72
0.60

Sulphur

C&rhon

idb,Go(5glc

PRODUCTION OF SOt

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AMERICAN SULPHURIC ACID PRACTICE

^dbvGooglc

PRODUCTION OF SOt 73

DplizsdbvGoOglC

74 AMERICAN SULPHURIC ACID PRACTICE

^dbvGooglc

PRODUCTION OF SOj 75

Sintering machines of this type are also used to treat lead ores
aa a preparation for blast furnacing.

The gas from a sintering machine is not only low in SOt,but
as it is high in COjand CO, it is not good acid material. SOthas
been hard to concentrate up to recent years, but a new process
is now on the market which makes available very weak gases.

Silica gel is put out by the Davison Chemical Co. at Baltimore.
While this material has been known for years, its commercial
production was not possible until the researches of Prof. W. A.
Patrick of Johns Hopkins, on gas mask absorbers during the war.
Apparently any condensible gas is adsorbed by this material,
the capacity of which is very great, and a small rise in temperar
turo serves to drive out the adsorbed gaa. This is so much the
case that the additional gas pressure produced by the slight
increase in temperature caused by laying ones hand on the
apparatus is easily measured.

The action is unquestionably surface condensation, the small
drops of "gel" being full of sub-microscopic cracks, so that Prof.
Patrick says, "if you consider the measure of the 'gel' drop in
centimeters, you must measiu'e the area of the cracks in acres."

This plant consists of three towers in series, each capable of
being cut out. Only one is used at a time, one being discharged
and the third in reserve. The temperature is raised or lowered
by forcing steam or brine through horizontal pipes laid in the gel
mass. Vertical pipes were tried, but the channeling action of
the gas was too -great. This opens up a new type of contact
plant where the concentration of SO3 in the gas can be very high,
thus cutting down plant and particularly mass, very greatly.
The advantage of being able to mix air and 80^ instead of air
and sulphur, is at once apparent. When sulphur is burned in air
and that mixture taken into the system, the nitrogen that was
in the air, the oxygen of which helped form the SOi goes along
and dilutes the gas, whereas by having the S0» ready burned,
that dead gas is avoided.

If there is sufficient oxygen present, the contact mass is more
efficient as the concentration of the gafi increases. By sufficient
oxygen is meant the excess that ia needed to give good results.
So the use of a gas mixture made from SO3 direct works out as
follows: In a gas made by burning sulphur in the air and contain-
ing 7 per cent SOs, 12.3 per cent of the total is the nitrogen that
accompanied the 3.5 per cent oxygen necessary to make the

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76 AMERICAN SULPHURIC ACID PRACTICE

SOi. This concentration process reduces the amount of gas
to be handled, raises the concentration of the gas, and leaves
just as much oxygen to form SOa and furnish the excess necessary
for this formation.

Silica gel should be tried out along the following lines, as the
concentration of platinum in the mass drops the conversion
drops, also, but not in the same proportion. Therefore, there
is a point, to be determined, to which it will pay to drop the
conversion, catching the unconverted SOi with silica gel, and
returning it to the gas stream.

The saving will be in plant cost of platinum. Suppose that
with 10 per cent of the amount of platinum required for a 97
per cent conversion you are able to get a 60 per cent conversion
and recover the SOi at reasonable expense. At the standard
rate of platinum used, for a plant burning one ton of brimstone
an hour, 90 pounds avoirdupois, of platinum would be required.
At S95 an ounce, troy, that is $1,385 a pound avoirdupois or,
$124,650 for platinum. Ten per cent of that would be $12,465,
quite a difference.

Without anywhere near sufBcient research work done upon
this subject, I do not state the above as either an accomplished
fact, nor as a certainty— it is simply a possible lead. The
Davison Chemical Co., Baltimore, Maryland, hold the basic
patents on silica gel, and will furnish the most complete informa-
tion upon this subject that exists.

Water is an obstacle to the adsorption by silica gel, as it is a
great moisture adsorber, and the moistiu^ would be given up,
under certain conditions, along with the SO*, which would have
to be dried again before conversion. Of course there would
be no moisture in the gas just leaving the strong acid of the
absorption towers.

When the contact process first became an accomplished fact
many people looked for it to displace chambers entirely, but the
cost of the platinum required has prevented the fulfilment of
their hopes. Is it too much to hope that silica gel may bring
this about?

OTHER USES OF SO.

Liquid S0» was first made commercially from zinc smelter
gases in this country by the Davison Chemical Co. in Baltimore
ftroimd 1870. It is interesting to note that the first sulphite

^dbvGooglc

PBODVCTION OF SOi 77

paper pulp in this country was made with liquid SOj by the
Mitcherlich process, then the pulp mills began to bum their own
sulphur, and now the pendulum has swung back again.

For liquid SOi the aormal boiling point is — 11°C.

For liquid SOi the lat«nt he&t of vaporization, at — lO'C. (dimin-

iabes as the temperature rises) 03 . 4 cal.

Vapor pressure temp. C..,. -10 10 20 30 40 60
Pressure (atmospheres) 1.0 1.63 2,26 3,24 4.51 6.15 8.18

Critical temperature = 156°C. Critical pressure = 78.9 atmospheres.
Specific heat, between - 20° and + ISCC. - 0.31712 + 0.0003507( +
0.00000672P

ACTION OF METALS

The commercial product, containing 0.07 per cent HiO, attacks
iron above VCC, forming a solid crust of ferrous sulphate and
thio-sulpbate, but the metal is not further attacked. Anhydrous
SOi does not attack either iron or steel.

USES

For refrigeration, because of its cheapness, ease of handling,
and the fact that it is neither acid nor alk^in in its action.

In the manufacture of sulphite pulp.

For petroleum refining.

As a solvent for organic fats and resins.

As a sewage disposal agent.

So far as I know, there are three plants in this country making
liquid SO). The Tacoma Smelter, of the American Smelting
and Kefining Co., Tacoma, Wash., has a plant that has been in
operation about5years, — operating as follows: The gas from the
converters, containing 2.5 per cent to 3 per cent SOi, and at about
300°C.| is lead to a scrubber tower,' brick lined and loose brick
packed, into the top of which is fed a small amount of water, just
enough to prevent it all vaporizing. TherunofEcleans thegas, but
because of ite temperature contains practically no SOj. The
gas then goes to another tower, of the same construction, but
larger in diameter, to which water is admitted through spray
nozzles at the top, the water being in sufficient quantity to cool
down and absorb practically all the SOt, the scrubbed gases
going out the stack. See Fig. 11.

The liquor flows by gravity to a heat exchanger, made of
lead pipe, outside of which flows the desulphurized Uquors,

^dbvGooglc

AMERICAN SULPHURIC ACID PRACTICE

hot, from the following process. Then to 12hui. lead pipes,
horizontal, into the bottom of which is blown steam, which
vaporizes the SOi, which comes off through a gas outlet on top,
and thence to the compressor. The water, aft«r the SOt has
been blown off, flows down to heat the heat exchanger.

Before the compressor is a scrubber, fed with 66°B^. acid, to
remove moisture from the S0». This 66° acid drops to 60° in a
week, and has to be renewed.

The compressor is a bronze, singte^tage, direct-driven one,
compressing to about 60 lb., although under perfect conditions
45 lb. will do it. The liquid SOi then goes to lead cooling coils,
over which water drops, and thence to a tank car.

An iron cylinder for the compressor only lasts six weeks.

Fta. II.

The stor^^ tank, built to stand 300 lb., has a safety v^ve
with a pipe running to the absorber tower, where any SOi will
be caught and the non-condensiblc gases will escape to the stack.

This plant started to produce in 1917, making 10 tons of Uquid
SOj per day. In 1920 the production was increased to 30 tons
per day, and in 1921 it will be 50 tons. The product is shipped
partly to Crown Willimette, where it is combined with SOi
produced on the ground, to make a 25 per cent gas to make a
strong cooking liquor for making sulphite pulp. The rest of the
production goes to Los Angeles for oil refining.

At Tacoma, with coal at $8, SOj from a 3 per cent gas, includ-
ing overhead, but with no charge for the gas, is (1920) {8 per ton.

The plant of the Virginia Smelting Co., at Norfolk, Va., has

Without steam or pover plant, a 10-ton per day plant coeta (1920) S30,000.
Vnthout Bteom or power plant, a 30-toa pei day plant coats (1920) $45,000.

^dbvGooglc

PRODUCTION OF 50, . 79

been leased to Beer, Sondheimer, & Co., who are recovering the
SOj in a process very Bimilar to the one at Tacoma, except
that it is much smaller, and the Hquid SOj is shipped in cylinders.

There is a small plant in Wisconsin which produces SOi from
brimstone directly for the purpose of compressing and selling.
I have been unable to get any details.

Dr. Ralph McKee, head of the Department of Chemical
Engineering at Columbia, is a world's authority on liquid SOi.
He has furnished some of the information contained in this
section, and sees a great future for the industry^ some of the
reasons for which are given below.

Liquid SOi will not bum nor explode, will not attack steel ,
containers, and costs H^ a pound, F.O.B. point of manufacture,
against 7ff for gasoline and I6i for carbon-tetrachloride (1920).

The U. S. Bureau of Chemistry does not like the use of liquid
SOi for the extraction of oils to be used for food, if any other
solvent can be used.

Mr. James E. Steely, of the West Virginia Pulp and Paper
Company, Inc., haa furnished some notes on the production and
use of 30i in the pulp industry.

In the manufacture of bi-sulphate liquor, it is desirable to have
SO] gas at as high a percentage as possible, as the solubility of the
gas in water increases in the per cent of SOj in the gas. This
solubility also increases with a reduction in temperature ; there-
fore the gas is cooled as low as possible, usually in some form of
lead-pipe cooler.

It is also necessary to keep the SOa in the gas as low as possible,
SOs being a very undesirable component of gas for sulphite pulp
manufacture.

A 15 per cent to 18 per cent SOi gas meets the above requirements.
Liquid SOi is a most desirable material to work with, and if it could
be delivered at the mill at sightly above the cost per pound of
sulphur, as compared to elemental sulphur, it would be in very
wide demand. However, under present (1920) conditions, the
cost of producing liquid SOj together with increased cost of
fre^ht and containers for handling would make the proposition
prohibitive in ordinary times. The efficiency of operation in a
sulphite acid plant is very high, and maintainance cost of first-
class equipment comparatively low ; therefore it would seem that
only in special cases would liquid SO3 be attractive to sulphite
pulp manufacturers.

^dbvGooglc

80 . AMERICAN SVLPHVRIC ACID PRACTICE

' The chief source of SOj for sulphite pulp manufacture is ele-
mental Bulphur, burned in the same types of burner that are used
in acid manufacture. Very little SOj is produced by any of these
machines, but to make assurance doubly sure, at some plants a
pyrometer is installed in the combustion chamber and the tem-
perature maintained around ISOCF., at which point 80i disso-
ciates into SOi and 0. Other plants depend solely upon gas
analyses.

Pyrites, particularly from Spain, used to be the chief source of
SOi for pulp making, but the Louisiana sulphur discoveries, and
the interruption to Spanish deliveries by the War, cut down its
use so that today (1920) Mr. Steely does not know a single plant
in this country running on pyrites. The market price of Spanish
pyrites has not gone low enough to justify plants that used to use
it returning, and also most important, the bumeiB, usually of the
Herreshoff or Wedge type, must be operated with the greatest
care to prevent formation of SOj, due to the catalytic action of the
hot iron oxides in the cindeiB.

There are two general schemes for makihg bi-sulphite liquor.
In each case the SOj is cooled as low as possible. The first
scheme is to use a'tall tower filled with lumps of lime stone, over
which a slow stream of water is passing. The gas is admitted to
the bottom of the tower, and is absorbed by the water, fonning
sulphurous acid, which in turn dissolves the stone to make
calcium-bi-sulphate liquor.

The second scheme consists of passing the gas through towers
containing a solution of milk of lime. The two are brought
together in such a way that they combine and form a clear
solution of bi-sulphite.

When rosin is extracted from yellow pme waste, enough SOa
remains in the wood to cook the pulp. Both United States and
Canadian patents on this process are applied for by R^pb
McKee and A. A. Holmes.

The city of New Haven has experimented with hquid SO*
on sewage disposal. The sewage \^as going into the bay ; if an
acid was added the colloidal sludge was precipitated. HiSO«
was first used, then SOj. If this sludge is dried and extracted,
considerable amounts of fats and oils are recovered, gasoline
being used as the solvent. The report says the recovery will
pay costs, including bond interest.

Liquid SOx is a solvent for di-ethylamine, analine, di-pbenyl-

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PRODUCTION OF SOt 81

amine, benzylamine, P-toIuidine, A-napbtbylamiue, B-naphthyl-
aminc, phenyl, B-naphthylamine, benzidine, chrysaniline,
carbazol, quinolin, pyridine, acetanilide, acetnapbtalid, benzene,
toluene, tri-phenyl-methane, di-phenyl-flouren, phenantbren,
naphtbalene, nitrobenzene, limonen, pinene, anthracene, B-di-
bromnapbthalene. All fatty alcohols from methyl to capryl,
benzyl alcohol, menthol, borneol, 0-creaol, B-naphthol, hydro-
quinone, picric acid, phenol-chloro (and di-chloro) acetic acid,
A-brom-butyric acid, benzoic acid, sahcyhc acid, M-oxybenzoic
acid, B-naphthoic acid, acetic-ethyl-ester, succionic-acid-di-
ethyl-ester, aeopropyl-aceto-acetic-ester, fumaric-acid-di-ethyl-
ester, cinnamic-acid-di-etbyl-eater, malic-acid-di-metbyl-estet,
mandelic-acid-di-ethyl-ester, acetic-acid-bomyl-ester, ricanelic-
acid-propyl-ester.

The following are also soluble — KI, Nal, NH»I, Rul, tri-methyl-
sulphoneum-iodide, tri-methyl-ammonium,-iodide, KBr, ammo-
nium-thio-cyanate, methyl-ammonium-chloride, di-, tri, and
tetra-methyl-ammonium-bromide, sublimed ferric chloride, co-
balt-thio-cyanate. More compounds for which liquid SOj is a
solvent are continually beii^ discovered.

CANADIAN SITUATION

Dr. McKee shows a picture of the smelter of the International
Nickel Co., with clouds of SOb coming out of the stack — 1,000 tons
a day. There are numerous copper, nickel, and zinc smelters
in the Dominion, and the lai^e pulp mills near at hand are import-
ing sulphur from Louisiana and Japan, while this SO2 is worse
than thrown away — it is acutally hurting the nearby farms.

The Tennessee Copper Co. showed that the production of acid
from smelter fume was not an impracticable dream, and when the
acid was produced a market was found for it. The method of
producing liquid SO2 from smelter, fum^ is already in successful
operation, and the market for the product is ready and waiting
at the door.

^dbvGooglc

CHAPTER VI
A BRIEF DESCRIPTIOIT OF THE CHAMBER PROCESS

The Chamber Procese for the manufacture of sulphuric acid
takes its name from the lead chambers which constitute the
chief essential part of the apparatus. It differs from the other
important process of making sulphuric acid, the contact process,
both in nature of the plant proper and in the chemical reactions
involved. The purpose of each is to oxidize SOj up to H1SO4.
The chamber process does this by means of the reactions between
SOs, the higher oxides of nitrogen, oxygen, and water, at low tem-
peratures, while the oxidation in the contact process is accom-
plished by a catalyzer, usually finely divided platinum, at a
comparatively high temperature.

The normal product of chamber plants is sulphuric acid of 50°
to WB^.' Contact plants normally produce acid of 98 per cent
HaS04 or higher strengths. The chamber process makes 50° to
60° acid more cheaply than the contact process can make acid
of that grade. The chamber process cannot, however, make high-
strength acid. Each process therefore has its distinct field.

The essential parts of a modem chamber plant are:

1. BurnerH of some kind for the production of SOi.

2. DuHt settling apparatus, except in those cases where brimstone is
burned to make SOj.

3. Glover Tower.

4. Chambers.

5. Gay Lussac Towers.

6. Acid Circulating Apparatus.

7. Fans and flues.

S. Apparatus for introducing the oxides of nitrogen.

The gas produced in the burners is derived from the oxidation
of elemental sulphur, iron sulfide, iron-copper sulfides, zinc sulfide
or mixed sulfides. It contains from 5 per cent to 10 per cent
SOa, depending on the material burned, 8 per cent to 12 per cent
oxygen, and nitrogen, with, in special cases some COi or possibly
CO.

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A BRIEF DESCRIPTION OF THE CHAMBER PROCESS 83

When necessary this gas is drawn through some form of dust-
settHng apparatus to remove the greater part of the dust which
would otherwise contaminate the acid. •

If nitre potting is practiced, the gas next passes around the
nitre pots. These are cast iron vessels set in the gas flue, into
which are introduced nitrate of eoda and sulphuric acid. The
hot gases cause these compounds to react to form nitric acid
vapor, and a mixture of sodium sulphate and sodium bisulphate.
The latter is tapped off molten, at intervals. The nitric acid
vapor is reduced to NO by the hot SOi and is carried along with
the gas.

The gas mixture next enters the Glover tower at a temperature
of aWF. to l,000°f . It is in this tower brought into intimate
contact with a mixture of 60°B^. sulphuric acid carrying iii
solution NiOg, and chamber acid of about 50° B^. The hot gas
with its considerable SOi content, reacts with the acid and de-
nitrates it or removes from it ite NtOi, forming some HiSOi and
converting practically all the NjOj into NO, a gas, which goes
on with the main gas stream. Bteam and some weak sulphuric
acid vapor are alao formed and go on with the gas. Leaving the
Glover tower the gas mixture contains then a somewhat reduced
percentage of SOi, nitric oxide (NO), oxygen, nitrogen and steam
or weak acid vapor. Its temperature has been reduced to
about 200''F. .

If nitre potting is not practiced it is customary to introduce
some fresh nitric acid into the Glover tower top.

The acid issuing ffom the Glover tower at the bottom is
mMntained at a gravity of about 60° B4. It has a temperature
of 200°P.-300°F. and is passed through a cooling system con-
sisting of a tank containing lead pipe coils through which cold
water is circulated. The acid should leave this 6ooler at as low
a temperature as possible, certainly not over 80°F. A part
of this acid is elevated and introduced into the Gay Lussac towers,
and the remainder is shipped.

The gas mixture from the Glover tower is conducted into the
chambers, usually from 3 to 10 in number, in series. From 1 to
2 hrs. is occupied by any given portion of the gas in passing
through the set of chambers. Steam or atomized water is
introduced at various points. By the reactions between S0»,
oxygen, the oxides of nitrc^en and water, sulphuric acid is
formed. This collects in the bottoms or pans of the chambers.

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AMERICAN SULPHURIC ACID PRACTICE

When these reactions have gone on for the proper period of
time and the gas finally reaches the end of the last chamber the
SOa percentage has been reduced to less than }^q of 1 per cent,
and the nitrogen oxides are practically all in the form of NiOj.
It is highly important that the SOj percentage be reduced below
Ho "f 1 per <^*iit or else the recovery of the nitrogen compounds

OtN fi?y^maif>h9iv

Lvsiac Tor^eri

H^Oas sprciy or sham /5
iniroduccd in to chambers
af mcny points

2H0*tS(k *iO*HiO = ZHShlOs
ZHSHOs i-UsO - 2Ms504 ^NgOj
Fio. 12.— Flow Sheet of Chamber Process.

will be incomplete. It is almost as essential that the SOi per-
centage be not less than Jloo of 1 per cent for the same reason,
and also because of increased corrosion of the lead. These
points will be taken up in more detail later on.

By properly regulating the amount of water or steam intro-
duced the acid made in the chambers is kept at approximately
SO^Bfi. It is not permissible to allow the continued formation of
acid of much greater concentration because of the tendency of

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A BRIEF DESCRIPTION OF THE CHAMBER PROCESS 85

such acid to take into solution some of the oxides of nitrogen, in
which case they are no longer available for reaction with SOj.

The acid-making reaetions generate a large amount of heat
which is carried off mostly by radiation from the lead chamber
walls. The chambers should therefore be housed in a well-
ventilated building.

From the chambeiB the gases pass into the Gay Luseac towers.
Their function is to recover the NjOj. This is accomplished by
brii^ng the gas into intimate contact with cold 60° B4. sulphuric,
acid, which takes 86 per cent to 90 per cent of the N2O1 into
solution, forming what is known as nitrous vitriol. Perfect
recovery of the NjOi is never attained because the cost of appara-
tus to accomplish it is prohibitive.

The gas which leaves the Gay Lussac towers consists of 94 to
96 per cent nitrogen, 4 to 6 per cent oxygen with traces of other
things. It is discharged into the atmosphere through a stack.

The acid issuing from the Gay Lussacs, carrying usually from
1 per cent to 2 per cent NjOj, is elevated to the top of the Glover
tower and the NiOs there reintroduced into the system.

Figure 12 shows a conventional plan of a chamber plant and
indicates the reactions which occur in the various parts of the
apparatus.

^dbvGooglc

CHAPTER VII
DUST SETTLING APPARATUS

A chamber acid plant will usually require some provision for
removing dust from the burner gases. This varies from almost
nothing in the case of brimstone burners, to rather large and
elaborate chambers for use when very fine sulphide ore is burned.
It is highly important in order to insure uninterrupted operation
to provide suitable and adequate means for dust removal. If
any considerable amount of dust is carried into the Glover tower
by the gas it causes the following disagreeable and serious results :
The packing of the Glover tower will become obstructed, inter-
fering with passage of the gas. The acid will be contaminated
and rendered impure. Even though this may not be of impor-
tance to the consumer of the acid, it will cause gradual fouling and
obstruction of pipes, valves, tanks etc., in the acid plant and will
make uniform running impossible.

There are two general principles applied in dust removal, which
are: decreasing gas velocity, and causing change of direction of
the gas stream. It is hardly necessary to consider some of the
older proposals for washing the gas by water or acid, ae these
involve cooling the gas so much that the Glover tower will not
function properly. In general, it is necessary to retain the tem-
perature of the gases as high as possible from the furnaces to the
Glover tower. Dust chambers for acid plants should therefore
be compact and well insulated.

The Cottrell apparatus has been used in a few acid plants
with considerable success. It probably has a distinct place
in acid plant design when the sulphur bearing material burned
produces very fine dust. This form of treater is hardly justi-
fied otherwise, as it is expensive to install, and involves some
operating expense. The following information is furnished by
the Research Corporation, 31 West 43rd St., New York:

Cottrell Precipitatorb for Cleaning Roaster Gases

The problem of satisfactorily cleaning the sulphur dioxide gases prior
to their oxidation and conversion into sulphuric acid has long been a

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DUST SETTLING APPARATUS 87

troublesome one for acid makers to solve. In contact acid plants it is
of course esaential that the gasee be completely freed from suspended
particles of dust or fume prior to their passage through the catalyst
and it is almost equally desirable in the caee of chamber plants that the
sulphur dioxide gases be thoroughly cleaned if the plant is to operate
at high eflicieDcy and produce a clean acid of good quality. In the
latter case, however, the problem is complicated by the fact that the
sulphur dioxide gases must be cleaned at a very high temperature
whereas in contact plants the gases may be cooled during the cleaning
process or may be cooled first and then purified.

In both cases the Cottrell Processes of Electrical Precipitation offer

a very satisfactory method of cleaning the gases, and several Precipita-
tion Installations are today in use for such purposes.

In designing Cottrell Precipitators for cleaning roaster gases the
temperature at which the gases must be cleaned and tbe character of
the suspended matter to be removed from such gases are governing
factors. Of course the size of tiie installation depends directly upon
the volume of gas to be cleaned and this in turn is fixed by the quantity
of material being roasted per unit of time and by its sulphur content
as well as by the percentage of sulphur dioxide in the gases leaving the

iiz^dbvCoOglc

88 AMERICAS' SULPHURIC ACID PRACTICE

furnaces. These factors must therefore be known or approximated in
order that a precipitation plant of suitable capacity may be provided.
Two types of precipitators are today being installed for cleaning the
hot furnace gases in sulphuric acid plants. These types differ widely
from each other and the decision as to which type should be installed
is based largely upon the t«mperature and fume or dust conditions in
the particular plant under consideration. In cases where the gases
must be cleaned at temperatures of 1,000°F. and over and where the
suspended matter to be removed is mostly dust rather than fume, pre-

cipitators of the so-called plate type, in which the gases pass horizontally
between the collecting and discharge electrodes, have proven highly
Batbfactory, On the other hand, where the gases can be cooled to a
temperature of about 600°F. or under before cleaning and where the
suspended matter to be removed is fume rather than dust, precipitators
of the pipe type, in which the gases pass upwards between the collecting
and discharge electrodes, would in general be the more suitable.

Figure 14 is a photograph of a Cottrell Precipitator of the pipe type
which was recently installed under the supervision of the Research
Corporation at a plant in Wisconsin, Here 17,500 cubic feet of gas

iiz^dbvCoo^lc

DUST SETTLING APPARATUS 89

per minute at a temperature of 500°F. are cleaned. These gases come
from three Mathey rotary kilns roasting Wisconsin zinc ore concentrates,
and after being cleaned are used for the manufacture of sulphuric acid
by the contact method. The precipitator as installed consists of two
units, each having 36 collecting electrode tubes or pipes. These pipes
are of steel, 12 in. in diameter and 15 ft. in height. Means are provided
for rapping both the discha^e and the collecting electrodes in order to
remove from time to time any dust which may have adhered to them.
The levers for operating the pipe rappers may be clearly seen in the
photograph. The bottom header is a reinforced concrete chamber into
which the collecting electrode pipes project and. in which the collected
material is deposited. This is later removed by hand through doors
which are provided for this purpose. Should it be desirable similar
installations could be readily provided with hoppers and screw conveyors

Fia. 15.

SO that the collected dust could be taken out of the precipitator con-
tinuously and automatically. This precipitator occupies a space ap-
proximately 17 ft. wide by 28 ft. long and has an overall height of
about 35 ft. The amount of power required to operate the installation
is about 18 KW.

Figure 15 is a drawing giving the general arrangement and overall
dimensions of a precipitator of the horizontal flow or plate type, designed
and installed by the ReBeareh Corporation, and Fig. 13 is a view looking
in a lengthwise direction through a precipitator of this kind which was
installed in a chamber acid plant near Baltimore, Maryland, and f^ch
is particularly designed to withstand the high temperatures at which
the gases must be cleaned in such a plant. This installation operates
at a gas temperature of 1,100°F., while occasionally temperatures as
high as 1,400°F. have been recorded in the precipitator.

A precipitator of the size shown in Fig. 14 will clean the hot gases
produced by the roasting of 40 to 45 tons of fines pyrites per twenty-

^dbvGooglc

90 AMERICAN SULPHURIC ACID PRACTICE

four hours. With a sulphur dioxide concentration of 7H per cent to
8 per cent this means that the volume of gas passing through th^ in-
stallation is about 17,500 cu. ft. per minute at a temperature of 1,100°F.

As will be noted from an inspection of Fig. 15, the precijatator is
divided into two sections, each of which is provided with a damper at
both inlet and outlet ends. This makes it possible to shut off either
section from the system when inspection or repair is required or when
it 18 desired to clean the electrodes. Such cleaning may be necessary
every few days if a very dusty ore is being roasted in the furnaces.
For the above reason it is desirable to so design the plant that each sec-
tion will have sufficient capacity to handle all the gas for short periods
of time and in this way continuity of operation with clean gas is prac-
tically assured.

Among the more important benefits obtained by the use of the Cot-
trell Processes for cleaning roaster gases in sulphuric acid manufacturit^
plants the following may be mentioned:

1. The quality of the acid is improved, due to the removal of the
dust carried by the furnace gases.

2. More efficient operation of the nitrating pots can be obtained due
to the absence of dust in the gas at this point in the system.

3. Plant shutdowns for cleaning the Glover towers, wifh the atten-
dant loss of acid and Umttation of production, are avoided.

4. The life of the lead chambers is increased, due in part to elimination
of dust deposition.

5. A material is collected usually having more than sufficient value
to carry the operating cost of the installation.

The simplest dust settler is an enlargement of the gas Sue to
reduce the gas velocity. A considerable amount of valuable data
has been gathered on this method of dust settling, and it is pos-
sible to design a dust chamber of this kind with assurance as to
its performance.

It seems to be well established that reduction of the velocity
of the gas stream to not over 5 ft. per second is necessary to
allow proper settling within a reasonable distance of travel.
Even at this rate of speed a flue of moderate height, say 10 ft.,
will have to be 60 ft. or more long to allow the dust particles "to
settle out. It will be readily seen that for a large acid unit a
dust chamber of this type requires a great deal of ground space.

Baffle walls to make the gas take a tortuous course are, in
this form of dust chamber, of doubtful value. One baffle
immediately in front of the inlet opening is good to spread the
gas stream, but if a large number of baffles are put in they impede

^dbvGooglc

DUST SETTLING APPARATUS 91

the draft, raise the gas velocity, and often give poorer net results
than empty chambers.

Wires or chains hung in a dust chamber of this type have a
very good efEect. Their virtue of course Ues in the fact that dust
particles impinge on them and lose their velocity and fall or else
cling to the wires or chains. They do not interfere with draft to
any serious extebt. It is well to provide some means of shaking
suspended wires or chains as dust clings to them to some extent.

An interesting account of the performance of dust chambers
hung with wires at the Copper Queen smeltery is given in an
article by Geo. B. Lee in the Engineering and Mining Journal of
September 10, 1910. Two tests described showed that in a
100 ft. loi^ chamber with gas velocity about 4J^ ft, per sec.,

62.8 per cent of the total dust was deposited with the chamber
empty, and 77 per cent when h\in^ with wires.

Several interesting proposals have been made along the lines
of inserting shelves into the chambers, the idea being that by
using them the distance which a dust particle must fall before it
finds a resting place is greatly reduced. The Howard dust
chamber which provides horizontal metal shelves a few inches
ap&rt is one example of this. The Wedge dust chamber does the
same thing except that the shelves slope sharply toward the
outside walls and in that way the dust all slides down against the
walls and can be more easily drawn. This principle is a good one
so far as setthng dust is concerned, but the structural difficulties
are considerable for large units or where the gases are very hot.

Figure 16 shows a longitudinal section which applies to either
the Howard or the Wedge chambers described, while the trans-
verse sections show the horizontal position of the Howard
shelves and the inclined position of the Wedge shelves. The
Howard chamber has been installed in several plants with

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AMERICAN SULPHURIC ACID PRACTICE

satiBfactory results. I do not know whether any chambers
fotlowing the Wedge phin have been built.

Dust chambers employing the centrifugal principle have been
used in ^me places for acid work. They have not been as
popular as their merits warrant. A. P. O'Brien many years
ago used such a dust chamber at Richmond, Va. This is de-
scribed in the Mineral Industry, Volume 9, as retaining 75 per
cent of the dust entering, which is very good. More modem
applications of this plan have been made at the American Steel
and Wire Company's acid plants at Donora, Pa., in connection
with Hegler roasters, and at the Garfield Chemical and Manu-
facturii^ Company's plant at Garfield, Utah, where fine copper
concentrate is roasted in Herreshoff furnaces.

Chambers of this type are cylindrical with gas inlet tai^ential
and near the top, and with gas outlet through a central pipe lead-
ing from a point near the bottom. Figure 17 shows the essential
features. The velocity of the entering gas should be as high as
possible without too much impeding the draught. Good clearance
requires entering gas velocity not under 25 t. per second.

Centrifugal dust chambers are very small and compact for the
work they accomplish and have much to recommend them for
acid plants for that reason. In cases where it is desirable to
hold up the temperature of the furnace gases so that the Glover
tower will concentrate well, the small radiating surface of the
centrifugal chamber is an advantage.

The Anaconda Copper Mining Co. has in its acid plants
two dust chambers of a unique design which has probably not
been used elsewhere. These chambers have given excellent
results and are so compact that they deserve description. They

^dbvGooglc

DUST SETTLING APPARATUS 93

use both the principles of decreased velocity and change of
direction to accomplish clearance. The form of this chamber is
a cylinder with inverted conical bottom, and in general appearance
resembles the centrifugal chambers.

Referring to Fig, 18, the gas enters through flues 1-1 into
space 2, distributes radially, passes through the 4-in. vertical
slots, and rises into space 3. Space 2 is separated from space 3
by reinforced concrete cone 5-5, From space 3 the gas leaves
the chamber through passage 4 which does not communicate

sTof!..4'-Wiav .

-"^a^

Section * -A

with space 2. The dust which drops in space 3 falls through the
vertical cast iron pipe 6 and is drawn off with the dust which falls
in space 2, at gate 7. This chamber is entirely self cleaning.

The original chamber at Anaconda cleans the gases from
roasting 150 tons of copper concentrate per 24 hours, all of which
passes J^-in. screens. It is 32 ft. in diameter and 43 ft. high
outside. It offers very little resistance to the passage of the
gas and in this respect is better than the centrifugal chambers.
Its cost of construction is somewhat higher than that of a centrifu-
gal chamber, but it is a very satisfactory apparatus from an
operating point of view.

^dbvGooglc

CHAPTER VIII
THE GLOVER TOWER

The Glover tower is the firat division of the acid plant proper.
It receives through a flue entering it near its bottom the gaa
from the burners. This gas contains essentially SOj, oxygen,
nitr(^en and — if nitre ia potted in the flue — a small amount of
NO. Its temperature may be up to 1,000''F. or liZWF. Into
the top of the Glover tower are fed nitrous vitriol {60" sulphuric
containing NaOg in solution), and chamber acid about 50°B£.
The purpose of the tower is to produce an intimate contact
between the gas and the acid.

With this statement of the duties of the Glover tower in
view, it is clear that the tower must be constructed in such a way
as to be acid and gas tight against pressures of a few ounces,
and it must be of such materials and buUt in such a way as to
withstand the action of gas at 1,000°F. and sulphuric acid of
60° or erB^. at SOOT.

A modem Glover Tower consists of a lead shell supported
by steel or wood framework, a lining of acid- and heat-resisting
brick, and a packing of acid- and heat-resisting material placed
in such a way that gas may ascend through' it freely and acid
descend over its surfaces. The structure is built in a lead,
briek-lined pan which may be integral with the tower or fairly
distinct from it. A brick-lined flue enters near the bottom to
deliver the hot furnace gases into the tower, and another flue of
bare lead leaves the top of the tower and carries the gases to the
chambers.

As it is desirable that the acid which issues from the Glover
tower shall flow by gravity to coolers and tanks, the tower
proper is built on a suitable foundation from 10 to 20 ft. high.

The weight of the tower is very great and the stability of the
foundation must be beyond question. In modem plants rein-
forced concrete, or structural steel on a heavy concrete base or
piers, are the forms of construction used. A smooth level floor
at the desired height is obtained by one of these methods, and
on it is laid down a sheet of Ught lead — 6 or 8 lb. per square foot

^dbvGpO^^lc

THE aWVER TOWER 95

— aa a protection against leakage or overflow of acid. This lead
extends out beyond the edge of the foundation a few inches, or
i3 turned up to form a shallow pan which is drained by pipes.

The pan of the Glover tower is frequently made of lead weigh-
ing 60 lb, per square foot i.e., about 1 in. thick. It may be
made somewhat lighter with safety if the masonry lining is well
done.

The sides and top of the Glover tower are of lead not less than
10 lb. per square foot and better 15 or 20 lb.

A sturdy framework of wood or steel or a combination of the
two, supports the lead, and, above the top of the tower, a plat-
form carrying acid tanks. This frame consists usually of 4
posts or columns with horizontal members between them which

J^^-Lsad Loop& JUL ToMTtTap^

T LevdSfraM L

"'..♦Y turned ipyer-.,,^

'Anghlrvns

Fia. 19.

suppwrt the lead, or which carry small vertical pieces which
support the lead. Horizontal or vertical straps are burned to the
lead sheetfi and nailed or bolted to the supporting members of
the framework. As the lead sheets are supported inside by close
contact with the lining wall, the outside straps on the side sheets
need not be very close together.

The top lead is supported by straps nailed to wooden joists
or by loops of lead passing over iron pipes, or by small iron hooks
supporting rods burned to the lead. Several of these schemes
are shown in Fig. 19.

As mentioned earUer the pan of the Glover tower is often
quite distinct from the tower proper which sits in it, though
sometimes the upper edge of the pan and the lower edge of the
side sheets are burned together, in which case the pan is not very

^abvGooglc

96 AMERICAN SULPHURIC ACID PRACTICE

clearly defined. It cannot be said that either plan is very dis-
tinctly better than the other though it is eaey to get into trouble
with the latter method if the details are not carefully designed.

The pan and the sides of the Glover tower are lined with brick,
usually in recent years laid up in acid pixiof mortar, thou^
formerly and sometimes now, laid dry. So much stress has been
put upon the quality of the brick used for this purpose that it
seems to be a rather common idea that very exceptional clays,
and methods of manufacture are necessary. It is difficult to
lay down any analysis figures which show the fitness of brick
for this purpose. Of course the higher the sum of siUca and
alumina the better. The sum of CaO and MgO should not be
over 3 or 4 per cent. Very satisfactory acid resisting brick may
contain up to 6 or 7 j>er cent FeO. As a matter of fact in almost
any part of the United States one can find within two or three
hundred miles entirely satisfactory brick for making tower lininp.
As a test if the brick is mechanically sound and strong, it should
be soaked for a week or more in sulphuric acid and then allowed
to stand in the weather for several weeks or as long as one can
wait. If no spalling or cracking or swelling occurs after a long
period of weathering, the brick will stand up well in the tower.

The mortar used in laying the brick consists of silicate of soda
and finely ground silica with a small percentage of barium sul-
phate if desired. This mortar seta up very slowly as the set is
due to evaporation of water only. After this initial set has taken
place, sulphuric acid is nm over the brickwork. This reacts
with the siHcate of soda and gives the mortar a permanent set.
The bottom of the pan is lined with 4 or 6 in. of brick. H the
pan is open, the sides are lined with 4 in. of brick. The lining
wall of the tower proper is 18 to 24 in. thick in the lower part
where the heat is high. A few feet above the top of the gas inlet
flue the thickness can be decreased and after the middle of the
tower is reached 9 to 12 in. thickness is correct.

Figure 20 shows the lining and packing of a Glover tower. The
packing of Glover towers is essentially acid-resisting solid mate-
rial which shall present a large amount of surface to the gas
and acid passing through it, thereby causing intimate and thor-
ough contact between them. Many materials have been used
for packing. Coke was formerly well thought of because it
offered much surface and was light. It is rarely used now be-
cause it is not so permanent or satisfactory as other things. In

^dbvGooglc

THE GLOVER TOWER

the courae of months or a few years coke breaks up and impedes
the passage of the gas and has to be renewed — an expensive and
dangerous job. Like any other non-symmetrical packing, coke
exerts some lateral pressure on the walls of the tower, which is
undesirable.

Another class of material used formerly but not much now, is
rough fragments of quartz or other natural or artificial silicious
material. This is better than coke in that it does not break down
readily, but it is open to the objection of creating lateral thrust.
In using these rough unsymmctrical packings one cannot fore-
tell very accurately what resistance to gas passage will be
encountered, and sometimes very unexpected things in this way
are encountered.

^dbvGooglc

98 AMERICAN SULPHURIC ACID PRACTICE

Much the moBt satisfactory kind of packing ia acid-resisting
brick or shaped pieces of symmetrical form, hud up 80 that all
the thruat is downward and none on the walls. With such
packing one can accurately determine how much area for gas
passage exists and how much wetted surface for gas acid contact.
In using unsymmetrical packing these things are very indefinite.
With symmetrical packings also there is no thrust on the walls
of the tower.

There are many kinds of symmetrical packings, some patented
and some for which very exclusively superior virtues sre^laimed.
In deciding between the various kinds available one should con-
sider that the most elaborately designed shapes do not as a matter
of hard practical fact give much better results than plain rec-
tangular brick of standard dimensions. If packing is to be used
at a point near to the factories which make the special shapes it
is well enough to take advantage of the fact and use them. It
does not pay however to ship fancy packing? many hundreds of
miles if good standard brick can be obtained locally.

Above the top of the Glover tower are located two tanks,
one to receive nitrous vitriol and the other chamber acid. These
aci<k are fed into the tower through suitable ilistributors which
should uniformly spread the acids over the entire top surface
of the packing. The nitrous vitriol and chamber acid are best
kept separate until they are inside the tower, because on mijdng
them some fuming off of the nitrogen oxids occurs.

The chief function of the Glover tower is to denitrate the
nitrous vitriol, the solution of N^i in sulphuric acid, which
comes from the Gay Lussac towers. This nitrous vitricJ is
broken up by the hot SOi, the acid is freed from its nitn^en
compounds, which are mostly reduced to the form NO, a gas,
which proceeds with the gas stream into the chambers.

In order that this action may be complete and the acid issuing
from the Glover tower be entirely free from nitrogen-oxides it
is necessary that the nitrous vitriol be diluted with water or weak
acid at the top of the tower. It is necessary however that the
acid issuii^ from the tower be not less than SO'Sg. as that is
what the Gay Lussacs require. This requirement limits the
amount of weak acid which may be introduced. Fortunately
the usual roaster or burner gas has a sufHciently high tempera-
ture to allow the introduction of much more weak acid that the
amount necessary to accomplish complete denitration, and the

^dbvGooglc

THE GLOVER TOtVER 99

Glover tower becomes a means of concentrating almost all of
the chamber acid to 59° or 60° acid. This is its second (unction.

A third function though an incidental one is that the roaster
gas is cooled to a temperature at which it will not harm bare
lead.

Of course the concentrating capacity of a Glover tower depends
largely upon the temperature of the roaster gases. If they enter
the tower at l.OOOT. all the chamber acid can be concentrated
to 60° or even 61". If their temperature be two or three hundred
degrees lower not 'all the chamber acid can be concentrated.

In the- matter of dimensions and of cubic contents there seems
to be a surprising difference of opinion, shown by modem
designers. Varying SOa percentages and temperatures account
for some of the difference but by no means all.

Lunge states that the net packed volume of a Glover tower
should be in the neighborhood of 320 cu. ft. per ton of sulphur
or about 80 cu. ft. per ton of 60° acid made. This refers to
European practice and small units.

A large American plant recently erected has a Glover tower
whose net packed volume amounts to 33 cu, ft. per ton of 60°
acid.

Many American plants erected within the last few years have
around 50 cu. ft. per ton of 60° acid produced, and that figure
probably approaches modem opinion of ttus point.

The vertical dimension of the packing is usually from 20 to 30
ft. There is some possibility of makit^ this dimension too great
to be good for the concentrating capacity of a tower in that the
gas temperature may fall so low that condensation will take place.
If gases entering the tower are hot, say over 1,000°F., a 30 ft.
dimension is quite proper, but if the gas temperature is below
800° it is well to hold the vertical dimension of the packii^ lower.

The horizontal area of the packing will of course be fixed by
the cubic contents and the height, and will, from the above, vary
between 1.66 and 2.5 sq. ft. per ton 60° acid produced. The
overall he^ht of the Glover tower is usually from 10 to 15 ft.
more than the height of the packing proper to allow for the gas
distribution chamber below and the acid distribution space above .
the packing.

The outside horizontal dimensions are greater than the hori-
zontal dimensions of the packing by 3 or 4 ft. to allow for. the
lining walls. ■ Jf"

^dbvGooglc

100 AMERICAN SULPHURIC ACID PRACTICE

As an eicample of the above observations a Glover tower for
a unit to produce 100 tons of 60° acid per day would assume
dimensions as follows:

Cubic contents of packing @ 50 cu. ft. per ton 60° acid 5,000 cu. ft.
Vertical dimenBion of packing 25 ft.
Area of packing 5,000 -I- 25 - 200 sq. ft.

Assume that the tower has square section, than the horizontal
dimensions of the poking will be 14 ft. 2 in.

The overall height of the tower will be 25 + 15 - 40 ft.

The outside horizontal dimensions will be about 17 ft. X 17 ft.

^dbvGooglc

CHAPTER IX
THE CHAMBERS

The gas mixture coming from the Glover tower consists of
SOj, NO, 0, N, and water and weak acid vapor, A period of
from 1 to 2 hours is required for reaction between them sufficient
to convert substantially all of the SOg into aulphurie acid.

A place in which the gases may react, a chamber or series of
chambers then, will be required of such volume that each portion
of gas mixture will occupy from 1 to 2 hours in its passage from
entrance to exit of the series. Liquid sulphuric acid forms and
condenses within the chambers, which must therefore be con-
structed of such material and in such fashion as to retain liquid
sulphuric acid.

The acid-forming reactions are, taken collectively, exothermic.
It is essential for the proper progre^ of the reactions that the
temperature of the gas mixture shall not rise much above the
boUing point of water. It is therefore necessary that the cham-
bers be constructed of such material and in such fashion that the
heat of reaction can be readily carried away by radiation. '-

These considerations together with the experience of many
years dictate the volume, the materials, and the method of
construction of the chambers.

Sheet lead possesses a desirable combination of the essential
characteristics so predominantly that it is universally used as the
basic material for chamber construction. It is cheap, it resists
acid well, it can be readily shaped, and its pieces can be burned
together to make gas- and acid-tight joints. Furthermore it
conducts heat well. Other materials have been tried from time
to time but none so well meets the requirements.

It has been found best to provide instead of one single lat^e
chamber several smaller ones, usually three or more. Several
good reasons for this exist. Mixing and stirring up the gas mix-
ture accomplished by passing through flues from one chamber to
another has been found to accelerate the reactions. By dividing
the space into several small chambers more radiating surface is
101

^dbvGooglc

102 AMERICAN SULPHURIC ACID PRACTICE

provided than if a single chamber were used. It is more con-
venient structurally to build several small chambers than one
large one. A modem chamber set therefore consists of from
three to ten chambers in series.

The individual chamber consists of three parts, pan, side or
"curtain" walls, and top, all of sheet lead. The pan is ordi-
narily of lead weighing 8 or 10 lb. per square foot — i.e. >^ to Ka
in. thick — with the bottom horizontal and the sides from 18 to SO
in. high. The pan is designed to be a reservoir for the acid made
in the chamber and is supported strongly so that it will safely
carry acid to within an inch or two of its top edge.

The side or curtain walls extend from the upper edge of the pan
to the top of the chamber. They are of sheet lead of 6 to JO
lbs. per sq. ft. in weight. They are supported by lead straps
burned to the sheets and fastened to a wood or steel framework
surrounding the chamber. It was formerly common to allow
the bottoms of the curtain sheets to extend down into the pan
to within about 2 in. of the bottom. The acid in the pan then,
80 long as it was maintained more than 2 in. in depth, made a seal
which retained the gas. This plan though followed for years and
still used sometimes is not a sensible one. It wastes lead on
original construction and after about two years that part of the
lead which is Immersed in the acid becomes so corroded that holes
appear and much repair work or even reskirting becomes neces-
sary. The usual plan of recent years is to bum together the top
edge of the pan and the bottom edge of the curtain walls. Figure
21 shows the two methods.

The top of the chamber is usually of lead of the same weight as
the curtain walls. It ia ordinarily horizontal and the sheets are
supported by frequent straps fastened to rafters of wood or
steel. The sheets of the top and the curtain walls are burned
together when they meet.

The bottoms of fRe chambers should always be far enough
above ground to allow convenient inspection for leakage, say 6
or 7 ft. minimum, so that a man may walk about. This is im-
portant because leaks invariably develop and if the chamber pans
were laid on the ground much loss of acid and damage to founda-
tions and pans would result before the trouble was detected.

Concrete piers properly placed in the ground to carry the
weight of the chamber structure and the pan full of acid are first
Bet. On these are fixed wood or steel posts surmounted by wood

^dbvGooglc

THE CHAMBERS 103

or Bteel sills. On the sills is laid down a wood floor to carry the
chamber pans. Between and around the pans the floor is of wood
slats well apart, or perforated steel, a construction in any event
which wUl allow free circulation of air up the sides of the cham-
bers. It is well to build the floor on which the pans are to rest
of plain boards, not matched — tongue and grooved — in order that
leaks may be readQy located. If the floor is too tight it may be
difficult to decide just where the hole in the lead is, as the acid
may travel some distance before it finds a crack or crevice through
which it can issue.

The lead walls and tops of the chambers are supported by
wood or steel framework or a combination of the two. For very
large chambers steel is necessary because of the long spans and
great height of columns. For small chambers wood is more

Fio. 21.

economical and perhaps better adapts itself to fastening to the
lead. Certainly it is not so fireproof though there is not any
unusual fire hazard about chambers inherent in the process
itself.

Two somewhat different general plans of wood framing for
supporting the curtain walls have been used. The first, which is
probably most used, provides posts of rather large section spaced
perhaps 6 or 8 ft. apart. Secured to these are l^hter horizontal
rails 3 of 4 ft. apart vertically. Horizontal lead straps to corre-
spond to these rails are burned to the lead curtain walls and nailed
or cleated to the rails. On the top of the posts rests a heavy cap
or crown timber. The curtain sheets are turned back over the
top of this crown piece and part way down its outside and there
nailed. The theory of this method of support is that almost all
of the weight of the curtain sheets ia carried by the crown piece,
and the straps on the sides simply prevent lateral movement.

^dbvGooglc

104

AMERICAN SULPHURIC ACID PRACTICE

Tliere are of course many variations of detail in this acheme.
Figure 22 shows the essential features.

The other system, shown in Fig. 23 provides vertical posts or
studs of comparatively small cross section, much closer together,

say 20 to 30 in. No horizontal rails are used. The straps are
burned to the curtain walls vertically, a row to correspond to
each vertical stud, and cleated to the studs. A light cap at the
top of the studs serves merely to hold them in position. The

TTTT"

curtain sheets are not turned over it but are curved in toward
the center Une of the chamber. The studs are appropriately
braced and held in position by horizontal and diagonal members
spiked to their outside faces. When the sides of the chamber pan

^dbvGooglc

THE CHAMBERS 105

are of 10 lb, lead and the studs are not more than 24 in. apart
it is not necessary to support the pan sides with planks. The
theory of support by tnis method is that each vertical strap
supports its particular small sectJon^perhapa four square
feet — of the curtain sheet, and the whole load is uniformly
distributed.

There is some difference of opinion as to which is the better of
•these two general systems of support. The first described plan
has been more generally used, but the second plan has some very
important advantages in practice as well as in theory. Lead is
a metal which has practically no elasticity. Under stress, par-
ticularly when warm, it flows. When a sheet 20 or 30 ft. long is
suspended from a crown piece as described, with light horizontal
straps at rather large intervals to prevent sway, it unfortunately
does not all remain just where it was placed. When the chamber
is heated up to 200^. a considerable expansion occurs. When a
stop and cooling takes place, it does not go back up again. On
again heating, downward expansion again takes place. Further-
more there is some creep caused by stretching or fiow. The net
result of these influences in the course of a year or two, is that
much of the load is transferred to the straps where it does not
belong, and distortion of the curtain sheets results, or straps are
pulled off, usually both. Another weak feature of this support
plan is in the fact that behind the crown piece just where the
strain is greatest on the lead, and where radiation is most ob-
structed, the lead is inaccessible for repair.

In the vertical-stud system each small rectangle of the lead is
supported by its strap and the expansion of the lead with heat-
ing shows itself in very slight curves between straps. Nolai^e
unsightly and damping distortions occur. At the line where the
side turns to the top, the lead is entirely accessible. From an
erection point of view this framing plan is excellent also.

Steel framing for supporting chamber lead has been increas-
ingly used of late years. Its use has been necessary in some of
the large units in which individual chamber dimensions are so
great as to make timber construction out of the question, or at
least very awkward. In some modern plants of small dimensions
.the desire for permanency and fireproof construction has dictated
the use of steel.

The construction is simple and usually follows the idea de-
scribed first above under wood framing, i.e., vertical posts or

^dbvGooglc

106 AMERICAN SULPHURIC ACID PRACTICE

columns 8 to 12 ft. apart are used with horizontal memberB 3
OF 4 ft. apart to which the lead is attached with straps. Angles
are probably most used for both vertical and horizontal members
though BometiiQj^ I beams for columns and channels for hori-
zontal pieces are B«en. The chamber top is supported by I beams
or pairs of channels across the short dimension of the chamber,
with pairs of small tngles between them running longitudinally
of the chamber to which the lead straps are fastened.

Chambeis should always be protected by a building. The
chief reason for this is to prevent wind pressure from reaching the
lead Less important consideratiooB are protection from sun,
rain and snow, and facihty of proper control of the process in
bad weather. The chamber framing should be in no way con-
nected with the framing or walls of the building as it is essential
thtft movement of the building due to wind be not transmitted
to the chambers. Ample openings in the walls below the
chamber fioor, and roomy ventilators in the roof are necessary to
assure free circulation of cool air along the side walls of the cham-
bers. Modem chamber plants are housed in steel or brick
buildings.

It has been mentioned that one prime object of dividing the
chamber space into several small chambers instead of using a
single large one is to cause mixing and invigorating reaction by
passing through connecting Sues. Much thought and experi-
mentation has been spent upon this subject of connections be-
tween chambers.

The most simple plan is to run a Que from the centre of the end
of one chamber to the centre of the end of the following one.
Another similar method is to use two or four direct horizontal
fiues between the ends of the adjoining chamber. Sometimes
the gas is taken from near the bottom of one chamber and led to
a point in or near the top of the following one. Or a flue will
leave the lower left hand comer of the end of a chamber and enter
the upper right hand corner of the nest or vice versa, the object
being apparently to have entrance to and exit from a given cham-
ber at pointfi most extremely distant from each other. The
purpose of all these latter designs is to avoid having dead comers
or wedges in the chamberB in which the gas moves sluggishly
or not at all, or in a word to avoid short circuiting. An arrange-
ment sometimes used which is intended to introduce the gas
into a chamber in such a way that it will conform to the natural

^dbvGooglc

■THE CHAMBERS

107

movement of the reacting gases in the chamber is shown in
Fig. 24.

This is based on the idea that any given portion of gas mixture
will proceed through the chamber in a spiral course. Radiation
at the walls causes the gas nearby to cool and descend. On
reaching the bottom it is forced in toward the centre and reaction
heat there causes it to rise again toward the top where it is drawn
toward the side again by the descending stream. There is
meanwhile a forward movement. This movement of course
takes place on each side of the central vertical plane. Tlifi flue
connections shown inject the gas on each side near the bottom
and direct it toward the centre where it rises and immediately
and natiu-ally begins its double spiral progress.

Many designers have used special structures between the
chambers to insure thorough mixing of the gases and - often
cooling as well. These often accomplish the work for which
they are designed. Sometimes they coat more money than an
additional pliun chamber which would give the same net result
in tons of acid made and the intricacy of their lead work some-
times makes for heavy repair costs after they are a few years old.

In the 1918 "Transactions of the American Institute of Chemical
Engineers" Dr. L. A. Thiele describes his Multiple Tangent
System of introducing gases to the chambers.

His idea is to avoid the large amount of waste space, particu-
larly in the comers, where the circulation in the chambers ia
sluggish. An additional advantage is a very considerable saving
in area.

Gas is introduced from the top of the Glover tower, through
flues, which vary in area and length, the largest in area being the
shortest; this makes for varying rates of cooling, thus varying
pressures and rates of flow-all of which results in more rapid circu-

^dbvGooglc

108

AMERICAN SULPHURIC ACID PRACTICE

lation and better mixing. The flues are arranged as shown in
the accompanying sketch, 'around the circumference of the top,
Fig. 25.

If the outlet should be in the centre of the bottom, the gas
would be a spiral cone, the outside parts of the bottom being
dead space. Thus the outlets are arranged on a circle in the
bottom, concentric with the reaction chamber, and with a
diameter half that of the reaction chamber.

This arrangement is reported to save floor space and lead, and
start remarkably easily.

Such an arrangement is in service at the plant of the Fairmount
Chemical Co., Fairmount, W. V. It is running on coal brasses,
which of course produce a large amount of COj, so the figures are

not of the value that they would be if the conditions were more
nearly standard, but Dr. Thiele expresses himself as well pleased
with results.

To briefly cover a few of the best known arrangements of this
kind, the Lunge Plate Column ia one of the early proposals.
This is essentially a comparatively small lead tower packed with
stoneware plates spaced a few inches apart. These plates have
numerous small holes in them so arranged that holes in one do not
occur directly below those in the next above. The plates have
slightly raised circumferences and the rims of the holes are
also riused so that some acid always Ues on each plate and drips
down through the holes and splashes about as fresh acid forms
or is fed in. This apparatus is not for big plants for size of
plates is necessarily limited.

The Gilchrist Pipe Column is a lead tower with many hori-
zontal lead pipes extending through from side to side, both ends

^dbvGoo^lc

THE CHAMBERS 109

being open to the air. CirculatioD of air through the pipes gives
some cooling effect and the mixing is attained by the gas forcing
through between them.

Lead towers packed with brick or coke, or quartz, similar in
construction to Gay Luseac towers are sometimes used between
chambers. These may be used dry or may have cool acid circu-
lated over the packing.

A series of two or three open towers with neither packii^ nor
circulation of acid has been used.

Chambers are fitted with steam or water connections or both,
for introducing the necessary water to make acid of proper
Eitrength.' Steam is usually put into each chamber at two or
three places only, as it spreads well. These are usually in the
top, sometimes in the front end wall. Water must be introduced
at several points and in a very finely divided condition for
otherwise drops would go quickly down to the bottom without
entering into the reaction. Special atomizing nozzles of glass
or stoneware or platinum are made for the purpose. The water
for this purpose mtist be filtered and delivered to the nozzles at
uniform pressure usually about 60 lb.

Steam distributes through the reacting gases better than
water spray unless the apparatus for introducing the latter is
carefully taken care of. Water of course is much cheaper to use
if live steam has to be used. If a uniform supply of waste steam
is available it is quite acceptable. Water has the advantage
over steam in that it exerts a considerable cooling action on the
gas mixture which in summer particularly is valuable.

In order that the operator may know the gravity of the acid
being made in any given chamber at any time, small gutters
are burned to the inside of the chamber walls at one or two
convenient points. A portion of the acid running down the
walls is diverted by them to an opening in the curtain through
which it Sows over a sealing lip into a small jar in which is kept
a hydrometer. By observing and recording the hydrometer
readings from time to time the operator is enabled to control
properly the admission of steam or water to the individual
chamber.

One or two thermometers are inserted into each chamber.
If one only is used it is placed in a side wall at the centre and
about 5 ft. above the workit^ floor. If two are used one is
placed near each end. These thermometers are made with a

^dbvGooglc

110 AMERICAN SULPHURIC ACID PRACTICE

long stem, usually about 12 in., below the graduated portion.
This stem is turned 45° or 90° from the graduated part and is
inserted through a rubber stopper inside the chamber wall, the
graduated part being vertical and conveniently read. Such
thermometers are stock articles with the large supply houses.

The last one or two chambers of a set are frequently equipped
with bell jars or s^ht glasses in order that the color of the gas
may be observed.

For drawing off the acid from the chamber pans and for
communication between them, pipes are led from the bottom of
the pan to a boot near the end or between the chambers, or small
alcoves are made on the pan ends which are joined beneath the

fioor by pipes. In any case at least one end of each such pipe
should be accessible for blowing out accumulations of mud.
Figure 26 shows details.

CHAMBER VOLUME

The number of cu. ft. of chamber volume which must be
provided for making a given tonnage of acid depends upon
several factors. It may first be well to note that it is customary
to speak of the performance of chambers as using a certain
number of cu. ft. per pound of sulphur per 24 hours. This
expression of rating was broi^ht into use to do away with the
uncertainty that existed when one spoke of volume per unit of
acid. It was found that the manufacturer whose product was
50° acid often spoke of his production in terms of 50° acid while
he whose product was 60° used that as a basis, and yet others
had in mind 66° or even 100% HjSO*.

In order to make common ground of comparison the idea of
using sulphur itself as a basis has come into general use. Even
this ia not always common ground as one man will reckon on
sulphur contained in the ore burned, another on sulphur burned

^dbvGooglc

THE CHAMBERS 111

out of the ore, and a third on sulphur in the acid made. Of
course only the last is correct.

There is a divergence in claims of performance and a divergence
in performajice of modem acid plants, in respect of cu. ft. of
chamber space per pound of sulphur in acid made per 24 hours,
of from about 8 to 20. An averse of these two extremes, say
14, ifl probably not far from the volume actually used in most
plants. The plants which run on 8 or 10 cu. ft. per pound ot
sulphur have special arrangemenl^ such as towers fans, etc., in
connection with their chambers. Some plants having small
plain chambers in which the ratio of radiation surface to volume
is comparatively high run on 10 to 12 cu. ft. Some few plants
have been constructed in recent years in which large units — 100
to 300 tons 60° acid — contained only 4 or 6 enormous chambers.
The ratio of surface to volume is very low — mixing, cooling, and
impingment are largely sacrificed, but construction cost per
cu. ft. of chamber space is very low. In these plants around
20 cu. ft. per pound of sulphur was provided and is used.

These observations bring out the fact that merely to say that
a plant is working on so many cu. ft. of chamber space does not
determine whether its performance is all that should be expected
or not. If two plants of different design are built and each
costs $500,000, each produces 100 tons of acid a day with the
same operating costs, and one operates on 8 cu. ft. and the other
on 20 cu. ft. the performance of the latter is just as creditable as
that of the former.

It is the opinion of many designers that plain chambers of
moderate size and simple design give the most satisfactory
results all things being considered-

LEAD SPECIFICATIONS

One of the largest Chamber Acid plants in the country answers our
inquiry as follows:

"It has not been our practice to make any other specification except
that lead ^all be what is known to the trade as 'chemical lead.'

"We have always purchased this from the same company and the
quality has been uniform. It must be free from other metab, and
SufBciently ductile to permit of rolling out into thin sheets. The
addition of small percentages of copper has been advocated by some
engineera, but we have had no experience with this alloy. For the
construction of acid valves, fans and other apparatus that requite

^dbvGooglc

112 AMERICAN SULPHURIC ACID PRACTICE

structural strength, we use a mixture of chemical lead with 7 per
cent to 10 per cent antimony.

Life of Lead

"The exact life of lead in chamber plants cannot be accurately stated,
as it depends too much on local conditions. I would say that the life
ia influenced chiefiy by the temperature and whether or not scouring
action obtains. We have had chambers to run without interruption
for nearly 10 years, but repairs were made to various parte during the
interval."

^dbvGooglc

CHAPTER X
GAY LUSSAC TOWERS

The Gay Lussac towers follow the chambers in the course
of the gas. They receive from the chamberB normally a gas
mixture consistit^ essentially of nitrogen about 92 to 96 parts
by volume, oxygen about 4 to S parts by volume and the oxids
of nitrogen NO and NOi from ^o to 1 per cent by volume.
Of course small amounts of CO^ and other gases are present
but ordinarily have no bearing on the subject. There are a few
special cases where carbonaceous fuel is used in the furnaces
from which the SOi is derived, in which CO* must be reckoned
with. These are unusual and need not be considered in a
general discussion. The temperature of this gas entering the
Gay Lussacs is only slightly above that of the atmosphere.
The result desired from the Gay Lussacs is the recovery of the
oxides of nitrogen by absorption in 60° sulphuric acid which is
fed into them.

The Gay Lussac towers then should be built of such material
as to resist the action of comparatively cool 60° acid and gas.
They should be designed in such a way as to bring the gas and
acid into as intimate contact as possible and yet allow reasonably
free passage for the gas. They must be of such height as to allow
a sufficient degree of contact between gas and acid to accomplish
substantially a 90 per cent recovery of the nitrogen oxides.

These requirements differ from those of the Glover tower in
Jrhe matter of temperature of gas and volume. In the Glover
tower the gases enter at temperatures so high as to be injurious
to bare lead and it is therefore necessary in constructing a Glover
tower to provide & heavymasonry lining wall to protect the lead
shell. No such protection is required in the Gay Lussac towers
wherein the gas temperature rarely reaches ISOT. The Gay
Lussac tower therefore need be simply a well supported lead
shell completely filled with packing, excepting of course the gas
chambers above and below. This statement does not apply in
those cases where non-symmetrical packing such as coke or
quartz is used because such material, in a column 20 to 40 ft.
8 113

^dbvGooglc

114 AMERICAN SULPHURIC ACID PRACTICE

high, exerts so much lateral thrust as to bu%e and cut the lead,
and masonry supporting walls are necessary. It is unusual to
use such packii^ now. With the symmetrical packings, bricks,
rings or other shapes, the weight is all carried on the bottom.

Some designers still build Gay Lussac towers with lining
walls even though symmetrical packing is used, but it is a waste
of material and a waste of good absorption space. Also it is
actually bad for the lead shell to have an interior wall, in that
gas gets in between the masonry and the lead, circulates sli^-
^hly, and the nitrogen compounds oxidize up to nitric acid
which often corrodes the lead badly. ^

With this exception the general construction of the Gay
Lussac towers is much like that of the Glover. A massive
foundation is put down of sufficient height that the acid issuing
from the tower pans may run by gravity to circulation tanks.
This usually means on a level site that the top of the foundation
will be about 10 ft. above the ground. The top suriace of this
foundation is carefully levelled and made smooth by trowelling.
A sheet of light lead 4 to 6 lb. per square foot is next laid. The
edges of this sheet may be turned up a few inches to make
a shallow pan and a drain pipe put in, or else the edges are
projected a few inches beyond the concrete and turned down
sightly to throw any acid leakage away from the foundation.
This lead is also turned up around the footings of the columns
of the framework.

The tower pans are made of 15 or 20 lb. lead and are usually
24 in. high. False bottoms of 10 lb. lead are placed inside over
those portions of the bottom on which the brickwork is to rest.
The side sheets trf the tower are hung, fastened to the frame and
burned together. They may be burned to the pan or extend
down inside it. The latter method is not so bad here as in th^
chambers as the acid is cold. However it wastes lead and has
no particular advantages. The side walls are usually of 10-lb.
lead.

Ordinarily the top is not put on the tower till the brickwork is
in. Through the open top the brick and packing material
is introduced. It is perhaps easier and safer to open three or
four holes in one side and put in the packing through them.
When the packing is finished these holes are closed by the lead-
burners. All danger of bricks falling and injuring the workmen
is done away with if this plan is followed. The top lead is of the

^dbyGooglc

GAY LUSSAC TOWERS 115

same weight as the side sheets. A chamber 4 or 5 ft. high is left
without packing at the top to provide for the [nvper acid dis-
tribution and leave the exit flue free.

The base structure for supportii^ the packing and the packing
proper are substantially as described under the Glover Tower.

There should be on each Gay Lussac tower a carefully designed
acid distribution system with suitable tanks for feeding it. This
apparatus is described under Acid Circulation.

As to volume, dimensions and number of Gay Lussac towers
suitable for a unit of given size a considerable difference of opinion
seems to exist if one may judge by an examination of different
plants. Reverting first to the classic Lunge we find Gay Lussac
towers compared in volume to the total chamber space which
they serve. Lunge states that the packed volume of the Gay
Lussacs should be not less than 1 per cent of the chamber space
and better between 2 per cent and 3 per cent. This method of
proportioning would be satisfactory if all chamber space did the
same work but such is not the case. As mentioned before some
chamber sets use 20 cu. ft. of apace per pound of sulphur and
others less than 10 cu. ft. Lunge of course refers to continental
practice of several years ago in which the larger amounts of
chamber space were used. It is more pithy in this day to pro-
portion and speak of Gay Lussac volumes in terms of sulphur
made into acid of 60°B£. On this basis Lunge advocates not
less than 100 cu. ft. of packed volume per ton 60° acid produced
and for really good nitre recovery up to 200 cu, ft.

This range from 100 to 200 cu. ft. of packed volume per ton
60° acid is about what is found in modem American plants.
Certainly the upper figure should be approached but this is not
always done. With Gay Lussacs well proportioned and skill-
fully operated whose packed volume amounts to 200 cu. ft. per
ton of 60° acid made in the plant, a recovery of about 90 per cent
of the nitre can be made. The total nitre introduced into the
modern plant amounts to 25 to 30 per cent of the sulphur.
The loss of nitre then on the above basis amounts to 2.5 to 3
per cent of the sulphur.

The absorption of nitre in the Gay Lussac towers is of course
much more rapid in the earUer part than the late parte. Without
attempting to formulate or to give exact figures it may be said
that in a case where the Gay Lussac space was divided into three
towers in series it was found that the first tower retained about^

^dbvGooglc

116 AMERICAN SULPHURIC ACID PRACTICE

65 per cent of the nitre in the gas entering it, the second tower
about 60 per cent of the remainder and the third tower about 60
per cent of that yet remaining. It muBt be considered that prob-
ably about 5 per cent of the nitre is not recoverable by solution
in Sulphuric acid. The above will then work out as follows:

9S per cent total recoverable.
1st Toirer 65 per cent of 95 percent — 61.7S
2d Tower 60 per cent of (95 - 61.75) = 10.96
3d Tower 60 per cent of (95 - 81.70) = 7.98
Total 89.68

As explained these figures are intended simply to give a rough
idea of the relative recovery accomplished by the different zones
of Gay LuBsac space.

Having decided upon the volume of Gay Lussac towers the
number of towers and their dimensions are next calculated. In
order to secure uniform distribution of gas and acid throughout
the packing, it is well to make the horizontal section not too
large and consequently the vertical dimension long. A high
tower with small horizontal section makes a much better nitre
recovery than a low tower with large horizontal section, the
packed volume in botli cases being identical. This is to some
extent due to more uniform distribution of gas and acid through
the packing, but in larger measure to higher gas velocity and
consequently more thorough breaking up and mixing of the gas
with the acid. The minimum amount of horizontal section will
be dictated by the pressure necessary to force the gas through the
packing. It is not desirable to use high pressures because the
leadwork of the flues, fans and towers will not stand them. Cer-
tainly the pressure at the entrance of the first Gay Lussac should
be not over ^o or %o of an inch of water or say 12 to 15 mm.
For ordinary packing a gross horizontal sectional area of 2 sq, ft.
per ton of 60° acid made should be provided to accomplish the
above result. The total vertical dimension of the tower packing
should then be 100 ft. if we wish to provide 200 cu. ft. packed
volume per ton of 60° acid made. It is not practical to use a
single tower 100 feet high because of the difficulty of pumping
acid of 1.7 sp. g. to such an elevation, and so it is customary to
use two or three towers in series. If two towers be used the
height of each will be 50 to 60 ft. allowing 10 ft. in each for the
spaces above and below the packing. Likewise if three be used

^dbvGooglc

QAY LUSSAC TOWERS 117

the height of each will be 43 ft. As the tower bases will be at the
leaBt 10 ft. above the ground and the feed tanks about 12 ft.
above the top of the tower it is seen that to the above figures
some 22 ft. must be added to get the vertical distance of the
acid lift.

It should be remarked that many planbs will be found in which
the. Gay Lussac tower scheme does not check up at all closely
with the line of reaaoning presented above. Unquestionably
somewhat wide variations can be made from it without sacrificing
good work. The figures presented are however quite certain to
yield excellent nitre recoveries.

To give a concrete example of Gay Lussac towers for a plant "
to produce 100 tons of 60° acid:

Total packed volume @ 200 cu. ft. per ton 20,000 cu. ft.

Sectional area @ 2.25 225 sq. ft.

Vertical diinension „'„- = 89 ft.

Using 3 towers packed height each say 30 ft. Total height each
allowing 10 ft, for spaces above and below packing 40 ft.

If the section be made square the horizontal dimensions will
be 15 X 15. In the writer's opinion it would be better to make
the section rectangular say 9 ft. X25 ft. and to admit the gas at
three points on the long side. Such a plan probably more fully
utiUzes the packing than the square section.

The course of the gas should be upward in all the towers as
it has been demonstrated that a given tower performs better
absorption with the gas going upward, than downward. The
Sues between the towers then will leave the top of the first,
descend and enter the bottom of the next.

^dbvGooglc

CHAPTER XI
ACID CIRCULATION

The acid circulating syBtem will be in this discussion taken
to include tanks, coolers, pumps, pipe lines and distribution
apparatus.

Tanks are almost always provided at the top and bottom of
each tower. They are certainly indispensable when intermittent
pumping is used, i.e., by acid e^s or montejus. The Sow of acid
into and out of each tower must of course, be uniform and con-
tinuous and during the periods when the eggs are filling there
must be a stock <^ acid at the top to feed the towers and there
must be a place at the bottom to accommodate the acid issuing.
Even when continuous pumping apparatus such as centrifugal
pumps or air lifts is used, it is advisable to have tanks both above
and below, although in this case they need not be so large.

Three kinds of tanks are used for this service, viz., lead-lined
wood tanks, lead tanks supported by skeleton iron framework,
and iron tanks. The lead-lined wood tanks are most used and
the iron tanks least.

Wood tanks are always of rectangular section for conven-
ience of framing. Usually they consist of rather heavy sills and
caps with upright posts, strongly put together with bolts and
dowels. Inside this frame, 2 or 3 in. plauks are spiked, making
a smooth and solid wall all round. Lead usually 10 lb. per square
foot is then put in and turned over the top caps and an inch or
two down outeide. The burned seams should be some little dis-
tance from the comers as they are the places most likely to break
open.

A neat way of making a wood tank frame, particularly for
small tanks is to build up a crib of 2 X 4 or 2 X 6 material as
shown in Fig. 27, This of course, leaves 2-in. strips of the lead
open for the air, but no bulging of any moment occurs.

Lead tanks with iron frames are always made circular. The

iron frames consist of four or more upright angle iron pieces with

flat circular bands or hoops riveted inside. The number of hoops

for a tank 4 ft. 6 in, or 5 ft. high is usually four, one at the top,

118

^dbvGooglc

ACID CIRCULATION

119

one near the middle and two below the middle where the presBure
is greatest. The dimensions of the iron parts vary with the sise
c^ the tank. For a 10 ft. diameter X 5 ft. deep tank, the angles
would be about 4 X 4 X M and the bands i X H- Ten- or 12-
Ib. lead is used in tanks of this type. They are very satisfactory
if the details of design are correct, and very neat in appearance.
Iron tanks have come into use to some extent in the last few
years for 60° acid. There is no particular reason why they should
not be as satisfactory as are iron tank cars or storage tanks.
They cannot be so readily repaired in case of leakage as can lead
tanks but on the other hand, for several years at least theysre
not so likely to leak They should not of course, he used for
acids much under 60°B^.

Circulation tanks of any construction are usually made from
4 ft. 6 in. to 5 ft. high. This makes them easy to look into and
allows light construction as no great pressures are produced.

The capacities of cireulation tanks vary widely for plants of a
given size. It is not desirable to tie up too great a tonnage of
acid in circulation and yet reasonable capacities should be pro-
vided to carry over periods in which minor repairs to lines, valves,
etc., may be necessary. It would seem that tanks large enough
to contain at least two hours' normal Sow should be provided
at the top and bottom of each tower. At the bottom of the Gay
Lussac tower which produces finished nitrous vitriol, somewhat
more space is desirable, up to six or e^ht hours' flow, say. This
allows a stock of nitrous vitriol to be held which is highly desirable
in restarting the acid process in case of a shut down.

It is a very good plan to have two small tanks at each point
instead of one lar^ one. If this is done one tank may be cut
out to clean or repair without disturbing operations. The pipe
lines leaving a circulation tank should have machined seats of
hard lead (or iron, if iron tanks are used) at their points of exit

^dbvGooglc

120 AMERICAN SULPHURIC ACID PRACTICE

from the tanks, and plugs or stems to correspond. In case
valves in any line have to be changed or the line opened for any
reason, the plugs can be set and the flow of acid stopped. It is
convenient to have a washout pipe of generous size in the bottom
of each tank as well as the service line. This washout is ordi-
narily closed with a blind Sange.

Stor^e tanks for sulphuric acid are made of mild steel plate
with riveted joints. They are of circular section, have flat
bottoms and dome or conical tops. They are similar in general
features to large tanks used for stor^e of oil, except that as the
liquid they contain has a high specific gravity they are heavier
metal. It is highly important that all seams shall be perfectly
tight because any leakage, however sl^ht, causes serious outside
corrosion in a short time. The bottom of the tank shoidd be
supported on masonry walls or piers a short distance above the
ground in order that the bottom seams can be inspected. The
pipe for drawii^ off the acid is equipped with a seat and plug
or a long stem or with an inside swing pipe so that the flow of
acid from the tank may be stopped in case of a failure of a valve
or pipe. Every storage tank should have one or two manhole
castings with blind flanges bolted on in its side near the bottom
in order that the mud may be cleaned out of it from time to time.
If such cleaning is necessary only at long intervals, say over
one or two years, the mud may be flushed out with a strong
stream of water. There will be produced during the time of such
washing acid solutions of a strength which attacks iron, but the
injury done Jhe tank during the few hours required for washing
out is negligible. Removal of mud from a storage tank by
hand is a serious and dangerous task.

The acid issuing from the Glover tower is so hot as to be injuri-
ous to pipes etc., and far too hot to absorb nitre when it is put
over the Gay Lussacs, hence coolers are necessary at the base of
the Glover tower. These are open-top tanks containing leftd-
pipe coils through which cold water is circulated.

This is sometimes augmented by spraying water on the outside
of the tank or by making it with double walls and circulating
cold water between them. The hot acid is discharged into the
top of the tank and leaves it at the bottom through a pipe which
rises up almost to the top again. In this way the cooler is
always kept full and the acid takes its natural course, i.e., as it is
cooled it sinks to the bottom and runs off.

^dbvGooglc

ACID CIRCULATION

121

The tanks are made with wood boxes lined with lead or with
iron framework, as described above. Some times a brick lining
is put inside the lead. If the tank is jacketed it is made with the
shells heavy enough to be self sustaining. The coils are made of
Ij^-in. or l}^-in. lead pipe. They may be made fiat spirals or
upright spirals. If flat, several are placed superimposed. If
vertical, they may be of different diameters and set concentric-
ally or may be of the same size and set side by side. The cold
water enters at the bottom and circulates upward and leaves the

Detail of Acid Di&chorg*

top, in this way the cold water is brought into contact with the
cooler acid, and. the warmed water with the hot acid. Superim-
posed flat coils are not to be recommended on account of the
inconvenience of repairing or replacing them. Uniform upr^ht
coils are best in this respect and give fully as good results as
regards cooling. A sketch of a cooler with this type of coils is
shown in Fig. 28.

Between 1 and 2 sq. ft. of coil surface should be provided
per ton of acid per 24 hours going through a cooler tank. The

^dbvGooglc

122 AMERICAN SULPHURIC ACID PRACTICE

cooler tanks should have an acid capacity such that the acid
will be in contact with the coils from 1 hour to IJ^ hours. For
example, if the tower is discharging 300 tons of 60° acid per 24
hours, the total surface of the pipe coils should be perhaps 450
sq. ft. and the acid capacity of the coolers should total around 15
tons or 285 cu. ft. These proportions may be varied properly
with the temperature of the acid issuing from the Glover and the
temperature of the cooling water. They work well if the former
is 275°F. and the water 60'*F., i.e. the acid will issue from the
cooler at a temperature around 70°.

There should always be at least two coolers with the inlet
launders and discharge pipes so arrai^ed and of such size that
any one cooler may be cut out, emptied and washed while the
entire acid stream goes temporarUy through the others. A
generous washout pipe leading to the sewer should be provided
on each cooler tank.

Pumping sulphuric acid presents difficulties which are not
encountered in pumpii^ water, oil and other familiar liquids.
It is corrosive to many metals and it quickly destroys any packing
material. Hence, any pmnp which depends upon a flexible
packing for tightness is out of the question. Reciprocating, or
plunger pumps cannot be used at all and even centrifugal pumps
which involve glands packed with flexible material are trouble-
some. These facts have led to the almost universal use of an
apparatus known vdriously as the acid egg or blow case, or monte-
juB. The air lift or pulsometer is also widely used and to an
increasing extent, the vertical submerged centifugal pump.

The acid egg is a cast- or wrpught-iron vessel provided with
three openings for pipe connections. One of them which just
enters the egg is connected to the supply tank and through it the
acid enters the egg by gravity flow. The second which also
just enters the egg, serves alternately for the admission of com-
pressed air and the biow-off. The third pipe extends almost to
the bottom of the egg and through it the acid is forced out of the
e^ and up through the discharge line to a tank on top of the
towers. To operate this device, the blow-off valve is opened to
atmospheric pressure and the compressed-air valve is closed.
T^e valve in the feed line is opened and the egg allowed to flll
with acid. Next the valve in the feed line is closed, the blow-
off valve is closed and the compressed-air valve is opened. The
compressed air flows into the egg and forces out the acid through

^dbvGooglc

ACID CIRCULATION

123

the discharge line. When the egg is empty or near^ so, the
compressed air is shut off and the blow-off valve is opened. When
the pressure is relieved, the feed line is once more opened and the
cycle begins again. Figure 29 shows a typical layout. It is
important that the blow-off pipe be carried up above the level
of the top of the feed tank in order that acid may not run out
through the blow-off line when the egg is filled. The blow-off
valve is of acid proof construction. The arrai^ment shown is
operated by hand. A convenient modification is to have a check
valve in the feed line instead of a hand-operated valve. There
have been many clever automatic devices developed for operating
the compressed air blow-off valves. Almost all of them depend
upon the action of a float within the ^g to open and close the

Fio. 29.

valves or ports. The Kestner Automatic Egg was an early and
much used apparatus of this type but is probably not being in-
stalled in this country now. Descriptions of it can be found in
Lui^ and other publications of several years ago. Simpler and
more satisfactory automatic valves are now being made by the
Schulte and Koertit^ Co. and the Monarch Manufacturii^
Works, both of Philadelphia. Both of these consist essentially
of a small lead casing in which a fioat works. When the egg is
empty the lower part of this float, which ia conical^ seats in a
depression whose sides are pierced by ports connected with high-
pressure air, and closes them. When the acid rises up about the
float it rises off these ports and its upper surface seats against
the orifice of the blow-off pipe, thus admitting air to the egg and
closing the blow off. The acid is blown out through the usual
discharge pipe and when all out the air also escapes and the

^dbvGooglc

124 AMERICAN SULPHURIC ACID PRACTICE

pressure within the egg decreases to such an extent that the float
drops and closes the air inlet and opens the blow off.

It is to be considered that any automatic apparatus requires a
certain amount of attention to keep it in order. Also that the
flows of acid into and out of tanks must be kept under observa-
tion. One man can easily operate a lai^ battery of hand-
operated eggs and the latter are almost trouble proof. It is a
question therefore, whether or not, everything considered, auto-
matic apparatus is more satisfactory than hand-operated. As
regards economy of air and power, the matter is largely one of the
care- with which the apparatus is operated and maintained. To
be sure, a careless pumpman can waste a great deal of air. On
the other hand an automatic valve which is not working properly
can do the same. Air pumping at best, is a very inefficient
method of using power.

Eggs for pumping sulphuric acid were formerly almost always
made of cast iron, but as the size of chamber units increased and
the volumes of acid to be raised correspondingly increased, it
became desirable to make very large eggs. In cast-iron, these
would be enormously heavy and expensive and so the egg made
of wrought-iron plates, riveted together was evolved. Such
e^s are now in use of a capacity up to 250 cu. ft.

Cast-iron eggs are made in several different shapes, one of
which is shown in Fig. 30. Usually only two pieces are necessary
to make up the complete egg, i.e., there is just one flanged joint
to be made. This joint is made tight with a gasket of 10- or
12-lb. sheet lead. Three flailed nipples are cast integral with
the egg body. In some cases a depression, or well, is made
below the nipple designed for the discharge pipe and the latter
dips into it, the idea being to get all the acid out of the egg at each
pumping. This is a rather unnecessary refinement as in a short
time the bottom of the egg accumulates some sediment and the
end of the discharge pipe is in a " welt " in this sediment anyway.

^dbvGooglc

ACID CIRCULATION 125

It is unwise to line iron eggs witb lead as some minute opening
in the latter is sure to develop. When this occurs the lead is
very soon blown away from the iron by the action of the air and
soon the iron is exposed to the action of the acid anyway. Cast
iron eggs of ample thickness, up to 2 in. last for many years if
only acids near M^B^. are bandied in them.

Wrought-iron eggs should be made of as high grade wrought-
iron plate as can reasonably be obtained. The usual design is
shown in Fig. 29. A ca8l>-iron saddle is riveted on one side and
this covered with a plate on which are cast the usual nipples.
This plate is bolted to the saddle which also serves as a manhole.
As mentioned, eg®s of this type are especially suitable in the
large sizes.

For elevating acid of 50° or less, iron eggs are not suitable as
too much corrosion results. For this service the air lift is much
used. It is a satisfactory device but it uses a very large amount
of power and has some other disadvanta^ies which make it less
suitable than eggs for pumping 60° acid.

In its simplest form, the air lift is a U-ehaped pipe with one
limb longer than the other and with a pipe for carrying com-
pressed air entering the long limb just above the turn at the
bottom. The acid to be elevated is fed into the short limb and
the long limb discharges into an elevated tank. To operate,
acid is allowed to flow into the pipe until the acid is level in both
limbs, then the compressed air line is opened somewhat. The
' air produces an emulsion or mixture of acid and air bubbles.
When sufficient air has become mixed with the acid that the
column of mixture filling the long limb is lighter than the colunm
of solid acid in the short limb, a flow is established. To get good
results with an air lift the long limb should be not more than
two times the length of the short limb and it is preferable to
make the ratio 1}4 to 1 when elevations permit.

Ordinarily, as in elevating acid from the chambers to the top
of the Glover tower, the elevations are such that a single air lift
cannot be arranged above ground, i^,, the he^ht of the chambers
above the ground is very much less than one half the height of
the Glover tower top above ground. In order to get a sufficient
length of the short limb of the Uft a pit or well is sunk into the
ground and the pipe extended down into it. While this is a very
common procedure, it sometimes leads to considerable trouble
and serious loss of acid in case of leakage. In a well particularly.

^dbvGooglc

126

AMERICAN SULPHURIC ACID PRACTICE

inspection is impossible and a leak may exist for some time
before it is suspected. To repair, it is necessary to draw the
pipes out.

In order to do away with the well, or pit, the multi-eta^
lift was developed. This simply amounts to putting together

-€]I^)

^ZD

&^ yy>

FlO. 31.

Fio. 32

several simple lifts of increasing he^ht until the final elevation
is reached. It has the advantage of being all above ground and
in sight. It is necessary of course, to so adjust the admission
of air to each lift that it will take away all the acid which the
preceding lift delivers to it. Once properly set, an air lift goes

on elevating acid without supervision. It would seem from
the theory of this method of lif tit^ acid that the air should be
forced in through many small orifices rather than a single larger
one. We find in practice both arrangements and from the '
author's experience, it must be said that there does not appear

^dbvGooglc

ACID CIRCULATION 127

to be any great difference in general results. Details of two
common schemes are shown in Figs. 31 and 32. At the top of
the long limb it is necessary to provide a box, or pot, to receive
the mixture of acid and air, in which the two can separate and
from which the acid can run into a tank or another lift and the
air escape. A baffle of some kind prevents acid from splashing
out of the air exit. Figure 33 shows such an arrangement.

From the standpoint of economy of
power and supervision, the centrifugal
pump would appear to be the best way
of elevating acid. Concerning power,
there has never been any question as
to the economy over air pumping.
Maintenance of centrifugal pumps has
for years been the thing that has pre-
vented their general use and the stuffing
box where the shaft enters the case the
particular point of trouble. Sixty de-
gree acid rapidly destroys rubber, or
flax, or any of the ordinary flexible ma-
terials used for packing. Many metallic
packings and combinations of metals
with the flexible materials have been
tried with indifferent success. Special,
and often highly ingenious glands have
been devised but so far as the author
knows, all of these leave much to be
desired.

A centrifugal pump which approaches
the problem from a different angle has
been put into use during the past three
or four years and appears to be very
satisfactory. This is a pump with a
vertical shaft. The whole pump is Fro. 34.

placed in the tank from which the

acid is to be pumped or in a boot connected with it. The
shaft extends a short distance up above the top of the tank or
boot and is driven by a belt or direct connected motor. The
stuffing box trouble is entirely sidestepped. This pump is
shown in Fig. 34. One of these pumps working in 60° acid has
been under the author's personal observation for more than

^dbvGooglc

128 AMERICAN SULPHURIC ACID PRACTICE

a year, during which time not a cent has been expended for
repairs. To give an idea of power consumption, it may be said
that one of these pumps equipped with a 5 H.P. motor elevates
about 250 tons 60° acid per 24 hours to a height of about 90 ft.
The vertical pump has no particular advanta|;e of course, over
the horizontal pumps in the matter of power.

The pipes used for conveying acid from one part of the appa-
ratus to another are mostly of lead. They are joined together
and to lead tanks by burning. When lead pipes are joined to
iron apparatus or when the joints are not permanent as in case
of valves, iron flanges are used. The method of making a flanged
joint is shown in Fig. 35. Oval flanges with two bolts are
suitable for small pipe, but for larger sizes, 2-, 3-, 4-in. or larger,
the 4- and 6-hole circular flanges are better.

Iron pipe is very successfully used in certain places in an
acid plant. For example, the lines carrying 60°B4. acid from the
eggs or centrifugal pumps to the tanks at the tower tops can
much better be of iron than of lead. These lines often have to
sustain pressures of 75 to 90 lb. per sq, in. If they are of lead,
they gradually swell and grow thin and sometimes suddenly
split open and deluge a large area with acid. Iron pipes, partic-
ularly extra heavy iron pipes, last for years in this service and
when they do fail they give ample warning by first showing
minor leaks. They are best made up with flanged joints using
lead gaskets, so that any piece may be replaced without taking
down a long run of pipe. Turns should be made by bending the
pipe in fairly long radius arcs instead of using fittings. Another
advantage which iron pipe possesses is its superior rigidity.
Lead pipe is likely to be badly shaken and eventually cracked by
the blow off of eggs, while iron pipe can be very securely bolted
to framework to prevent such shaking.

^dbvGooglc

ACID CIRCULATION

129

As the dischai^ lines from eggs or centrifugal pumpe deliver
acid at rather high velocity, provision must be made at the
points of delivery to prevent splashii^. This is done by nmnii^
the pipes into splash eggs or covered boots as shown in Fig. 36.
If the form shown in sketch A is used, it can well be made of cast
iron.

It is necessary to have some method of knowii^ how much
acid each top tank has in it, in order that the pumping may be
done at proper times and the flows maintained. Three schemes
of merit are in use, viz., floats, pneumatic indicators and electrical
indicators.

In the float system a hollow lead float rests on the acid in
the tank and has fastened to it a chain or cable or wire which
runs over pulleys to a convenient point near the pumps where

r ' Tank

it is fastened to a weight running on a graduated board. As
the acid rises and falls the float moves the we^ht up and down
and indicates the level. This works well enough but it is rather
cumbersome.

In the pneumatic scheme a bell or pot is set on the bottom of
the tank. A small bore metal tube is connected to it and runs to
a mercury gauge at the desired point. A compressed air line
or a small air pump communicates with this tube. Air is admits
ted to the tube until all the acid is blown out of the latter and
out of the bell in the tank and then shut off. The head of acid
in the tank then compresses the air in the bell and the tube
and the pressure exerted is indicated in the mercury gai^ which
ifi graduated to show the stage of acid in the tank. Absolute
tightness of this apparatus is imperative as the most minute'
leak renders it unreliable.

Electrical indicators are simplest and best. An ordinary direct
or alternating light circuit is employed. Lead rods of varying
lengths are hung in the tank to be indicated. An incandescent
lamp on a board is provided at the desired point of observation

^dbvGooglc

130

AMERICAN SULPHURIC ACID PRACTICE

to corrcBpond to each. One side of the light circuit is connected
to one socket terminal and the other side to the lead rod. The
metal of the tank is connected with the other socket terminal.
When the acid in the tank is in contact with the lead rod the
current flows through the acid and lights the lamp. When the
acid falls below the rod, the circuit is opened and the light goes
out. It is customary to use at least two rods and lights to each
tank or as nutny levels as desired can be shown by usii^ more.
It is a good plan to provide a bell or horn connected to all the
tanks to call attention to any tank which is in danger of
overflowing. Figure 37.

HOVUghi-ari

DISTRIBnTIOIl

The fundamental purpose of the towers, both Glover and Gay
Lussac, is to bring acid and gas into as intimate contact as
possible. This makes it necessary to distribute or sprinkle the
acid over the entire area of the tower packing as uniformly as
possible so that in flowing down through the tower the surfaces of
the packing material may be covered with a constantly changing
film of the acid- There are two general methods of doing this.
One of these divides the total acid stream into many small
streams before entermg the tower tops and introduces each
stream through a small pipe, or opening. The other plan is to
divide the total acid stream into a few comparatively large
portions which are further broken up and distributed inside
the tower by spray nozzles or splash plates. The former method

^dbvGooglc

ACID CIRCULATION

131

is older and probably more used than the latter. It works
very well if the acid ia clean and the tower small. In some
of the large imite built in this country in recent years, the towers
have such great areas that the first described plan involves a
tremendous number of feed pipes and the second method is more
suitable.

There are many ways in which the division of the acid and
introduction into the tower can be accomplished. Two of these
are shown in Figs. 38 and 39. In Fig. 38 the acid is delivered
into a central compartment A. Around A are small compart-

Fios. 38 and

ments B, from each of which a luted pipe runs to some point in
the tower top. Acid overflows from A into B over lips on the
partition. These lips are all dressed to the same level so that
equal volumes of acid Sow over all. This apparatus is made of
lead and may of course, be square or rectangular or any desired
shape.

In Fig. 39 the internal compartment is omitted, the acid
being delivered into the shallow pan from which the small pipes
run directly to the top of the tower. These pipes project up
into the pan an inch or two and are covered by cups whose lower
edges are notched. The equal distribution of the acid depends
upon having each of these upstands precisely level and exactly

^dbvGooglc

132

AMERICAN SULPHURIC ACID PRACTICE

the same height. This is a difficult thii^ to determine and
maintain and this apparatus is consequently not to be recom-
mended. In any form of distributor box the individual streams
should be in s^ht at all times and any inequalities
easUy corrected.

With either of these arrangements or any similar
ones, the small streiuns of acid simply trickle down
into the tower and on to the packing. Some de-
signers consider it essential to provide one of these
small streams for each square foot of packii^ area,
i.e., for a tower 10 ft. X 10 ft. there would be 100
small streams. Other designers consider one strefuu
sufBcient for 6 or 7 sq. ft. It can be appreciated
that if one pursues a middle course in the matter,
the number of individual pipes required for a lai^
tower of say 250 or 300 sq. ft. area, is very great, costly to
install, and rather troublesome to keep in 'order, especially if
the acid carries some sediment.

The second described general method of distribution, i.e.,
by introducing a few comparatively large streams which are
sprayed out inside the tower, has much to recommend it. The
original division of the main stream of acid can be carried out in

■^

f\J

-T^S-

Jl.

^■-'■"^ ^^«.^

"••-...••••A

II II y g II n II 1 II

Etcvdtion

Co0e Ploh! A-A

much the same way as shown in Fig. 3S. The secondary com-
partments are much fewer in number. Each pipe enters the
tower top through a luted opening and has burned to its end a

^dbvGooglc

ACID CIRCULATION 133

spraying device. The simplest of these devices is the splash
plate as shown in Fig. 40. This is a casting of hard lead. Other ~
more elaborate spray nozzles of acid resisting material are also
suitable. Such sprayers can be depended upon to quite uni-
formly distribute acid over a 4- or 5-ft. circle, at a distance of
4 ft. below the nozzle. At 6 ft. below the nozzle they will spray
a 6- ft. circle. It is important that each pipe should or^nate
in an individual compartment so that if an obstruction occurs
in any sprayer it will be immediately known by the correspond-
ing compartment filling up. The nozzle can than be withdrawn
through the luted hole and cleaned. The distribution' afforded
by such an arrangement is even better than that given by the
multiple pipe scheme, and it is obviously much simpler, and
cheaper to build and less trouble to keep in order. Figure 41
shows a convenient layout embracing the described features and
including a gauging compartment.

INTRODUCTION OF WATER INTO THE CHAMBERS

While this subject does not properly come under acid circula-
tion, it may well be discussed at this point.

Water is put into the chambers as steam or as finely divided
liquid. If there is available to the plant an unused supply of
e^aust or by-product steam, or if there is no fairly pure water
available, it is proper to use steam in the chambers. Otherwise
atomized water should be used becai^e it is better for the acid-
making process and it involves no fuel expense. The only cost
is for driving a very small pressure pump.

When steam is used it is ordinarily introduced at two or three
points in the top of each chamber, more rarely at a point in the
front end wall. A convenient arrangement is to run the steam
main under the floor of the working aisles and to carry up one or
two risers alongside each chamber to the top where they run in to
the points of introduction. A cock or throttle valve is placed in
each riser 4 ft. above the working floor. A pointer mounted on
the wrench or handle swin^ in front of a graduated arc and
enables the operator to judge how much of a change he is making
when it is necessary to change the flow. Iron pipe is used to
carry the steam to within 2 or 3 ft. of the point of admission to
the chamber then a lead pipe is flanged to it, bent to form a trap
and its end burned into the chamber. Low pressure steam even

i,z.dJvCo(>glc

134

AMERICAN SULPHURIC ACID PRACTICE

BO low as 2 or 3 lb, can be used, but the pressure should be
uniform at all times.

In using liquid water, the introduction is done through many
small nozzles rather than through two or three large ones. There
are two reasons for this. One is that control of the amount of
water admitted into a chamber is accomplished by completely
opening, or completely closing a number of the supply pipes.
The other that even well atomized water does not spread out
into a very large voiiune of the reacting gas and so the sprays
must be numerous to assure each portion of the chamber of its
proper amount of water.

The spray nozzles used in this country are made of hard
lead with platinum liners, or of stoneware or glass. The former

are much more expensive than the latter thoi^h they usually
last much longer. With platinum prices where they now are,
one can buy eight or ten stoneware or glass nozzles for the price
of one platinum nozzle. The principle used in all nozzles is to
produce a swiri in the water stream just before it leaves the
orifice. This is done in several ways, two of which are illustrated.
When working properly the water issues in a cone shaped sheet
which breaks into innumerable small drops. Figure 42.

As all the passages in these nozzles are small, the areas rang-
ing up to 1 sq, m.ra., it is essential that the water entering the
nozzles be very free from solid impurities or they soon become
plugged up. The water should not carry more than small
quantities of salts in solution because when a nozzle is not used
for some hours the water remaining in it evaporates and salts
deposit and choke it.

^dbvGooglc

ACID CIRCULATION

135

Pressures used on this equipment are usually around 60 lb.
per sq. in. at the nozzle. It ie important that the pressure
what-ever it may be shall be kept uniform within a few pounds.

There are two or three manufacturers in this country who have
made up excellent combinationB of apparatus for filtering and
pumping water for chamber sprays. Figure 43showB the arrange-
ment of an individual spray nozzle with cock and strainer, lute,

etc. The water is filtered through sponges and uniform pressure
maintained in the Unes by an electric plunger pump with relief
valve. In addition to this it is advisable to use a strainer as
shown just proceeding each individual nozzle to catch any pipe
scale or anything that escapes the main filter. In cold weather
when there is danger of the small spray lines freezing, a steam
pipe leading into the supply tank wanm the water.

^dbvGooglc

CHAPTER XII
INTRODUCTION OF ITTTRE

The recovery of the nitre in the chamber process is never
complet«. The average loss is probably from 3 per cent to
4 per cent (96 per cent NaNOs) of the sulphur in the acid actually
produced. It is necessary then to introduce into the plant
per 24 hours from 15 to 20 lb. of new nitre for each ton of 60°
acid produced.

While it is the custom to speak of introducing "nitre," the
thing actually wanted and done is to introduce into the gas
mixture the gaseous oxides of nitrogen. This is done in two ways.
The first and probably most frequent is to decompose sodium
nitrate by sulphuric acid and heat in cast iron pois placed in a
flue between the furnaces and the Glover Tower, The heat of
the furnace gases is depended on to produce the reaction. Some-
times the nitre pots are placed in brick settings alongside the
gas flue and heat is supplied by means of coal fires beneath them.
The nitric acid vapor is led immediately into the gas Sue however.

The other plan is to make liquid nitric acid in a separate
plant and introduce it into the top of the Glover tower.

In either case the chemical reactions and the end results are
the same. The reactions which take place in the nitre pot
whether it is in the gas flue, in a separate setting or in the nitric
acid plant are these:

NaNO. + HtSO* = NaHSO* + HNOi
2NaN03 + HjSO* = NajSO* + 2HN0j

The nitric acid comes oS as a vajwr. The acid sodiimi sulphate
and normal sodium sulphate remain in the pot as a liquid mass
and are tapped off from time to time. If the pot is in or near
the gas flue the nitric acid vapor mingles with the hot burner
gas and reacts with it substantially as follows :

2HN0, + 3S0, + 2H»0 = mSO* + 2NO

In the nitric acid plant the nitric acid vapor is cooled suffi-
ciently to condense it to hquid HNOg. This when introduced

^d by Google

INTRODUCTION OF NITRE

137

into the Glover tower is reacted upon In the same way, i.e.,
HtSOt and NO are formed.

Nitre pots are used in the gas Que and are of very simple design.
They are generally of rectangular shape, open at the top and
have a spout at one end for tapping off the nitre cake. Figure
44 shows a conventional dee^. These potB have capacities
ran^ng from about 3 to 4 cu. ft. up to 20 cu. ft. Larger sizes
become difficult to handle when they break and have to be re-
placed'. The small sizes accommodate 25 to 50 lb. chaises and
the larger up to 200 lb. The thickness of metal is from 2 to 4
in. The matter of materiid is somewhat puzzling. Some foun-
dries claim great superiority for their special cast iron formulas.

JEL

=£

. n n.

I have seen pots of these special irons, which also cost a special
price, give very poor service, and some have very long lives.
The same can be said of pots made of good ordinary cast iron by
local foundries. Probably design and care in pouring have aa
much to do with the life of a pot as special metals. Pots usually
fail by cracking or goii^ through flaws rather than by actual
corrosion.

The number of pots which should be provided varies with the
size of the unit somewhat, but should be never less than two and
preferably more.

This on account of the desirability of having as nearly uniform
evolution of nitric acid vapor as possible, and to carry over the
periods of changing a broken pot for a new one. If the unit is of
50 tons 60° capacity, the normal amount of nitre introduced per

^dbvGooglc

138 AMERICAN SULPHURIC ACID PRACTICE

24 hours will be from 750 to 1,000 lb. There will be timee when
more than that will have to be potted for a few hours so it will
be well to have pot capacity to introduce at the rate of 2,000
lb. per 24 hours. Two hours per charge is the minimum
time which should be allowed for the decomposition of the size
charges ordinarily used. If therefore two pots are provided each
should be able to handle 1,000 lb. per 24 hours in 12 chains or
83)^ lb. per charge and should have a volume of about 10 cu.
ft. If three pots are provided they should be of 7 cu. ft. volume
or if four pots of 5 cu. ft. volume.

The pots are supported well above the bottom of the flue on
beams, in order that the hot gas may play freely around them.
The spout extends out through the wall a short distance. If the
pots are small and the span for the beams is not long ordinary I
beams are used for support and last very well. In case large
pots are used and the flue is 10 or 15 ft. wide, deep cast channels
filled with reinforced concrete stand up splendidly.

Chai^ng of the pots with nitre and acid can be done from top
of the flue or from the side. In many respects charging from
the top is more satisfactory. It does away with the rather
laborious handling of a heavy loaded charging ladle and it puts
charging and tapping at different levels which is desirable. If
both operations are done on the same floor the cake pans or
laimders are most inconvenient to work over. The nitre is put
into the pot through a cast iron pipe with bell top if the chai^ng
is done from the top. If the charge opening is in the side of the
flue a lai^ scoop or ladle with a sufficiently long handle is used.
The acid is fed in from a measuring pot or box throi^h a heavy
cast iron pipe. The special high silicon irons and also fused
silica are being used for these pipes of late as even a heavy cast
pipe does not last long. Figure 45 shows an arrangement of nitre
pots in a flue.

The nitre cake is usually tapped off into shallow pans, allowed
to cool and harden, then broken up and removed. When condi-
tions permit and there is no use for the nitre cake, a simple means
of disposal is to tap into a launder in which a stream of water runs,
when the molten cake dissolves and is flushed away. Several
ways have been devised for closing the spout after the charge
has been tapped. A plate and screw clamp is sometimes used.
Or the end of the spout is machined out to take an iron plug.
Sometimes wooden plugs are used. If the spout is loi^ outside

^dbvGooglc

INTRODUCTION OF NITRE 139

the flue a ball of mud will be sufficient. It is well to use a scheme
which does not depend too much on machined Biu^aces for
tightness.

POTTING WITH FUEL

While the general features of the method just described, i.e.,
in placing nitric pots In the flue and utilizing the heat of the SOi
gas to effect the decomposition of the nitre, would seem the best
and most economical possible arrangement, it has some drawbacks
which are so annoying that many acid plants are now equipped
with nitre pots in independent settings and fired with fuel.
When this plan is used the operator can have at all times just the
degree of heat he wishes to decompose his nitre. If the process
has become badly disturbed by some breakdown or stop he
can decompose the extra nitre the emergency demands and get
into normal condition quickly. The weakness of the flue potting
lies in the fact that just at those times when an unusually lai^e
amount of nitre should be potted the flue is eold, e.g., when start-

ed byCoOglc

140 AMERICAN SULPHURIC ACID PRACTICE

iu^ up the plant after a shutdown or when any unusual occurrence
disturbs the flow of hot furnace gas about the nitre pot«. In
choosing between Sue pot and independent pots the source of the
SOi must be regarded. If the sulphur supply is in the form of a
uniform high-grade pyrites which will make a hot gas and allow
long campaigns with the roasting furnaces, flue potting is quite
proper. If the gas is cold or if it is an unreliable metallui^cal
by-product gas, independent fuel fired pots probably are meet
economical. Fuel cost is not a very important consideration as
with well designed settings a ton of ordinary soft coal will decom-
pose 3,000 to 4,000 lb. of nitre.

The best form of pot for fuel fired settings is shown in Fig. 46.
This is a modem retort such as is used in nitric acid work. It
is simple and- strong and is a design which has been very generally
adopted of late years.

An ingenious plan used in connection with fuel-fired pots is
used at the works of the Tennessee Copper Co. The retorts are
substantially standard nitric acid casting as shown in Fig. 46.
The nitre is fed in continuously by means of a conveyor and at the
same time the proper amount of sulphuric acid for decomposing
it is run in. Both nitre and acid may be varied as desired to
meet the demands of the acid process. When a retort is filled
up to a certain point with fused nitre cake it is tapped. There
are several retorts in the battery and the introduction of nitric
acid vapor into the flue is continuous. This arrangement is
described in an article by A. M. Fairlie in Chemical and Met-
allurgical Engineering of September 25, 1918.

At some sulphuric acid works Uquid nitric acid is made in a
separate plant and tile nitric acid is introduced as needed into
the Glover tower. A comparatively recent modification of this

^dbvGooglc

INTRODUCTION OF NITRE 141

scheme is to make instead of straight nitric acid, mixed acid,
i.e., a mixture of nitric and sulphuric acids.

In either case the nitre retorts are the same and are about aa
shown in F^ 46. Other forms of retort and setting are to be
found in some of the older plants, but the larger and more en-
lightened manufacturers of nitric acid seem to have come to the
conclusion that the form shown is most satisfactory.

In making straight nitric acid the condensation of the vapor -
to liquid is effected in what ia known as the Hart condenser.
It consists essentially of a pair of upright manifolds of stoneware
or high silicon iron with glass tubes between them. The glass
tubes are cooled by trickling cold water over them. The final
condensation of nitric vapor and recovery of the most of the
lower oxides of nitrogen is done by passing the gases through
several stoneware towers in series. A counter current stream
of water, then weak nitric acid is advanced over the towers. The
liquid nitric acid made is received and stored in glass or stone-
ware vessels. It is possible to use with fair success iron or lead
tanks if only strong nitric acid be put into them and if they are
kept tight from air leakage. The high silicon irons can be used
with success for containing nitric acid of any strength.

The nitric acid made in this way is conveyed to the top of the
Glover tower sometimes by elevating the glass carboys containing
it, sometimes by pumping it up through stone or special iron
pipe lines. More rarely it is mixed with sulphuric acid and the
mixed acid then handled in any apparatus suitable for sulphuric
scid. This mixing of nitric and sulphuric acid must be done in a
closed vessel provided with eoolii^ coils as it fumes badly
otherwise.

The handling of straight nitric acid especially in lai^e quanti-
ties is rather troublesome and this fact led to the development of
the plMi of making mixed acid directly, which will now be de-
scribed. Mixed acid as mentioned can be handled in lead or iron
apparatus with very little more wear and tear than straight
sulphuric acid causes.

The plant for making mixed acid directly consists of retorts
similar to those used when making stra^ht nitric acid. The
nitric acid vapor issuing from them is conducted through pipes
of silicon iron into a small tower of acid-proof masonry construc-
tion paclsed with acid-proof bricks or shapes, over which cold
sulphuric acid of 60°B& or higher strength is circulated. The

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142

AMERICAN 8ULPHVRTC ACID PRACTICE

nitric acid vapor is condensed and a warm mixture of nitric and
sulphuric acids issues into a cooler whence it is pumped up and
&g^m introduced into the tower. The operation is exceedingly
simple and gives a high recovery. The product containing up to
20 per cent HNOi is contained and pumped in lead apparatus.
Its volume is such that it is very nicely controlled in introducing
it into the Glover tower. The Fig. 47 shows an installation in
which 4,000 lb. of nitrate of soda is comfortably handled in an
eight hour shift. The fuel used amounts to about 900 lb. ordi-

nary bituminous coal per ton of nitre. The recovery is 96 per
cent or better. Some of these plants have been operating at
least 3 years. Except for charging the retorts the operation is
conducted by one man.

In the writer's opinion this last described method is the most
satisfactory and economical way of handling the matter of getting
the nitre into the chamber process.

It should be mentioned that a water solution of nitrate of soda
is used to a limited extent in the Glover tower and in the cham-

^dbvGooglc

INTRODUCTION OF NITRE 143

bers as a meauB of nitre introduction. It ia a plan which has the
serious disadvantage of fouling the acid with sodium sulphate:
if the acid is to be used for the manufacture of fertilizer this is no
particular drawback. If more than a small proportion of the
total necessary nitre is put into the Glover tower as a regular
procedure in this way it very soon makes trouble in that pipe
lines and valves become obstructed and the tanks and coolers
fill up with it. As an emei^ency measure to tide over a few days
when for some reason the regular source of nitrogen oxides is out
of commission a solution of this kind can be used in the Glover
without serious results. Certainly though a few days is the
limit. If the solution be Introduced into the chambers and the
chamber acid is drawn off for use in making acid phosphate or
some other use in which sodium sulphate is not objectionable,
very little trouble results. In any event it is unusual to use a
nitrate solution as anything more than as in an auxiliary, or a
temporary way of putting nitrt^n oxides into a chamber system.

ITO FROM AHHONIA OZIDATIOD

About 30 per cent of the European acid plants are supplying
the oxides of nitrogen to their chambers by oxidizing ammonia
and introducing the gas. So far but one plant in this country,
that of the American Cyanimid Co., at Warners, New Jersey, has
used this process, which gave them splendid results. It is not
in operation at the present time, as nitr<^n from Chile saltpeter
costs less than from ammonia now.

In January, 1919, the British Ministry of Munitions issued a
booklet on " The Oxidation of Ammonia Applied to Vitriol Cham-
ber Plania," This is the most complete publication on the sub-
ject, and I will quote from it very freely.

Mr. W. S. Landis, of the American Cyanimid Co., has furnished
the following information regarding their New Jersey installa-
tion.

In their process of oxidation the platinum gauze is heated by a
current of electricity, instead of depending upon the heat of the
reaction entirely. Of course the current costs money, but the
operation is so free from trouble of any kind, the labor reqviired
practically negligible, and the product so uniform, that opinion
differs as to the best practice. (Though it will be noted in all
(so far as I know] reports on this subject that when results have

^dbvGooglc

144

AMERICAN SULPHURIC ACID PRACTICE

been wanted electrical heating of the catalyzer was practiced.)
At Wameis an oxidation unit was set up under each chamber,
and the operator looked in as he went by. The gas was con-
trolled by a 2-in. valve, and the plant ran steadUy, with no ad-
iustment.be]n>nd change of quantity of NO made, as the condition
of the chambers demanded it, which adjustment simply meant
open or close the 2-in. valve.

Bactricat Cfr>r>ejf»iti_

'Cataliit Unit FnarK

Outside of the ease of operation, stronger acid may be made.
Both denitration and nitre pottii^ absorb heat, which, if not
required for other purposes, may be utilized in the Glover to
concentrate. At Warners this was done. The nitric oxides from
the converters were fed to the Glovers, all the heat that was
B^ved from the pottii^ went to concentrating, and the result
was a constant return of 61°B£. acid, which often, forloi^perioda.

^dbvGooglc

INTRODUCTION OF NITRE 145

stayed up to 62°, and occasionally reached 62,5° — with complete
denitratioQ — which is pretty fair chamber acid.

A patent on this subject, TJ. S. Patent |1,173,524, was issued
on Feb. 29, 1916.

It is necessary to introduce the mtric acid through the roof of
the Glover or chamber, as otherwise the acid, running down
the side walb will quickly destroy the lead.

The British Ministry of Munitions standard converter consists
of an upper and a lower cone, of aluminiun, the small ends of the
cones being flanged to the inlet and outlet pipes, the large ends
also being flanged, but to the catalyzer frame. The internal
section of the catalyzer frame, was about 4-in. X 6-in. (that at
Warners was larger), and was simply a pair of aluminum flanges
between which the platimun wire, gauze-wire being 0.065 (.003")
in. mm., square mesh, 80 mesh per inch — was held in place and
insulated by mica and asbestos. The English used two gauzes in
each frame, held apart by silica rods, the lower gauze alone having
silver terminals. When electric current is not used to heat the
gauze, three or four gauzes are necessary.

Ninety per cent to 95 per cent efficiency of oxidation will be
attained without electric heating of the gauze, and 98 per cent
with the current.

The capacity is 1.5 tons of HNOj per square foot of converter
cross sectioQ per 24 hours.

The aluminum used in this construction must be very pure;
and either mica or clear silica must be used for the peep holes.

The catalyst container must fit tight. Any air leaks may be
luted with a mixture of asbestos powder and thick water glass.
Allow this paste to set before heating the catalyzer.

The following precautions are essential in handling the catalyst :

1. Great care should be taken that the platinum gauzes are
absolutely clean. They are boiled in pure concentrated hydro-
chloric acid and rinsed in distilled water before fitting, and should
on no account be touched with the fingers afterwards or otherwise
soiled.

2. The box containii^ the catalyst as sent from the makers
should not be opened except immediately before fitting.

3. Fitting should be done in a clean room free from dust, not
on any account in a workshop, and the fitter should have clean
hands and clothes.

4. It is essential that the greatest possible care be taken to

^dbvGooglc

146 AMERICAN SULPHURIC ACID PRACTICE

keep the gauzes clean while the catalyst unit is being fitted to
the converter. If the completed converter Ib not at once con-
nected to the inlet and outlet pipes, the apertures of the lower
cone and bend pipes at the top should be closed with corks to
keep out dust until this is done.

As the electrical resistance of the gauze is low, the current must
be low voltage, but high in amperage. The maximum, or start-
ing, current for a 4-in. X 6-iii. gauze is 12 volts, 300 amperes.

The mixture of air and ammonia may be supphed to the con-
verters in either of two ways:

1. By producing air and ammonia gas separately, and mixing
them in the proper proportions — 1 vol. NH| to 7.5 vols, air — in
an aluminum mixii^ chamber, with tangential inlets and baffle-
plates.

2. By passing a stream of air throi^h aqueous ammonia in a
suitable apparatus.

The second method is by far the better, and will alone be
described.

Purified ammonia liquor, 20 to 25 per cent. NHj, "free from
sulphur," is the source of the anmionia. It is fed at the proper
rate to an ammonia still, and there met by low pressure steam
blown in at the bottom, cither directly or through coils, and a
current of air. Anmionia gas is hberated, mixed with the right
proportion of gas for oxidation, and if the top of the column is
kept cool, the gas is fairly dry. Moisture has no influence upon
the oxidation, but is liable to condense in the filters and impair
their efficiency. Iron pipe, fitted with red lead and oil, may be
used up to the filters.

This still should work imifonnly and with little attention, and
not be liable to breakdowns. It should have a low steam con-
sumption, which depends upon its being kept hot below and cool
above. It should deliver ammonia, or air and ammonia, at a
definite rate.

The kind of ammonia available and the amount required will
of course influence the design.

Where the amount required is small the ammonia may be
generated by boiling mnmonium sulphate or ammonium chloride
with milk of lime in an iron boiler with a reflux cooler, with a
small balancing gas holder between the boiler and the converter.
This method would be useful at coke ovens or gas works, where
such salts are by-products. It has the additional advantage

^dbvGooglc

INTRODUCTION OF NITRE

147

that the ammonia is pure, as there is no Bulphur. On a large
scale ammoniacal liquor is more economical. Gas liquor should
not be used directly, because of the impiuitiea.

An ammonia still of Brunner, Mond & Co. is shown (Fig. 49).
Purified ammonia liquor of 25 per cent is run in at such a speed

that the top compartment is kept at 8 per cent to 9 per cent
ammonia, and 20° to 22°C. The bottom compartment is heated
to 95" to IWC. to exhaust the ammonia. Air is passed at the
proper rate, and Che mixture through a slag'wool or glass-wool

^dbvGooglc

148

AMERICAN SULPHURIC ACID PRACTICE

filter. A little Bteam is neceesary in the filter before the con-
verter to avoid condensation.

The United AlkaU Co. replaces the bubbling tower with a tall
coke tower. Steam and air are introduced as before, but ammo-
nia liquor ia introduced at a point two-thirds up the tower. The
upper portion of the tower thus act^ aa a cooler and gas filter,
and no further filtration b necessary. This is also shown
(Fig. 50).

*- I Liqijorfrom

'Armonlarank
, — ^Ghiios
.Iwim Nrchvl Savrv
,ibrfr/Mrirff

Air pressure depends upon the type of apparatus used, but
should not f^ below 5 lb. per sq. in. The air must be pure and
free from dust; if the plant is near sulphur burners of any kind
the wr must be purified by passing through a lime box. There
must be an oil trap after the blower. The air must be metered —
the Builders' Iron Foundry, Providence, Rhode Island, furnishes
good meters. After filtration iron pipes must twt be used —
aluminum, stoneware, or glass. The glass-wool filtering mediiun
will probably need renewing every month, as it fills up with dust.
Moisture can be kept out by introducing a httle steam to prevent
condensation.

The apparatus is started by switching on the ciurent and heat-
ing up the gauze to visible redness. The mixture of ur and

^dbvGooglc

INTRODUCTION OF NITRE 149

ammonia is then admitted at a bIow rate, until the catalyzer ia
uniformly dull red hot (650°C.), then the rate is increased to the
maximum, the current being rejjuced as necessary. Very little
further attention is required for weeks of running. If the gauze
gets too hot the heating current, or the proportion of ammonia
in the mixture, of both, should be reduced.

When electric heating is not used the plant is started by heating
the gauze to redness with a hydrogen flame, turning on the air
and ammonia mixture full, and removing the flame, after which
the window is bolted into place.

New platinum gauzes are somewhat inactive, and should first
be ' activated" by passing at a fairly slow rate a mixture with an
excess of oxygen, say, 1 vol. NHj to ten vols, air, and putting on
full current till the gauzes are heated BRIGHT red (800° to
OOCC). After an hour or two the platinum becomes activated,
and the white fumes of ammonium nitrite and nitrate leaving
the converter (after cooling) change into clear red fumes of
oxides of nitrogen. When this occurs the current is reduced
and the ammonia brought up to the ratio of one to 7.5 air.

If electrical heating is not used, start with the ordinary gas
mixture.

If spots show on the heated gauze and do not disappear rapidly,
the catalyzer must be taken to pieces, the gauze boiled in pure hy-
drochloric acid, and the catalyzer reassembled. If the gauzes heat
up unevenly it is usually a sign that the wire is too small, and the
unit must be replaced. If in the activation any unevenly heated
places are left they will take a long time to finally become active.

The gases leave the converter at about 400''C.. They consist
of NO, steam, nitrogen, and a shght excess of air. The converter
reaction is as follows:

4NH, + 50, = 4N0 + 6H,0.

At this temperature the gas is colorless, as the secondary oxida-
tion of NO to NOj has not begun.

The gases may be used with or without cooling.

Without cooling, the gas is conveyed through a lagged alumi<
num pipe, or if slightly cooled through a stone-ware pipe, to the
Glover tower, chamber, or dust catcher of the system. The
temperature must stay high enough to prevent water condensa-
tion in the main. There must be no pressure poasibiUties that
burner gas could back up, in case of breakdown.

^dbvGooglc

150 AMERICAN SVLPHVRtC ACID PRACTICE

If the burner gas does back up to the gauze it will rapidly
become poisoned, and will have to be removed and boiled in
hydrochloric acid. Therefore it is better to have the gas enter
at a point where there is a slight suction, as in the Glover tower.

If the gaa is cooled it is passed to a condensing cooler, where
about 70 per cent of the water produced in the reaction is sepa-
rated. If the cooUng is performed sufficiently rapidly the con-
densate will contain from 1 per cent to 5 per cent of the total
oxides of nitrogen as nitrous and nitric acid, aad any trace of
ammonia (0.05 per cent to 0.25 per cent) which may have escaped
oxidation. This is the result from a very efficient cooler-up
" to 25 per cent of the oxides of nitrogen may be in' the condensate.
The cooler may consist of a silica spiral, connected directly with
the bend on the converter hood, by suitable asbestos packing,
and cooled by water. A spiral of 10 turns of fused silica S-pipes,
the turns 2'-0" in diameter, the pipe Ke-in- thick and IJ^-in.
in diameter, will do the work. The condensate may be collected
in a stoneware WoulfE's bottle, and then drawn off to the Glover's;
or it may run direct to the Glover.

The cooled gases, at about 30° to 50''C., now brown with oxida^
tion from NO to NOj, pass through stoneware pipes with a
stoneware stop cock if desired, and with down pitch towards the
point of entry, to the chamber system.

Remember that hot gases may cause warping at the point of
entry, and provision must be made for it.

An advantage of using a cooler is the better analjrtical check
on the process. Tests on the condensate for unconverted am-
monia should be made from time to time to cheek up the working
of the converter.

If there is more than one Glover to be supplied it is better to
have a small independent converter for each, rather than have one
larger one try to supply several, as uniform distribution is very
difficult to get.

The accompanying table shows the quantity of ammonia that
must be oxidized to replace any given quantity of nitre (NaNOj).
If the consumption of nitre varies the converter may be run
below capacity — it may be run down to 25 per cent of capacity
at 100 per cent efficiency, and will run well at 15 per cent. One
of the great advantages of this system is its uniform running,
and this should be taken advantage of if possible, by keeping the
rest of the plant going at a imiform rate.

^dbvGooglc

INTRODUCTION OF NITRE
Table 5

Metric tone of H,80,

Grama of ammonia required per hour, if

Sulphur

burned

day of 24 hours

of the sulphur burned, per cent

Tons
per day

05% plant
efficiency

98% plant
efficiency

0.5%

...

2.5%

.265

.77

.702

.53

1.65

1.584

100

120

1,06

3.1

3.17

160

200

240

2.12

6.2.

6.35

160

320

400

480

6.6

19.25

19. S

250

500

1,000

1,250

1,500

15.85

46.2

47.5

600

1,200

2,400

3,000

3,600

26.4

■77.0

79.2

1,000

2,000

4,000

6,000

Up to 3,000 g. NHi per hour, use 1-4-in. X 6-in, converter.
Above 3,000 g. NH» per hour, use 2-4-in. X 6-in, converter.

The analj^cal control of oxidization of ammonia is of the utmost
importance, and considerable difficulty. With the methods
here given the efficiency of any particular converter cannot be
determined closer than 3 per cent. This is sufficiently accurate
for works operations.

Determination of Ratio NHa:Air before oxidation

The method consists in aspirating a known volume of the air-
ammonia mixture through a sufficient quantity of standard
sulphuric acid colored with methyl orange or cochineal, contained
in a wash bottle connected with an aspirator. A Winchester
bottle of water is placed between this and the aspirator, just to
equaUze the gas pressure in the inlet tubes to the converter, so
that no gaa bubbles through the acid until the aspirator is
started.

The quantity of acid is sufficient to neutralize exactly 0.1 g, of
NHj. The indicator end point is quite sharp, and experiments
show that the absorption of ammonia is complete with a single
wash bottle. Each experiment should be conducted at such a
rate as to last about 10 minutes, and be repeated every 20
minutes. An alternative method is to use a lai^er volume of

^dbvGooglc

152

AMERICAN SULPHURIC ACID PRACTICE

standard acid in two wash bottles, to aspirate for a longer time,
say half an hour, and titrate back with standard alkah.

A typical experiment gave 1.13 liters of water aspirated {i.e.,
1.13 1. of air in the air-ammonia mixture) to 0.1 g. of NHj.
This gives a ratio vol. NHiivol. air of 0.116, which is about the
ratio for conversion of ammonia to NO* (0.114).

Determination of ratio oxidized NHi :AiT, after oxidation.

An aliquot part of the oxides of nitrogen and air,' from the
converter, taken from a T-tube after the cooler (see Fig. 51)
is aspirated through:

FiQ. 51.

1. A Drechflel waah-bottle containing:

100 c.c. distilled water,
20 c.c. N/NaiO, solution,
20 C.C. HaOa solution {20 volumes).

2. A Drechsel wash-bottle containing:

50 c.c. distilled water,

10 c.c. N/NajOs solution,

10 C.C. HgOa solution (20 volumes).

The N/NaiOt is prepared by adding 78 g. NaiOi to 1 kg.
powdered ice in small quantities at a time, with stirring: then
adding 1 Uter distilled water and filtering through glass-wool.

^dbvGooglc

INTRODUCTION OF NITRE 153

It is kept in a bottle with a capillary tube through the cork to
allow the traces of Oj to escape.

3. A 10-bulb tube containing:

5 C.C. N/10 potassium permanganate solu-
tion.
10 c.c. 50 per cent H,SO*.

All connections are made with ground joints, a stopcock being
inserted at the point where the gas sample is taken from the T-
tube, as shown in the Fig. 51. The aspiration is effected by-
means of water droppii^ slowly from an aspirator bottle (about
1 liter per hour) into a measurii^ cylinder, and 1,500 c.c. of
water are collected; the experiment thus lasts 90 min.

The two drechsel wash-bottles (1) and (2) are then emptied into
two 250 c. c. Erlenmeyer flasks, the bottles being then washed,
out with diatilled water and the liquid in the flasks titrated
separately with standard H2S04, using litmus as indicator, and
boiling if necessary. The end point is taken at the change blue
to purple, and not blue to red, on account of the hydrolysis of
the nitrous acid. This end point is easily recognized with a
little practice. Methyl orange is useless on account of the
action upon it of the nitrous acid, but Sodium Alizarine Sul-
phouate ("Alizarin Red. I. W. S., Hochst") has been used with
very satisfactory results. The contents of the permanganate
bubbler ar» washed out into an Erlenmeyer flask, treated with
a slight excess of N/10 oxalic acid, warming if necessary, and
the excess of oxalic acid titrated back with permanganate. It
is assumed that the reduction of the permanganate is due to
NO, and the NHg equivalent of this is calculated as follows:

2N0 + 30 = NzOft,
that is, 2N0 (calculated as NHj) requires 3 atoms or 6 equiva-
lente of oxygen, i.e., 60,000 c.c. N/lOKMnO,: i.e., 34 g. NH. =
60,000 c.c. KMnO*.

. ■ . 1 c.c. N/lOKMnb, = 0.000566 g. NH,.
Ebcamples of calculations.

It was found in one experiment that the oxides of nitrogen had
neutralized a quantity of the alkali in the two vessels correspond-
ing to 0.159 g. NHa, reckoning equivalents in nitrogen contents.

XT .. .- ... J HNO, HNO2 NH, „„,.,
1 C.C. N alkali neutralized = -j^ = -j^ = y^ = 0.017 g.

NH,.

iizcdbvGoogic

154 AMERICAN SULPHURIC ACID PRACTICE

The permanganate in estimation (3) was titrated with N/10
oxalic acid. It was found that 3.5 c.c. of N/lOKMnO* had been
used up. This corresponds with 0.0035 g. NO, and this ia
equivalent to 0.002 g. NH|.

After the converter and the cooler, all the unconverted NHi
will have been removed and the oxides of nitrt^^ are then totally
absorbed in the absorption bottles. Now in the estimation
of the ratio of NHi to air in the gas entering the converter, we
have determined the weight of NHt associated with a given
volume of air (the latter being simply equal to the volume of
the water run out of the aspirator bottle). If there were no
change of volimie of the air after the converter, we shoidd be
able to make a direct comparison of the weight of the oxides of
nitrogen, corresponding with 1.5 litres aspirated (these oxides
being calculated as NHi) with the weight of NHi associated
with the same volume (1.5 litres) of air in the mixtiure of air and
NHj entering the converter.

The aspirated volume after the converter, however, does not
represent the volume of air which was associflrted with the
ammonia corresponding to the oxides of nitrogen collected, be-
cause a portion of this air has been used up in the oxidation.
This consumed oxygen consists of two parts:

1. A portion used in burning the NHi to NO in the converter.

2. A further portion used in oxidizing the NO to higher oxides,
which are then absorbed.

The first portion is the same in all cases, and is calculated as
follows:

4NH, + 50i = 4N0 + 6H,0
25 volumes of air become 20 volumes of Ni :
i.e., the contraction of the air volume is here
(25 - 20) X 22.4
4 X17

= 1.647 litres per g. NH, burnt.

(Since the NHt is completely absorbed from the gas in the
aspirator, before the converter, and the oxides of nitrogen from
the gas in the aspirator after the converter, it is only necessary
to consider the volumes of air.)

The further contraction, due to secondary oxidation, will
depend upon the particular higher oxide of nitrogen produced.
Of these, only two, namely, NjO» and NjO*, can possibly be
produced by the oxidation of NO by atmospheric oxygen, and

^dbvGooglc

INTRODUCTION OF NITRE 155

it is therefore, neceasary to calculate the contractions for these
two cases only.

(a) 4NH, becomes 4N0 + 0, = 2NiO,
that 5 volumes air becomes 4 volumes Nj:

that is, there is a contraction of 1 volume, i.e.,

j - ' :- litres = 0.329 litre per g. NHj

(b) 4NH, becomes 4N0 + 20i = 2N,04
10 volumes of air becomes S volumes Ni
that is, a contraction of 2 volumes, i.e.,

\^y^lf litres = 0.658 litre per g. NH,

The aspirated volume, 1.5 litres, must therefore be increased in
the ratios:

(a) (Weight of oxides of N expressed as NHs) X (1.647 +
0.329) : 1, when these oxides are absorbed as NiOg;

(b) (Weight of oxides of N expressed as NH,) X (1.647 +
0.658) : 1, when these oxides are absorbed as N1O4.

The volume of air so corrected is then directly comparable
with the volume of air associated with the ammonia in the aspira-
tion before the converter, and if equal volumes are compared,
the we^hts of NHs in each (that after the converter being
calculated from the titrations, as described) will give an imme-
diate figure for the efficiency:

wt. NH, after conversion (as oxides) „ .

. T.TTT ■ , — — '^^ X 100 = eflSciency,

wt. NH3 before conversion •"

the weights beii^ referred to equal volumes, as described.

AIR VOLUME COSKECTIOn

In the experiment described above, the -weights of NH»
corresponding with the oxides of nitr<:^en collected in the alkaline
peroxide and permanganate, respectively, were 0.159 g. and
0.002 g. Since in a good experiment the permanganate
figure should always be very small, it is only necessary to use the
first figure, namely, 0.159 g. in correcting the air figure.
This correction will be as follows :

(a) Gas assumed to be absorbed as NjO, :
corrected volume of air = 1.5 + 0.159 X (1.647 + 0.329) litres
= 1.5 + 0.314 = 1.814 litres.

^dbvGooglc

156 AMERICAN SULPHURIC ACID PRACTICE

Now in the aspiration before the converter, it was found that
0.1 g. Nifi was contained in 1.13 litres.

, " . NH| in 1.814 litres before conversion = -^ — jTS — ~ ""

0.1605 g.
Oxidized NHg after conversion - 0.159 + 0.002 = 0.161 g.
0^
"0.1(

(b) Gas assumed to be absorbed as NjO^:
corrected volume of air = 1.5 + 0.159 X (1.647 + 0.658) litres
= 1.867 litres.

1 867 X 1
NHt in 1.867 litres air before conversion = — — j-t^ — - =

0.1650 g.
. „_ . 0.161 X 100 „ „
. . Emciency = nTpA — ~ "'■" f*'" *'*"'■

The difference between the two values is thus seen to be only
about 2.5 per cent, which is within the limits of experimental
error. The true value lies between the two, and nearer the NiOj
^ure, since experiments have shown that about four-fifths of
the oxides are absorbed as NaOt when no oxidizing agent is
present in the liquid, and this ratio, therefore, represents the
composition of the gas before absorption.

To the amounts of oxides of nitrogen collected in the absorption
bottles must be added that present in the condensed water
separated from the cooler. The analysis of this condensate is of
value in estimating the unconverted ammonia, all of which
separates in the condensed water in the form of nitrite and nitrate.
The condensed water is collected throughout the whole experi-
ment and its volume measiu^d.

An aliquot part is titrated with N alkali and litmus for acidity,
and the acidity of the total expressed as NH, (1 c.c. N/NaOH =
0.017 g. NH,). Another aliquot part is distilled with NaOH and
the ammonia collected in a measured volume of N/HsSO*. This
ammonia was combined with an equivalent amount of acid, and
its value must therefore be added to that found in the previous
titration, to obtain the total OXIDIZED NHg in the condensed
water. This is divided by the total weight of NH, passed
through the converter durii^ the run, and the result, multiplied
by 1(H), gives the term which must be added to the efficiency

^dbvGooglc

INTRODUCTION OF NITRE 157

calculated from the absorption bottles, to give the true efficiency.
In the experiment described the values were:

Unoxidized NHj = 0.3 per cent

Oxidized NHs ^ 0.1 per cent

.-. Total efficiency = 100.1 + 0.4 = 100.5 or 97.6 + 0.4 =
98.0

If the proportion of air and ammonia entering the converter is
BUch as to form NO, this could not be absorbed in the alkaline
peroxide, and in this case it is necessary to add a measured volume
of oxygen slowly to the gases aspirated from the converter. This
is done by connecting a graduated gas-holder containing oxygen
to a T-piece on the connection of the first bottle, the rate of
addition of oxygen being controlled by passing it through a small
wash-bottle containing water. About 300 c.c, of oxygen are
added during the whole run of 90 min. This volume (300
c.c.) is subtracted from the volume of water collected ^nd the
usual correction for contraction apphed to the remaining volume :
1,500 c.c. - 300 c.c. = 1,200 c.c. = 1.2 Utres.
GENERAL REHASKS

In the eBtimation of the ammonia, the balancing water column
in the Winchester bottle should be such that the gas pressure
before the converter is just sufficient to bubble through the water.
As soon as the aspirator is started bubbles will pass, and the rate
should be adjusted so that the color of the indicator changes in
about 10 min. When indications of a color change appear, the
rate of aspiration should be reduced so that about one bubble
per second passes, and the absorption bottle should be shaken.
The connecting tubes and the upper part of the tube in the wash-
bottle should, of course, be dry.

The alkaline peroxide bottles should be carefully fitted together,
so that on opening the tap connecting with the outlet from the
converter, on bubbles (or at most one or two) pass before the
aspirator is started. The rate of aspiraton must be slow, as
stated. If white fumes appear in the second bottle, or the per-
' manganate is discolored, or depoats much MnOt, the experi-
ment will usually be found to give an incorrect result.

If oxygen is added it should be let in slowly, as stated, in order
to insure that the whole of it passes through the aspirator bottles,
and not backwards into the converter main,

^dbvGooglc

158 AMERICAN SULPHURIC ACID PRACTICE

To insure that the pressures are equalised in the aapu^tor
bottles, these may be provided with gauges, consisting of U-tubes
containing water.

Hydrogen peroxide solution is usually acid, and allowance
must be made for this in the titrations.

(ft) Determination Without the Use of Cooler. — If the hot gases
from the converter are utilized without previous cooling it has
been found that a short length of aluminum tubing, inserted as a
T-tube in the main from the converter, is generally sufficient in
itself to cool the aliquot part of the gases which are slowly passing
through it to the absorption system. It has been usual to neglect
the small portion of unoxidized ammonia in this case. As alter-
natives the following suggestions are based upon information
from those who have had occasion to carry out control tests on
hot converter gases:

1. The converter gas is drawn slowly throu^ a capillary tube
to an absorption system similar to that described above.

2. The first absorption bottle contains N/10 alkali without
peroxide. This, according to Fox (Journal of Industrial and
Ertgineering Chemistry, August, 1917), retains all the unoxidized
ammonia coming over, the amount of which is estimated after
the titration by treatment with caustic soda and sodium hypo-
bromite, when nitrogen is liberated and is measured (of.. Tread-
well and Hall, Quantitative Analysis, p. 622). A correction must
be applied to this volume of nitrc^n, since the reaction is not
quite complete (cf., Fox).

3. The second absorption bottle contains the same solution as
the first bottle in the method described above.

4. The permanganate tube is retained unchanged.

^dbvGooglc

CHAPTER XIII
DRAFT

Early chamber planta depended upon natural draft for the
movement of gases through the apparatus, but all modern plants
use fans. In this way larger volumes can be moved and the con-
trol is much more positive.

Fans are of two classes, viz., iron fans which are used at some
point preceding the Glover Tower, and lead fans, used at some
point following the Glover Tower. Sometimes both kinds are
used in the same system. It must be understood that if a fan
is placed between the sulphur burners or roasters and the Glover
Tower, high temperature, dry gases are to be handled and iron
is the only suitable material for the service. If the fan is placed
at any point beyond the Glover Tower, comparatively low tem-
perature gases laden with sulphuric acid mist are to be propelled.
For this service lead, usually stiffened by alloying with antimony,
is the most suitable material. Iron of course would be quickly
destroyed by the acid. Lead fans are more often used than iron
though the latter certainly deserve much consideration as they
hare many advantages.

The- arrangement most common for units of moderate size is >/
to use a sin^ lead fan between the Glover Tower and the first
chamber. Very often a second lead fan is used between the last
chamber and the Gay Lussacs. A less frequent plan is to use a
single iron fan just in front of the Glover or an iron fan, with a
lead fan between the last chamber and the Gay Lussacs. Any of
these arrangements of suitable size and with the other features
of the plant in conformity may give good results. It is well to
consider that the fans are of very vital importance to continuous
operation and that they have to be repaired and parts replaced at
fames. If there are two fans in a system with proper by-passes
Que of them may be cut out and worked on without causing a
shutdown. To be Bure a diminished production will probably
result but that is not nearly so serious as cooUng off furnaces and
discontinuing the acid making process. A further important
advantage of having a fan at each end of the system is that repairs

^dbvGooglc

160 AMERICAN SULPHURIC ACID PRACTICE

may be made on the chambers more readily by producing a slight
inward suction by varying the fan Bpeeds. Thifl is appreciated
after chambers become several years old.

Iron fans suitable for this work are similar in general design
to those used for many other purposes, such as ventilation of
mines, buildings, etc. They must of course be quite tight, able
to stand temperatures up to 1,000°F. and be of simple construc-
tion to avoid catching dust. The housing should be of cast iron
as plate housings will warp badly in the heat encoxmtered. The
shaft will be course be very hot for some distance outside the
housing and so the bearings mi^t be water cooled. The rotor
can be of cast iron or of steel plate with a cast hub spider. It
may be overhung or may have a bearing on each side of the hous-
ing. The former method is perhaps more convenient as the
inlet flue is not complicated by having a shaft and bearing on that
side.

The speed of iron fans should be from 500 to 1,000 r.p.m. in
order that they may blow the dust out and keep themselves
clean. It must also be considered that due to its high tempera-
ture the volume of the gas is more than twice what it is after
it passes through the Glover Tower. Consequently, the range
of speed specified is advisable in order to move the gas with a fan
not unduly large.

Several manufacturers in this country have stock designs

which with sl^ht modifications are entirely satisfactory for acid

plant service. These fans are very much less expensive than the

" lead fans and over a period of years require less repairs. Why

they are not used more is hard to understand.

Lead fans are in general much like the iron fans in design.
It is necessary on account of the low strength of lead to make the
metal much thicker than corresponding parts of iron. "Die
shaft which carries the rotor is necessarily of steel, but it is
entirely covered by lead imtil it leaves the housing. Usually
the lead of the spider is poured around a cast iron hub which
latter is keyed to the shaft. This is a detail which has given
trouble in many fans, but if the cast iron hub is generous in
size and made with dovetail grooves so that the lead can take
hold of it well, no slipping or working loose will occur.

There are several lead fans specially deseed for acid plant
work on the market, and most of the manufacturers of blowers,
will alter their designs of iron fans and make them of lead if

^dbvGooglc

DHAFT 161

desired. Two widely used specially designed fans are tlie Pratt
and the Heinz-Skinner.

The Pratt fan, shown in Fig. 52, is made with both bearings
on one side, t.e., with rotor overhung. The gas enters on one side
only. The housing is of cast hard lead made in two pieces and
is self-supporting. It is so arranged that the top casting can be
lifted off to allow removal of the rotor. This is a well-designed
fan with the details perfected over a period of several years.
This fan is designed to run at rather high speeds up to 800 or 900 ■
r.p.m. It is therefore small comparatively and uses more power
than the large low speed fan.

The Heinz-Skinner, Fig. 53, has several novel features though
the principle upon which it works is the usual one. This fan has
its shaft extending clear through the bousing with a bearing on
each side. The inlet pipe branches just before it reaches the fan
and goes to an inlet on each side of the rotor. The housing is ia
two parts with a horizontal joint at the level of the shaft. The
joint itself is a lute made t^ht by an acid seal. The upper part
of the housing can be lifted off to change or work at the runner.
This fan both as to housing and runner is largely built up by
burning together rolled hard lead plates. It is entirely of hard
lead excepting, of course, the shaft. This fan is also very well

^dbvGooglc

162

AMERICAN SULPHURIC ACID PRACTICE

designed and if properly handled gives good service. It runs at
speeds up to 500 or 600 r.p.m.

The Wedge fan which has been used in several large acid
units built of late years is soraething of a departure from the
above types in the matter of size and speed. This fan so far as
I know is not made regularly by any manufacturer. The fans

so far made have all had runners 8 ft. in diameter and 4 ft. wide.
They run at speeds not over 200 r.p.m. They are enormously
heavy and costly but they run with surprisingly little power and
give very little trouble. Some of them have been in practically
continuous use for more than 4 years without being opened.
The housing of this fan is built up of ordinary sheet lead (15-lb.)
supported by angle iron framework. There is a gas inlet on one

^dbvGooglc

DRAFT 163

Bide only. The shaft rune in a bearing on each side of the
housing. One fan of this size will provide draft for a properly
designed plant to make 126 to 150 tons of 60° acid per day. It
consumes only 12 to 15 H.P. at 200 r.p.m.

These fans are mentioned specifically not so much because
they are more satisfactory than many others, but because they
represent types and because they are specially designed for acid
plant service.

FLtTBS

As the parts of the chamber system are enclosed in sheet lead
considerable areas of which are unsupported, it is essential that
flues, tower packing, etc., be so proportioned that no very great
resistances shall be offered to the passage of the gas. Of course,
the towers can stand somewhat higher differences between
internal and atmospheric pressures, than can the chambers,
because they are of heavier lead and the internal masonry lends
them stability.

It is well to BO design the plant that pressures corresponding to
1-in. of water shall not be exceeded in any tower and 0.75 in. as
a maximum for any chamber. Of course, h^her pressures will
be found in many plants and it should not be inferred that they
are- particularly dai^erous; however, the fact is that lead at a
temperature of 200''F. is not very stiff and in the course of some
years high pressures cause distortions which make trouble.

Calculations for flue areaa must be made for individual cases,
but the following statements will give an idea of proper areas
which should be provided in a simple one-fan system. If the
gas entering the acid system contains an average of 7 per cent Sd
by volume, it will be necessary to put through the plant about
80,000 cu. ft. per 24 hours per ton of 60" acid made, at O^C. and
760 m.m. This will be increased somewhat by the reaction
temperature and decreased as SO) and go to make liquid H1SO4.
In the early parts of the system for example, the gas temperature
may be lOO'C. which would make 80,000 cu. ft. at 0" = 109,000
cu. ft. = 1.26 cu. ft. per sec. If we wish the gas velocity to be
10 ft. per sec. our flue area in this part of the system would be
.126 eq. ft. per ton of 60° acid made. For a 100 ton unit the
flue area should then be 12.6 sq. ft. which is almost exactly that
of a 48-in. diameter flue.

In the back part of the system where the gas temperature is

^dbvGooglc

164

AMERICAN SULPHURIC ACID PRACTICE

perbapB 45°C., the volume wiU have decreased od this account to
about 86,000 cu. ft. The reaction and condensation of SOj and O
to liquid acid will have removed about 10 per cent by volume or
8,600 cu. ft. so that the volume of gas per ton of acid will be
about 77,400 cu. ft. per 24 hours = .9 cu. ft. per sec. and the
necessary fine area will be 9.0 sq. ft. which is the area of a pipe
about 41 in. diameter.

If several small flues are to be used instead of one large one,
or if there are many bends or very long distances between parts
of the apparatus which the Hues connect, some allowances to
compensate for increased friction should be made. The basis
of 10 ft. per sec. is a safe one however for the flue connections
found in most plants.

For tower packing, no very definite figure can be given as a
minimum of necessary open area, experience and data on different
types of packing are necessary. It is also necessary to consider
the length of the column of packing through which the gas must
pass. It is well in a Glover tower having a packed column
25 or 30 ft, high to provide a gross horizontal packed area of not
under 2 sq. ft. per ton of 60° acid made. For Gay Lussafs,
where combined packed he^hts amount to 75 ft. or more, 2 to
2.5 sq. ft. per ton of 60° acid made should be provided. Con-
siderable divei^ences from these specimen figures may be made
with entire propriety by using fans at various points of the
system.

Circular lead flues are to be preferred to rectangular sections.

iizcdbvGoogIc

DRAFT 165

They are stronger from the nature of their section and are
simpler to support. Sharp angles are to be avoided,. in general,
in lead construction. Circular flues are best made of 10-lb. lead.
The supports are flat or edge bands of iron as shown in Fig, 54.
The edge bands are slightly more expensive to apply but are
distinctly better in the long run. Bands should be frequent as
in the later yeara of the life of a plant insufficient support of
fines causes much trouble.

^dbvGooglc

CHAPTER XIV

TESTING

The control tests made about an acid plant are largely per-
formed by men who have little knowledge of the refinements of
" chemical and physical measurementfl and consequently no h^h
degree of accm'acy is customary. Nor is a h:^h degree of accu-
racy necessary. The tests and instruments to be described are
intended only to represent such work. They are for the operator
rather than for the chemist.

THERHOMETBRS AND PTROHBTBRS

It is desirable in many parts of the plant to know the tem-
peratures of the gases and acids involved in the process and for
obtaining these, thermometers and pyrometers are used. Every-
one is familiar with thermometers and little need be said concern-
ing them. In the United States the Fahrenheit scale is almost
universally used. For taking acid temperatures, straight stem
thermometers with inclosed paper scales reading up to 220''F.
are best. They are tess expensive and more easily read than the
engraved instruments. It ia well to have a few thermometers
reading up to 400° for testing the acid issuing from the Glover
tower. Chamber thermometers having stems bent at 45° or
90° from the graduated portion are regularly made by the
manufacturers of chemical apparatus. The stems are inserted
into the chambers through rubber stoppers. In reading a
thermometer it is important that a line from the eye to the end
of the mercury column be at a r^ht angle to the latter.

For ascertaining high temperatures such as those of the gases
entering the Glover Tower, the pyrometer is used. When
certain dissimilar metals or alloys are placed in contact with each
other and heated, an electric current is set up which can be
measured by a galvanometer and the corresponding degree of
heat shown by a needle on a graduated scale. For the purposes
of the chamber-acid plant what are known as base metal couples
for insertion into the flue are most suitable. This form of
couple, shown in Fig. 55 consists of a pipe or tube of one
metal and a rod of a different metal inside it and insulated from

^dbvGooglc

TESTING

167

it except at one end where the tube and the rod are welded
t<^ether. This welded end constitutes the couple and is inserted
into the gas whose temperature is desired. Couples made of
platinum, and platinum alloyed with rhodium or iridium, are

excellent but far more expensive. The only precautions neces-
sary to be observed in using pyrometers are to have all the wire
connections clean and tight and to keep the couple reasonably
free from dust.

Several couples may lead through switches to one galvano-
meter. Temperatures exceeding 1,200''F. are not often encoun-
tered in flues so that an instrument graduated to 1,500" or
l.eOOT. is suitable.

HTDROHETERS

The hydrometer is an instrument used for showii^ the concen-
tration of sulphuric acid. It is made of glass and consists of a
cylindrical fioat weighted at its lower end and with mercury, or
shot, and surmounted by a thin stem
containing a graduated paper scale.

The acid to be tested is placed in a tall
jar and the hydrometer allowed to sink in
it until it comes to rest. On account of
surface tension, the acid will curve up ■*—
against the stem as shown in Fig. 56.
The readily should be taken across the
surface of the acid on line AA, not at the
top of the curve line, BB.

The hydrometer universally used in
chamber-acid plants in this country is
called the American Beaum^. This is an
arbitrary scale originally devised by
making up a solution of pure salt, NaCl, 15 parts and pure water
85 parts by weight; immersii^ a hydrometer in it and calling the
mark 15°, The point to which the hydrometer sunk in pure
water was called 0°. The distance between these marks was
divided into 15 equal parts, thus establishing the degree BeaumS.
After many years of disagreement over the exact details of

^dbvGooglc

168 AMERICAN SULPHURIC ACID PRACTICE

obtaining the degree and as to its relation to specific gravity, the
U. 8. Bureau of Standards adopted as the oflgcial American
standard the relation expressed thus:

Degrees BeaumS = 145 — = — p-

In England Twaddles Hydrometer is most used. It is based
strictly upon a specific gravity relation. Specific gravity 1.0 =
0° Tw — and each succeeding degree represents an increase of
.005 in specific gravity, e.g., 5° Tw = 1.025 sp. g. This scale is
very little used in the United States.

Standard hydrometers are made for use io liquids at 60"P.
If the liquid is warmer than BCF. the hydrometer will read low
and vice versa, if the liquid is colder than GCfF, Where sulphuric
acid is said to be so many degrees Beaum6 it is understood that
the statement refers to the hydrometer reading at OO^F. When
it is desired to determine what the hydrometer would read at
fiO°F. in acid which is warmer or cooler than WF., the hydro-
meter is read at the existiug temperature and the temperature of
the acid taken with a thermometer. The hydrometer reading is
then corrected, increased if the acid is warmer than 60" and
decreased if colder.

If the acid is near 40''B^. .031°B6. for each IT. above or below 60°
If the acid is near 50°B*. .028''B6. for each IT. above or below 60°
If the acid is near eCB^. .026''B^. for each I'F. above or below 60°
V^ The Manufacturii^ Chemists Association of the

United States has adopted the tables of Ferguson
and Talbot as a standard for the relationships be-
tween specific gravity, degrees Beaumd, degrees
Twaddel and per cent H,SO«. This table is very
generally used in the United States. It can be found
in Chapter XXIII, Table 1.

Hydrometers most useful in the chamber acid

plant are the loi^ 12-in. form with a range from SO* to

^_^ JL 70° graduated to tenths of each degree and the short

f e-V^ \ chamber 5-in. hydrometer with a range of 40 to 60°

^T ^r graduated in degrees. The former is used for testii^;

the tower acids and the latter for the chamber drips.

Hydrometer jars for control testing are made of glass or lead

in the form shown in Fig. 57. The acid enters the main jar from

the bottom and assures the jar being full of the current Sow.

^dbvGooglc

GAS TESTING

The coDstituente of the gaaes regularly determined axe SOt and
oxygen. The Orsat apparatus is very generally used for deter-
mining both of these in the gases entering the aystem. In the
latter parts of the plant where the SOi percentage of the gas is
very low the Great is not suitable.

The Orsat apparatus consists essentially of a measuring burette
graduated to 100 c.c, two absorption pipettes, connecting capil-
lary tubes with stop cocks, and a levelling bottle. One pipette
is charged with SCB^. caustic soda solution which absorbs SOj
and the other with a solution of pyr<^allic acid in cauetic soda,
which absorbs oxygen. This is shown in F^. 58. To operate
the Orsat apparatus the end of the glass capillary is connected

with the vessel containing the gas to be analyzed by a rubber
tube. Three-way cock E is turned to open from burette B to
waste. Bottle A is raised to expel air from B and fill B with
water. Cock E is turned so that B communicates with V,
bottle A is lowered and the burette drawn full of gas. In order
to be sure of a fresh complete gas sample the cock is turned to the
waste position and the gas in burette expelled. A second sample
is drawn and the bottle manipulated so that the water in the
burette stands at O when bottle A is held so that water in A and
B are level, with cock E closed. Cock to C is now opened, bottle
is raised and gas all forced into C. The gas is drawn back and
forth between B and C five times, then with level of liquor in C
at original mark and cock closed a reading is taken in B with
water in A and B held level. This reading is noted. The gas is
again drawn back and forth between B and C twice and the

^dbvGooglc

170 AMERICAN SULPHURIC ACID PRACTICE

reading in B taken as before. If the two readings check, all the
S0» is considered to have been absorbed in C. If the second
reading is greater than the first the gas is sent into C again and
until two readings do check. The final reading in cubic centi-
meters represents the per cent SOi by volume. Next the gas is
manipulated into D and the same procedure gone through as
with C. The difference between the readii^ obtained from
absorption in C and that in D indicates the per cent of oxygen by •
volume. It is well to keep a thin rubber bulb on the back limb
of D so that fresh air is not drawn in on the pyrogallic acid
solution with each test, otherwise the absorbing power of the
solution is quickly destroyed.

In gases free from COi and which contain several per cent of
S0» the Orsat test will answer very well for testing in connection
with chamber control work. The accuracy is perhaps not high,
but the test can be reliably performed by any reasonably intelli-
gent person and it gives a good basis for estimating necessary
changes in nitric feed and workii^ the SOj furnaces.

The caustic soda solution used is made by dissolvii^ about
300 g. pure caustic soda in a litre of' Water. It is not necessary
to have these proportions exact.

The pyrogallic acid solution is made by dissolving about 12 to
15 g, pyrogallic acid in 125-150 c.c. of the above caustic soda
solution. This amount is a suitable volume for chaining the
customary Orsat pipette. The caustic solution can be made up
in any volume desired and kept indefinitely in a glass-stoppered
bottle. The pyrogallic acid solution is best made up as it ia
wanted to charge the pipettes. It is well systematically to
change the solutions once a week or at sufficient intervals to
assure that the solutions do not become sluggish.

A direct test for SOi suitable for any gas found in chamber
work is the Reich Test. This depends upon the reaction between
iodine and SOj - 21 + SOj + 2HiO = 2HI + HSOt, and upon
the fact that a solution of cooked starch produces a deep blue
color in a solution containing free iodine, and that the color
disappears as soon as all free iodine has been reduced to HI.

The test is performed in apparatus shown in Fig. 59. Bottle
A is charged with a definite we^ht of iodine dissolved in EI
solution and colored with starch. Syphon tube C is opened and
the gas under observation is drawn through the iodine solution
until the color just disappears. The amount of water drawn

^dbvGooglc

TESTING

171

from B is noted and it represents the amount of gas drawn
through the iodine solution, less the SOj absorbed. Knowing the
amount of iodine used and the volume of gas drawn, the per cent ^
SOi by volume is readily calculated.

As a rule tests are made in a chamber plant at a point near the
Glover tower where the SOi percentage is from 5 to 8, and at a
point near the Gay Lussacs where the SOi percentage is under
^0- F*^'' the former it is convenient to use a ^o normal iodine
solution, i.e., one which contams 12.7 g. iodine per litre. For

Fio. 60.

each test 10 c.c. of this solution is used and a table is made up in
the following way.

Ten cubic centimeters of >fo normal iodine contains .127
g. iodine. According to the reaction above this amount of iodine
will react with .032 g. SO*.

21 : SO, - 10 C.C. N/10 I : wt, SO,
2 X 127 : 64 = .127 g. : .032 g.

.032 g. SO, =- 11.184 c.c. SO, at O'C. and 760 m.ra.

The total volume of gas drawn into the iodine solution in any test
ia then the amount of water syphoned from the bottle B plus

^dbvGooglc

172 AMERICAN SULPHTJRIC ACID PRACTICE

11.184 c.c. which is the volume of S0» absorbed. Therefore

per cent. SO, = — ^^\^ + 11.184
*^ c.c. water

and c.c. water = . „■-. — 11.184

per cent. SOi

From this equation Table 6 is constructed.

In the rear of the system a 1/500 nonual iodine solution is
suitable. This contains .254 g. per litre. Table 7 is con-
structed for this solution in the same way as described for 6.

In using the Reich test, at any point in the chamber system
following the Glover tower, a modification is necessary. The
nitrc^n oxids contained in the gaa mixture render the test as
described above worthless in that they reoxidize the HI formed
and prevent decolorization of the solution. This can be pre-
vented and the test made fairly accurate by adding to the iodine
solution just before making the test, 10 or 15 c.c. of a solution
containing 100 g. sodium acetate and 100 g. acetic acid per
litre.

In Fig. 59 bottle A should be a 12 oz. salt mouth bottle fitted
with a two hole rubber stopper carrying two tubes. One of these
extends to within a short distance of the bottom. Its end is
drawn down so that the opening is only 1 or 1^ mm. in diameter
in order that the gas bubbles shall be small. The second tube
goes barely through the stopper. This arrangement is for all
practical purposes ae good as the expensive and elaborate absorp-
tion bottles and when it is broken, it is quickly and cheaply
replaced. The syphon bottle B should be at least two or three
litres. Two graduated cylinders, a 500 c.c. and a 1000 c.c. should
be provided.

The yio normal iodine solution is made by dissolving 15
or 20 c.c. of potassium iodide crystals in 25 c.c. of water. Into
this solution dissolve 12.7 g. iodine crystals. It is important
that the KI solution be very concentrated or else the iodine will
be slow to dissolve. When solution is perfect, make up to one
litre with water.

The J-^oo normal solution is made by making up 20 c.c. of the
}io normal solution to one litre with water.

Starch solution is made by mixii^ 5 or 6 g. soluble starch to a
thin paste and pouring into 500 c.c. of boiling water and allowing
to boil for 5 min. The addition of a few drops of chloroform or

iiz^dbvCooglc

Table fl. — Standard SOi Tabi/b
10 C.C. N/10 Iodine. O'C.-VeO mm.

Percent
SO.

C.e. water

Fercent
80.

Cc. water

Percent
80.

Cc. water

11,173

4.1

262

8.1

127

6,581

4.2

255

8.2

125

3,717

4.3

249

8.3

124

2,788

4.4

243

8.4

122

2,226

4.6

237

8.5

120

1,863

4.6

232

8.6

119

1,587

4.7

227

8.7

117

1,387

4.8

222

8.8

116 .

1,231

4,9

217

8,9

114

1.0

1,107

5.0

212

9.0

113

1.1

1,006

5.1

208

9-1

112

1.2

921

5.2

204

9-2

1.3

849

6.3

200

9,3

109

1.4

788

5.4

196

9.4

108

1.5

734

6.6

192

9.5

107

1.6

688

5.6

189

9.6

105

1.7

647

5.7

,185

9-7

104

1.8

610

5.8

182

9-8

103

l.fl

677

5.9

178

9-9

102

2.0

548

6.0

175

10.0

101

2.1

521

6.1

172

10,1

. 99.5

2.2

497

6.2

169

10.2

98,5

2.3

476

6.3

166

10,3

97-4

2.4

466

6.4

104

10,4

96.4

2.8

436

6.5

161

10,5

95.3

2.6

419

6.6

158

10 6

94.3

2.7

403

6.7

166

10,7

93,3

2.8

388

6.8

153

10,8

92.3

2.9

374

6.9

161

10,9

91.4

3.0

362

7.0

149

11,0

90.6

3.1

350

7.1

146

11. 1

80.6

3.2

338

7.2

144

11.2

88.7

3.3

328

7.3

142

11.3

87.8

3.4

318

7.4

140

11.4

86.9

3.6

308

7.5

138

11.5

86.1

3.6

299

7.6

136

11.6

85,2

3.7

291

7.7

134

11,7

84.4

3.8

283

7,8

132

11,8

83.6

3-9

276

7.9

130

n,9

82.8

4.0

268

8.0

129

12.0

82.0

This table is calculated using 2.86tl g. aa the weight of the litre of SO..

^d by Google

AMERICAN SULPHURIC ACID-PRACTICE

Table 7. — SO, by Reich Test
10 C.c. N/500 Iodine

Per cent SO, ■

C.C. water

Per cent SO,

C.c. water

.010

2,236

.060

373

.OlS

1,491

.065

343

.020

1,118

.070

319

.025

894

.075

298

.030

745

.080

279

.036

639

.085

263

.040

659

.090

248

.046

497

,095

235

.050

447

.100

224

.055

406

oil of cinnamon to the cooled solution prevents souring. Only a
few drops are used for each test.

The acetate solution is made by dissolvii^ about 100 g.
sodium acetate crystals in water, adding 100 c.c. acetic acid and
making up to one litre with water. About 10 c.c. of this is used
for each test.

TESTING FOR HITROGEH OXIDES

There are several materials about a chamber plant to be tested
tor their content of nitrogen oxides. The nitrometer method is
suitable for any of them and every plant should have one in use.
This instrument can be had in several different forms with com-

Plain invArff Tu

^=iac

pensating attachments but for the control work about a chamber
plant the simplest form, consisting of a simple graduated burette
with thistle top and two-way stop cock, and a plain levelling tube,
is quite satisfactory. Figure 60 illustrates this.

The nitrometer method depends upon the fact that in the pres-

^dbvGooglc

TESTING 175

ence of sulphuric acid mercury will react with nitric acid or any of
the nitrogen oxides above NjO, to f own HgiSO* and NO, a colorleea
gaB. By observing the volume of gas derived from a known weight
of the compound to be examined,!^ nitric acid or sodium nitrate
content, or equivalent, can be calculated at 0°C. and 760 mm.
1 c.c. NO = .00281 g. HNOs
1 C.C. NO = .00379 g. NaNOj

In performing a nitrometer test one should know in a general
way the amount of nitrogen oxides contained in the material
under examination and should figure out a suitable quantity for
introduction into the nitrometer. If the graduated tube is of 60
c.c. capacity, a quantity of material should be used which will
evolve a volume of gas preferably between 25 and 50 c.c. of NO.

The nitrometer is prepared by opening the stop cock into the
reservoir A and raising the levelling tube until the mercury barely
appears in the bottom of A. An accurately we^hed or measured
amount of the material under examination (in solution if a solid)
is put into A. The cock is slightly opened and A is almost but not
quite drained. Next about 10 c.c. of concentrated pure sulphuric
acid is put into A, the cock opened slightly and the acid drawn
into B as completely as possible without drawing in air. Tube B
is now well shaken for about two minutes to bring the mercury and
the solution into thorough contact. When one is assured that
complete reac Jon has taken place a reading is taken of the volume
of NO which has been evolved. The acid in B has a specific
gravity about J^ that of mercury so to observe the gas volume
under atmospheric pressure the readii^ is taken with the mercury
surface in C held at a point above the mercury surface in B equal
to 3^ (rf the length of the acid column. For example, if the acid
column is 14 c.c. the mercury in C will be held 2 c.c. above the
mercury surface in B when the reading of gas volume is taken.
A correction for temperature and pressure must be made in most
cases. It is sufficient for the class of work under discussion
to determine a correction factor for the usual room temperature
and the normal barometer and to use this factor in all cases. This
factor is determined by the following formula:
B ^ 273
Factor = 760^ T+273

B = Normal barometer in m.m.

T = Normal temperature in degrees Centigrade.

^dbvGooglc

176 AMERICAN SULPHURIC ACID PRACTICE

The observed gas volume is multiplied'by this factor and the
rcBult is the gas volume at 0°C. and 760 mm. pressure. The
mateiialfi about a chamber plant to which the nitrometer test
will be applied aie nitrate of soda, nitre cake, nitrous vitriol and
mixed acids.

To test nitrate of soda, dissolve 50 g. in water and make
up to one htre. With a pipette introduce 2 c.c. into the nitro-
meter and perform the test as described.

Per cent NaNO, = c.c. NO X 3.79
To test nitre cake, dissolve 5 g. in water and make up to 25 c.c-
With a pipette introduce 5 c.c. into nitrometer and perform
test as described.

Per cent NaNO, = c.c. NO X .379
To teat nitrous vitriol containing not over 70 oz. NaNOj
per cu. ft., introduce 2 c.c. with a pipette into nitrometer and
proceed as described.

Oz. NaNOi per cu. ft. = c.c. NO X 1.91

To test mixed nitric-sulphuric acids, it is usually necessary
to dilute with concentrated sulphuric acid in order to avoid
having to measure an exceedingly small quantity for use in the
nitrometer. It is not well to try to use less than 2 c.c. of a solu-
tion for test as pipettes smaller than that are not very accurate.

A quick method of estimating the amount of nitrogen oxides
in nitrous vitriol is by a titration with potassium permanganate
solution. This assumes that all the nitrogen oxide existe as
N^i and reacts thus:

5N,0j + 4KMn04 + 6H^0, = 2K,S04 + 4MnS0*
+ lOHNO, + H,0

Lunge and other writers on this subject recommend perform-
ing this test by measuring a known amount of permanganate into
a dish and nmning in nitrous vitriol from a burette until the
permanganate is decolorized. This is perhaps slightly more
accurate than the way which will now be described.

Fill a 50 c.c. burette with standard permai^anate. solution.
Draw a little water into a porcelain evaporating dish or casserole
and run into it, from the burette, an amount of permanganate
slightly less than needed. Now measure into the dish with a

^dbvGooglc

TESTING 177

pipette 5 c.c. of nitrous vitriol. This ehould decolorize the
permanganate. If it does not, repeat, using less permanganate.
Next add permanganate from the burette until a faint color,
which remains on stirring, appears in the dish.

This plan is much more convenient than the first described
in that it is not necessary to fill, empty and clean a burette for
nitrous vitriol for each test. It very closely checks the first
method also. It is convenient to use a permanganate solution
of such strength that 1 c.c. indicates 2 oz. NaNOs per cu. ft.
of nitrouB vitriol when using 5 c.c, nitrous vitriol for each t-est.
In this, if the nitrous vitriol carries 50 to 60 oz. per cu. ft.,
there will be drawn 25 or 30 c.c. of permanganate tor each test
and a 50 c.c. burette is suitable for measuring it. SucK a per-
manganate solution is made by dissolving 7.44 g. KMnO* crystals
in water and making up to one litre.

EXIT GAS

A useful thot^ rather rough test to determine if the Gay
Lussac towers are functioning well mechanically is made by
drawing several cubic feet of exit stack gas through a bulb tube,
partly filled with 60° sulphuric acid. The bulb tube is shown in
Fig. 61. It is chatted with 100 c.c. of 60° sulphuric acid and the

Fio. 61.

gas is bubbled throi^ it for several hours. Its content of
nitrogen oxides is then determined by the nitrometer. This
test will show approximately how much nitre loss is being suf-
fered by reason of insufficient contact between the gas and the
acid in the Gay Lussac towers. Its results will often point out
poor distribution of gas or acid or the need for further Gay
Lussac towers.

^dbvGooglc —

178 AMERICAN SULPHURIC ACID PRACTICE

DRAFT MEAStlREMENTS

It is desirable to observe daily the gas pressures at several
points in the chamber system to be certain that fans are working
properly and that no obetnictions exist. The following points
certainly should be examined; entering and
leaving the Glover tower, before and after each
fan and entering and leaving the Gay Lussac
towers. In some plants further observations
may be necessary. Two instruments are most
useful for this work, viz., the small diameter
U tube and the Ellison gage. The U tube is
simply a glass tube of J^ to 1 cm. bore bent to
a U shape with the limbs about 1 in. apart.
This need not be more than 6 in. long. Behind
this is placed a graduated paper scale marked in
inches and tenths or in millimeters. One limb
of this tube is connected to the fiue or chamber
whose pressure is to be determined, and the
other left open to the atmosphere. The dif-
ference between the level of water in the two
limbs shows the difference between atmos-
pheric pressure and that in the Sue. Figure
62 illustrates this.
A much more sensitive instnunent is the
Ellison gauge, shown in Fig. 63. It is suitable for measuring
very small differences of pressure as well as measuring considerable
pressures with accuracy. In this instrument as shown, one limb

Fta. 62.

is vertical and the other at a small angle with the horizontal.
Any movement of the Uquid in the vertical limb is accompanied
by a movement about ten times as long in the sloping limb behind

^dbvGooglc

TESTING 179

which the graduated scale is placed. The Ellison gauge is filled
with a Bpecial oil colored red and the Bcaic with which it is
equipped is graduated to show directly hundredths of an inch
of water and thousandths can be fairly accurately estimated by
the eye. There is a leveUiug tube ou the case and the base is
equipped with levelling screws. This is a very practical and
satisfactory instrument.

The apphcation of the tests described will be taken up iu the
chapter on operation.

^dbvGooglc

CHAPTER XV
OPERATION

To successfully operate a chamber acid plant one should
get clearly in mind the chemical and physical changes undei^ne
by the gas mixture in its course through the plant. One must
know what the ideal attainable conditione are in each part of
the plant and make such observations as are necessary to know
that they are being closely approximated.

First, to state the process briefly and simply, we have in the
normally operating plant a steady uniform amount of SOj com-
ing into the chambers and moving through them at such a rate
that say 90 min. are occupied in the passage from one end to
the other. Such an amount of nitric oxide is introduced into the
gas by nitre pots and in the Glover tower as will oxidize sub-
stantially all of the SOt to sulphuric acid in that 90 min . This
amount of nitre must be very accurately proportioned or results
will be bad. A sufficient amount of water or st«ajn must be
introduced into the chambers at various points to make the acid
formed therein have a concentration of approximately 50°B€.
The Gay Lussac towers through which the residual gas from the
chambers is passed must be fed with a suitable uniform amount of
cold 60°B6. sulphuric acid to take into solution 85 to 90 per cent
of the nitrogen compounds existing in the gas. This solution,
the "nitrous vitriol,"' must be fed back uniformly into the Glover
tower and there diluted to such an extent that the hot incoming
gas will remove and carry on with it in gaseous form all of the
nitrogen compounds. This is, of course, the main source of the
nitric oxide to the process, constituting by simple inference
85 to 90 per cent of the amount required. The other 10 to 15
per cent is supplied by potting new nitre or adding nitric acid.

The chemical reactions which take place in the chamber
process have been subjects of much controversy and there is still
much difference of opinion concerning some of them. Without
attempting any discussion of the various theories, a brief state-
ment of the ideas of Lunge will be given. These may or may not

^dbvGooglc

OPERATION 181

be Coirectly representative of the chamber process, but they
give a good basis for reasouiiig and are very well borne out by
the phenomena of the chambers.

The reactions which take place in the nitre pots or the retorts
of the nitric acid plant are:

(1) NaNOj + HiSO, = NaHSO, + HNO»

(2) NaHSO* + NaNOs = Na^O* + HNO,

The first reaction takes place at low temperatures and the
latter at higher temperatures. Nitre cake as usually made is
a mixture of Na»SO, and NaHSOi.

In the Glover tower, nitric acid is reacted upon thus:

(3) 2HN0b + 3S0, + 2Hp^= 3H^0, + 2N0

In the Glover tower, nitrous vitriol is reacted upon thus
"(denitration") :

(4) 2HSN0( + SOj + 2H,0 - SH^O* + 2N0

In the Glover tower this reaction probably also takes place:
- (5) 2N0 + 2S0, + H,0 + 30 = 2HSN06

In the Glover tower and the first chambers these two reactions
4 and 5 are the predominating ones. The only oxide of nitrogen
which exists in quantity is NO. This is a colorless gas which
explains the fact that front chamber gases show little red
color.

As the gas mixture becomes leaner in SOj the following reactions
take place:

(6) 2HSN06 + H,0 = 2H,S04 + N,0,

(7) N,0, + 2S0« + 20 + H,0 = 2HSN0.

These two reactions take place more and more as the gas
approaches the last chamber. The predominating oxide of
nitrogen is N»0» (probably a mixture of NO and NOi), which is
a red gas and which gives the gas mixture its red color.

If conditions are ideal, the gas mixture entering the Gay
LuBsac tower contains substantially all its nitrogen oxide as NiO)
or equal parts of NO and NOi. This is absorbed by the sulphuric
acid in the Gay Lussac packing thus:

(8) N,0. + 2H^04 = 2HSN0» + H^

If an excess of NO exists it is not absorbed by the Gay Lussacs,
This condition exists when there is a considerable amount of SO3

^dbvGooglc

182 AMERICAN SULPHURIC ACID PRACTICE

in the gas mixture entering the Gay Lussacs. If an excess of
NOi exista, it partly reacts with the sulphuric acid in the Gay
Lussacs thus:
(9) 2N0, + HjSO, = HNO, + HSNO*

This reactioD is uot complete and some NO* goes through and
shows as a red cloud at the stack. This condition exists when an
undue amount of nitre is introduced with the entering gas and
the SOt is completely converted to sulphuric acid sometime
before the gas reaches the Gay Lussacs.

The time of passage of the gas through the chambers is some-
thing which varies in different plants and which depends upon
the style of work done. In some chamber plants the period is as
short as 1 hour and in others more than 2 hours. It is simple to
calculate from the SOj analyses, the make of acid and the volume
of the chambers what the period is. This should be known by the
operator. The amount of nitre necessary to be introduced for
normal work is also dependent on the individual characteristics
of the plant and upon the style of work. In modem American
plants, an average amount is probably 25 to 30 parts sodium
nitrate for each 100 parts sulphur. For example, if 100 tons 60°
acid is made per day, the sulphur in the SOi used is approximately
25 tons or 50,000 lb. The sodium nitrate equivalent of the
nitrous vitriol plus the new nitre will amount to 25 or 30 per cent
of 50,000 lb., or 12,500 to 15,000 lb.

If absolute uniformity of all the factors of the process could be
maintained, the operation would be very simple. Involving
as it does h^h temperature, dusty, corrosive gas and sulphuric
and nitric acids, many irregularities occur and it is in meeting
them properiy that the skill in operatii^ lies. It is of course,
much simpler to operate a plant derivii^ its gas from brimstone
burning than to operate one on blast furnace gaa or some of the
other metallurgical by>product gases.

In years gone by, chamber acid plants were almost entirely
operated by rule of thumb methods. Operators by considerable
periods of experience became often very skilled in handling the
process, depending upon such observations aa color of the gas
mixture in the chambers, effervescence of nitrous vitriol on dflu-'
tion with warm water and various other equally inexact phe-
nomena. The old hand at the business did well sometimes but
several years were necessary to make an old hand. In recent

^dbvGooglc

OPERATION 183

years, particularly since metallurgical gases have come to be
used to a considerable extent, more exact methods are being
employed, for control of the acid process. It is true that there
are plants still operated by the old plan, but certainly better
work can be done in any plant by making accurate observations
and records.

The thing of chief importance in the chamber process is the
proper proportioning of nitre to SOj. The amount of nitre
derived from the nitrous vitriol and from the nitre pots or fresh
nitric acid must at any given time be precisely enough and not too -
much, to convert substantially all of the SOi coming in at that
time to sulphuric acid durii^ the period of passi^ of that gas
through the chambets. If the amoimt of nitre is not sufficient
all of the SOi will not be converted to sulphuric acid. The SOi
remaining unconverted will pass out and be lost. The nitrogen
compounds will exist as NOj and NO with NO in excess and as
NO is not absorbed by the Gay Lussac towers, that excess will
be lost. There will be loss of both sulphur and nitre. If the
amount of nitre introduced be too much, there will be no loss
of SO,.

The SOi will all be converted to sulphuric acid some time before
the gas mixture finishes its passage through the chambers and
during that time, oxidation of the NO present will proceed and the
gas entering the Gay Lussacs will contain NOi and NO with NO*
in excess. NOi is pari,ly but not completely absorbed by the
Gay Lussac towers and the part that is not absorbed passes out
into the atmosphere as a red cloud. In the absorption some
nitric acid is formed which is not particularly good for the lead.
From these statements it can be understood that nitre loss occurs
if the amount of nitre originally introduced be either too large
or too small to completely convert its accompanying SO* in just
the proper time.

The original establishment of these conditions is done by trial.
To maintain them, the modem acid maker depends mainly upon
periodical observation and recording of the temperatures in the
chambers at many points throughout the system, and upon period-
ical determinations of SOi in the gas mixture at a point just
preceding or following the Glover tower, and at another point
just preceding the Gay Lussac tower. There are other indica-
tions which are made of use to some extent such as the concen-
tration and appearance of the chamber drips, the color of the gas.

^dbvGooglc

184 AMERICAN SULPHURIC ACID PRACTICE

the appearaace of the exit stack, the nitrous vitriol determina-
tions, etc., but these are used more to con&nn the temperature
and SOs knowlec^ than anything else.

To illustrate in a concrete way how these observations are used,
we will assume that hourly observations and records are made of

1. Temperature and °B^. of drip on each chamber, -

2. 80s in gas entering Glover tower.

3. SOi in gas entering Gay Lussac towers.

4. Nitrous vitriol.

5. Atmospheric temperature.

The operator comes on and immediately makes a set of rec-
or(^ as above. If the percentage of SOi in the gas entering the
Gay Lussac towers is correct he knows that 90 min. before, the
nitre was properly proportioned to the SOj. He looks back on
his record sheets and observes that at that time the SO* entering
the Glover was say 8.0 pet cent and that the temperature of the
front chamber was 195°F. If the gas entering the Glover is still
8.0 SO2 he can reasonably assume that the front chamber tem-
perature should be within a degree of ISS'F. If it is much under
ISS^F. the amount of nitre entering is deficient and if much over
ISST. the nitre feed is more than necessary. If the SOi in the
gas entering the Glover has decreased to say 7.6 per cent the oper-
ator will know by experience that his front chamber temperature
should be somewhat less than 195''F., say 190''F. If on the other
hand, the gas entering the Glover has increased to say 8.2 per cent
he will know that his front chamber temperature should be pei>
haps 197° or I98'F. He will in the one case decrease the nitrous
vitriol stream s%htly and continue such adjustments untfl the
desired temperature is attained. The correctness of the opeiv
ators adjustments will be shown by the SOj determination at
the Gay Lussacs 90 min. later. This system of observation and
adjustment is carried out constantly and if faithfully attended to,
produces excellent results.

A further elaboration of the plan of control by SOj tests has
been proposed and carried out successfully by A. M. Fairlie.
This plan is as follows: An S0| test is made at a point near the
Glover tower. A short time later an SOs test is made at another
point some little distance along say at the end of the leading
chamber. The time between the tests is approximately that
occupied by the gas in passing between the two test points. As-

^dbvGooglc

OPERATION 185

Burning uniform gas velocity, for any given SOf percentage at the
first point there is a certain proper SOa percentage at the second
point to assure perfect conditions at the entrance to the Gay
Lussacs. If the 80j at the second point is not correct, an adjust-
ment in the nitre feed is made. This is a most excellent method
of control and in certain cases where the gas supply fluctuates
widely, its practical value is high.

Control of the nitre feed lies in two things, the nitrous vitriol
and the nitre pots, oi* the nitric acid. Of the total the nitre
derived from the nitrous vitriol amounts to between 85 and 90
per cent, and the added or new nitre to 10 to 15 per cent. It is a
very good plan-to decide upon a suitable amount of new nitre to
be used at the beginning of each shift and to maintain it constant
throughout the shift, barring, of course, large irregularities.
The minor changes necessary, such as the ones specified above are
taken care of by changing the flow of nitrous vitriol. This can
be accomplished readily by means of a long distance control
arrangement. If the frequent small changes desirable are made
by varying the amount of nitre potted, the potting schedule
becomes very intricate. If it is done by varying the flow of new
nitric acid, many trips to the top of the Glover tower are neces-
sary as it is hardly feasible to make nice changes in a stream of
liquid ranging from knitting needle to pencil size with any long
distance methods. The nitrous vitriol, on the other hand, is a
rather ample flow, and its nitre content is low so that its control
is very convenient.

To illustrate by an example, suppose a system running normally
with 8 per cent gas ajid proper nitre feed of which 87 per cent is
from the nitrous vitriol and 13 per cent new nitre. The gas
decreases to 7.6 per cent, i.e., 5 per cent. The nitre feed should
be decreased 5 per cent. This can be done by decreasing the
nitrous vitriol flow by 5.75 per cent (since 5 per cent is 5.75 per
cent of 87). If the change is made by varying the new nitre, this
will have to be decreased by 38.5 per cent(8ince 5 is 38.5 per
cent of 13). With suitable tank space for nitrous vitriol, these
minor changes are not often reflected back to the Gay Lussac
towers which go on running with constant flows.

To decide upon the amount of new nitre to be used for a shift,
the operator will observe the stock of nitrous vitriol in the tanks
and whether the nitrous vitriol is of normal grade. If the stock
ia right and the nitrous vitriol normal he will establish or con-

^dbyCooglc

186 AMERICAN SULPHURIC ACID PRACTICE

tinue the introduction of the normal amount of new nitre. If
the stock is low or the nitrous vitriol below normal in nitre content,
he will establish a rate of introduction of new nitre somewhat
above normal in order to brii^ the nitrous vitriol stock and grade
back where it belongs. If, on the other band, stock or grade of
nitrous vitriol are above normal, he will have an opportunity to
run with less than the normal feed of new nitre.

The drips on the chambers are tested hourly. They should
be kept between 48° and SCB^ — not higher, because the nitrogen
compounds begin to be taken into solution, and not lower, be-
cause concentration capacity of the Glover tower will be over-
taxed. The control of the acid strength lies in the amount of
water or steam admitted to the chambers. Ordinarily the hy-
drometer readings are taken without correcting for temperature,
although for strict accuracy, corrections up to .5°B^. should be
added. The bottom acid in a chamber is always slightly higher
in strength than the drip.

The acid issuing from the Glover tower coolers should be ob-
served several times a day for strength and temperature. It
should ordinarily be kept between 59° and 61° after applying the
temperature correction. The minimum represents the lowest
proper strength for Gay Lussac feed. Above 61° there exists
danger of incomplete denitration in the Glover unless the burner
gas is very hot. The temperature of the acid issuing from the
cooler should be not over 80°F. and preferably less. From time
to time, the coils in the cooler become encrusted and. when the
acid temperature rises above 80°F. the cooler should be drained
and washed out with a hose. It is well to test this acid from time
to time by the nitrometer to be certain that no nitre is being
retained by the acid. If denitration is not complete, the feed of
weak acid on the Glover must be increased.

The nitrous vitriol issuing from the first Gay Lussac tower is
tested with potassium permanganate once an hour. Any great
variation from the normal should be accounted for. This
normal nitrous vitriol is something which will be decided upon
for each system. It is right in one plant to run with perhaps 35
oz. NaNO] per cubic foot and in another with 70 oz. or more.
Several considerations enter. The amount of absorbable nitre
entering the Gay Lussacs in a given system will be fairly con-
stant. The nitre content of the nitrous vitriol will then depend
uptm the amount of acid fed to the Gay Lussac tower. The

^dbvGooglc

OPERATION 187

smallest permissible amount is that which can be divided and
distributed over the packing with sufficient thoroughness to
assure wetting the entire area. If any of the packing remains
dry, or nearly so, the nitre laden gas will pass through that part
of the tower without having the nitre recovered from it, A good
safe quantity to assure wetting is one ton of acid per.square foot
of horizontal area per 24 hours. If the tower has for example, an
area of 200 sq. ft., about 200 tons per day should be put over it.
This quantity may be exceeded and assurance of complete wetting
made doubly sure, but a greater amount than that mentioned is
not necessary. If the plant served by this tower makes 100
tons 60" acid, the nitre entering the Gay Lussac tower will
amount to about 12,500 lb. NaNOg and if 87 per cent recovery is
made, the normal nitrous vitriol will be 45 to 46 oz. per cubic
foot.

If, as in many plants, the horizontal area of the Gay Lussac
towers is proportionally less, a smaller acid circulation will be
used and nitrous vitriol of higher nitre content produced.

In any event, a proper normal will be established and any wide
variation from it indicates an irregularity in process, or acid
flow.

An observation and record of drafts should be made once a day
by the instruments already described. Any important variation
from normal should be investigated. Sometimes in a Glover
tower, for example, there will be a very gradual increase in the
packing resistance indicated by an increase in the difference
between the pressures at bottom and top. This indicates usually,
the accumulation of sediment or dust in the packing, and when
it reaches a certain point, flushing out is necessary.

LABOR FORCE

The number of men required to operate a chamber plant is
snuill, but care and reliability are absolutely essential. In
order to ^ve an idea of the normal labor force required, assume
a 100-ton unit having mechanical burners, flue nitre pots and
acid eggs for pumping. There will be, on each shift, one fumace-
man, one nltreman, one pumpman and a chamberman who
exercises general supervision. On the day shift will be a repair-
man and two laborers. This force may be reduced in certain
small plants by havii^ the furnaceman attend the nitre pottifig

^dbvGooglc

188 AMERICAN SULPHURIC ACID PRACTICE

as well as the furnaces. In case a nitric-acid or mixed acid plant
is used instead of flue pote, one man will produce enough nitric
acid in one shift to run the plant 24 hours.

The whole operation should be supervised by a man of experi-
ence and judgment. It is a false economy to run even a modest
sized plant without such a man.

iiz^dbvCooglc

CHAPTER XVI
CONCENTRATION

Sulphuric acid made in the chambers is only, at its best, 52° to
SS^B^., and where an acid of greater concentration is required
it is necessary to concentrate this chamber acid. There are
various methods of doing this.

Before the introduction of the Glover tower, chamber acid was
concentrated in lead pans, up to 60° or 61°B£. Since the Glover's
introduction it has been an easy matter for manufacturers to
bring their chamber acid up to 61°B^. in the tower, as described
under that subject.

Lead pans are still used in old works that have no Glover
tower, and in concentrating waste acid.

The vapor from boiling, dilute sulphuric acid consists almost
entirely of water vapor: therefore, the acid will become more
and more concentrated, as the boiling proceeds, as long as
60°B6. is not exceeded.

In pan concentration lead pans are almost universally used for
the concentration of acid up to dO^BS. Above this point, lead
is acted upon, necessitating the use of other material.

Pans may be heated by direct flame, either from the top or
bottom, by steam, or by the waste heat from pyrites or sulphur
burners.

When the purity or appearance of the acid is of less importance
than the saving in fuel, or in labor, top firing is generally used.
The pans are generally 30 ft. long, 4 ft. 11 in. wide, with sides
17 in. high. They are built from heavy lead, 15 to 30 lb. to the
sq. ft., and always in one piece; the corners are never cut, but
are folded over.

It is necessary to protect the lead from the direct action of the
fire. The fire box is always built separate from the pan, and is
only connected to it by an arch which extends the length of the
pan, and a fire-proof clay slab at the bottom. The pan inside is
protected by acid-proof bricks or slabs. At the long side these
extend up to the arch, while on the short, or fire side, they only
reach to the top of the pan, and there is placed the fire-proof

^dbvGooglc

ISO AMEniCAN SULPHURIC ACID PRACTICE

slab to the Gre box. There are openin^^ left Id the bottotn of the
partition slabs, so the acid can circulate freely. The pan is
always raised 3 ft. or more above the grouod.

The acid is introduced at the end nearest the fire box, and
drawn out at the far end. Evaporation is very rapid, both
because the hot gases come into direct contact with the acid, and
because the chimney draught carries away the water formed.
The damage to the pans is very sl^ht, as the brick lining protects
the lead from direct heat, and up to 60°, or even fil^B^. the acid
has very little effect upon lead. But above that degree of con-
centration not only does the acid act upon lead, but its boiling
point gets close to the temperature at which lead begins to
soften.

Keeping the acid at a constant level also protects the pans.
Except for repairs the acid is never drawn off entirely, but as
the concentrated acid sinks and is drawn off from the bottom
fresh weak acid is added at the top. Efforts at water coolii^;
have not been successful, as Ifiari PJIT' "*" jackets start leaking
easily, and cause trouble.

The greatest destructive effect is at the fire end of the pan, and
to keep it as cool as possible the weak acid is added here, through
a pipe throt^h the arch. The syphon to withdraw concentrated
acid is at the cool end of the pan, but even then the acid is too
hot to use, and is run into shallow lead cooling pans, stayed with
wood or iron frames.

If the pans need staying it should be done by cast-iron or
pressed-steel grids, as their large radiatli^ surface will help keep
the lead cool.

Coal used will vary from 2 per cent to 10 per cent by weight of
the acid concentrated, varying with quality of coal and size of
pan. A long pan is most economical.

One square foot of pan surface will concentrate 150 lb. of
chamber acid to 61°B4. per 24 hours.

The strength of concentrate is regulated by the fire and the
weak acid fed.

No data ia available as to the loss of acid in this method of
concentration, but it is probably more than for bottom-heated
pans, as the stream of hot gases carries away acid in minute
drops, that are very hard to condense. We meet this same mist
in the contact process, and it gives us the same trouble.

The spray of acid from the stacks is not only a loss, but a

iiz^dbvCoOglc

CONCENTRATION

191

nuisance, and sometimes the basis . of suits by neighboring
property owners. Gas, instead of coal, firing has been tried aa
a remedy, without much success, and the only relief has come
from the use of higher stacks, causii^; a better diffusion in the air.

Lead pans heated from below are always smaller than those
usii^ "top fire," and are built in seta. The reason for this is
that the-pans nearer the fire are worn out first, and it is cheaper
to have a small pan to replace. The concentration is very regular,
the weak acid Sowing in at one end, and running from one pan
to the next, until it runs off sufEciently stroi^ at the other end.

The pans are rectangular, 5 to 7 ft. on a side, and about 15 in.
deep. There are four to six in a set. The acid is carried from
pan to pan by overfiow pipes, so that it takes the acid from the
bottom of one pan to the top of the next, as the acid is stronger
at the bottom. The Sow of weak acid is so regulated that the
proper concentration of acid is obtained at the last pan.

The pan bottoms are protected from the fire by iron plates,
these plates being heavier at the fire end. The iron, being a
good conductor of heat, also assists the heat distribution. Some-
times copper plates are placed between the pan bottom and the
iron plate to prevent, by their good conducting qualities, local
overheating and buckling of the pan.

The general plan is to place the fire under the weak pan. In
this way the strong pan does not receive much more damage
than the others, and evaporation goes on satisfactorily as welL
The old practice was to place the fire under the strong pan,
because the boiling point of the strong acid is the h^hest, but
on account of the wear on the pan it has been found more
economical to reverse the operation.

Bode gives the following table, where the fact that the greatest
heating takes place at the third pan shows that the fire is badly
utilized :

1st
pan

2nd
pan

3rd
pan

4th
pan

5th
pan

pan

25°
110'

112°
113°

150°
120°

160°
128°

148°
134°

145°
140°

U3°C.

24'
110°

110°
113°

146°

us-

156°
126°

145°

142°

142°C.

idb,Go(5glc

192 AMERICAN SULPHURIC ACID PRACTICE

He estimates, for English practice (1910), that a aet of six pans
will cost $500, and the maintenance will be 12 per cent;. Total
coet of concentration 55f! to 65^ per ton.

Coal required is about 15 per cent of the weight of the acid
concentrated, and each squae foot of pan area will produce 85 lb.
of 60° acid every 24 hours.

Fans for utilizing waste heat from pyrites or brimstone burners
must be designed for each special case, the principles being the
same as for bottom-heated pans. Sometimes the pans are
placed over the dust flue, but protected from the direct action of
the burner gases by brick, or often over the burners themselves.
This method of concentrating is very cheap, requiring only part
of a man's time, and the maintenance chaises, Bode says,
lOf! to 18^ per ton (1910).

Steam pans are of many forms, all dependUig upon slow
evaporation far below the boiling point of the pan acid. Steam
is introduced through a lead coil, which lies on the bottom of the
pan, the condensation returning from it to the boiler. There is
no acid mist escaping, so no injury to vegetation ia possible;
but steam coil concentration ia so expensive that the writer does
not know of a single installation in the United States.

OTTALITY OF LEAD

Lead as heavy as that used for concentratii^ pans is difficult
to bend cold, so a light fire ctf shavings is made on the part of
the lead plate to be bent, and the lead softened sufficiently to
be easily manipulated.

W. B. Hart, Journal of the Chemical Soci^, 1907, writes as
follows:

Lead may fail from either or both chemical or phj^ical faults:

The effects of impurities are as follows:

(a) With bismuth and tin, lead forms alloys of low fusibility,
causing local perforation. Acid may concentrate in these leaks,
and become strong enough to attack the lead itself.

{b) Aluminum, tin, or zinc may cause sudden failure at certain
stages of the concentration.

(d) Electrolytic action may be set up between deposits of
impurities and the lead.

^dbvGooglc

CONCENT RA TION 1 93

(e) Antimony may have a strong and harmful chemic^ effect,
and copper, arsenic, and silver very little. Copper may even
be helpful under certain conditions. By constant use copper
may be entirely dissolved out, and ite corrosive effect upon other
impuritiea lost. This will sometimes explain the sudden failure
of a pan that has been in good condition for a long time.

(J) Pure lead, under normal pan conditions, is undoubtedly
less affected than the impure metal.

Faulty physical conditions may be due to bad remelting, use
of unsuitable castit^ temperatures, and too severe pressure in the
rolling operation.

(a) Production of a loose crystalline structure, by casting the
metal at too high a temperature, causing leakf^e.

(b) Production of a surface more susceptible to attack, by too
severe pressure during rolling.

(c) Strong acid action in the temporarily physically altered
form of lead, before the annealing effect can take effect, explains
the failure of pans that have been in use a very short time.

(d) Altered physical condition can make unsuitable even a
lead of exceptionally pure chemical composition.

COMCEHTBATION PROM 60° TO 66°

Concentration of sulphuric acid naturally resolves itself into
three divisions — first, chamber to 60''B6.; second, 60°to66''B^.,
or "93.19" (per cent), as it is often called, and from 93.19 per
cent HiSO* up to 97.50 or 98 per cent HjSOt.

Ordinary pan concentration, as just described, is the usual first
step. For the second several methods are used, and are presented
in what the writer considers their order of merit.

First, because very simple and efficient, comes the "heat ex-
changer." As applied at one large works, this is a continuation
of the lead pans.

A series of five lead pans concentrates the acid to SZ^Bfi,, and
the acid leaves the last lead pan at a temperature of from 285° to
320°F., practically the temperature of the first pan. The highest
temperature usually comes in the third pan.

From the last lead pan the acid flows to a pulsometer, or air
lift, which raises it to the top of the heat exchanger. The heat
exchanger is a lead-lined steel tower, further lined with three
courses of acid-resisting brick, and filled with broken quartz. It

^dbvGooglc

194 AMERICAN SULPHURIC ACID PRACTICE

is 12 ft. high, and 21 in. in diameter inside the brick. The acid
trickles down throi^ the broken quartz packing, and meets the
aBcending gases, rich in SOi, from the covered iron pan, which is
Bet directly over the flame. The falling acid is cool enough to
absorb practically all of the 80i in the ascending gas, and while
it does take up some of the moisture driven off too, it is not
enough to hinder the concentrating operation. The unabsorbed
gas, now almost entirely steam, passes from the top of the heat
exchanger to two lead-lined condensing towers, filled with coke.

which catches any drops of acid. The passage of the gases
through the heat exchanger and condensii^ towers is induced by
a steam jet, attached to the exit flue of the second tower.

From the bottom of the heat exchanger the acid, enriched by
the SOi absorbed, flows to the iron pan, where it is concentrated
to 66°B6., and is then syphoned off to a tant-iron box, equipped
with cooling coils of lead, where it is cooled down to SCF,
Thence it goes to storage.

The temperature of the iron pan is unheeded. The first lead
pan is kept at 285° to 310°F., and upon the fire necessary to
accomplish this depends the d^ree of heat of the iron pan.

^dbyGoogle

CONCENTRATION 195

The lead pans hold the following temperatures:

No. 1 about 320°F
No. 2 about 330
No. 3 about 360
No. 4 about 345
No. 5 about 330

The Eessler apparatus really covers two steps of the concen-
trating field, as it will bring chamber acid up to 98 per cent HjSOi
in one operation. In this apparatus hot air is used to concentrate
the acid. The operation requires that a current of hot air shall
be brought into contact with the liquid, to immediately reduce
its temperature. The air must become thoroughly saturated
with steam and acid vapor. The apparatus must be so con-
structed that it will stand the action of hot acid, and that the
deposits do not give any trouble. Under these conditions the
acid may be concentrated at a temperature far below its boiling
point, for instance, to concentrate acid to 95 per cent H^SOi,
boiling at 280''C., the temperature needs to be only 180° to igO^C.

The part of the apparatus where the gases are saturated with
-acid vapors, and the temperature greatly reduced, is called the
"saturator. " Immediately above it is placed the "recuperator,"
where the acid vapors are caught. This recuperator resembles
the dephlegmating columns used in the rectification of spirits.

The saturator is a trough built of acid-proof slabs, surrounded
by a thick lead jacket, both of which must resist, hot acid and
gases. Between the bottom and cover of the saturator there are
placed several partitions, to force the hot gases into immediate
contact with the acid. In this way the gases are quickly reduced
to ISCC, and the acid as quickly gives off its water and some
acid vapor. The acid is run off from the saturator in the con-
Gentrat«d state, at the end furthest from the fire box.

The recuperator consists of a tower, lined with a«id-proof
brick, and containing 5 horizontal plates, dividing the tower up
into 6 equal parts; each plate, however, is perforated by 100 holes
with raised edges, so that there is always a film of acid on the
plates. The holes are covered by inverted porcelain cups with
jagged edges, forming an hydraulic seal, so that ascending gases
must bubble up through the acid on the plates. The chamber
acid runs to the top plate first, and then by overflow piping to the
other lower ones, and finally to the saturator. The gases from

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196 AMERICAN SULFHURW ACID PRACTICE

the saturator are drawn up through the holes, and so through the
descending acid, by an injector, and SO* is absorbed, and a little
water given up, as in the tower of the just described heat
exchanger.

A thermometer is placed at both top and bottom of the recu-
perator, for temperature control. The lower one should stand
at SOOT., the upper a little under 200"^

After leaving the recuperator the gases pass through a coke
tower, to recover any acid spray.

Ninety-eight per cent HjSOj can be made in one operation, from
chamber acid. Gas firing is most satisfactory, and requires 8
per cent coke, on the acid concentrated. The injector requires
2 per cent steam, also figured on the concentrate.

The Benker system is a third modification of the heat ex-
changer, all being based upon the principle of the Glover Tower,
althoi^h I do not know who first applied this ^stem in this way.
The Benker system uses a cascade instead of a pan, however, for
the final heating.

Two parallel rows of duriron or tantiron plates, are arranged
in cascade form, with the flue running up between the two rows.
On account of the great fire space, and the thin film of acid,
evaporation is very rapid. The cascades are covered, and the
gases are lead to a packed tower, which removes the SO*, the
drai^ht being provided by a fan. A cooling box is necessary,
between the cascades and the tower, as the gases, owing to the
intimate contact with the heat, due to the thin film of acid, are
too hot for good working of the tower. The gas passes through
a coke tower after the tower.

The acid leaves the tower at the bottom, at a concentration of
61° to 62°B^., and a temperature of 300°F., running direct to the

Such a plant, to cost, in 1916, S3,500, will furnish 9 to 10 tons
of 92 to 93 per cent HiSOj, clear as water, in 24 hours, with a
coke (for gas) consumption of 12 to 15 per cent on the acid made.
At this concentration losses will run about 3 per cent, and higher
on 98 per cent acid.

Because of the thin film of acid on the plates, the temperature
of the acid will get higher than in either of the two previously
mentioned systems, giving this method greater capacity, but
driving off more SO*: and as the tower acid is less efficient, the
higher the SOi content of the ascending gases, the losses are consid-

^dbvGooglc

CONCENTRATION 197

erably greater. Of the three, the writer prefers the "heat
exchai^r,"

The objection to the use of direct heat in all concentrating
systems is that at the high temperatures, up to 800°C., from direct
flame there is considerable dissociation of the acid into HjO and
SOg, requiring very large spaces, usually coke boxes, to give
room and thus time to assist in reassociation. For instance, in
a Kessler system, concentrating 5 tons of 66°6£. acid per 24 hours,
a coke boic 24 ft. long, 8 ft. wide and 6 ft. high is needed: and this
coke box, with its supports, constitutes a large proportion of the
cost of plant.

The Buffalo Foxmdry and Machine Co. system gets away from
this by combining outside and direct heatii^, as follows:

The hot gases pass from the fire around the acid pot at a
temperature of approximately 800°C.; thence to a heat exchanger,
where they heat air that is under 5 lb. pressure and then pass into
the tee that is at the bottom of the concentrating tower, at a tem-
perature of approximately SOO^C, This tower, of four 2-ft. 6-in.
sections of cast iron, 36 in. in diameter inside of lining, is lined
with sheet lead and acid-resisting brick, discharges the vapors,
now well cooled down, through a 12-in. I.D. lead pipe, to a 6-ft. X
6-ft._^ X 3-ft. scrubber, where any acid carried over is condensed.
There is very little dissociation at the temperatures employed,
and this small scrubber, is ample in size.

The weak acid feed is to the heat exchanger, which is heated
by the concentrated acid, hot from the pot. From the heat
exchai^r the weak acid goes to the top of the tower, trickling
down over the tower packing meeting the ascending gase^ from
the tee, and runs off into the acid pot. The final concentration
takes place in this pot, and the overflow from it is 66°B€. and plus
acid, which is cooled for storage by heating the feed acid.

This pot, in addition to its acid feed from the tower, receives
the heated air under pressure, from the heat exchanger, near the
bottom. A small removable liner is placed to receive the im-
pingment of the air and protects the pot. A collar of high-silicon
iron, carried on lugs, and outside of which is the outlet, pre-
vents the weaker acid from reaching and attacking the pot itself.
The arrows in the sketch show the course of the acid within
the pot.

The an* introduces heat and agitation, furnishing, in effect,
"direct flame," but at a low enoi^h temperature to avoid acid

^dbvGooglc

198 AMERICAN SULPHURIC ACID PRACTICE

^dbyGoOglc

CONCENTRATION 199

disBocktioD and, of course the heat outside the pot is ^milar
to that applied to the bottom of a pan.

The vapors rising from the pot pass to one leg of the tee, the
other one of which receives the gases from the heat exchanger,
and up through the tower.

The same number of heat units is applied as sometimes give a
dissociation up to 25 per cent, at a concentration to 97.5 per cent
in a direct heated [>an system, but the distribution is better.

Tubes and small castings are made of high-silicon iroc-lat^r
ones, such as the pot and tower sections, are close grained
semi-steel.

This system uses 8 per cent to 10 per cent of coke on the acid
made depending upon the strength of the feed, and finaJ concen- '
tratioQ of the acid.

PLATmnii snLLS

The concentration of sulphuric acid in platinum dishes is still
carried on to a small extent in this country, when very pure acid
is required, as for laboratory use. But with platinum at $145
an ounce (1920), the contact process can use it more economically.

In the platinum still of today only the pan is platinum, the bell
being a lead water jacket. The size of the still depends upon the
production — roughly 75 oz. of platinum per ton of 95 per cent acid
produced per 24 hours. A dish to turn out seven tons of 95 per
cent acid daily would weigh 45 lb., be 33>^ ft. in diameter, and
cost $78,300. The rim of the dish has a groove in which the lead
bell sets loosely, condensation forming an hydraulic seal. There
is an overflow pipe from this seal, to remove the weak acid
condensed.

A lai^e pipe runs over from the top of the bell, and dips down
into a condenser, through which the vapors pass, the weak
condensate frora here and the seal being added to the feed. Two
or three stills make up a set, the acid from the first one going by
gravity to the next, for further concentration.

The still is carried upon a cast-iron frame.

Acid fed to platinum stills is first concentrated in bottom-fired
lead pans, to furnish it as pure and clean as possible. Glover
tower acid contains too much dissolved iron sulphate, which
settles out to form "crusts" in the platinum stills. The stills
are cleaned by running them as nearly dry as possible, and wash-
ing them out with hot Water or weak acid, which dissolves tiie

^dbyGoogle

200 AMERICAN SULPHURIC ACID PRACTICE

crusts. The frequency of cleaning depends entirely upon
the acid fed, it may be every day, it may be every three
months.

The acid is kept very shallow in the still, from 2 to 3 in. only,
and even comparatively small heat fluctuations cause large varia-
tions in the concentration of acid produced. Coal firing is not
sufficiently steady, so gas, usually from a producer, is used, and
gives excellent results.

The lead work on such a set of stills has to be renewed in two
years. The platinum is also slowly dissolved, losses running
from .2 to .3 g. per ton of 98 per cent acid made.

TITREOSn, CASCADE COHCENTRATORS

The continuous cascade concentrator was originated in Eng-
land, and at first consisted of four or five glass retorts arranged
in cascade over a coal- or a gas-fired furnace. Porcelain dishes
set in an acid-proof brick chamber were later substituted for
glass retorts. One of the most serious drawbacks to this system,
whether using glass or porcelain, was the heavy breakage of the
pans and the difficulty of getting high fuel efficiency; hence the
system was not generally adopted.

With the development of vitreoeil (fused silica) in 1906, there
was a more general adoption of the use of cascade systems, and
several were installed in this country. The largest is at the plant
of the Davison Chemical Co., at Baltimore, Md.

Plant for full range of concentration (50° to 66''B6.) is com-
posed of rectangular trays and circular basins. The trays mea- .
sure 24 X 12 X 6 in. and are used only in the operation of the
plant covering the rai^ from 50° to WB^. This portion of the
plant is uncovered, as the fume from acid below 60°B^. is practi-
cally acid free. The basins are used on the range 60° to 66°B6.
and may be either 12 in. or 16 in. in diameter. This portionof
the plant must be covered, as the fiunes from acid of higher
strength than 60°B£. carry sulphuric acid and it is essential
that these fumes be scrubbed of their acid content before allowing
them to pass out into the air. If higher strengths than 66°B£.
are required, the aeid from the cascade may be run directly into
iron pans, which would be so set up as to be fired from the same
firebox as the basin cascade, and the fumes from this acid re-
covered by one of the systems previously described.

^dbvGooglc

CONCENTRATION 201

In the full range plant, the tray and basin cascades are set
up so as to allow a continuous flow from one to the other and to
allow a fire from a single firebox.

There is but slight loss of acid in the concentration up to 66°B^.,
this usually amounting to about 2 per cent, based on the weight
of finished acid, and usually running in strei^h from 10° to 12°B^.
for the entire distillate. For the fuel efficiency of the cascade
concentrator, it is usual practice to concentrate over the range 60°
to 66°B^. with a fuel consumption of about 14 per cent, while
over the range 50° to 66°B6., the fuel consumption is usually
about 17 per cent. The above percent^e figures are based on
the weight of finished acid and figuring oa soft coal as a fuel
running about 13,000 B.T.TJ. Breakage in usual operation
amounts to about 5 per cent on the basins and about 1 per cent
on the trays per annum.

The cascade concentrator is appficable to the concentration
of sulphuric acid from either a brimstone or pyrites set. Sludge
acid may be recovered in the cascade plant if free from high per-
centages of mineral or organic matter, which will cause excessive
frothing due to evolution of SOj. Sludge acids carrying only
small amounts of oi^anic matter, and in which the frothing would
not be excessive, may be readily carried on in this type of plant
by using a specially designed basin.

The cascade type of concentrator, using vitreosil dishes is
especially recommended where freedom from contamination
during concentration is desired.

Vitreosil is imaffected by sulphuric acid of any strength or at
any temperature. Its melting point is about 1,750''C., although
there is slight softening around a temperature of 1,400°C. Vit-
reosil due to its extremely low coefficient of expansion .00000054
per degree centigrade, over the range 0° to 1,000°C., about }i^
that of glass, is applicable to high temperature operations.

The process of the Kalbperry Corporation, worked out from
the tower developed at the plants of the Franklin H. Kalbfieisch
Co., cannot be described, aa it is a trade secret, unpatented,
licenses being issued for its use. One important feature is that
it will give a high degree of efficiency on concentrating very
dirty acid, the concentrate being perfectly clean. Operating cost
is low, in 1916, it being 50 cts. per ton of 97 per cent acid pro-
duced. Exclusive of buildir^ and license, this tower cost, in
1916, about $4,000.

^dbvGooglc

202 AMERICAN SULPHURIC ACID PRACTICE

The license charge is a flat fe« of $3,500, in return for which the
client receives complete detail working drawings, bills of material,
flow sheets, and can obtain the service of a skilled operator for
a time to demonstrate and put the tower on a working basis.

Nitric acid alone cannot be handled in steel or iron containers,
because of its corrosive action, unless it is sufficiently dilute. As
in most nitrating operations water is liberated, and must be
cared for, sulphuric acid fulfills the double function of diluting
nitric acid to a point where it will not attack iron containers too
energetically, and of absorbing the water liberated.

It is impracticable to remove this water without separating
the two acids and reconcentrating them, and a brief description
of the most successful method of separation is in order.

Nitric acid boils at 188°F., water at 212''F., but a mixture below
91 per centacjd boils at a higher point still. 68.5 per cent HNOs
boils air251.5°f% which is the highest boiling point of nitric acid
of any concentration, and i^tric acid of any concentration, if
boiled alone, wUl approach that concentration, by the loss of
HNOj if above that concentration, of water if below 68.5 per
cent. It will then evaporate to dryness, remaining at 68.5
per cent.

So it is necessary to use something to retain the water, letting
the HNO) fumes pass to the condensers, and sulphuric acid is an
ideal substance.

A tower 21 ft. high, 3 ft. in diameter, packed with quartz, with
openings for steam. at the bottom and for the concentrating
mixture at the top, with sulphuric acid opening at the bottom and
fume (HNOj), outlet at the top, is the apparatus required.

The concentratng mixture, strong HjSO* and weak HNOj, is

J.J. ,, , , per cent HiSOi „

denved from the formula , „ „„ , — uTLrr^ = S

per cent HjSO* + per cent HNOi

H = per cent HNOj in mixture,
* . h = per cent HjSOi in mixture,

then, S = IqqZT^

S is therefore directly proportional to HiSO*, and inversely
proportional to HiO, and is a direct measure of the heat-develop-

D,pl,zsdbvG0(>glC

CONCENTRATION 203

ing capacity of the mixture: and since a definite amount of HNOi
requires a definite amount of heat to volatilize it, it must be high
for high HNOi, low for low.

With HjSO* about 84 per cent the mixture automatically falls
about right for complete denitration.

The addition of water, in the form of steam, is the one weak
point. It takes about a pound of steam to distill a pound of
HNO>.

The concentratit^ mixture is fed in at the top and tricklesdown
over the quartz, meeting the steam blowing in at the bottom.
The heat from the steam, and that from its reaction with the
HjSO*, volatihze all the HNOj, which rises, being pulled throu^
by suction.

As it approaches the top the steam begins to condense, and
havii^ greater affinity for the HiSOt than for the HNO», unites
with it, leaving the vapors practically water free. The reverse
of this process takes place in the decending mixtures, more and
more HNOt is driven oS in its downward passage, until at the
bottom there is no HNOt, the mixture being only HjSOi and
HiO. A top temperature of under 200°F, is excellent operation,
and that at the bottom should run 300 to 330°F.

The rate of feed mixture and steam must be correct, or imme-
diate trouble insues. Too httle mixture means too Uttle HjSO*
to unite with the steam, the excess of which escapes at the top,
raising the top temperature, and giving weak nitric acid. Also,
too much steam may first Uberate, and then condense and
reabsorb HNO».

If too much concentrating mixture is used, there will not be
heat enough to vaporize all the HNOt.

The weak sulphuric acid is then concentrated in lead and iron
pans and the heat exchanger, up to 66°B6.

The vapors from the concentrating towers are almost entirely
HNO,, with a little H»0, NO and NO,, and traces of Na, NjO,
and CO). All the water, and practically all the HNOt, are con-
densed, a httle HNOj going over as a spray into the absorbtion
towers, where it condenses. The NO is oxidized to NOj by the
air present, and then reacts as follows with water:
2N0i + H,0 = HNO, + HNO,

The HNOi is absorbed, and the HNOi reacts as follows:
3HN0i = 2N0 + H,0 + HNO,,

^dbvGooglc

204 AMERICAN SULPHURIC ACID PRACTICE

the NO being oxidized and the product decompoBed over and
over again, until it is practically all acid.

Spent acids from the nitration of nitro-cellulose, nitro-glycerine,
or ftimilftr substances contain so small an amount of low oxides
of Nitrogen actually in chemical combination with HiSOt, that
whilst dilution of the spent acid in the denitrating tower is neces-
sary, such dilution need not be carried to anythii^ like the extent
that is necessary when handlii^ spent acid from nitration of
hydrocarbons: and in the case of spent acid from glycerine it
may be regarded as more of a distilling process than dinitration;
the principal function of the tower in this case (nitro-glycerine)
is to remove the nitric acid as such from S/A in a most highly
concentrated state, and decompose traces of N.G. in S/A.

But "spent" from the nitration of hydrocarbons, in the manu-
facture of T.N.T., picric acid, etc., usually contains about 2 per
cent nitric acid and 4 per cent of the lower oxides : in the case of
one lai^ T.N.T. plant in Canada it was the equivalent of 7 per
cent of 100 per cent HNO» — certainly well worth recovering.

These lower oxides are in large part not free, but are combined
as definite compounds with sulpbiuic acid, and the Buffalo
Foundry & Machine Co. has worked out a plant which will
make a 98 per cent recovery at low cost.

Their process for handhng S/A from nitro-^ycerine or nitro-
cellulose is based upon careful heat control : and this includes the
superheating of the steam introduced, furnishing the amount of
heat required with the minimum of water, thus keeping down the
amount of water which must be removed by, and later from, the
sulphuric acid.

A X2-in. column of high siUcon metal If^ged with 4 in. of
asbestos, or acid proof lined C.I., 35 ft. high, is fed at the top with
heated acid, the temperature being controlled within approxi-
mately 1°C.,. automatically. This top temperature is kept under
lOO'C, the exact point depending upon local conditions (Fig. 66).

If it is at 100°C., the recovery wUl be in 93% HNO,v
If it is at 95''C., the recovery will be in 97% HNO»''

The steam, carrying 100° of super-heat, is introduced through
high-silicon iron tubes, full of small holes, 6 in. below the surface
of the liquid in the bottom. The bottom temperature is main-
. t^ned at approximately SOO'C, The amount of steam intro-
duced being kept down, the H1SO4, absolutely denitrated, runs

^dbvGooglc

CONCENTRATION

205

out 78 per ceiit-80 per cent, instead of the customary 60 per cent
that obtains from the ordinary denitrating system. At this
strength iroD paus may be used for concentrating, eliminating
lead pans entirely.

The fume leaves the tower at the top, and is carried down
through a condenser, from which the condensate Sows to a re-
ceiver. From this receiver the non-condensible gases are sucked
throt^h oxidizing towers, in series, similar in construction to the
denitrating tower, but of greater diajneter and less height. In
th^e towers good construction, low velocity, plenty of air, and

good atomizing of the absorber make the oxidation good enough
to make a 98 per cent recovery.

The absorbing liquid fed to each tower is from the base of the
succeeding tower, raised to a receiving tank above the tower, and
fed through an atomizer, with valve control. The fume is fed
at the bottom of each tower, and drawn off at the top.

Mr Authur Hough, the designer of the apparatus, stated that
the increased operating efficiency of a modem dynamite plant, of
10 tons per day capacity, using the improved acid recovery
system, amounts to many thousands of dollars per year.

Corrosive liquids, like strong mineral acids, cannot be handled
by pumps, bo the pulsometer has been developed. It is shown
in section in Fig. 64; is made of chemical stone ware, and operates

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206 AMERICAN SULPHURIC ACID PRACTICE

as follows: Up from the three openings shown lead tubes, not
over an inch and a quarter in diameter. The inlet, indicated by
"acid" comes from a raised supply, which, flowing in, of course
rises to an equal height in the two other tubes. Sufficient pres-
sure of air is then blown in at the appropriate opening, to over-
come the head of hquid. This air blows all the liquid out of the
air inlet, blows down and under the partition, and of course rises
through the hquid, up throtigh the "out" tube. It is kept from
entering the incoming tube by that tube being extended near to
the bottom of the pulsometer than the bottom of the partition.

The air, rising through the outgoing tube, carries up with it
bubbles and regular "slugs " of Uquid, these slugs being sometimes
two inches thick. If the tubes are too lai^ in diameter the slugs
will not form, the air just blowing up through, and agitating the
liquid.

The heigbth to which a Uquid can be raised by this apparattis
depends upon the hydrostatic head of the entering liquid, air
pressure, diameter of tubes, and Uquid itself— nitric acid can be
raised to four times the hydrostatic head.

BATTERY ACID

Battery acid is pure sidphuric acid, from 1.118 sp. g. to 1.125
sp. g.

As the fume from the concentration of acid from 60° to 66°B^.
runs about 1.1 sp. g., and is usuaUy clean, and of good purity, it
is an easy matter to condense this fume, and concentrate it, using
Vitreosil, as platinum is not necessary for this work.

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CHAPTER XVII
OUlXUfE OF THE CONTACT PROCESS

The^l^Contact^Proc^^ tt^M^its name from the fact upon
which~it~3^e5as — thatSOt i md O^wiircomb mno^form SOa .
"iiriflpr prjippr wiT^rfi^.in ne of temperatuTe, c oncentrat ion, aim*
purity of gas, In C^n^H^tBqaMa^ WlWlLtJviHoatiijL

Catalytic action has been known since 1834, when Mitsnerlicii
concluded that the formation of ethyl ether and water from
ethyl alcohol, in the presence of sulphuric acid did not depend
upon the dehydrating power of the acid, nor upon any inter-
mediate product being formed, but that the mere presence of
the acid facilitated the reaction, although it did not in any wi^
^nter into it.

Miteherlich suggested calling this contact action, but the
next year Berzilius called it catalysis, and the latter name,
while certainly no better nor more descriptive, is the better
known.

SCOPE

While from its great affinity for sulphur tri-oxide, water
would seem the l<^cal "absorber" in this process, thus rendering
possible by this one method the production of any and all degrees
of concentration, with practically no change of apparatus for
different concentrations, from the very weakest to 100 per cent
SOj, we are practically limited to the making of fuming acid,
because water will aoL^o.

When S0» comes into contact with water vapor a white misH^
is formed. As to its character, two opposing views are held.
One is that it is minute drops of HjSO*, the other is that in the
presence of the water vapor a double molecule, SjOi, is formed,
and that this molecule is not easily absorbed.

Whatever the actual reason for, or character of, this mist,
it resists all attempts to condense it, passing through as many
as six scrubbers, with sulphuric acid as the scrubbing agent.
It is, however, partly removed by condensation, when filtered
through fine coke or asbestos fibre. It causes trouble when
present before the conversion by ite activity as an arsenic or
207

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208

AMERICAN SUWHVRIC ACID PRACTICE

lead carrier, and in the absorber house, because it passes, iu
apparently undiminished volume, right through the absorbers
and out of the fume stacks, simply throwing away that much
goodSOs.

This mist is, of course, what limits our product.

Sulphuric acid of 98.3 per cent concentration, or more, holds
very firmly to its small percentage of water, but as concentration
drops below that point the space above the acid contains water
vapor, aod especially where the temperatures are at all high,
as in the first scrubber or absorber tower.

So we are in practice limited to sulphuric acid of not less than
98.3 per cent concentration as an absorbing medium, which in
turn means that we must make an acid of higher concentration
than that: in other words, "fuming." For this reason the
hopes of the pioneers in the industry, that this process, requiring
a smaller, more compact plant, would ultimately entirely super-
cede the older process, have not been realized. It has, however,
entirely eliminated the Starck process of distillation of Bohemian
shales, and the "cracking" of sulphuric acid into SO* and HtO,
the sulphur tri-oxide being absorbed as in our process.

TECHNOLOOT

There are three steps in the production of sulphurio acid by
the contact process.

FiQ. 67. — Layout for contact plant.

(a) Production of SOj from some sulphur bearing material,
as pyrites or brimstone. (While this process has not yet been
adapted to the utilization of metallui^ical gases, as the Anaconda
Company, for instance, is doing with the chamber process, the

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OUTLINE OF THE CONTACT PROCESS 209

Davison Chemical Co. silica gel promises great things in this
direction.)

(b) Oxidation of the SOi to SO,.

There are two processes used extensively in this country, the
Badische, the rights for which are controlled by the General
Shemical Co., and the Sehroder-Grillo, controlled by the New
Jersey Zinc Co. The methods of cooling the burner gas, the
contact mass, and the means of bringing the purified gas up to
the temperature necessary for conversion are fundamentally
different in the two processes.

But they are alike in that both require a clean gas for the
conversion of SO; into SOs, and that the same underlying
principles control their absorbtion systems.

The production of SO2 has already been covered in Chapter V,
the methods in use being common to both the chamber and
contact processes. After this the gas must be

Cooled;

Freed from dust, moisture, small quantities of SO3 formed in
the burners, and other impurities;

Freed from any mechanically carried sulphuric acid;

Filtered to remove any last traces of liquids, which at this
point is usually a sulphuric acid mist;

Heated to the conversion temperature;

Converted;

Cooled;

Absorbed ;

The acid weighed and delivered.

LuQge says, ironically, in his "Sulphuric Acid and Alkali:"
"There, are 279 sulphuric acid plants in the United States today,'
of which 44 employ chemists." Working within the compara-
tively narrow limits that we must in this process, a well equipped
laboratory is a necessity — even more than in the chamber
process — for this must be controlled all the way through by
analysis. If the acid in either the scrubbers or absorbers gets
too low in concentration we will soon be face to face with a badly
corroded system; if the absorber acid gets too high, its absorbing
properties fall off very fsist, and we loose SOj out of the stacks.
Acid is bought and sold on analysis, both as to concentration and
purity.

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210 AMERICAN SULPHURIC ACID PRACTICE

The "strength" of the gas is detennined at regular (every
two-hour) intervals, by the Reich Btarch-iodine test: it is most
important that this test be made frequently and regularly,
because in a well conducted plant the loss due to imperfect
conversion is the largest loss, and the gas strei^hs, both relative
and absolute, give us all our information upon this important
point.

The method used is that of Reich for the estimation of
sulphurous acid in gas, and while of no higher degree of accuracy
than any other color test, is sufficiently accurate to control the

process. This test, and the pyrometers for reading the converter
temperatures are our only guides, but with a properly made mass
and clean gas, are enough to insure a satisfactory conversion-

Thia is of course occasionally checked by the laboratory,
using the KjCOj method.

The early investigators worked along serenely at this process
in the belief that SOs and must be present in stoichometrical
proportions, and many believed that nitrogen had a distinctly
bad effect, aside from its diluting the gas; which means, of
course, more gas to move, heat, and cool. Those who were

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OUTLINE OF THE CONTACT PROCESS 211

Workmg to put it upon a commercial basis, and bbw in the air
the natural supply of oxygen, tried to get a burner gas that ran
20.3 per cent SOi, which left just enough oxygen to oxidize the
SOj to SOj. But the rate of conversion was low; the process
would not become a success.

In 1878 Winkler, reaUzing that reactions do not go to con-
clusion but rather to a state of equiUbrium, showed that there
must be an excess of air to get a good rate of conversion, and
while he never reached 100 per cent efficiency, he frequently was
able to get up to 99 per cent. This is high for general practice,
as the production suffers when conditions that wiU] allow so
high a conversion are maintained.

This discovery of Winkler's put the contact process upon a
commercial basis.

Suppose that the plant is burning 1,000 lb. of sulphur an hour,
with an 8 per cent entrance gas. If the SOi content is increased
to 9 per cent the amount of sulphur must be 1,130 lb. per hour
and correspondingly more acid made, without any increase of
expense except in the one item of raw material-less than 50 per
cent of the cost anyway. The same labor and overhead pay for
the increased production.

Acid production may be figured as follows:

Let a — available S0| = sulphur burned X 2.5 X per cent yield,
h ~ pounds water made per 1,000 lb. fuming acid,
X " weight of weak acid used per day,
tf = weight of fuming acid produced per day,
e = per cent strength of weak acid,
rf = per cent strength of fuming acid.

But as the SOj content of the gas goes up, above a certain
point, the rate of conversion goes down. This point is not the
same for all plants, nor is it a constant for any one plant, varying
with the contact mass and the purity of the gas, which in itself
varies with the weather, etc. Seven per cent may be taken as a
safe starting point, however, and the best working conditions for
the individual plant then determined. It is impossible to draw a
curve showing per cent conversion plotted against per cent SOs

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212 AMERICAN SULPHURIC ACID PRACTICE

in the gaa — and it is equally impossible to show, except for the
individual plant, at what point the decreased conversion ceases
to be overbalanced by the increased production.

Gases leave the converters around 3S0°C.; much too hot to
make possible any high degree of abaorbtion, which should be
conducted not far from 40''C. (KMT.). The methods of remov-
ing this heat used by the Badische and the Schroder processes
are fundamentally different — the former uses it to heat the incom-
ing gases, the latter wastes it by radiation. The net result is a
gas of the proper temperature, which is brought into intimate
contact with sulphuric acid, not less than 98.3 per cent, by towers
and tanks, such as are described in the chapter on absorbtion,
the SOa absorbed, and the remaining gases passed out through
the stack. This remainder consists of N, 0, the minor gases
contained in the air, and practically all the unconverted SOi
— this latter constituting by far the greater part of the loss in
the system. The S0» absorbed by the acid, either in the scrub-
bers or absorbers, and slowly oxidized to S0», thus becoming part
of the acid, is not only inconsiderable, but is not a loss.

The degree of concentration of the finished product must
depend upon the market to which it goes. Higher acid ia made
more slowly, as the absorbing power of any acid varies directly
as its vapor pressure, and reference to the curve trf vapor pres-
sures in Chapter XXIII will show the very rapid increase in
vapor pressure with concentration, of "fuming." While acid
of 80.5 per cent S0» will absorb practically 100 per cent of the
SOi in any gas passed through it, at 88 per cent SO, it will only
take up 23 per cent.

The freezing point must be considered very carefully in decid-
ing what concentration of acid to make. A glance of the curve
of freezing points, Chapter XXIII, shows a wide range of choice.
Eighty-four and five tenth per cent SOa will remain liquid at
the lowest temperature of any really concentrated acid. The
addition of a few per cent of nitric acid drops the freezing point
many degrees, but spoils the acid for some purposes.

COSTS

A thousand pounds of 100 per cent sulphuric acid made by the
contact process cost, in 1914, from $7.50 to S8.50. A plant to
bum 1000 lb. of brimstone an hour cost then $150,000. This

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OUTLINE OF THE CONTACT PROCESS 213

does not include power house, sulphur storage, ehops, office,
laboratory, or any auxiliary buOdings. Operating labor will
be 134 to 1}4 ^°^B hours per 1000 lb. acid. Capital expense
must of course be figured for each case.

Where depreciation leaves off and maintenance begins is a
difficult question to answer. The usual practice is to take a figure
gained by experience for depreciation, and all renewals above
that are chai^d to maintenance. Maintenance will vary so with
the management that it is not possible to give any figure that
could serve as a guide.

An industry handling corrosive material expects very rapid
depreciation. Weak sulphuric acid, and nitric acid, even in small
quantities, destroy iron and steel very rapidly. The usual
method of handling sulphuric acid, by compressed air, puts
serious strains upon parts of the apparatus. When acid mixtures
are made a great deal of heat is evolved and high temperatures
result, producing expansion that will have serious results unless
the design of the plant {)rovideB for expansion bends as liberally
as on steam lines. Expansion joints are not practicable for pipe
work to handle corrosive liquors.

Fuming sulphuric acid does not destroy cast iron by dissolving
it, but by bursting. Cracks appear, in no particular direction,
and sometimes the fitting actually suddenly explodes with a
considerable report. Examination of the broken pieces rarely
shows a Saw. Dr. Kneitsch suggests that the acid enters into
the pores of the iron and becomes vaporized, producing sufficient
pressure to burst it. At any rate, steel castings are far less
liable to rupture, and as the pores are smaller would seem to
bear out this theory.

Acid is moved by "blow cases" — horizontal air tight tanks of
stee! — with the acid outlet pipe running down almost to the bot-
tom of the tank. When air pressure is put on the tank the acid
rises in the pipe, and is thus forced around without the use of
pumps, upon which acid is very hard.

All iron gate valves should be used. The writer prefers sheet
asbestos packing, although sheet lead is widely used; this is open
tb two objections — the direct action of the acid upon lead, and
the additional corrosive effect of the electrolytic action, between
two metals, in the presence of an acid. Brass valves have a very
short life where there are any acid fumes in the air, in spite of
which they are frequently used on air lines. Any valve that ia

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214 AMERICAN SULPHURIC ACID PRACTICE

exposed to sulphuiic acid and is not frequently eased by opening
and closing will soon become useless.

The use of rising spindle valves is not to be thought of. A
valve left open by mistake can be attended with very serious
consequences, and the only safe way is to try each valve each
time : any type of valve that indicates whether it is open or shut
without actual trial tends to promote carelessness in this respect.

Shower baths, where the full stream is released by one turn of
the handle, frequently inspected, should be placed at convenient
intervals. When a man gets any acid on himself he wants water,
and he wants it in a hurry.

The first aid boxes should contain a bottle of a solution of bi-
carbonate of soda, boracic acid, an eye cup, vasoline, absorbent
cotton, and sui^cal tape. This will care for any probable injury
until medical aid can arrive.

LABOR

Such a plant requires on each shift a foreman, bimier man,
engineer, fireman, and absorber-house man, wfio also attends to
the scrubbers. Three men, a millwright, a pipe fitter, and an
electrician, can attend to all maintenance, and the outside help,
tmskilled labor, will bring in sulphur or ore, coal, pack filters,
remove ashes and cinder, help the maintenance crew, and keep
the outside clean. The flize of this crew depends upon local
conditions.

The operation of a well-designed contact plant is easy and
ple^ant, and it is always possible to get a good grade of labor.
The writer prefers Americans, and likes them young enough to
be easily trained.

In any continuous process codperation between the shifts is an
absolute essential. Eivalry is to be discouraged, as it tends to-
wards evils such as trying to bum more sulphur on one shift than
the condition of the burners warrant, leaving the following shift
to pull the plant out of the hole. Try above everything else to
make the men realize that the DAY, not the SHIFT, is the unit
of time, and that to gain an apparent temporary advantage, such
as the burning of a couple of thousand pounds more sulphur than
the shift before, and leaving the plant in such condition that the
following shift cannot come within four thousand pounds of the
required amount, is not a victory at all. Have a meeting that
all three foremen MUST attend, every week. Post your monthly

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OUTLINE OF THE CONTACT PROCESS 216

yields OQ a plant bulle.tiD board. Let all the men know what
the results are. Success of all kinds appeals to all men, and when
the figures are posted the men will forget all about the Athletics
or the White Sox, while they digest — and more important-, dis-
cuss — the comparisons. Where there are few men employed
they come to know each other well, and as friends will get along
better together than enemies, ao unpopular man has no place
in such an organization.

SUUTDOWH

Because of the corrosive effect of sulphuric acid upon iron, a
plant making or handling it must be very carefully prepared for
a shutdown, either temporary or permanent. If the work is
done as outlined below the plant will be in good condition to
start up at any time on short notice, and at small expense.

It is a good plan to start in at the burners and work through, as
in this way nothing is likely to be overlooked,

All traces of sulphur must be burned, the burners thoroughly
cleaned, and then painted, inside and out. The outlobk will
dictate the extent of repairs and replacementa of arms, etc. All
bearings must be well greased.

Get the preheaters going, and run the blowers for several hours,
thus forcing ho,t air through the converters and absorbers, which
will remove n^oet of the SO*.

All gas lines must be washed out thoroughly with a little soda
ash and water, then rinsed out with water and allowed to dry,
and then blanked off into convenient sections, the blanks being
air tight. Fittings at low points in the lines must be removed,
putting on the blanks there.

Pump tanks are filled up with soda ash and water, rinsed, and
allowed to drain. The pumps should be washed, greased, assem-
bled, and painted, and put back into the tank again.

The soda solution from the tanks should be pumped over the
towers for 2 hours, when the interior will be neutral. If the shut-
down is to be long, the packing and lining should be removed, the
inside of the tower washed, dried, and painted, and then the
tower sealed tight. ,

The acid-soaked, coke in the coke filters may disintegrate in
time — it does not always do so. The most thorough way is to
remove the coke, neutralize it with lime water, wash it, wash the
filters, paint them, and replace the same coke. Then seat up

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216 AMERICAN SULPHURIC ACID PRACTICE

the filters tight. Or the filters may be simply sealed up, taking
a chance od the coke standing up.

The blower must be washed out with soda water, dried, and
painted. All bearings must be greased. The cylinder head of
the engines must be removed, and the inside of the cylinder
greased.

The converter mass ia safer inside the converter than anywhere
else, and as there ahould be no S0» nor S0» nor moisture left
inside after the blowing out with hot air, simply blanking off the
preheaters and converters is the best thing to do.

The absorber house can be treated as was the Bcrubber house,
with the addition that the brick linings of the pump tanks should
be removed.

All acid lines should be washed out with soda, dried, and
blanked off in sections, all valves being greased.

All iron work, such as on the buildings, should be carefully
painted.

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CHAPTER XVIII
PORIFICATIOIf OF GASES

In the Contact Procesa, to get any reasooable degree of con-
vereion, the gas must be of a certain concentration, certain tem-
perature, and CLEAN.

Impurities in the gas are both mechanical and chemical, and
each class of treatment is necessary.

A distinction must be drawn between an impurity that is
merely a diluant, and one that has in it»elf a bad effect upon the
result, either from its effects upon the system or upon the contact
mass.

The first class is well represented by atmospheric nitrc^n,
present to the ejttent of 77 per cent (by weight) in the air drawn
into the system. This means that about four-fifths of the gas
handled, cooled, and heated, is worthless; but this handling is
more economical than the use of pure oxygen would be. The
nitn^en, also the minor gases of the atmosphere, have no effect
upon the contact mass nor upon the life of the system, and leave
the stacks as inert as they were upon entering the burners.

Mechanically-carried dust will finally stop the contact action
simply by covering the mass and preventing its coming in contact
with the gas. If in sufficient quantity it might clog the system.

Moisture dilutes acid, and the action of dilute acid is well
shown in Table 21, Chapter XXIII, covering the action of
sulphuric acid of various concentrations upon iron.

Sulphur as a sublimate will crystalize out somewl^re in the
system, possibly causing a complete block.

Sulphur trioxide unites with water vapor to cause the mist
spoken of in the last chapter.

Arsenic, antimony, lead, mercury, selenium, tellurium, and
silicon tetra-fluoride are all enemies of the contact process,
chemically, and the greatest of these is arsenic. They destroy
almost entirely the catalytic action of the platinum; they "poi-
son" it; and the action cannot be reobtained in any known way,
short of removing the mass, recovering the platinum in the form
of platinic chloride, and making up the mass again.
217

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218 AMERICAN SULPHURIC ACID PRACTICE

Arsenic can be partly, and some authorities say completely,
removed from the mass by passing chlorine, or, better, hydro-
chloric acid g^ through the mass, and then removing the gas by
blowing heated air through. But at ordinary convertii^ tem-
peratures part of the platinum is converted into chloride, carried
off, and deposited somewhere in the system.

Lead, mercury, and their salts form compounds, or perhaps
alloys, with platinum, which destroy the catalytic properties
of the platinum. It is theoretically, but not practically, possible
to volatilize the lead.

Nitric acid rapidly destroys iron work.

Silicon tetra-fluoride, chlorine, and hydrochloric acid stop the
catalytic action of platinum while actually present : but as soon
as the impurity has passed by the action goes on without any bad
effect. In this respect these impurities differ from arsenic and
antimony.

The gas, under suction, leaves the burners not far from 500°C.,
carrying with it all or any of the impurities mentioned above.

The order usually observed in purifying the gas is to remove
first the sulphur vapor, then dust, excess heat, SOi, arsenic and
the other contact "poisons," moisture, and the sulphuric acid
"mist." The arsenic may be partly removed, but a fuel contain-
ing much of it. will soon destroy the usefulness of the mass, so
great care must be exercised in the purchase of ores or sulphur.

Although SOj begins to form at KWC, and sulphur melts 2°
h^er, there is probably always some unbumed sulphur escaping
from the burner, due to incomplete mixing with air. The tem-
perature is high enoi^h to bum this sulphur vapor, if sufficient
oxygen is present, as is always the case after dilution with air
at the back end of the burner. This results in combustion in the
combustion chamber, and in cases where very hot burners pro-
duce large quantities of unbumed, vaporized sulphitt, even back
into the cooling due. This of course cuts down the cooling sur-
face, and throws an additional load upon the cooling system,
whatever form it may take, which follows.

Dust recovery is a mechanical problem, the dust being carried
slowly through brick dust chambers, sometimes depending solely
upon the very slowly moving gas to afford an opportunity for
the dust to settle out, and sometimes equipped with baffle plates.
These chambers have a bottom sloping to one side, and at the
bottom of the slope iron clean-out doors. One of the many

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PURIFICATION OF GASES 219

advantages of brimstone over pyrites is the absence of dust; no
provision at all need be made for it.

As the bulk of the dust carried over comes from the iron oxides
left after roasting pyrites, and as FejO* is an active catalytic
agent, particularly at the temperature of the dust flue, some SOi
is produced at this part of the line.

This dust is so fine that without some method of agglutination
it is practically impossible to smelt it. It is free enough from
sulphur to be a welcome addition to a blast furnace charge, when
properly a^lutinated — for a fair sized plant a sintering machine
of the type described in Chapter V is the best from every angle,
but briquetting will make a salable product, under most condi-

Fio. 69. — Cooling coils.

tions. Large lumps usually have "green" cores, but the dust is
roasted through and through. I speak of iron furnaces as possible
customers, but frequently the cinder is valuable for other metals,
as copper or zinc, and if the pyrite carries gold or silver there is
almost certain to be a concentration of the precious metals in
the dust chamber, due to their votility.

The brick walls of the dust chamber are very poor conductors
of heat, so there is little cooling effect felt in the chamber.

The first fundamental difference between the Badische and the
Schroder-Grillo processes is in the method of cooling the gases.

The Badische process effects the cooling by evaporating water.
A large tower, usually 8 ft. in diameter, by 12 ft. high, receives
the gas: and within that tower, where, owing to the ample space,

.Ckio'^lc

220 AMERICAN SULPHURIC ACID PRACTICE

the gaa travels slowly, SS^B^. acid trickles down over br6ken
quartz, making an intimate contact with the gaa. At this con-
centration of acid, the gaa, at its temperature of 500°C., aimply
distills off water, great clouds of steam being formed: but as there
is no decomposition of the acid, and consequently no SOj formed,
there is no mist. Because of the lai^ amount of water removed
as steam, it is constantly necessary to "butt down" this coohng
acid.

This cooling tower must not have any exposed iron work, as
acid of such low concentration attacks it very rapidly. The
towers are usually lead, and the piping and tanks lead-lined.
The pumps are hard lead, on an iron frame. Towers are some-
times built of iron, chemical brick-hned, but any leak through the
lining will soon let throi^h enough acid to attack the metal.'

Pass^e through this cooling tower lowers the temperature of
the gas to 250°C.; below the decomposition point of the real
scrubber acid. The gaa enters the second tower, which is much
smaller in diameter than the first, or cooling, tower, and rises
through 99 per cent HsS04. There is so much moisture in the
gas that the acid, in absorbing this moisture, drops 1 per cent
in its passage down the 12 ft. of the tower. This of course
necessitates constant "butting up," as 99 per cent is at the top
of the curve of vapor pressures, which corresponds almost exactly
with the absorbing properties of sulphuric acid. The gas leaving
the tower is free from moisture.

Experiments with the use of 88 per cent H2SO4 for cooling,
showed that the temperature of the entering gas was sufficient to
decompose acid of that concentration, forming a large amount
of mist. Eighty-eight per cent was chosen, as it is the lowest
concentration that is safe to apply hot to iron and steel.

The Schroeder process removes heat by radiation. The gas
is passed through a long iron flue, which is water cooled, usually
by passing it through a tank of water, and delivered to the first
scrubber at 250''C. This temperature is low enough so that the
scrubber acid is not decomposed. When running on pyrites
lead must be used in the construction of this flue, because enough
HiSOt, formed from the moisture in the air and the SOj formed
by the catalytic action of the iron oxides, is condensed, to destroy
any iron work. Only if the temperature of the gas is kept up to
400''C. is it safe to use iron, and at that temperature the scrubber
acid ia decomposed.

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PURIFICATION OF OASES ' 221

After passing the scrubber towers what little acid condensee is
cool enough and strong enough not to be harmful to cast iron.

In the writer's experience it has been necessary to keep the
temperature of the acid in the first scrubber down to 9^F. to
prevent dissociation of acid, and consequent formation of mist.
twenty cubic feet of 98 per cent acid, at 95°F., will cool a
thousand feet of gas at 450° to SWC, to below the dissocia-
tion temperature, and at the same time dry it thoroi^hly, leaving
it entirely free from moisture or miet.

It is difficult to give any figures on the amount of water neces-
sary to cool the acid, owii^ to local conditions. Water in the
South, particularly if from shallow rivers or ponds, gets warm
enoi^h in summer to seriously complicate the cooling.

It may be assumed that no fuel having over a trace arsenic
would ever be used for the contact process, so that no company
that makes lower concentration acid by diluting fuming with
water need ever fear getting any arsenic into its mass, which
should last indefinitely. So much chamber acid carries arsenic
in relatively lai^ quantities that the plant that depends upon
purchased acid for the weak acid it requires must exercise the
greatest and most constant care. If the gas is properly cooled,
so that no mist is formed, there is no need for concern, even with
a considerable amount of arsenic in the scrubber acid : but if any
mist forms, and there is over 0.02 per cent arsenic in the scrubber
acid, trouble may be looked for with confidence, as that mist is
the arsenic carrier par excellence, and it will go through any kind
of filter or scrubber that the writer has ever seen.

Too much stress cannot be laid upon proper cooling, for only
by keeping the temperature down can this mist be prevented.
Its formation must be prevented, because after once forming we
do not know how to remove it from the gas.

To prevent spashing of acid, and the consequent spray that
the draught will carry over, two devises are in use. The acid
may be introduced onto a cast iron plate, through a funnel.
The plate, covering the entire inside diameter of the tower, is as
shown in Fig. 79. Normally the acid goes through the many
^-in. holes onto the filler inside the tower: the gas rises through
the 2-in. holes, which are guarded against the entry of acid by
the surrounding cast iron nipples, and thus the gas gets into the
space above the plate with a minimum of splashing. When the
small holes become do^^ed, as sometimes happens, the acid rises

^dbvGooglc

222 AMERICAN SULPHURIC ACID PRACTICE '

high enough upon the plate to relieve itaelf through the large
holes.

The other method is to pump the acid to a reservoir, from
which it floTTS gently through porcelaiu tubes to the surface (A
the filler.

The acid must be delivered at the top of the tower, as it flows
down by gravity, but the gas may pass in either direction that
plant convenience dictates.

The coohng coils, filled by gravity from the tower are cast
iron pipe, usually 6 in., laid horizontally. The a«id is admitted
into the lower section of pipe, so that water dropping first upon
the top pipe and then on to the tower one will reach the coolest
acid first, and reserve its greatest cooling action, by evaporation,
for the hot acid at the bottom.

Figure 7S, in Chapter XIX, showii^ an absorber tower, tank,
and equipment, illustrates equally well an ideal scrubber tower.

As the hot gasses direct from the burner have greater volume
than those later on, it is customary to use a lai^er tower, or two
small ones in parallel, for the first tower.

The amount of moisture taken out of the air drawn through it
by the scrubber s^tem is large. I have seen a plant handhng
150,000 cu. ft. air per hour remove 3,500 lbs. of water, in 24 hours,
on adampdayin winter from the air, and over 6,000 lbs. insummer.

The unit of a scrubber system is a tower, set of water cooled
cooling pipes, and a tank with a turbine pump. For our ideal
plant a tank holding 100,000 lbs. of acid is a good size. This
tank should be horizontal, 6 ft. X 24 ft. of ^-in. boiler plate,
unUned, with a cleanout hole in the bottom, turbine pump of 20
cu. ft. a minute capacity, set through a manhole in the top, man-
hole for cleaning out, proper connections to receive and diachai^e
acid, and a gauge glass in the end. The acid is pumped to the
top of the tower, and is spread by a distributer, so that in its
passage down throi^ the tower it comes into very intimate
contact with the gas, flows from the towers to the cooleiB by
gravity, and thence back to the tank.

Do not depend upon the gai^e glass reading for accurate in-
formation about the quantity of acid in the tank. The acid that
passes up into the gauge glass when the tank is filled is practically
withdrawn from circulation, and retains its original specific
gravity. So as that in the tank becomes diluted by scrubbing,
or Btroi^er by absorbing, that in the glass will float upon, or, sink

^dbvGooglc

PURIFICATION OF GASES 223

into, thia acid of different Btrength, and will not stand at the level
of that inside. The writer has found 5 in. difference between a
gauge glass and a stick measurement.

Each tank should have a 1-in. vent pipe, leading outside the
buildii^, to relieve the pressure caused by incomii^ acid. For
sampling, a 2)^-in. gate valve, or a 2^-in. nipple and cap should
be set in the top. Do not uae a tapped hole and pli^, as plugs
stick badly, roi^h handling with a wrench makes them loose
their comers quickly, and then they are very hard to get out. A
cap on a nipple is much better, and a gate valve best of all.

Types of pumps are discussed in Chapter XIX.

The towers of different designers vary greatly, although all have
the same function : to bring into intimate contact the scrubber
acid and the gas. Twelve feet high seems to be the only com-
mon dimension. The internal diameter varies from 3 ft. 6 in.
to 8 ft., they may be lined with lead or acid-resisting brick, set
in Pecora or other acid-resisting cement, and filled with broken
quartz, chemical-ware rings, or cast-iron filling pieces.

The cooler pipes, always warm, afford excellent opportunities
for the growth of any water plants, particularly those of a slimy
nature, and slime and mud collect upon them very quickly.
Any fore^ matter acte as an insulator, and should be removed
at once. Rubbing with a piece of burlap is the best way to
clean these pipes, although a broom will do a fine job.

The current of gas carries some acid aloi^ with it mechani-
cally, and some method of mechanical condensation and filtera-
tion is necessary to remove it. A large tower filled with pea
coke, followed by another filled with buckwheat size, each
tower having a trapped drain in the bottom, will remove most
c^ the spray, and a good part of the mist that forms. These
towers ^ould be large enough (not under 10 ft. in diameter) to
permit a slow movement of the gas, and should have a depth
of at least 10 ft. of coke, with ample space at the top and bottom,
for entrance and exit of gas. In practice about as many plants
take the gas in at the top and release it at the bottom as do it the
other way. The writer prefers to remove the gas from the top,
believing that in the open space at the bottom, with acid dripping
from the coke above, some new spray is formed, which is carried
along by the suction. When a tower is newly packed there is
undoubtedly some dust taken along from the top, but the coke
soon becomes damp enough to prevent this.

iiz^dbvCooglc

'224 AMERICAN SULPHURIC ACID PRACTICE

The quantity of spray caught will vary, but will be Bu£Bcient
to make the installation of a small blow case to save the drip well
worth while. It should be so piped that all the coke towers, or
"spray catchers," run into it, and can run to a storage tank.

While much mist is condensed by the coke, enough is still
left in the gas to make further filtration necessary. While
cotton is occasionally recommended as a filtering medium, I
have never known it to last a week. The condensed acid is
strong enough to carbonize the cotton rapidly, even in the cold,
causing it to turn to a black dust — of course worthless
for filtering.

So asbestos fibre has come to be the one material used. It
is picked over, usually by hand, to break up the lumps it packs
into during handling and storage, and is then blown by a light
current of air, which "fluffs" it. The apparatus required is a
covered wooden trough, with air, controlled, by a haad valve,
admitted at one end through a 3^-iQ. pipe. The fibre is blown
down the trough to a lai^ box, with one side made of burlap,
through which the air escapes. The longest staple asbestos
possible should be procured. Grade 201A of the H. W. Johns
Manville Co. is an excellent product. On account of the light-
ness of the asbestos fibre it is necessary to bring the gas in at the
top, driving it down through the filter: otherwise the strength
of the draught will carry it away. A good form of filter is a
set of cylindrical tanks, three or four in number, 6 ft. in diameter
by 4 ft. high, in parallel, with a screen of %-m. boiler plate,
punched with ^-in. holes, set on lugs 12 in. from the bottom.
There are usually two sets of these filters, in series.

The fibre is spread smoothly over this screen, to a depth of
15 in.; 7,5 sq. ft. filtering surface, per hundred pounds of sulphur
burned per hour, in each series will do good work, and will require
a little over a pound d fibre per square foot every time they ,
are packed.

These filters work better when moist, so moisture in itself is
harmless. But where there is arsenic in the mist the filtSfS'jK,^
rapidly become impregnated with it and must be clean^ to
prevent the arsenic from reaching the converter mass. When
the filters are drained constantly there is less necessity for
frequent cleaning than where the condensate is allowed to
accumulate in the bottom, to be removed at intervals.

Cleaning simply consists in removing the manhole cover and

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PURIFICATION OF GASES

225

taking out the old asbestos with a fork, then spreading the new.
The blower must be stopped while the work is under way.
Only experience can tell how often it is necessary to repack
filters — one plant may need it every 3 weeks, another every
6 months. When the asbestos is so^y it is time to repack it,
but being damp will do no harm at all.

AI! attempts to regenerate the asbestos have failed, not that
it is hard to wash out the acid, but that wet asbestos packs into a
cement.

Unslacked lime, nut or pea size, has been tried as a filtering
material, and does its work well, but is hard to keep open, as the
calcium sulphate formed crumbles, and the dust packs. Also,
the condensed acid is lost.

The Tetelow Chemical Co. uses, on gases that contain a little
chlorine, a weak mOk of lime wash, where first a bisulphite is
formed with the SOi, which reacts with and retains the chlorine.

The Tyndall test shows any mist in the gas that is invisible to
the naked eye. An apparatus, shown in Fig. 70, consists of C,
a small flask with a rubber stopper, through which two glass
tubes pass, and A, a lens, the focus of which is just beyond the
flask: all enclosed in a wooden box, painted black inside. The
flask is filled with the gas to be tested, either by direct pressure,
or, if on the suction end of the system, by an aspirator bottle,
the ends of the tubes corked, the flask replaced in the box, and
a beam of sunlight directed through the gas in the flask, via
the lens. If there is any mist it will show in the path of the
beam as the motes dance in a beam of sunhght in the old dusty

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226 AMERICAN SULPHURIC ACID PRACTICE

attic. But if the gas is dty a disk of light shows on the side of
the flask where it passes through the glass, and that is all.

If, through faulty design, it b impossible to prevent the
formation of this mist, this arsenic carrier, the greatest efforts
must be made to remove as much of it as possible, because
arsenic is more hable to get into the system via the scrubber
acid than through the fuel burned, and if there is no mist this
arsenic will not be taken from the acid, ultimately getting to
the converter mass.

Fia. 71. — Roots blower.

Without proper provision for cooling mist will form. One
of the plants built in a hurry to respond to the demand for
fuming acid at the beginning of the European War, in 1915,
was not provided with sufficient cooling area, and although
operated with great skill, and giving in all respects but this very
satisfactory results, showed all the bad effects of insufficient
cooling — the filters had to be cleaned very frequently, arsenic
went through to the converter mass, and the exit stacks were
always fogging.

The blower is placed at the end of the scrubber system, so
that the maximum pressure may be available to force the gas

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PURIFICATION OF GASES 227

through the converter mass. This blower is always a valveless,
direct-acting blower, of the Roots type. These engines are so
well known that any extended description is unnecessary.
They may be built either direct connected to a steam eu^ne,
or to be belted to shafting or a motor, and act over a very wide
range of speeds very efficiently. The usual guarantee is that the
slip will not exceed 15 per cent. As the rotors have K2S-iii-
clearance, and no sliding surfaces, these engines have a very
long life. The small clearance is not sufficient to cause much
slip. If a sudden stop in the suction line occurs the partial
vacuum formed will cause the blower to reverse itself for several
. revolutions, against the steam pressure.

If arranged this way, the pressure at the engine is almost twice
the suction, mainly because of the resistence offered by the
converter mass: but also because there are usually more showers
in the absorber house than in the scrubber house. Our ideal
unit will show, for normal runniii^, about 12 in. of water suction
at the blowers.

^dbvGoogle

CHAPTER XIX
CONVERTING

The second step ia making Sulphuric Acid by the Contact
Proceaa id the conversion of SOt to SOj, by bringing it into
intimate contact, at a suitable temperature with finely divided
platinum.

A mixture of 80» with air will slowly oxidize to S0», but so
slowly that this action is valueless from a commercial stand-
point. Many substances have a catalytic action upon this
chemical reaction, that of FeiOg and FetO*, among the common
substances, being very marked. All the metals of the platinum
group posses this activity, but none other to the extent that
platinum itself, in a finely divided state, does.

The catalyzer itself is entirely unacted upon, and its simple
presence is oU that is necessary. The effect is without doubt
adsorbtion, or condensation of gas upon the surface of the
catalyzer. When glass is wet by water the water is not absorbed
— it is held however by the force we call adsorbtion — and some
solids have this effect upon some gases. It is probable that
there is a concentration of gas in a condition to react, and by
the law of Mass Action the reaction must be hastened. Reason-
ing along these lines, the plan of the Davison Chemical Co. to
use liquid SOi, recovered from fume stacks by their new silica
gel process, should give high yields and capacity, because of the
"strong" gaa used.

Six factors enter into the conversion; catalytic agent, which
is always finely divided platinum; sulphur dioxide; air, supplying
oxygen; temperature; time, and impurities.

The Badische process, worked out mainly by Rudolf Knietsch,
uses platinized asbestos as a catalizer, a solution of platinio
chloride being sprayed over the asbestos fibre, which is then put
into the converters and dried. The mass then looks Uke wool
died a lemon yellow, is soft and fluffy, and is not subjected to
any fumacing at all. It dries out very rapidly in the converter,
the chlorine of the platinic chloride is driven off, and metallic
platinum left in an extreme state of division.

The Badische conversioB unit is made up of a preheater.used

^dbvGooglc

CONVERTING 229

for starting up and in emergencies, two converters and three
transfere. The drawii^ shows the general arrangement of the
converter — the gas enters at I, filling the space A, goes up the
closed bottom tubes B, and down through C containing the
converter mass, into D, and through the outlet to the absorb-
tion system. C ia made about three inches in diameter, to
provide for uniform cooling of the mass by the incoming stream
of cold SOi and air. It is this form of converter that gives
the Knietsch process its economy of fuel, and is patented in this
country under United States patents 652,119, 688,020, and

823,472, dated respectively, June 19, 1900, December 3, 1901,
and June 12, 1906. Of these 652,119 is the fundamental one,
the others being modiEcations thereof. See fig. 70.

The Schroeder-Grillo process uses platinum deposited upon
m^nesium sulphate for the mass.

Pure magnesium sulphate, with the. water of crystalization
driven off, is coated, not impregnated, with platinum to the
extent of 0,3 per cent of its weight. This gives a very large
surface, as the salt in this state is very porous, and the platinum
is spread out thin over a wide area. The magnesium sulphate
is spread out upon a flat surface, 6 in. thick, and the platinic
chloride is sprayed on through glass nozzles connected by rubber
tubing to the bottles of solution, the bottles being suppUed with
air under pressure. At intervals the mass* is turned over with

^dbvGooglc

230 AMERICAN SULPHURIC ACID PRACTICE

wooden ehovela, aa it is of the utmost importaJice to get the
platimim oa evenly.

The spriyred mass is then put into the furnace previously
used to dry the magneeium sulphate, and heated to redness for
half an hour. By this time all the chlorine has been driven
off, leaving the platinum in an extreme state of division.

The mass is then allowed to cool and is put into tight cans,
weighed, and put away until needed, as it will keep indefiimtely.

Usual practice is 4.5 per cent of platinum on the weight of SOi
per hour. This will give a 97 per cent conversion with good
handling. A smaller proportion of platinum will give a lower
conversion, and in each case it must be determined whether it is
better to have a smaller investment, and loose more SOt out of
the stacks. For instance, ^ the platinum investment will about
double the stock loss — 2)^ per cent platinum on the hourly SOi
will give about 953^ per cent conversion, other conditions being
equal to the 97 per cent conversion with 5 per cent platinum.

The sulphur dioxide and air are intimately mixed in their
passage through the burners, scrubbers, and blowing engines,
and are freed from impurities as much as possible, so that the
gas entering the converters contains, SOi and as active agents,
and the nitrogen and other inert gases of the air as diluanta.

Dr. C. L. Reese has proved experimentally that moisture
present will not affect the mass, but as of course acid would be
formed the plant would suffer. COi is harmless. The worst
of the impurities liable to be encountered is arsenic, which
"poisons" the mass by forming a glassy coatii^ of a salt of
arsenic and platinum, as little as 2 per cent of As on the weight
of platinum being sufficient to render the mass inert. Dr.
C. L, B«ese says that As can be removed from the mass by
passii^ HCl in with the gas mixture, but my advise is not to
let any get into the mass — the action seems to be that the As
coatii^ simply encloses the platinum so that it cannot come
into contact with the gas mixture.

Dust of all kinds has a purely mechameal coverii^; action,
which is just as effective as the arsenic in preventing contact,

HtSOt "gums up" the mass, making it difficult to penetrate.

TEMPERATURE

2S0, + 0, = 2{80» + 40250 B.T.U.), on the authority oS

Prof. J. W. Richards. The reaction proceeds slowly at low

^d by Google

CONVERTING

231

temperatures, really beginning at about 200''C., and continuing
to increase in velocity with rising temperature. However,
the reaction is reversible and above 420''C., decomposition of
SOs sets in, becoming more marked with further increase of
temperature, until at 1,000°C. SOj cannot exist, in the presence
of the catalizer.

The best temperature to carry is entirely dependent upon the
condition of the mass and the "strength" of the entering gas,

and it will vary with variations in these two, and therefore is
a purely local condition. From 375°C. to 425°C. is about right.

The enterii^ gasea must be heated sufficiently to start the
reaction, as they have been well cooled by the scrubbing, and
the converted SO3 must be cooled before absorbtion.

Here lies the fundamental difference between the Badische
and the Schroeder-Grillo processes — the former makes its
converber into a heat exchanger, and heats its entering gases by
taking the excess heat from its SOj, where the latter uses fuel
to heat up, and then wastes the heat generated in the converter.

The Badische conversion unit has been described. The

ncizoJ^vCoO^^lc

232 AMERICAN SULPHURIC ACID PRACTICE

Schroeder-Grillo unit is a vertical cylinder of cast iron, 5 to 8 ft.
in diameter, built up in 18 in. to 2 ft, sections, flanged, joints
packed with asbestos wicking, all held together by stay bolts
from the top to the bottom flanges. Each section contains a
perforated cast iron floor, upon which hes ^^-in. mesh iron wire
screen, and upon this the mass. There are usually 5 sections
to a converter, and 4 converters to a unit. For a converter
7 ft. outside diameter the normal amount of mass is 7500 lbs.
evenly divided among the 5 trays, and carrying 0.3 per cent Pt.
That means about $190,000 worth of platinum at today's {No-
vember, 1919) prices, of $145 per ounce. Such a plant will burn
1000 lbs. of sulphur an hour.

During the war, at one large plant, the quantity of mass was
cut in half, concentration (per cent of Pt) remaining the same.
This dropped the conversion from 97 per cent to between 94
per cent and 95 per cent — this brings up the question of the bal-
ance between stack losses, which represent raw material, power,
and labor, and the investment in platinum. This will be con-
sidered in the chapter on accounting.

Good recording pyrometers are absolutely necessary for con-
ducting this operation. Leeds & Northrup, Philadelphia;
Industrial Instrument Co., Foxboro, Mass.; and the Taylor
Instrument Co., Rochester, N. Y., can be depended upon to
furnish good ones.

The Schroeder-Grillo preheater is a brick box, full of 6-in.

^dbvGooglc

CONVERTING 233

boiler tube pipe, vertically set, flanged, connected by return
bends, through which the gas passes to the converters, all heated
by coal or oil fireB, flue gases passing around the outside of the
pipes. For a plant burning 1,000 lb. sulphur per hour, 4 con-
verters, each 5 sections high, will be used, and the preheater to
each one will contain 250 ft. of 6-in. pipe, plus the return bends.
The pipe is set vertically to prevent flue dust from settling on it,
insulating the gas inside. Such a plant will use 6 tons of steam

coal daily in summer, 7 to 8 in winter. On 1919 coal prices, that
is, over 50 cts. per 1,000 lb., 100 per cent acid produced — well
worth saving. But even with this high fuel cost, the writer
prefers this system to that of the Badische because of its
simpler operation.

The gases from the Schroeder-Grillo converters, consisting of
N, SOa, unconverted SOj, and impurities (mighty few of these
however) are at a temperature around 350''C., much too hot for

^dbvGooglc

234 AMERICAN SULPHURIC ACID PRACTICE

absorption; so they are cooled by passing through 250 ft. of cast
iron pipe, set horizontally, between headers, and arranged to
have a spray of water drip over them in warm weather. These
pipes must be equipped with drain cocks, because upon starting
up there is always some moisture in the mass, which will come
from the hot converters as sidphuric acid vapor, and will condense
here, effectually trapping the sj-stem if not removed.

Time of contact is controlled by the blowing engine, and will
vary so with the plant that no rule can be laid down. For the

Fio. re.

size of blowing engine figure the volume of gas necessary to
provide a 7 per cent gas for the sulphur to be burned, at 80°F.

The only pressure is that of the blowing engines, sufficient to
overcome the friction of the system, and keep the current of gas
moving.

The early experimenters thought a stoicometric mixture of
SOa and necessary to get a good conversion, but were never
able to convert over 77 per cent of their SOi, and then only imder
laboratory conditions. The production of pure oxygen was
expensive, and later proved a needless expense, as air was shown
to give excellent results, the nitrogen having no deleterious effect
whatever,

^dbvGooglc

CONVERTING 235

Ferric oxide comes to it« maximum as a catalytic agent at
STS'C, at a point where the dissociation of S0» ia very marked,
which ehminates it as a possible contestant with platinum.

It is necessary to use a catalytic agent that will do maximum
work at or under 450°C., and platinum is the only one known so
- far.

Some experimental work along the lines of colloidal precipita-
tion of the platiniun upon the mass have been done, notably by
Botho Schwerin, in U. S. patent 1,098,176, owned by the Chemical
Foundation, 81 Fulton St., New York. In view of the fact that
the investment is the greatest part of the cost of contact acid,
anything to increase the surface of platinum exposed will pay
well, and should be followed up.

Kurt Albert, in U. S. patent 1,018,402, also owned by the Chemi-
cal foundation, claims to have reached a 94 per cent yield with
iron and strontium oxides as a catalyzer. This with the Davison
adsorption system on the exit stacks to prevent the loss of uncon-
verted SOi offers a fertile field for research.

Dr. Knietsch formulated the law of mass action as follows :

SO, iooVko^
SO, ~ 1 + Vko;

when K = concentration in volume per cent. This shows the
conversion we may obtain, but nothing about velocity of reaction
or proper temperature.

Each plant rnvsi develop its own suitable working conditiona,
and adhere as closely as possible to them. If the operator starts
out to make a 7 per cent "gas" — 7 per cent by volume — he will
not be far wrong.

Although it is necessary to dry the gas as much as possible, an
absolutely dry gas will stop the reaction. It is not possible to
remove the last traces of moisture with our scrubbing systems, but
they remove all that might be dangerous, as an excess would be.

Uniformity of temperature is of the utmost importance — ^tbe
control should be within S'C. If the mass is injured in' any way
it is likely to require a higher temperature to get conversion, and
that is about the only way there is of detecting mass " poisoning. "

GAS CONTROL

The Reich test for SO, in gas, with the pyrometer readings, is
our guide. This test is conducted as described in Chapter XIV.

iiz^dbvCooglc

236 AMERICAN SULPHURIC ACID PRACTICE

The laboratory should occasionally cheek this by the KtCO«.
test.

This gas test should be made not less often than every 2 hours,
on both the entrance and exit gases. Be sure the gas passes
through the apparatus for a minute before each test, to make
certain that it is the gas of the present, not of 2 hours ago, that
is being tested. Quarter inch pipes, kd off of the gas mains,
and controlled by valves, bring the gas to the test.

In figuring conversion after the test, it must be borne in mind
that the volume of gas is decreased by the amount of oxygen the
SOi has taken in its oxidation.

Slide bule for SOa to SOi conversion*
In general, if an equation can be written in the form
f(x) =f(y),f(z)
a slide rule may be so constructed that the value of any variable
can be found if the others are known. As a simple illustration,
consider the computation of conversion in the contact process for
the manufacture of sulphuric acid.
Let a = per cent by volume of SOi in entrance gas,
b = per cent by volume of SOi in exit gas,
c = per cent conversion = per cent SOj converted
toSOa-
These quantities are related by the equation
10,000 (a - b)

°" 10O.-?|>

This form of equation is not suitable for the construction of
a slide rule, but it may be rewritten as

100 3\ . /lOO 3\

/lOO _ 3\ _ /:
la 2) '■ \

SO; In

0..1 '^.^vT.

ib' ' ' Is'o' ' ' Ibb"

ft CBnwnlon

SOi — S0» slide rule set, 10 per cent entrance, 0.7 per cent exit
= 94 per cent conversion.

> From Chemical and Metallurgical Enffijuerinf, September 15, 1919.

iiz^dbvCoOglc

CONVERTING 237

The Blide rule scales for the solution of this equation are in the
accompanying figure. The upper scale is laid off proportionally
to \ag ( nj , the slide to log (-r- — 5 1 , and the lower scale

to log 11 — Tj^l • These scales are laid off from right to left bo
that the marked values a, b, c will increaxe from left to right,
as this is the most natural method of reading scales. The proper
values of SOt in burner gas and exit gas are set together, and the
conversion read opposite the arrow. The zero point {i.e., 1(^)
of the lower scale is moved to the left relative to the upper one,
to make the rule more compact, and the arrow displaced the same
distance to give the correct reading.

^dbvGooglc

CHAPTER XX
ABSOKBTION

As stated briefly in Chf^iter XII, water is not a satisfactory
absorbing agent for 80a, and as the water in diluted HiSO* acte
like water, it is necessaiy to use strong (not less than 98.3 per
cent) sulphuric acid. You might say that the gas is scrubbed
with the absorbii^ medium, for the apparatus used is a gas
scrubber of some type, the object beii^ to get as intimate an
association as possible of the gas and the acid.

If sulphuric acid of less than 98.3 per cent is heated in an open
pan at 350°C. water will distill off until this "critical" point,
i.e., 98.3 per cent is reached — if the original acid is of a higher
concentration than the "critical" strength, S0» will come off
until the strength drops to 98.3 per cent — after it has reached
that point however it comes over at that strength until the end.
Of course pan concentration cannot go to this point profitably,
because the losses by entrainment increase very fast with the
strength of the pan acid.

At 98.3 per cent and lOO^C. sulphuric acid has a minimum
vapor pressure in vacuo, and at this point its Bp.g. is the highest.
At this point absorbtion of SOg is practically 100 per cent.

The heat of combination of SOi and HiO is 180,540 B.T.U.,
according to Richard's "Metallurgical Calculations," which
runs the temperature in the absorbing apparatus up to the point
where cooling is always necessary. This is usually done by
circulating the absorbing acid, keeping a large volume in service,
and coohng the storage tank and circulating system with water.
The first tower will require, for a unit plant of 1000 lbs. S per
hour, not less than 250 ft. d cooling pipe, aside from necessary
connections.

As fuming acid is very hard on iron or steel, tanks uid towers
must be carefully lined with an acid-resisting material. The
writer does not think much of any of the asphalt bitumens that
are used for this purpose, prefering a good acid-proof tile, well
laid in acid-proof cement. The cost of towers thus protected
is high, but worth that cost.

^dbvGooglc

ABSORBTION 239

Aa the strength of the acid in the tower increases, so does the
vapor tension, and the absorbing qualities fall : also the tempera-
ture being high works against good absorbtion, so it is usual
to arrange 6 towers in series, fresh acid being added in the last
one, at intervals, the towers nearer the first one being replenished
from those behind, and the acid made being drawn from No. 1.
The temperature in the later towers is progressively lower than

■^r

Ico

I \

jj3a

■^

r»

> «

r-«

r-A,

PartiiJ prmuTa Fnrtial prnBure dus in SOi

Fia. 77.

in the first, and as the strength also gets nearer and nearer to
that point where the vapor tension is negligable, the percentage
absorbtion is increasingly great, and if the acid in all towers is
above the dead line of 98.3 per cent, so that no "mist" tB formed,
the absorbtion will be practically complete.

The use to which the acid is to be put of course determines the
strength to be made, but the season of the year has an influence
also: and a look at the freezing curve, in Chapter XXIII, will

iiz^dbvCoOglc

240

AMERICAN SULPHURIC ACID PRACTICE

show why. Acid of about 103.6 per cent with a freezing point
of 10°F. is a good winter strength to aim at.

While anal^iis is necessary to determine the strength of acid
in the variods toweis, experience will soon teach the operator
how often to sample: and while this system is very flexible, and
will stand a lot of bad handling, it is easy to handle welL

If the Feld washer, made by the Bartlett-Hayward Co., of
Baltimore, can be designed to stand fuming acid it will be an
ideal piece of apparatus, and as the rotating part is hung from
an overhead bearing, out of the acid, it seems reasonable to hope
that it will. Of course there is bound to be some vibration,
which in time is sure to open up the joints in the acid lining.

Coaliivi 0>il -e Ptpffj

It has been proposed to build the tower of stone-ware, but this
seems impracticable to the writer, because of the h^h tempera-
tures in the first toweis, which would be reasonably sure to
crack the stone-ware if a draft of cold aii struck the outside.

Apparatus of the type shown in the cut on this page
is very satisfactory. The pump is a centrifugal, made by
G. C. Bretting, Ashland, Wis., belt driven, 1700 R.P.M., deliver-
i:^ 40 cu.ft. of acid a minute, and requiring 7^ H.P. It is
built with a manhole cover, so can be hoisted into place by a
chain block on a mono-rail, and fastened with set screws. As the
pump is about the only part of the system that is likely to get out
of order, this ease in changing is very important. The pump
made by the Kutztown Foundry & Machine Co., Kutztown, Pa.,
is also a good one.

^dbvGooglc

ABSORBTION

241

Failures of the wrought iron piping come apparently not from
corrosion, but from bursting. These bursts are alwaj-s longi-
tudinal, and can be welded. The writer has seen many bursts,
but never one on a welded pipe, either at the weld or anywhere
else in that vicinity, which seems
to show that when the internal
strains have been relieved by the
springing open of the pipe in the
first burst, the acid alone cannot
burst it.

Failure to provide for expansion
in pipes handUng the hot acid
from the tanks is sure to result in
broken fittings, as the acid is so hot
that expansion is considerable.

There are more likely to be tower.

"spills" of acid in this department than in any other, so the floor
must be one that will stand such acid. Common red brick, laid
dry in sand, makes a splendid floor.

The gas coming from the converters is hot. The heat is used
in the Badische system to heat up the incoming gases, but in

Fio. 79. — Distributor

the Schroeder-Grillo process the heat must be removed by some
other means. The simplest means is a cast iron or steel header,
with 6-in. wrought-iron pipe running to another header. For our
standard unit 450 ft. of 6-in. pipe will do the work, without

^dbvGooglc

242 AMERICAN SULPHURIC ACID PRACTICE

help in wtater, but will require the help of a spray of water in the
summer.

Drainage must be allowed for in the bottom of the cooler, as
no matter how well the mass is made up the magnesium sulphate
is sure to contain some moisture, which of course will form acid
and condense in the cooler. This blocks the system.

The "absorber man" has little to do but sample and shift ias
acid, as it increases in strength, and could easily handle four
^}Borber units; so where the production is sufficient it is custom-
ary to house two units in the same building, in parallel. Weak
acid is usually received, and strong delivered, at this end.

^dbvGooglc

CHAPTER XXI

CONVERTER MASS

The most costly part of a contact plant is the platinum, and
every effort is being made to find a suitable substitute, and failing
that, to reduce the amount necessary. As the catalytic action is
undoubtedly a surface condensation, the logical thing to do is to
spread the platinum out as thin aa possible. Much research
work has been done along these lines.

As with varying conditions it is not possible to use any stand-
ard plant, a simple laboratory converter is useful, and will be
here described.

Five (6) 2-in. C.I. tees, connected by close nipples, and a
2 X 6-in. fiange at the outlet, on another close nipple, the whole
stood upright, and a circle of 10 mesh iron wire screen resting

243

^dbvGooglc

244 AMERICAN SULPHURIC ACID PRACTICE

in the bottom of each tee, Qpon the upper end oE the close nipple.
The maas is put in through the outlet, held from nmning out by
a piece of screen sprung in, the companion flange, in which there is
B%X 2-in. bushii^, put on, the thermometer put in the bushing,
connected up with the gas supply at the lower end, and started off.
Plastic asbestos is the beat covering, and such a system must
be covered, as the area is large in proportion to the volume.
(Fig. 81.)

Sodium free magnesium sulphate is melted in its water of
crystalization (it contains 52 per cent) in a crucible, stirring con-
tinuously after it melts, both to prevent its sticking and to make
it porous — the porosity depends directly upon the amount of
stirring. In about 35 min. the mass will be free from water and
solidifies, when it is heated to a dull red, and poured out to cool.
After cooling it is broken to pass a ^-in. screen, but to stay on a
3^-in. one. The platinic chloride is then sprayed on with a glass
nozzle, from a solution made up as later described in this chapter,
the mass put back in the furnace in the crucible and heated to a
dull red, when the chloride is reduced to metaUic platinum and the
mass turns black. It is then ready for use.

Such a plant will enable the research laboratory to work out
any. problems in connection with the gas to be used.

PREPARATION OF MASS

Platinum has increased in price within the last e^ht years, up
to 1920, from $12 to $145 a Troy ounce, and as the quantity
necessary to get a 97 per cent conversion, in a plant burning 12
tons of sulphur a d^ of 24 hours, is about 1,300 oz. — $188,500
— every effort must be made to spread it out very thin.

The logical thing to do is to deposit it upon a base of such
uneven surface that a very large area is exposed in a relatively
small volume. This base must also be unaffected by the gases
passing through, by the temperature, and by the chemicals used
in depositing the platinum. It should also be of such a nature
that the platinum can be easily recovered.

Asbestos fibre fulfills perfectly the first four requirements, and
is lai^ly used. It has the fault of packing under any consider-
able weight, BO the converter must have shelves only a few inches
apart, thus having comparitively shallow layers of platinized
asbestos.

^dbvGooglc

CONVERTER MASS 245

Dehydrated magnesium sulphate answers all five requirements,
plus the fact that it does not pack.

The base is coated by spraying with a solution of platinic
chloride, made by dissolving platinum at the rate of 125 gr. Ft
per liter beaker in twice the theoretical amount of aqua regia.
This is heated over a sand bath. The beaker should stand in a
porcelain dish containing water, lai^ enough to hold the entire
contents of the beaSer, in case of accident.

About 80 per cent of the platinum will dissolve readily. This
solution is poured into a porcelain dish, which, for safety's sake,
stands inside a lai^er dish, and is concentrated. More aqua
regia is added to the imdissolved portion, until all has gone into
solution.

The solution is then analyzed and diluted to contain 7 gr. per
e.c.* Because of the high at omic we i ght of sol^itiqnq^ ontaininff
platinum, they diffuse slowly, go mixing must be very carefully ,
and thoroughly done. fThis, is diluted to 3^a before using.

The asbestce fibre musT be very carefully "fluffed," and the
solution sprayed on from glass bottles, through a rubber tube
with a glass nozzle, drawn to a fine opening, using low-pressure
air to drive the solution out. The asbestos must be turned over
continuity, to get as even a distribution as possible: a pitchfork
makes a good tool.

This mass is put right into the converters, where the heat of
starting up reduces the platinic chloride to metallic platinum
before the first SOj arrives for conversion.

The m^nesium sulphate used must be pure. The New Jersey
Zinc Co. supplies a very high grade.

A small reverberatory furnace is used for calcining the "mag.
sulph." lots of 250 lb. to 500 lb. being a charge. Thirty-five to
40 min. is sufficient time to melt the salt in its own water of
crystallization and drive the water off. The furnace should be at
a dull red heat, and the chai^ rabbled continuously, as otherwise
it will harden and stick to the hearth. The more it is rabbled
the more porous it becomes.

* The Avoirdupois pound is the usual unit of weight in the sulphuric acid
industry, but platinum ia weighed in the Troy (or Jewelers') scale. The
following comporiHonti of the two scales are helpful:

1 pound Avoirdupois =• 7,000 grains = 16 Avoirdupois ounces,
1 pound Troy — 5,760 grains = 12 Troy ounces.

I pound Troy - .8229 pounds Avoirdupois.

^dbvGooglc

246 AMERICAN SULPHURIC ACID PRACTICE

After the charge is drawn it is broken and screened, pieces
above % in. being broken, and below % in. rejected.

Various plants use varying amounts of platinum per unit of
mass — 0.2 per cent to 0.3 per cent are the most usual.

The spraying is done the same as with asbestos fibre, but the
mass is put back into the furnace for 20 or 30 min., at a dull red
beat, and rapidly turns black, from the reduction of platinic
chloride.

RBGEHERATION

Asbestos is difficult to dissolve, so when it is necessary to.
recover the platinum it is simpler to dissolve the platinum in aqua
regia, filter, purify the solution, and make new mass, than to try
to dissolve the asbestos.

A spraying with a solution containing 20 per cent HCl, 7 per
cent HNO), and a little soluble organic matter, such as starch or
sugar, and returning the mass to the converter, will serve for
regeneration if the mass is not in very bad shape. The effect
is to dissolve (partially) and redistribute the platinum, and dis-
solve the impurities and have them carried off in the gases from
the burning organic matter.

If the mass from magnesium sulphate to be regenerated con-
tains a large proportion of fines it should be put into a wooden
tub, with a solution similar to that used for ordinary regenera-
tion, and water added as the solution boils down from the heat
of the reactions; and finally, after perhaps 10 to 24 hours, a
smooth paste results. It should be more or less sloppy. The
finer the material the less time required.

The result is a senu-solution of crystalline magnesium sulphate,
with platinum, which is fiunaced as was the new salt, and the
mass is then ready for use.

Of course this treatment results in some platinum being shut
up within the pieces of magnesium sulphate, and the action of
such quantities lost, so it is good practice to spray on 5 per cent
of the original quantity, after r^eneration. After several
regenerations the salt should be dissolved in a weak sulphurie
acid solution, the platinum recovered, and new mass made.

iiz^dbvCooglc

CHAPTER XXII

ACCOUNTING

Bt W. M. Lb Clkab

All well organized concerns recognize the advantages of Cost
Sheeta which reflect the costs to a very accurate degree, and it
is not considered necessary to dwell or argue upon this point,
because it is a conceded fact that without these records the
management cannot follow the destinies of its operations.

The usual factors entering into the cost of any product are
apprised here — i.e.

Labor, dinct, Repftira and Maintainance,

I^bor, indirect, Inauranoe, Taxes, etc.,

* Materials, dinot, Overhead,

Materials, indirect, Depreciation.

These various charges reflected in the cost sheets may come
through sub-cost sheets, such as Power House cost sheets, or
they may be charged direct to the Sulphuric Acid cost sheet,
depending entirely upon what basis the managment wishes the
cost data to be prepared. In either case the flnal result should
be identical.

The Direct Labor represent^ the labor actually employed in
obtaining the product. The Indirect Labor is labor that is
necessary to the operation, but which does not go directly into
the product, as for instance, foremans' time, laboratory time,
sweepers, oilers, etc., ■

Direct and Indirect Materiak are classifled along lines similar
to the Direct and Indirect Labor. Direct Materials represent
such items as sulphur, pyrites, etc., while the Indirect Materials
would be Nitric acid in some form (usually Chile saltpeter),
fuel etc.

The Repair and Maintainance charges should represent the

labor and materials expended which keep the apparatus in

operating condition, and do not add perceptably to the life of the

247

^dbvGooglc

248 AMERICAN SULPHURIC ACID PRACTICE

equipment. Charges falling into the latter cUseification should
be capitahzed.

The Charges, (or Taxes, Insurance, etc., should be determined
as nearly as is possible to estimate them. It may not be amiss
to state that accounting authorities do not consider the United
States. Government Income and Excess Profite Taxes to be a
part of the manufacturing cost, and are in reality a division of
profits with the Government.

The charge for Depreciation should represent the diminish-
ment in value due to wear, tear, and obsolesence, as nearly as it
can be estimated. With proper care the buildings will last a
long time, while the chambers, the most costly part of a chamber
plant, should be amortized on an 8-year basis, although they
will frequently go 10. Other parts of the plant must be taken
care of with regard to their varying life. The thought I wish to
bring out is that no one figure will do for a plant making corrosive
chemicals. Buildings at 4 per cent and Power House Equipment
at 10 per cent, will fit in very well.

The charges for Overhead should represent General Office
salaries, etc., which are not charged under the classifications
previously discussed. If desired the details on the cost sheets
may be carried out to the minute8:t details, but ordinarially
this is not considered necessary.

The basic feature to be borne in mind in the t>reparation of
the Cost Sheet is, that EVERY CHARGE that has any bearing
upon coets is reflected therein. The details of these items and
their arrangement is of course important, but only secondarily
so.

It is probably unnecessary to add that the costs should be
refiected upon the pounds of 100 per cent acid produced.

It is difficult to lay down any specific rules or instructions
regarding the cost information which should be furnished daily,
as this feature depends entirely upon what the management
considers necessary for its information. It is very important
however that the management know the number of men, cost of
labor and materials used, and the production daily. The
author's opinion is that all elements of cost should be calculated
daily, some factors must of necessity be estimated, which by
the preparation of a monthly progressive sheet would at the
end of each month very closely tie up with the monthly coet
sheet.

^dbvGooglc

ACCOVNTINQ

Per 1,000 lb. H,SO,

lAbor 1.3 hr. @ 48c.

(Production roughly 3,825,000 lb. per mo.}

Say S275,O0O.0O investment per line.

Interest 6 per cent 16,500

Dep. 26 per cent 68,750

Insurance 3 per cent 8,250

Taxes 1.5 per cent 4,125 *

(97,626

Labor fl24

Materials, 330 lb. 8 , 3.03

Coal 50

Superintendence 16

Office and labor inclutting supplies 076

Capital 2.12

S6.500

Repairs not included.

Steam not included.

^dbv-Googlc

APPENDIX

TAHK CAR TABLE

The Standard Tank Car for acid is 78 in. in dianeter, and the
length of the side is 27 ft. 6 in. The two ends are dished out-

oU^L-i^_J L

Hore

Carve 'a''% OfptH va. % CenfonH Curvr for PliKnC/6'nJifr
Ltngifuilmal^itii HoriiBntal '

furm 'S'-%&!pth vi.foConfmH Cvrvg for OiihtdEne/
TotolVolumsofCi^rmderR<fferTeettoinOjrv^'A'-a7SS4D^
To*al'-AjlumeQfSSndil^fsrr3tliginCurve'6''2TTh^{I>-b}

Q'Insiels OipmefarofTBtih^aad Radius ofOiihed End
L • Lenath of Plain CuU'ndiical H>rfof Tank
h'TofalDmihofOishadEnd
h - 0.134 D

, the radius of the dish always being the same as the
iter of the tank itselt

^dbvGooglc

APPENDIX , 251

Other sizes of "tanks" are used for acid — so many in fact
that it would be out of the question to give a gaugeing table for
all sized tanks. However, with the tank curve a table for
any sized tank can be quickly prepared.

To prepare such a table, first find the area of the vertical
section of the car in feet: then multiply this by the length of
the straight side of the tank — this will give you the number of
cubic feet in the cylindrical part of the tank. Then prepare a
table giving the per cent of height for every inch of height — then
set down opposite each inch the per cent of the capacity of the
tank that is represented at that height — for instance, in the
table given, at 16 in. the per cent of the total is 20.54. Then
multiply this by 913+, which is what the cylinder holds full,
and you get 135.55 cu. ft. Then figure from the formula given
how much the dished ends hold full, look on the "end curve"
to see how much the ends hold at 20.54 per cent, and you will
find it is about 8.4 per cent. From the formula the ends hold
about 37 cu. ft., and you get 3.08 cu. ft., which added to the
135.55 cu. ft. of the cylinder gives you the amount of acid in
the tank; 138.63 cu.ft.

Because of the varying relations between the length and
diameter, it is not possible to work it all out in one formula,
so a table must be prepared as above.

From a hydrometer the density of the acid is then determined,
its weight per cu. ft. looked up, and the total weight calculated.

While there may be some errors in the last place of decimals,
it is not possible to read a stick to within one-hundredth of an
inch, and after a tank car has been in service a very short time
it will be distorted more than any error in this curve.

^dbvGooglc

AMERICAN SULPHURIC ACID PRACTICE
Table fob Stamdaiid Tank Caa

Height

of acid

Fteroentof

No. of

of acid

Per cent of

No. of

in tank,

depth

cu. ft.

in tank,

depth

cu. ft.

inches

1.28

2.24

51.28

491.02

2.66

6.09

52.56

506.96

3.84

11.67

53.84

523.58

S.13

17.88

55.13

538.10

6.41

24.81

56.41

553.65

7.69

32.49

£7.69

669.00

8.98

40.93

68.98

584.42

10.26

40.86

60.26

599.73

11.64

59.36

61.64

616.17

12.83

68.52

62.83

030.28

14.11

79.23

64.11

645.33

16.38

90,65

65.38

660,29

16.69

102.32

66.69

676.20

17.97

114.07

67.97

689.72

19.25

126.24

69.25

704.14

20.53

138.63

70.54

718-71

21.82

150.97

71.82

732.95

23.10

163.31

73.10

746.74

24,39

176.43

74.39

760.22

25.67

189.78

75.67

773.57

26.95

203.26

76.96

786.69

28.24

217.05

78.24

799.03

29.52

231,29

79.52

811.37

30 80

246.86

80.80

823.76

32.09

260.28

82.09

835.93

33.37

274.80

83.37

847.68

34,65

289.71

84,65

859.35

35.93

304.67

85.93

870.77

37.21

319.72

87.21

881.48

38.49

334,83

88,49

890,64

39.77

350.27

89.77

000.16

41,05

365.58

91.05

909.07

42.33

381.00

92.33

917.51

43.62

396.45

93.61

925.19

44.89

411.90

94.89

932.12

46.17

427,42

96.17

938.33

47,45

443.04

97.46

943.91

48.72

458-98

98.73

947.46

50.00

475.00 half full

100.00

950.00

idbyGoOglc

APPENDIX

Tables and General lofonnation

SpBCmc Gbavitt

Manufacturing ChemiBta Association of the United States

Per cent

Weight of

Freezing

'Bt

%i. gr.

1 cu. ft. in

(melting)

H|SO<

pounds, av.

point, °F.

1.0000

0.00

62.37

32.0

1.0069

1.02

62.80

31.2

1.0140

2.08

63.24

30.5

1.0211

3.13

63.69

29.8

1,0284

4.21

64.14

28.9

1.0357

5.28

64.60

28.1

1.0432

6.37

65.06

27.2

1.0507

7.45

65.53

26.3

1.0584

8.55

66.01

25.1

1.0662

9.86

66.50

24.0

1.0741

10.77

66.99

22.8

1.0821

11.89

67.49

21.5

1.0002

13.01

68.00

20.0

1.0985

14.13

68.51

18.3

1.1069

15.25

69.01

16.6

1.1164

16.38

69.57

14.7

1 . 1240

17.53

70.10

12,6

1.1328

18,71

70.65

10.2

1.1417

19.89

71.21

7.7

1.1508

21.07

71.78

4.8

1.1600

22.25

72.35

1.6

1.1694

23.43

72.94

- 1.8

1.1789

24 61

73.53

- 6.0

1,1885

26.81

74.13

-11.0

1.1983

27.03

74.74

-16.0

1.2083

28.28

75.36

-23.0

1.2185

29.53

78.00

-30.0

1.2288

30.79

76.64

-39.0

1.2393

32.05

77.30

-49,0

1.2500

33.33

77,96

-61.0

1,2609

34.63

78.64

-74.0

1.2719

35.93

79 33

-82.0

1.2832

37.26

80.03

-96,0

1.2946

38.58

80.74

-97,0

1.3063

39.92

'81.47

. -91.0

1.3182

41.27

82.22

-81.0

1.3303

42.63

82.97

-70.0

1.3426

43.99

83.74

-60,0

,db, Google

AMERICAN SULPHURIC ACID PRACTICE

SpEciric GRAvnr

Manufacturing Chemists Association of the United States

Percent
H,SO,

Weight of

fYeesing

-B6.

Sp-ur.

1 cu. ft. in

(melting)

poundB, »v.

point, 'F.

1.3551

45.35

84.52

-53

3ft

1.3679

46.72

85.32

-47

1-3810

4S.10

86.13

-41

1.3942

40.47

86.96

-36

1.4078

50.87

87.80

-31

1.4216

52.26

S8.67

-27

1.4356

63.66

89.64

-23

1.4600

65.07 .

90.44

-20

1.4646

56.48

91.35

-14

1.4796 •

57,90

92,28

-15

I. 4948

60.32

93.23

-18

1.5104

60.75

94.20

-22

1.5263

62.18

95.20

-27

1.5426

63.66

96.21

-33

1.5591

65.13

97,24

-39

1.5761

66.33

98.30

-49

1.5934

6S.13

99.38

-59

1.6111

69.65

100.48

Below -40

1.6292

71.17

101.61

Below -40

1.6477

72,75

102.77

Bebw-40

1.6667

74.36

103,95

Betow -40

1.6860

75.99

106.16

- 7

1.7059

77.67

106.40

+12.6

1.7262

79.43

107.66

27.3

1.7470

81.30

108.96

39.1

1.7683

83.34

110.29

46.1

1.7901

85,66

111.66

46.4

1.7067

86.33

112.00

43,6

64 Ji

1.8012

87.04

112.34

41.1

1.8068

87.81

112.69

37.9

1.8125

88,65

113.05

33.1

65H

1.8182

Sd.SS

113.40

24.6

65H

1.8239

90.60

113.76

+13.4

65H

1.8297

91.80

114.12

- 1.0

1.8354

93.1fl

114.47

-29.0

idb,Go(5glc

APPENDIX

Allowance fob Teuferattbe

At ICBfi.,

.039°B4. or .00023sp.gr

= rp.

At 20''B6.,

.036°B6

or .00034 sp-gr

= VF.

At WBi.,

.035°Bfi

or .00039Hp.gr

= 1-F.

At WW.,

.031°BS

or .00041 ap. gr

= 1°F.

At 50°Be.,

.028'B6

or .00045 8p. gr

- IT.

At 60°Be.,

.oae-K

or .00053sp.gr

- rF.

At 63'Be.,

.026°Be

or .00057 8p.gr

-1°F.

At 66°B6.,

.OaaS-M. or ,00054 8p.gr

- rp.

Afpkoximati: Boilino Points

50°B^ 295°F.

Wm ■.. 386°F.

ei-Bfi 400^.

Si-Bi 415°F.

63°B« 432°^

64°B^ 451''F.

aS°B4 485'*F.

6a°Be 538°P.

l^EORETICAL PKODTTCTION FlQUBE

5H|2^ = 3.0585 Log of 3.0585 "- .485508

Specific GaAvm (at 65°F.) and Melting Point (Freeeinq Poi
Fuming Solfhuric Acin

TOTAI. Soi Fun So, Bp. an. Multthq <ni)E

2.05 1

8300

7.50 1

8480

12.95 1

8B57

18.38 1

8847

23.84 1

9086

29.27 1

9258

34.70 1

9429

40. 17 1

9607

45.63 1

9667

idb,Go(5glc

AMERICAN SULPHURIC ACID PRACTICE

Pbk CBNT TOTIL 80l «

81.03
81.99

8e.40
86.76
87.14
87.60

Toni. SOi Pu CI

iTU>80.-

PU CBHT Tor*

87.87

88.3^

88.60

88,97

89.33

89.70

90.07

90.44

90.81

91.18

01.66

91.91

92.28

92.65

93-02

93,38

93.76

Specific Heat

Swacamit

TouL 80i Pm tn

.3500

.3460

.4000
.4660
.5350
.6500
.7700

Vapor Tbnbion

Pas CBNT

ae-F.

104°F. 140°F.

H,SO.

M.M.

M.M. M.M.

61.7

10 25

70.0

3 8

81.5

1 1.5

at all temperatures.

^dbvGooglc

Vapor PitBSBtrBEs of Soue Qoauties or OLBnu
K volume oleum. H volume air.

Pre».

Pres-

Temp.

sure of

Bureof

sure of

°C.

oleum.

oleum,

oleum.

oleum,

30%

40%

50%

60%

70%

80%

100%

atm.

0.150

0.40

0,075

0.22S

0.375

0.600

0.65

4fi

o!050

0.125

0.350

0.575

0.650

0.87

0.100

0.175

0.350

0.S2S

0.775

0.875

1.20

0.140

0.225

0.450

0.676

1.025

1.200

1.60

0.200

0.276

0-660

0.825

1.400

1.500

1.85

0.225

0.350

0.700

1.025

1,650

1.900

2.26

0-275

0.400

0.825

1,275

2,060"

2.300

2.76

0,340

0.475

1,000

1.670

2.625

2.800

3.30

0.400

0.675

1.150

1.850

3.100

3.500

4.00

0.450

0.675

1.400

2.160

3.700

4.176

4.90

0.530

0.825

1.700

2.576

4.400

5.050

5,90

0.625

0.960

2.060

3.150

5.000

6.0OO

100

0.730

1.100

2.400

3.700

6.000

idb,Go(5glc

AMERICAN SULPHURIC ACID PRACTICE

■ Heat of Solutiok. (Dh. Knkitchb}
Determined Values

Oi Pm CBKT 80i Fib obht Fbb> 80i Pm cint Cuaum

fiO.32 41.07 40.46

60.18 49.12 66.46

63.86 62.13 79.05

70-24 S7.33 110.05

73.76 60 21 132.3

76.86 62.74 151.4

71.41 64.82 171.7

99.88 81. K 0.0 194.06

83.49 10.12 ' 221.4

85.26 19.75 246.27

87,3! 30,91 277.6

89.08 40.66 299.05

91.06 61.28 327.9

- 92.67 60,10 361.4

94.72 71.26 393.6

96.62 81.60 433.6

98-48 97.81 470.6

99.64 00.48 491.1

BtsAT or SoLnnoN or Boud Oleuu. (Db. Kneitche)

Determined Valuea

To**!. 80> P«B CBHT

Fmi so, Pi« cb»t

CjU-ORIU

89.4

42.3

271.0

90.73

49.63

303.2

92,6

59.2

330.4

94,6

70,1

369.2

06.28

70.76

408,8

98.14

97.32

436.1

08.64

99,34

481.4

09.84

90.77

486.0

id»,Googlc

HXAT OP SOLDTIOK O

ScLFHCRic Acid akd Oustni. (Db. Kmbitche)
Graphically DetermiDed

Oleum

Heat of

so„%

H,SO.,

Cal.

80,, %

Free
80,.%

C&L

solution

ofaolid

oleum, oaL

61.25

199

62.48

7.5

210

63.70

12.9

223.6

64.93

46.6

18-3

237.6

66,15

23-8

250

67.38

51.5

29.2

266

68.60

34.7

278

69.83

40.1

292

71.06

59.5

46.6

308

286

72-28

61.0

325

304

73.60

56.4

344

322

74.73

61.9

363

340

75.96

67.3

381

360

77.18

72.8

401

380

78,40

78 3

421

402

79.63

83.6

83.7

442

423

80.86

89.1

465

442

82.08

94.6

400

463

83.30

100

515

486

84,53

103

85.75

108

86.98

113

88.20

119

89.43

126

90.65

133

91.88

139

93,10

146

94.33

152

96.66

160

96-78

168

98-00

178

99-23

188

"■"^

100-00

193

^dbvGooglc

AMERICAN SULPHURIC ACID PRACTICE

ELiiOTBiCAi. Rbbistancb of Sclpburic Acid at 2S°C.
(Dk. Kkeitche)

«..%

H,SO., %

(ftm

80., %

H,SO<, %

Ohm

40.19

49.23

0.235

75.19

92.01

0.70

48.80

B9.79

0.29

76.73

94.00

0.72

S3. 27

65,14

0.245

78.46

96.11

0.795

57,64

70.55

0.345

78.52

96.20

0.79

60.28

73.85

0.475

79.55

97.46

0,80

61.07

74.82

0.525

80.22

98.27

1.10

64.00

78.40

0.60

80.98

99.21

1.95

65.14

79.80

0.67

81.27

99.66

2.2

67.04

82.14

0.74

81.345

99.64

2.7

68.53

83.97

0.75

81 . 425

99.74

3.5

69.12

84.68

0.76 max.

81 . 455

99.78

4-2

70.23

86.03

0.746

81.53

99.87

5.7

70.84

86.79

0.74

81 . 535

99.88

6 7

73.40

89.92

0.705

81.59

9g.95monohydrate

7,45 man.

Electrical Rebibtakcb of OlbuiC at 26°C.

Total
SO., %

Free
SO., %

Ohms

Total
80.,%

Free
80., %

Ohms

81.695

0.34

6.15

90,5

45.0

23,4

81.74

0,5

5.35

90.8

50,0

53,0

82.4

4,0

2.43

91.6

54,0

88,0

83,44

9,8

2.20

92.7

60,3

222,0

84.2

14,0

-=}^„„

93.4

64,0

287.0

84,7

16.7

94,6

69.6

759,0

85,2

19.4

2.23

95.4

75.0

1,265,0

86.3

26,5

2.95

96,35

80.0

4, 000. Oat 27

87,06

29.6

4.05

06,87

83,0

6, 650, Oat 32

88.3

36.3

6.65

98.16

90.0

61, 850, Oat 36

89,0

40.2

15.2

idb,Go(5glc

Attacking AtmoN upon Ibon

Decrease per squara meter per hour in grama after 72 hours action of add
acid at I8'-20''C. (85*'-68''F.l. (Dr. Kneitche.)

H,80fc%

80„ %

Cast iron

Ingot iron

Welding iron

48.8

39.9

0,2177

61.2

50,0

0.1510

0.3032

67.7

55.3

0.0847

0.0789

73.4

59.9

0.0662

0.0623

79.7

65.0

0.1560

0.1159

83.7

68.4

0.1388

0.1052

85.1

69.6

0.1306

0.1034

88.2

72.0

0.1636

0.1417

90.6

73.9

0.1750

0. 1339

92.0

75.2

0.0983

0.1040

93.0

76.9

0.0736

0,0987

0.0856

94.1

77.0

0.0723

0.0933

0.0708

95.4

77.9

0.1274

0.1471

0.1209

96.8

79.0

0.1013

0.0815

0.0988

98.4

80.3

0.0681

0.0533

0,0656

98.7

80.6

0.0583

0.0509

0,0570

99.2

81.0

0.0668

0.0418

0.0504

99.3

81.07

0.057

0.042

0.060

99.5

81.25

0.060

0.038

0.049

99.77

81.45

0.066

0,042

0,049

100.0

81.63

0.087

0.088

0.076

Total SO.

Free 80,

81.8

0.91

0.201

0.393

0.323

82.02

2.00

0.190

0.285

0.514

82.28

3.64

0.132

0.441

0.687

82.64

4,73

0.164

0.956

1.075

82.80

7.45

0.161

0.566

1.321

83.50

10.17

0.079

0,768

1.540

&1-20

12.89

0.270

1.024

0,892

84 62

16.16

0.271

1.300

0,758

85.06

18 34

0.076

1.988

1.530

86.00

23.78

0.070

0.246

0.471

88.24

34.67

0.043

0.033

0.063

90.07

45.56

0.040

0.018

0.019

CovroeinoH Carbok QaAPHirs

Oast iron 3.55 per cent, 2,787 per cent.

Ingot iron 115

Welding iron 0.076

^dbvGooglc

AMERICAN SVI^HVniC ACID PRACTICE

L..

llJ

■

'■

L,.

!. *

i,^

jrCe

■

90 95 KIO

Fto. 83. — BoillnB point* of nitric acid.

" : _ _ ;_

„ n

J : :: ::. :: : s ::

" _,' 5 fi-.

":-::_. z:: : ::: :^ :: :::: :

K) / n ,7 V

J - 1 ^

";_::: " : ::; :3 ""::::::: :

,0 --J ^ - „-.)_. ^ __. __. _

7S9 6l6i66 6 691 1 T 77798 86 87899
SOj.PerOint

Fia. 81. — F^VMing (melting} poiata of Butphuric add.

iiz^dbvCoOglc

leinparaKiratjSOctag f nwndt,Oat.and«u.fl'
Fta, 86.

^dbvGooglc

idb,Go(5glc

INDEX

Abn-Bekr-Alrhaaea, 1
Absorption, 14, 238

beat temperature for, 212

heat of combinstion of SOi and
H,0, 238

of SOi hj weaker acid, 209

Btrength of acid for, 212

towera, 238

water not satisfactory for, 238
Accounting, 247

Acid, proper strength to make, 239
Acid egg (blow case), 122, 213
Adsorbtion, 228
Alum, 17

epirit of, 1
Aluminum in lead, 192
American Cyanimid Company, 143
American makers of liquid S0|, 77
American Smelting & Refinii^ Com-
pany, 77
Ammonia as source of NO for
chambets, 143

analyses, 151

oxidation-reaction, 149

atiU, 147
Anaconda Copper Mining Company,

»2 ,.

duBt chambers, 92

large Wedge (an, 64
Antimony, cantAct poison, 217

in lead, 103

the Triamphial Car of, I

to harden lead, 112
Arsenic, carried by mist, 207

enemy of contact process, 217

in entrance, effect, 11

in entrance gas, 5

in lead, 193

removal from maas, 230

Asbestos, beat packing, 213
fluffed filter packing, 224
platinised, 228

Avoirdupois compared with Troy
weights, 24S

Bacon, Dr. Raymond P., Louisiana

sulphur, 28
Badische contact process, 209-228

converter, 228

patents bearii^ upon, 229
Battery acid, 206
Baum£ curve, 263

hydrometer, 167

tables, 253, 254, 255
Benker system, 196
Bismuth, efiect upon lead, 192
Blow cases (acid eggs), 122, 213
BoUman, Dr. Eric, 2
Brimstone, as raw material, 44

burning to SOi, 49
Brunner-Mond Co., ammonia still,

147
Bufialo Foundry & Machine Co.,
197, 198

apparatus for recovering acid,
197, 198
Builders Iron Foundry, meters, 148

Carbon dioxide, effect upon contact

process, 11
Cast iron not dissolved by fuming

acid, 213
Catalytic action of metallic oxides,

7,228
taw of mass action applied to,

236
Catalyser, 4, 6, 228

other than platinum, 236

^dbvGooglc —

Chalcopjrrite, 46

Cb&mber plant, reactione in, 180

operatioa, ISO
Chamber proceaa, deacription of, 82

flow sheet, 84

outline, 8 '
CbambeTB, construotion, 101, 102

protecting wind pressure on, 106

volume required, 110
Chambers, lead, 1, 2

acid must be concentrated, 189

control of acid strength, 186

position in chamber process, 83
Chemiatfl, need for, 200
Chlorine, in the contact process, 11
Circulation, promoting in chambera,
106

Gilchrist pipe column, 108, 118

multiple tangent system, 107
plate column, 108
Qean gas absolutely necessary for

conversion, 200, 217
Cobalt, 4
Combustion chambers, far sulphur

burners, 218
Concentration, Benker system, 196

bottom firing, IM

temperatures, lOI-lflJIi

by cascade, 201

by Kalbpeny system, 207

degree of depends upon its
market, 212

heat exchangers, 193

in fused silica, 200

objection to direct heat in
concentrating, 197

pan, 186

platinum stills, 109

top firing, 100
Conductivity of heat by sulphur, 40
Contact mass, different for different

methods, 209
Contact process, 4

early blunders, 210

outline, 10, 207
Conversion of SOt, slide rule for, 236
Converter for oxidizing NHi, 145

Badiache, 229

Sohroeder GriQo, 232

Converting SO. to 80^ 228

Coolers, acid, 120

Cooling, different methods, 209

gases, Badische method, 219
Schroeder, Grillo method, 220
Copper, 2

in lead, 193
Costs, by contact process, 212
Cottrell apparatus for dust settling,

86
Cubical expansion of sulphur, 39

Davison Chemical Co., Silica gal, 75
liquid SOi, 75
saving SO^ 228
De Beauvais, 1

Depreciation on contact plant, 213
Differences between Badische and
Schroeder-Grillo contact
processes, 209, 231
Distillation of ferrous sulphate, 4
Distribution of acid in Glover's and

Gay Lussac's, 130
Draft, 179

measurements, 178
Dnunage necessary for coolers, 242
Driiddng water, clarifying, 18
Ducktown Sulphur, Copper & Iron

Co., SOt from blast, 65
du Pont Co., 91
Dust settlmg apparatus, 86
Cottrell apparatus, 86
chamber with hanging wires, 91
Howard, 91
centrifugal, 92
Anaconda type, 92
effect in contact process, 217
Dwight & Uoyd sinterii^ machine.

Electrical conductivity of sulphur,

39
Ellison draft gauge, 178
Exit gas, 177

testing, 177
Expansion joints faihires with acid,

213

^dbvGooglc

Fans, 1S9

design of, 160
Ferrous sulphate, dietiUatioa of, 4
Fertiliier induBtry depends upon

HSO,, 17
Filtering material grade 201A as-

beatoa, 163
Flues, methods of supporting, 164

size of, 163
Foremen's meetings, 214
Frasoh process, 33
Freezing, acid, 15

point of acid aa .related to
product, 212, 240

curve of, points, 262

point of acid, 255
Frictional electricity of sulphur, 39
Fuming acid, 4

composition and uses, 17
Fused siUoa, for concentration, 201

Garbet, Mr., 1

Gas for contact process, best
strength, 211
control, 235
temperaturcfl, 212
Gauge glasses undependable, 222
Gay Lussac tower, reactions in, 181

deeoription of, 113

packing, 114

position in ohamber process,
85
Geber, 1

General Chemical Co., 209
Qlens Falls Machine Co., sulphur

burners, 49
Glover tower,

as a concentrator, 99

brick for, 96

chief function of, 98

construction, 94

description, 94

lining and packing of, 96

position in chamber proces3,83

reactions in, 181

size of, 100
Gold, 4

Hamish & Schroeder process, 5
Harrison Bros. A Co., 1
Mr. John, 2
Hart condenser, 141
Heat exchanger for concentrating

aoid, 193
Heins-Skinner taa, 161
H^h silicon irons, 141
Holker, 4

Hough, Arthur, 205
Humidity combines with 80|, 8
Hydrochloric acid in the contact

process, 11
Hydrometers, 167

Impurities in gas in contact process, 11
Iridium, 4

attacking action of sulphuric
acid on, 261

Jefferson, President, 2

Kalbperry Corporation, concentrat-
ing tower, 201

I^iboT for chamber process, 187

for contact process, 213, 214
Landis, W. S., 143
Lead, effect upon contact process, 1 1,
217
flowing, 105
life of, 112
methods of supporting, 95, 102,

104
quality for concentrating pans,

192
specifications. 111
weight of in chambers, 102
Lnnge, comments on American prac-
tice, 209
plate column, 108
theory of chamber acid, 9,

^dbvGooglc

Magnesium sulphate, in tlie Scbro-

eder process, 5, 228,

265
M^ufftcturera in the U. 8., 19, 27
Maaa action, law of, applied to

contact action, 236
Mass contact, p eparation of in, 244
Scbroeder-Grillo process, 229

r^eneratioD of, 246

tegtii^, 243
MoKee, Dr. Ralph, on liquid SO,, 41
Meltii^ joint of sulphur, 41
Mercury, enemy of contact process,

2, 217
Metallui^ical gases for SO,, 208
Meters, gas, 148
Mist, arsenic carrier, 207
Mixed acid to introduce nitric

oxides to chambers, 141
recovery of sulphuric from,

201
testily, 176
Moisture in contact system, 217
Dr. Reese's experiments, 230
taken from air-quantity of, 222
Montejus, 122
Mortar, to stand acid, 96

New Jersey Zinc Co., 209
Nitrate of soda, characteristics, 47

purification, 48

testii^, 176
Nitre cake, disposal of, 138

testing, 17S
Nitre losses, 183

absorption of, 115

feed control of, 185

introduction of, 136

methods of introducing, 138

pots, 137

potting with fuel, 139

reactions, 136
Nitric acid, 16

condensii^ the vapor, 141

curve of boilii^ points, 262

in mixed acids, 203.

Nitric acid, lower freezing point of
H,SO., 212
production in chambers, 13S
Nitrogen oxides — saving, 9, 10
Nitrometer, 174
Nitrosoeulphuric acid, 9
Nitrous vitriol in the Glover tower, 98
testing, 176
O
Oil of vitriol, 2
Operation, chamber plant, 180
Orsat apparatus, 169
Oxygen, pure In contact process
unnecessary, 217, 234
P
Packing for Glover towers, 98
for piping and valves, 213
Pan concentration, 186
bottom firing, 191
temperatures, 191
top firing, 190
Platinum, 2-S

as SO, catalyzer, 228
quantities for SO* oonveraion,

246
Poison, contact, Opl'a theory, 13

c atalyzer for oxidizing N Hi, 150
Dr. Krause theory, 3
list of, 217
Pratt fan, 161

Preheaters, Schroeder-Grillo, 232
Priestly, Dr. Joseph, 2
Production to figure for contact

plant, 211
Fulsometer, 122
Pump, acid, 127, 240

makers, 240
Purification of gases in contact

process, 217
Pyrites cinder, catalytic action of,219
burning, 53, 59
fines burners, 56

Henerhoff furnace, 57
MoDougal furnace, 67
Wedge fnmace, 61

^dbvGooglc

Pyrites, importation of Spanish, ',

lump burners, 55

prices, Si

propcrtiee, 45
Pyrometers, 166

dependent upon, 210

makers of, 232
Pyrrhotite, 46

Raschig, theory of chamber process,

Raw matcrisJe, 44

brimstone, 44

chalcopyrite, 45

galena, 46

nitrate of soda, 47

pyrites, 45

pyrrhotite, 45

spent oxide of iron, 46

line blende, 46
Reactions, time of, in chamber pro,
101
are exothermic, 101
Reese, Dr. Charles L., impurities in

contact process, 11, 230
Regeneration of contact mass, 246
Reich test for SOi, 170

made regularly in contact
process, 210

tables, 173, 174
Roebuck, Dr., 1
Rule of thumb methods, 182

Safety appliances, 214

Salt cake, 17

Saltpeter, 1

Scbroeder-Orillo contact process, 209'

catalyzer, 228
Scrubbing, need for, 13
Shut down, preparation for, of

contact plant, 215
Silica gel for recovering SOi, 75, 228
Silicon, 4

tetrafiuoride, effect upon con-
tact process, 11, 217
Silver in lead, 173

Sintering pyrites cinder, 68
Soda ash, 16
Sodium sulphate, 136
Solubilities of sulphur in various

solvents, 82
Solution, heats of, 258, 259
SOi, best percentage for conversion,
211
converting to SOj, 228
first step in making H:SO« tem-
perature of formation, 208
slide rule for converaion of, 236
SO,, oxidation of SOi to, 209
converting SO, to, 228
free table, 255, 256
in burner gas causes mist, 217
total table, 255, 256
Specific gravity, table of, 253, 254,

255
Specific heat and heat of combus-
tion, 41, 256
Squire, 4
Starck, Joseph, 4

process eliminated, 208
StMly, James E., on SO,, 79
Stoicometric mixture of SO, & O

won't work, 234
Strength of acid to make, 239
Sulphur, as in impurity in the con-
tact process gas, 11
impurities in, 34
in the U. S., 28
Japanese, 45
Louisiana, 34

physicochemical properties, 38
prices, 34
production of, 31
statistics,
sublimated, 217
uses, 36
Sulphur dioxide characteristics, 7
production of, 49
from brimstone, 49

metallurgical processes,

64
Pyr fines, 66

lump, 66
pyrite cinder, 68
zinc ores, 67

^dbvGooglc

270 ISl

Sulphur dioxide abeorbtion by silica
gel, 76
liquid, 76
ch&racter and uses, 77, 81
Sulphuric acid, characteristics, 8, 16
distributioa among indus-

triea, 18
makera in the U. 8., 19, 27
uses and production, 5, 16
Sulphuric acid, electrical resistance
of, 260

Tin, effect upon lead, 192
Towers, acid, various, 223
Troy compared with Avoirdupoia

weights, 245
Twaddle's hydrometer, 168
Tyndall test for dust in gas, 226

United Alkali Co., ammonia still.

Tank car table, 260, 252
Tanks, storage, 120

circuIatiDn, 222
Temperatures in chambers, cheeking,

109
Temperatures for abeorbtion, 212
for burner gases, 218

heat exchanger concentration,

195
in pan concentrating, 191
of conversion in contact process,

230
Tennessee Copper Co., acid from

met gases no dream, 61
ohaloopyrite as of sulphur, 46

SOi from blast furnace, 65
Testing contact mass, 243
exit gas, 177
gas, 166

instruments, 100
mixed acids, 170
nitrate of soda, 176
nitre cake, 170
nitrogen oxides, 174
nitrous vitriol, 176
Reich teat for SO., 170
Tyndall test (for dust I

225

1 gas).

Thennometere, 166

Time of reaction in chamber process,

Valves, proper ones for acid, 213
Vapor pressure as related to abeorb-
tion, 14, 212, 239
curves of pressures due to

wat«r and SO,, 239
of sulphur, 38
tables, 256, 257
Virginia Smelting Co., producing
liquid SO,, 78

Ward, Dr., 1

Water, introducing water to cham-
bers, 109, 133
effect upon contact process, 11
not satisfactory for absorbtion,
238

Weber, theory of chamber process, 9

Weight of acid, curve, 263

Weasel, 4

White lead, 3

Winkler, C. I., 4

theory of chamber process, I

Wollaston, Dr., 3

Zinc blende, properties, 46
ores, SO, from, 67
effect upon lead, 192

SFP 2 6 1921

idb,Go(5glc

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