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THE ELEMENTS OF CHEMICAL
ENGINEERING.

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THE ELEMENTS OF CHEMICAL
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LONDON:
CHARLES GRIFFIN & CO., LIMITED, EXETER STREET, STRAND,

THE ELEMENTS OF
CHEMICAL ENGINEERING.

J. GROSSMANN, M.A., PH.D., F.I.C.,

CHEMICAL ENGINEER AND CONSULTING CHEMIST, MANCHESTER.

WITH A PREFACE BY

SIR WILLIAM RAMSAY, K.C.B., F.R.S.

50 ^lustrations.

CHARLES GRIFFIN & COMPANY, LIMITED,

EXETER STREET, STRAND.

1906.

PREFACE

SIR WILLIAM EAMSAY, K.C.B., F.RS.

THE students who throng our laboratories are, for the most
part, well taught so far as scientific chemistry is concerned.
The study of the science, however, demands at least three
years ; indeed, a young man of more than average abilities is
not at home in the subject until he has spent a fourth year in
laboratory work. If it is required that a young chemist should
not merely know facts and theories, but should also be able
to help forward the science either in its theoretical or its
industrial side, a considerable part of the time must be devoted
to research. But at the end of his four or five years' training,
when he has probably graduated, and has been awarded a
degree, or a diploma showing that he is an associate of the
Institute of Chemistry, he is almost always woefully ignorant
of the properties of the materials required to carry out opera-
tions on a large scale, which are perfectly familiar to him on
the laboratory scale, when glass and porcelain and platinum,
water pumps and mercury pumps are available. The most
that can be expected of him is that he shall have a fair know-
ledge of the science, and that he shall have some notion of how
to tackle a new problem. It is with the view of attempting
in some measure to remedy this state of affairs that this work
has been written. It may be said that in Britain there is,
for the most part, a gulf fixed between the technical and the

VI PREFACE.

scientific chemist; a gulf which our Continental competitors
have managed to bridge ; for abroad it is by no means infrequent
for the technical chemist to become professor, or vice versa ;
and works problems often find their solution in University and
Polytechnicum laboratories, while the facilities of the works
are often extended to the scientific chemist. And abroad, the
works afford a training school for scientifically trained chemists,
such as are practically unknown in England. It is to be hoped
that the simple and lucid statement which Dr Grossmann has
given of the difficulties met with, and the methods of their
solution, in proceeding from the scale of laboratory to that of
manufacturing operations, may awaken the interest of many
chemical students, and lead them to 'demand tuition on these
lines ; and even if this work only induces teachers to pay
attention to the problem of cost, it will have contributed much
to the progress of the teaching of chemistry.

WILLIAM KAMSAY.

May 1906.

CONTENTS

PACK

INTRODUCTION, 1_2

CHAPTER I.
THE BEAKER AND ITS TECHNICAL EQUIVALENTS, . . . 3-20

CHAPTER II.

DISTILLING FLASKS, LIEBIG CONDENSERS, FRACTIONATING

TUBES, AND THEIR TECHNICAL EQUIVALENTS, . . . 21-35

CHAPTER III.
THE AIR-BATH AND ITS TECHNICAL EQUIVALENTS, . . . 36-45

CHAPTER IV.

THE BLOWPIPE AND THE CRUCIBLE, AND THEIR TECHNICAL

EQUIVALENTS, 46-56

CHAPTER V.
THE STEAM BOILER AND OTHER SOURCES OF POWER, . . 57-66

CHAPTER VI.

GENERAL REMARKS ON THE APPLICATION OF HEAT IN

CHEMICAL ENGINEERING, 67-74

CHAPTER VII.

THE FUNNEL AND ITS TECHNICAL EQUIVALENTS, . . . 75-81

vii

Vlll CONTENTS.

PAGE

CHAPTER VIII.
THE MORTAR AND ITS TECHNICAL EQUIVALENTS, . . . 82-93

CHAPTER IX.

MEASURING INSTRUMENTS AND THEIR TECHNICAL EQUIVALENTS, 94-105

CHAPTER X.

MATERIALS USED IN CHEMICAL ENGINEERING, AND THEIR

MODE OP APPLICATION, 106-122

CHAPTER XL

TECHNICAL RESEARCH AND THE DESIGNING OF PLANT, . . 123-140

CONCLUSION, 141-142

CURRENT PRICES OF CHEMICALS AND MATERIALS, . . . 142-148

INDEX, 149-152

ELEMENTS OF CHEMICAL
ENGINEERING.

INTRODUCTION.

THE student who has gone through a course of study in
analytical and theoretical chemistry often finds great difficulty
in adapting himself to the altered circumstances which regulate
chemical work when carried out on a large scale, arid therefore
fails to grasp the principles of chemical technology. It may be
laid down as a fundamental difference between theoretical and
practical work that whilst the question of cost does not enter
into theoretical work, it is the fundamental basis of all technical
work. Thus, if it were necessary to prepare nitrate of ammonia
in the laboratory in an extremely pure state, the cost of
materials, the amount of time spent, the labour, the breakage
of vessels, cost of heating, evaporating, and drying, the initial
cost of the apparatus, and final cost of packing in bottles or jars,
would be of no consequence so long as the object in view had
been attained. But if the problem were put to a student to
make nitrate of ammonia in the cheapest manner on a large
scale, the conditions in which the work would have to be carried
on would be fundamentally different. He would have to choose,
amongst a number of possible processes, the one which, when
all the above conditions are taken into account, enables the

2 ELEMENTS OF CHEMICAL ENGINEERING.

manufacturer to produce the article required in the cheapest
manner, not only as regards the cost of the raw materials, but
also as regards the initial cost of the plant, and the consequent
interest on capital expended, the depreciation of the plant, the
labour, the fuel, and the cost of packing, as well as incidental
charges in the management of the works and office.

But, apart from these questions, there is a great difficulty in
understanding the apparatus which is used on a large manu-
facturing scale. Without any intermediate stage, the student
must at once accommodate his ideas, which have been trained by
using extremely small quantities, to the use of extremely large
quantities; and whilst he would be quite capable of under-
standing how to mix nitric acid and ammonia to produce
nitrate of ammonia in a beaker or a basin, he would be totally
at sea if he were asked to construct the apparatus necessary to
carry this operation out on a large scale. I have endeavoured
in the first few chapters to make the transition from the small
laboratory scale to the large manufacturing scale not abrupt,
as it is now to the student, but gradual ; and for this purpose I
have tried, where possible, to represent the operations which are
carried out on a large scale as almost natural evolutions arising
from the work with the laboratory apparatus, to which the
student has been accustomed.

CHAPTER I.
THE BEAKER AND ITS TECHNICAL EQUIVALENTS.

ONE of the commonest appliances used in the laboratory is the
beaker, made of glass or porcelain, and it will be instructive to
follow its evolution in working on a large scale.

Ordinary laboratory beakers are made in different sizes to
hold any quantity from an ounce or less to half a gallon or
more. They are applied for different purposes : for storing or
mixing liquors ; for dissolving solids in liquids, either in the cold
or by heat; and in some cases, though not often, for boiling
down, concentrating, and crystallising. For the latter purposes
porcelain basins are preferred. As the uses of both beakers
and basins are almost identical, we may, where convenient,
include the evolution of the basin in that of the beaker.

One of the simplest operations is that of mixing two liquids.
Suppose we had to make 100 c.c. or more of a solution of
sulphuric acid, containing approximately one part of H2S04 to
ten of water. We should measure 100 c.c. of water into a
beaker or dish, and add slowly about 10 c.c. o£ H2S04, stirring
all the time with a glass rod. Suppose, now, that we have to
prepare the same mixture on a large scale, say 100 gallons at a
time. The first question to decide would be, what material
should the vessel be made of ? We know that glass would not
do ; earthenware would stand the acid, but would be liable to
be broken; lead would stand cold acid of that dilution well,
and would not be liable to breakage ; therefore lead would be

4 ELEMENTS OF CHEMICAL ENGINEERING.

the best material for the purpose ; and in order to save expense,
the vessel would be made of comparatively thin lead, surrounded
with a wooden casing. The shape of the vessel would be pre-
determined, for the only practicable shape for casing would be a
figure in straight lines ; i.e. either a cube or an oblong box. As
regards the size, it is clear that as we have to mix the acid and
water, we must allow for splashing, and therefore make the box
about 25 per cent, larger, that is, to hold at least 125 gallons.
Now the bulk of 125 gallons equals 20 cubic feet ; we might
therefore have it either

2'0"x2'6"x4' high
or V 0" x 2' 0" x 5' „
„ 2'0"x3'6"x3' „
„ 2' 0" x 3' 0" x 3J' „

whichever dimensions may appear to strike our fancy, or to be
the most suitable for other purposes.

The mixing of the acid could be done with a wooden paddle,
which might be covered with lead; and as, in using the paddle,
it might knock with greater force against the bottom of the
vessel than against the sides, it will be advisable to have the
bottom of the vessel made of stronger lead than the sides. Con-
siderable latitude is permissible in choosing the thickness of the
lead ; the choice depends upon the number of years that one
would require the vessel to stand wear and tear. The sides
might be made of lead, '068 inch thick, the bottom 119 inch
thick. In practice it is not usual to express lead measurements
in that way, the custom being to take the weight of sheet lead
per square foot ; thus lead '068 inch thick is termed four pound
lead, and lead "119 inch thick seven pound lead. Therefore in
this case the way to express the quality of lead which should be
used would be four pound lead for the sides and seven pound
lead for the bottom. The joints where the lead sheets meet in
making the box would have to be burned by the hydrogen flame

THE BEAKER AND ITS TECHNICAL EQUIVALENTS. 5

as is the case in all chemical work, for it is clear that solder
could not be used for that purpose. The top should overlap the
casing.

We will now suppose that instead of being required to mix
weak vitriol, the problem was put to us to make a cold 10 per cent,
solution of soda-ash. In that case, if only a quantity of 100 c.c.
were required, one would measure 100 c.c. of water into a beaker
or dish, and weigh into it 10 grammes of soda-ash, and stir up
until it is all dissolved ; this would take considerably longer to
stir than the mixing of two liquids. Now if this operation is
extended, and if it should be necessary to prepare a solution of
this kind regularly on a large scale, say 200 gallons at a time,
the problem is, what vessel would be most suitable for the pur-
pose ? First of all, what is the material which could be used for
the vessel employed ? As soda-ash does not attack iron, and
iron, after all, is the cheapest material which can be used on a
large scale, it is evident that the vessel should be made of iron.
Cast- or wrought-iron could be used ; as a rule, however, cast-
iron is cheaper than wrought-iron, and also offers the advantage
of having a smoother surface, free from joints. In this par-
ticular instance, however, it might be as cheap, and perhaps
cheaper, to have an ordinary wrought-iron water-cistern 4' 0" x
3' 0" x 3' 3", and use it for the purpose. Two hundred gallons
of water might be put into this box, and 200 pounds of soda-ash
weighed and gradually put into it, the whole being stirred up
with an iron or wooden paddle until dissolved. But it will be
found that the labour on this would be considerable, and it would
therefore be advisable to construct an arrangement by which
the stirring could be done automatically by a machine. The
simplest form of a stirrer of this kind would be a centre shaft
with revolving cross pieces. It is clear that in that case the
vessel would have to be of cylindrical shape, which might be a
cylinder with a flat bottom. Most iron vessels are made with a
round bottom, and in this case it would be an advantage to have

ELEMENTS OF CHEMICAL ENGINEERING.

a round bottom, so that none of the soda-ash could lodge in the
crevices between the side and the bottom of the cylindrical vessel.
We should, therefore, construct a vessel shaped like a wash
kitchen boiler, only larger, with a flange on which we could
screw a plate to hold the gearing.

Figs. 1 and 2 show a complete arrangement of such an
apparatus, Fig. 1 in section and Fig. 2 in perspective. A is a

FIG. 1. — Sectional elevation of iron vessel and stirrers, for dissolving
soda-ash in water.

cast-iron pot with flange, across which is an iron plate B about
6" wide, bolted on to the flange ; through the middle of this plate
goes a shaft which rests on the bottom in a footstep C, and
passes through the collar D, which is fixed on plate B. The
shaft is best made square, and only rounded at the top and
bottom part so as to revolve in C and D. F and G are stirrers
at right angles to each other, either clamped round or fastened
through slots in E. H and J are spur wheels which change the

THE BEAKEE AND ITS TECHNICAL EQUIVALENTS. 7

vertical motion into a horizontal one. KK are the axle
bearers, while L L are fast and loose pulleys, which are worked
from the shafting above by means of an endless belt.

There are cases when it is not convenient to employ this
kind of stirrer, which, moreover, is not always very reliable, as
in revolving round in large quantities of liquids, particularly
those of a viscous nature, the liquor is apt to go round with the
agitator without properly mixing. In such cases, and where it

FIG. 2. — Perspective view of vessel represented in section in Fig. 1.

is desirable to employ a rectangular vessel, another kind of
agitation may be used, based on the working of a ship's screw.
Figs. 3 and 4 show such an arrangement.

A is a square tank, and B is a vertical shaft which moves in
footstep and collar as in Fig. 2, the latter being fastened on a
plate N. D is an Archimedean screw surrounded by a pipe C,
which is fastened to the bottom of the tank ; the bottom of it
is perforated so that the screw can draw the liquor from the
bottom of the tank, pump it up in the direction of the arrows,

ELEMENTS OF CHEMICAL ENGINEERING.

and deliver it at the outlet of the pipe. In this way every part
of the liquor is pumped through the pipe, and a thorough
mixing ensured.

The next step that we have to consider is the conditions
under which these operations would have to be carried on if it
were necessary to heat the liquid at the same time as it is being
mixed. Three ways are open to us to do this. The first way
is by simply blowing live steam into the liquid ; in that case
the volume of the liquid will become larger as the steam

Fio. 3. — Sectional elevation of vessel for mixing liquids by means of an
Archimedean screw.

condenses in it. Where this does not matter, it is the simplest
way of heating the liquid. The next arrangement would be to
pass steam through a coil contained in the tank and heat the
liquid in that way. The third way would be to heat the pot by
a coal or coke fire. Going back to Fig. 2, it can be easily seen
that if the pot were to be heated by open steam the arms of the
agitator would have to be cut shorter so as to allow of the steam
pipe going down at the side of the pot, as otherwise, if they
were brought near to the sides of the pot, they would knock
against the pipe at each revolution. Of course the pipe could

THE BEAKER AND ITS TECHNICAL EQUIVALENTS. 9

be brought along the outside and taken in at the bottom of the
pot through a hole bored through, but this would be an awkward
arrangement, as with any differences of temperature the liquor
might be drawn back into the steam pipe. In heating by means
of closed steam, an agitating arrangement like that described in
Fig. 2 would be awkward, unless the coil were specially made
to fit close to the sides of the pot, and such a coil would be
expensive. It will now be seen why it is sometimes advisable

YHI. 4. — Perspective view of vessel represented in Fig. 3.

co have a rectangular tank for purposes of this kind, and why
the agitating arrangement described in Fig. 3 is sometimes
preferable. In that arrangement it would be easy to use either
a steam pipe or a steam coil. The steam coil could be placed at
the bottom, and both the inlet of steam and the outlet for the
condensed water could be regulated by taps.

If the pot is to be heated by open fire, some new principles
which do not come into consideration in laboratory work will
have to be considered. When we heat a beaker in the laboratory
from a gas jet, it is simply placed on the wire gauze net and

ELEMENTS OF CHEMICAL ENGINEERING.

the flaiue applied underneath. It is natural that in that way
a great deal of the heat is lost by radiation ; and on a large
scale, where it is necessary to consider the question of economy
very carefully, it would not be advisable to heat the bottom of
the pot only. The arrangement should be such as to allow of
the heat being supplied to a much more extensive surface. The
simplest and most efficient way is to convey the hot gases from
the burning coal round the pot by means of the wheel flue
shown in Figs. 5 and 6.

Fig. 5 represents a vertical section, and Fig. 6 a plan of the

FIG. 5.— Vertical section of Wheel Flue.

arrangement. A is a cast-iron pot which rests on a solid brick
pillar B. The fire grate C is separated from the bed D of the
furnace by the bridge E, which also prevents the fuel from
being carried over. The gaseous products of combustion pass
over the bridge under the pot, then upwards through the flue K
into the flue F, where they are taken round from left to right
through G into a flue which conveys them to the chimney.
The chimney draught is controlled by a damper H. Even with
an arrangement like the above, a great deal of the available heat
is still lost. It is in many cases more economical to put two or
three furnaces together, working them from only one fireplace

THE BEAKER AND ITS TECHNICAL EQUIVALENTS.

under the front pot. The waste gases in that case pass from
the exit flue of the first pot, which otherwise would lead into
the chimney, under the second pot; they are then made to
circulate first round the second pot, then round the third pot,
and then into the chimney. In arrangements of this kind cold
liquor is fed into the coldest pot, namely, the third pot, and
syphoned automatically first into the second pot, and then into

FIG. 6. —Plan of Wheel Flue.

the first pot, which will always contain the most concentrated
liquor.

It is evident that one of the principal points to be considered
in the construction of an evaporating plant is that the products
of combustion should be used to the greatest advantage, that is,
that as large a surface as possible of the evaporating vessel
should be exposed to their action ; hence, the surface of the
vessel should be a maximum with regard to its volume. The

ELEMENTS OF CHEMICAL ENGINEERING.

instances which we have given so far are, theoretically,

not adapted to fulfil these
conditions. It is well known
that the half section of a
sphere offers the least sur-
face with regard to its
volume. It would be pos-
sible to increase the ratio
between surface and volume
by making the pot shallower,
but it will be more difficult
then to build a flue round
it. It is evident that there
is no reason why differently
shaped evaporating vessels
should not be used ; for
instance, one which would
resemble a bath, such as is
used for domestic purposes,
or a cylinder cut in two.
The latter would give more
surface in proportion to its
length. If, for instance, the
length were four times the
radius of the corresponding
cylinder, we should gain
25 per cent, in surface, as
compared with a half sphere
of equal volume ; if it were
eight times longer than the
radius, we should gain 40
per cent. As the flues follow
straight lines instead of curves, they will be easier to build,
easier to clean, and more economical to construct.

THE BEAKER AND ITS TECHNICAL EQUIVALENTS.

Figs. 7 and 8 represent such an arrangement.

The pan A A, which in this case is made of wrought-iron,
rests on the brick walls E E. The fire gases travel underneath
the pan, then upwards, and are divided by the pillar F ; they
then pass through the right and left flues B and C simultane-
ously, join up again in the front at D, and are taken from this
into the main flue. Dampers are provided in the flues B and
C to regulate the draft in each of the side flues, in case it should
be stronger on one side than it is on the other. The question will

FIG. 8. — Transverse section of semi- cylindrical evaporating vessel.

be asked : Why not always use a long pan ? The answer to
this will be apparent if drawings are made of a pot and of a pan,
the latter having a length eight times the radius of the corre-
sponding cylinder, each capable of holding 100 gallons. It will
then be noticed that for small quantities of liquid there is no
advantage in a long pan, as the side flues become so shallow
that the surface cannot be utilised to its best advantage in
economising heat. The question of cost of plant will also often
determine the shape of the evaporating vessel ; for whilst,
weight for weight, cast-iron is cheaper than wrought-iron,
vessels made of the former have to be constructed in much

ELEMENTS OF CHEMICAL ENGINEERING.

thicker metal, and therefore may become more expensive than
wrought-iron apparatus, always provided that in the latter
the cost of shaping and riveting is not excessive. A small
cast-iron pot may be cheaper than a wrought-iron pan, and a
large cast-iron pan may be dearer than a pot or pan made
of wrought-iron.

In the boiling down of solutions it often happens that solid
matters separate out and settle on the sides of the evaporating

FIG. 9.— Side view of Thelen Pan.

vessel. The crusts which are thus formed are dried by the
heat of the flue gases, and being in every case worse conductors
of heat than iron or metal of any kind, prevent the heat from
passing to the liquid, and thus doing its work economically. In
consequence of this, the evaporating vessel is unequally heated,
so that, where incrustation occurs, the undue rise of temperature
may tend to alter the shape of the vessel or to burn through
the iron. It is therefore in many cases advisable to have a
mechanical arrangement which keeps the sides of the evaporat-
ing vessel free from incrustations. This purpose may be

THE BEAKER AND ITS TECHNICAL EQUIVALENTS.

effected by means of an agitator, the arms of which are arranged
in such a manner that they traverse every part of the sides
of the pot. A better arrangement would be one which would
at the same time remove the precipitated matter altogether
from the liquid. Such a design is shown in Figs. 9 and 10,
and is known by the name of a Thelen pan.

A A is a pan similar to the one
last described. A shaft BB
works in bearings at each end
and is provided with arms, each
carrying a small movable shovel
at its end. The arms are ar-
ranged in such a manner that
the little shovels push all de-
posit towards the end of the
pan, where it is taken up by
another shovel and lifted bodily
out of the pan into a draining
vessel, from which the liquor
can drain straight back into the
pan. Several of these pans may
be so arranged that the waste
heat from one pan heats the
succeeding one.

A natural consequence of the
foregoing remarks is that an

evaporating pan should always be filled with liquor above the
highest point of the surrounding flues, otherwise these parts
would become overheated, and would soon deteriorate.

In the above-described apparatus the liquor to be concentrated
has been placed in a suitable vessel, and the fire gases pro-
duced from the combustion of fuel have been passed under and
round the vessel without coming into contact with the liquor
to be evaporated. But an arrangement could be designed by

FIG. 10. — Transverse section of
Thelen Pan.

16 ELEMENTS OF CHEMICAL ENGINEERING.

which the products of combustion would be passed over the
surface of the liquor which has to be concentrated. Such an
arrangement is occasionally used, but it has the great draw-
back that naturally the liquor becomes contaminated with dust
and objectionable impurities, such as sulphurous acid, which is
almost always present in the products formed by the combustion
of coal. This device is therefore not often used, though it is
possible that with the extension of gas for fuel it may be found
useful in certain cases in which it has hitherto not been applied.
An ingenious apparatus, termed a Porion evaporator, is built on
these lines, and is constructed in such a manner that whilst
the fire gases pass over the liquid, the latter is converted into
a fine spray by means of paddles revolving at great speed.

We have, so far, considered such technical evaporating
arrangements as have a close structural resemblance to the
Bunsen burner placed under a beaker or basin filled with liquid
as commonly used in laboratory practice. It is often found
more advisable in laboratory work not to use the naked flame
for these operations, but to use a water, sand, metal, oil, or air
bath, in order to obtain lower or higher and fairly constant
temperatures. Where similar results have to be obtained on a
large scale, there should be no difficulty, after the preceding
remarks, to elaborate arrangements of this kind suitable for
technical work, bearing in mind all the time that in working
on a large scale we have an important auxiliary in steam, which,
with few exceptions, chiefly found in experimental dye-houses,
is not to any great extent made available in college laboratories.
As a matter of fact, it is often more difficult to put together
a small laboratory apparatus with closed -in steam than it is to
construct a large apparatus in the works. As steam can be
produced at different pressures, and consequently at different
constant temperatures ; as it can, moreover, be superheated
to still higher temperatures than those which belong to it at
its relative pressure, we have a ready means of producing and

THE BEAKER AND ITS TECHNICAL EQUIVALENTS.

maintaining constant temperatures ranging from 100° C. to about
400° C.

Where a sand-bath, oil-bath, or metal-bath is used, the arrange-
ment will be almost identical with that used for the same
purpose in the laboratory. If we use vessels of pot shape, it
will only be necessary to place one pot inside a larger one, and
fill in the empty space between the two with either sand, oil,
lead, or any alloy which will give the required temperature.
AVhen steam is used, a similar arrangement may be resorted to,
but with this difference,
that the two pots will »*--
have to be jointed to-
gether steam-tight. Such an
arrangement is shown in Fig.
11.

It is necessary to let the
steam enter at the top, and to
remove the condensed water
and superfluous steam at the
bottom, so as to give the waste
steam and water a free passage.
In order to use the steam most
economically, it is necessary
to take care that no more

FIG. 11. — Steam-jacketed vessel.

steam is used than will conveniently condense, so that only
hot water may leave the apparatus. This may be either used
for feeding the boiler or for other purposes where hot water
is required, or it may be taken through suitable coils placed
in the liquid which feeds the boiling-down pan, and thus
serve to give that liquid a preliminary heating.

In constructing jacket pans, care must be taken to make
sufficient allowance in the strength and shape of the vessels to
stand the pressure of the steam, and it will in many cases be
found advisable to make the surrounding or outside jacket of

ELEMENTS OF CHEMICAL ENGINEERING.

wrought-iron, which will resist a greater amount of pressure for
the same thickness of metal than cast-iron. All apparatus of
this kind — in fact, all apparatus which has to stand exterior or
interior pressure — should be designed so as to present as little
surface of a plane shape as possible; all surfaces should represent
curves. This precaution need not be taken if we pass the steam
through a coil placed in a suitably shaped evaporating vessel ;
in that manner the initial expense is reduced; and as it is
possible to obtain welded coils of wrought-iron of almost any
shape, vessels of different material, and of pot, pan, or box shape,

CO a •"•• W0&

FIG. 12.— Steam- jacketed Bath.

may be used in conjunction with steam heating coils. The
objection to coils is, that where solids are apt to be deposited,
they are troublesome to keep clean, and when covered with
incrustation they become inefficient. An ingenious device has
been resorted to to overcome this objectionable feature, and
one which combines the advantages of a jacket and coil pan.
It has been found possible to cast molten iron round coils of
wrought-iron pipes, so that a cast-iron vessel may be obtained
which can be heated by steam passing through the sides which
define its shape. Fig. 12 shows such an arrangement, which
requires no further explanation.

THE BEAKER AND ITS TECHNICAL EQUIVALENTS. 19

Care should be taken in all cases to minimise radiation from
the evaporation vessel ; this is done either by surrounding it
with several courses of brickwork, or by coating it with
compositions which have little conductivity for heat, such as
the well-known compositions which are used for steam-boiler
coverings. In using coils for evaporating purposes, there is one
point which must be particularly watched. If steam is passed
through a coil which is slightly leaking, two things may happen :
the steam may escape into the surrounding liquid and cause
unnecessary dilution, or the surrounding liquid may be drawn
through that fine opening, and in that way loss may be caused.
Wherever a coil is used for evaporating purposes, it is therefore
necessary to test the condensed water from time to time, to see
that it is free from any of the substance which is placed in the
boiling-down vessel.

In special cases it will be found that the waste steam from
the steam engines may be utilised for evaporating purposes, and
wherever this is possible it should be done. We shall have
occasion to refer to this again.

We have, so far, only dealt with the commonest forms of
apparatus for evaporation, not only for the reason that they are
used more extensively than others, but because they illustrate
most clearly the principles on which such apparatus is con-
structed. In the space at our disposal, it is impossible to deal
with every kind of known apparatus, and special modes of
evaporation, such as Brine towers, the Glover towers, and others,
have therefore not been mentioned. These and many other
kinds of apparatus may be, and have been, constructed for special
purposes, but there is no necessity to describe every one in
detail. They are all based on the principles which we have
explained, — that is, to give as much surface to the evaporating
vessel as possible, and to use up waste heat.

Cases arise in which the vapours evolved from the boiling
liquids have to overcome a greater pressure than that of the

20 ELEMENTS OF CHEMICAL ENGINEERING.

atmosphere, or in which the pressure under which they are
evolved is less than that of the surrounding atmosphere, i.e.
about 15 Ibs. per square inch. These cases may be considered as
processes of evaporation or of distillation, for no hard-and-fast
line can be drawn between the two. For our purposes it will
be most convenient to treat all processes of evaporation which
take place in a closed system as processes of distillation, and
thus include in that category evaporation under increased or
diminished pressure. Taking that view, we proceed to the
next chapter, in which we will deal with apparatus used for
distillation and condensation, including the important subject
of evaporation in a vacuum.

CHAPTER II.

DISTILLING FLASKS, LIEBIG CONDENSERS, FRACTION-
ATING TUBES, AND THEIR TECHNICAL EQUIVALENTS.

WE have mentioned in the preceding chapter that evaporation
may be carried on under either increased or diminished pressure.
Practically speaking, all the apparatus which has been described
so far for evaporating can be easily converted into part of an
apparatus for boiling down under a pressure, or in a vacuum, by
simply putting a lid on the top of either the pots or pans
described. Evaporation under pressure will be dealt with later
on, when describing the construction and function of a steam
boiler. Before describing the form of apparatus used for
evaporation in a vacuum on a manufacturing scale, we will
consider the apparatus used in the laboratory for similar
purposes.

In its simplest form, this consists of a flask or retort into
which the liquid to be evaporated is placed. This vessel
is connected with a Liebig condenser, from which the condensed
distillate passes into a Woulfe bottle. If the latter is joined up
to a Bunsen pump, the distillation may take place in a vacuum.
It is well known that with diminished pressure the boiling
point of all liquids is considerably lowered, and that it is
therefore possible to distil or evaporate liquids at a lower
temperature in a partial vacuum than would be the case at
ordinary pressure. In laboratory work this is chiefly done
when the liquid which is to be evaporated would become

22 ELEMENTS OF CHEMICAL ENGINEERING.

partially or wholly decomposed if evaporated at its normal
boiling point. A solution of sugar, for instance, will partially
decompose and become discoloured if evaporated under atmos-
pheric pressure, whereas in a vacuum it yields pure white
crystals. But whilst in the chemical laboratory the above is
almost in all cases the only reason for which evaporation in a
vacuum is resorted to, it is found in practical work that, even
where one has to deal with stable substances, evaporation in a
vacuum may offer such advantages as to counterbalance the extra
cost of the apparatus, cost of condensing, and other incidentals.

We will now attempt to evolve, from the laboratory apparatus
which we have described, the simplest form of apparatus suitable
for technical purposes. We have first to consider how to
transform the flask which holds the liquid, and which in the
laboratory would be heated by means of a water-bath or similar
arrangement ; this we can replace by any of the pot-shaped
boiling-down appliances which we have mentioned, particularly
by a jacket pan, such as is shown in Fig. 11. We should simply
provide this pan with a lid, which, as it has to stand pressure,
would be of spherical or similar shape, and would contain a pipe
at the top for the purpose of carrying away the steam which is
given off.

In the laboratory apparatus the steam from the boiling liquid
would be taken through a Liebig condenser ; on a large scale the
latter might be replaced by an upright pipe, which may be
cooled from the outside by a stream of water trickling round
its circumference ; or the cooling water may be injected into
the pipe by a spray arrangement, and, mingling with the steam,
condense it. The Bunsen pump which would be used in the
laboratory arrangement would be replaced by a mechanical
vacuum pump, of which there are two kinds. If constructed
for keeping up a vacuum by drawing out the air only, it is
termed a dry air pump ; if it draws the condensed steam and
condensing water as well, it is termed a wet vacuum pump.

DISTILLING FLASKS, ETC., AND THEIR TECHNICAL EQUIVALENTS. 23

Fig. 13 shows such a simple arrangement, and represents the
principles underlying the construction of vacuum apparatus.

Alterations and additions naturally occur in improved working
apparatus.

24 ELEMENTS OF CHEMICAL ENGINEERING.

Thus it is advisable to have sight glasses A, one opposite to
the other, on the lid, so as to be able to watch the progress of
the operation. It is also necessary to make provision against
boiling over by means of a dome B, or otherwise, in the case
of liquids which produce a great amount of froth. There
are many minor details of construction which distinguish
different makes of vacuum apparatus made by different re-
puted firms. Some vacuum pans are supplied with pipes
through which the liquid can circulate, and which, therefore,
offer a greater surface to the heating steam ; some have means
of discharging salts which separate out without breaking the
vacuum. All these improvements add to the efficiency of the
apparatus, but they also add to its cost, and sometimes, by their
complication, cause frequent breakdowns. Where the con-
densing water is sprayed into the condensing tower, it will be
advisable to ensure that the water enters the tower under as
little pressure as possible, as otherwise a back pressure will
be produced, which will reduce the vacuum, or at any rate
will render it more expensive to keep up a good vacuum.
As the temperature at which a liquid will boil varies with
the pressure, or, to put it more clearly, but less scientifically,
as it is to some extent inversely proportionate to the vacuum,
it follows that the better the vacuum which is kept up in the
apparatus, the lower will be the temperature at which the
evaporation will take place, and the higher the efficiency of the
whole apparatus. It also follows that as water will boil at 50°
C. with a moderate vacuum, the steam which is used for heating
the vacuum apparatus will do its work as long as it is above
that temperature, so that, whilst in an open apparatus it would
be necessary to work with steam of over 100° C., with vacuum
apparatus, steam even at 50° C. will produce a sensible
evaporating effect. It is here, therefore, where the exhaust
steam from engines, which in most cases has a temperature
not much over 100°, will be found particularly effective and

DISTILLING FLASKS, ETC.. AND THEIR TECHNICAL EQUIVALENTS. 25

economical. As the boiling point of every liquid is lowered in a
vacuum, it is possible to distil substances by means of steam
which otherwise would not be amenable to that agent ; one
could, e.g., distil a substance boiling at 200° with steam of 150°
C. On the other hand, one has to be careful, on evaporating
liquids containing substances which decompose at certain
temperatures, not to use the steam at too high a temperature,
otherwise these substances, notwithstanding that the operation is
performed in a vacuum apparently kept below the decomposing
temperature, may partially decompose. The reason for this is,
that the sides of the vessel become temporarily heated nearly
to the temperature of the heating steam, and though the liquor
in the pan would be exposed to that temperature only for a
very short time, a slight decomposition would take place at the
contact points, and in the time required for an operation
might cause serious loss. In such cases, again, evaporation in a
vacuum often enables us to utilise waste steam with great advan-
tage. Where waste steam is not available, and where the steam
which comes direct from the boiler has to be reduced in pressure,
and consequently in temperature, this is clone by an apparatus
which is called a reducing valve — a simple contrivance which con-
sists of a valve which regulates the flow of the steam so that it ex-
pands at such a ratio as to reduce its temperature and pressure.
If we heat a liquid by means of closed-in steam, that is,
by means of a jacket, coil, or similar arrangement, steam is
ultimately evolved from that liquid. There is no reason why
this steam should not be conducted into the jacket of another
pan or through a steam coil or similar arrangement, and made
to heat up a further quantity of liquid and produce steam again,
though of lower temperature and pressure. An arrangement
of such a system is practically feasible, and is . known as
c multiple-effect evaporation.' Two apparatus coupled together
represent what is termed double-effect ; three, triple-effect ; four,
quadruple-effect, etc. It is possible thus to utilise heat for

26 ELEMENTS OF CHEMICAL ENGINEERING.

the purpose of evaporation more efficiently than by any other
system, but it does not follow that an arrangement of this
kind will be always the most economical in work. The cost of
evaporation in every case is composed of a number of factors,
including the cost of coal required to evaporate the liquid,
the cost of labour in attending to the boiling down, the interest
and depreciation on the outlay for plant, the repair for the
same, and other general charges which we need not consider at
present. If, for instance, we found that in order to boil down
a certain quantity of water, say 1000 gallons per day, we
required one ton of coal at 10s., if the labour in attending to
the pan came to 4s., and if the tatal cost of the apparatus were
£100, and the wear and tear of this, including interest
on the money laid out, came to £15 per annum, which is
Is. per day, the total cost of evaporation would come to 15s.
per thousand gallons. If, on the other hand, we found that
the original cost of the installation in multiple evaporation
were £1000, which at 15 per cent, would represent £150
per annum, or 10s. per day, we should find that, even if the
labour and other expenses were the same as with an ordinary
boiling-clown pan, the cost of evaporation would be still higher
by that system, although the amount of coal, or rather its
equivalent in steam, used for evaporation might only come
to three or four shillings per day, against the 10s. which we
had to spend on fuel in evaporation in open pans by direct
fire. These calculations do not represent actual facts, but are
intentionally exaggerated so as to show the necessity of not
being misled by only taking one factor into consideration when
the cost of an operation has to be considered. There is little
doubt that the principle of multiple evaporation will in the
future play an important part in the construction of evaporat-
ing apparatus. At present the apparatus in many cases is
still too complicated and too costly, and is therefore not used
to the extent which it deserves.

DISTILLING FLASKS, ETC., AND THEIR TECHNICAL EQUIVALENTS. 2?

We may now proceed to consider the construction of
an apparatus used for what is generally understood as
distilling. A convenient example of such an apparatus is
presented in the manufacture of nitric acid. In the
laboratory nitric acid is generally prepared by mixing
sodium nitrate and sulphuric acid in a glass retort con-
nected with a receiver which, being cooled, condenses the
vapours of nitric acid which are given off. It is well known to
the student of chemistry that this method of preparing nitric
acid is capable of various modifications. To start with, one
may aim from the outset at obtaining a very strong nitric acid,
one approaching HN03 as near as possible ; or one may be
satisfied with obtaining a weaker acid, say one containing only
66 per cent, of HN03. In the one case it would be necessary
to use pure dried sodium nitrate and strong sulphuric acid
containing at least 98 per cent, of H2S04. In the other case
ordinary commercial nitrate and sulphuric acid of commercial
quality of a specific gravity of 1*75, and equal to about 80 per
cent, of H9S04 in strength, may be employed. Moreover, the
quantity of acid may be chosen so as to yield a product in
the retort which may be either Na2S04 or NaHS04, or a
mixture of the two. If the proportions between sulphuric acid
and nitrate of soda are chosen in such a way that they may be
represented by the equation 2NaN03+H2S04 = Na2S04 +
2HN03, then the remaining mass in the retort will be sodium
sulphate in such a form that it will be impossible to remove it
from the retort without breaking the latter. If the operation
is carried on in such a manner that it may be represented by the
equation 2NaN03 + 2H2S04 = 2NaHSO4 + 2HN03, then the mass
formed in the retort will melt at the comparatively low tempera-
ture which is necessary to produce the liberation of nitric acid,
and it will be possible to pour out the molten sodium hydrogen
sulphate at the end of the operation without breaking the
retort. One difficulty will have presented itself in putting

28 ELEMENTS OF CHEMICAL ENGINEERING.

together the distilling apparatus, and that is how to make the
connection with the retort and the receiver tight, as hot nitric
acid will attack cork, rubber, or any other of the materials
which are generally used for the purpose of making joints
in ordinary laboratory work. With the facilities which one
has now in getting glass apparatus of this kind, this difficulty
is often overcome by having the retort neck ground into
the neck of the receiver.

If we now consider how we may construct an apparatus
suitable for manufacturing large quantities of nitric acid, we
must bear in mind all the points which we have explained in
connection with the laboratory process, and decide if the work is
to be done in accordance with the first or the second of the
equations given above. In practice, it is not usual to go as far as
2H2S04 in the second equation ; generally one and a quarter or a
little more is taken, i.e. just sufficient to form a compound which
will melt at "the temperature at which the retort is kept, and
which, therefore, will enable us to run off the charge in the retort
when the operation is finished. If the proportions chosen are
two NaN03 to one H2S04, so that Na2S04 results as the end
product in the retort, it will be necessary to use such an
apparatus as will enable us to chip out the contents of the
retort after each operation. For this purpose a cylindrical
vessel is generally used, about 5 feet long and about 2 feet in
diameter, provided with a cover in front, which is taken off after
each operation, so as to enable the workman to chip the sodium
sulphate, or salt-cake, as it is generally termed, out of the retort.
Apart from the extra labour which this involves, it is also
necessary to cool the apparatus for about twenty-four hours before
it can be opened and emptied and got ready again for another
charge. In this mode of working there is a saving in sulphuric
acid, and the product obtained is commercially more valuable, but
the relative charges for labour and interest on installation, and
the loss in fuel caused by the heating up and cooling down of

DISTILLING FLASKS, ETC., AND THEIR TECHNICAL EQUIVALENTS. 29

the apparatus between the charges, are considerable. For this
reason it is often preferable to use such an excess of sulphuric
acid as to produce a mixture of sodium sulphate and hydrogen
sodium sulphate in the retort, which, being liquid at the end of
the operation, can be let off through a convenient tap-hole,
leaving the still ready for another charge without loss of time
and with little expense for labour. In an apparatus which is
designed for this purpose, the still will have the shape of an
ordinary pot with a round cover on it, similar to the one shown
in Fig. 13 ; the dimensions of these pots vary considerably, the
charges they will hold ranging from a few cwt. to one ton and
more of nitrate of soda. They are provided with a pipe going
through the lid, through which the sulphuric acid is passed into
the still ; there is also a charging hole, sufficiently large to
enable the workman to throw in the nitrate of soda with a
shovel ; there is, further, a connecting piece on the top to
which the earthenware pipe conveying the nitric acid vapours to
the condensing plant is secured. We have already mentioned
that there is a convenient tap-hole at the bottom of the still for
letting off the molten residue. The still and all these parts are
made of cast-iron, as this resists the action of sulphuric acid
down to acid of 80 per cent, fairly well. But there is some
action, and it is necessary to allow for the gradual eating away
of the iron, and to make the bottom part of the still, as far as
it is touched by the sulphuric acid and the acid sulphate, of
sufficient thickness, say 2 inches or more. It is further
necessary to brick in a still of this description in such a manner
that the nitric acid vapours cannot condense in the upper part
of the still and on the lid, as the fumes of nitric acid do not act
nearly so strongly on the iron as the condensed acid does. The
lire gases are therefore conducted round the pot as we have
shown in previous examples, and in many cases taken over the
lid of the still, though this complicates the matter considerably,
and the same effect can be obtained by other means.

30 ELEMENTS OF CHEMICAL ENGINEERING.

Having settled the form which our laboratory retort would
have to take to enable us to prepare nitric acid on a large scale,
and the material of which it would have to be constructed,
we may now consider how to deal with nitric acid vapours so
as to get them condensed. First of all we must ascertain the
material of which the condensing part will have to be con-
structed. Iron is naturally out of the question, as it would
be destroyed, and at the same time would reduce the nitric acid
to lower oxides ; no other metal could be used except platinum,
which would be too expensive. We are therefore compelled to
use earthenware. Fig. 14 shows different kinds of apparatus
used for the purpose ; a number of receivers A A may be com-
bined with a plate tower B and an earthenware worm C, or
receivers only may be used, and the last traces of nitric acid
may be washed out in a tower filled with earthenware solid
or hollow balls, over which water or sulphuric acid is passing.
Here we meet with the difficulty which we have mentioned in
discussing the process as carried on in the laboratory, viz. the
joining up of the different parts. This in practical work is
effected by means of lutes or cements which are filled into the
interstices at the junctions ; thus the socket D would be filled
in with cement as far as it would hold the latter after the pipe
E had been placed in position. Naturally, it will be necessary
to choose such a lute as will resist the action of nitric acid
vapour, and a number of these lutes or cements are recommended
for the purpose. It will be sufficient to mention only a few.
Thus, where it is desirable -to allow a certain amount of play
on account of expansion by heat or for other reasons, a plastic
lute which does not set hard is advisable; for instance, one
made by heating up linseed oil with sulphur and old india-
rubber cuttings, and incorporating in the resulting mass barium
sulphate and asbestos fibre. Where a hard setting cement is
required, a mixture of sodium silicate and ground glass may be
used.

DISTILLING FLASKS, ETC., AND THEIR TECHNICAL EQUIVALENTS. 31

The principle of condensation is analogous to that of evapora-
tion. One may cool by air or by water, or by freezing mixtures,

but in every instance the apparatus, to be efficient, must be
constructed in such a manner that the largest surface is
presented to the cooling medium.

32 ELEMENTS OF CHEMICAL ENGINEERING.

The example on which we have demonstrated distillation
shows how important it is to carefully study the chemical
reactions which take place, so as to design the apparatus
accordingly ; how necessary it is to consider the action of the
chemicals used and produced on the material of which the
separate parts of the plant are composed, and how even the
smallest details, as in this instance suitable jointings, must be
attended to.

Fractionating distillation is a process by which mixtures of
liquids containing several constituents which boil at different
temperatures are separated. The general view is, that at the boil-
ing point of a mixture of liquids, the more volatile constituent
evaporates first, and carries with it only a certain quantity of
the higher boiling constituents. If, therefore, the part which
passes over is cooled, a product is obtained which consists
chiefly of the lower boiling parts of the mixture. As the
distillation proceeds, the residue in the retort will gradually be
freed from the more volatile part of the mixture, and its
boiling point will accordingly be raised. It is not possible to
separate every mixture by fractionating. Cases occur where
the mixtures at a certain point of the distillation form groups
which may be considered as combinations, and in that case,
although the distillate will pass over at a fixed temperature, it
will not be a pure compound, but a mixture or combination of
fixed boiling point. Thus a mixture of 8 per cent, of water
and 92 per cent, of alcohol cannot be separated by fractionating.
On boiling a weak aqueous solution of hydrochloric acid, water
will be given off until the residual product contains a mixture
of 20 per cent, of HC1 and 80 per cent. H20 ; and on boiling a
strong solution of hydrochloric acid in water, hydrochloric acid
gas will be given off until the remainder in the still is again
composed of 20 per cent, of hydrochloric acid and 80 per cent,
water ; and in both cases the boiling point will be found to be
110° C.

UNIVERSITY

DISTILLING FLASKS, ETC., AND THEIR TE'dHNICAL EQUIVALENTS. 33

The ordinary apparatus which is used for fractionating in the
laboratory consists of a flask provided with a fractionating
tube, which is connected with a Liebig condenser. Many
different designs of these fractionating tubes have been proposed,
though all are based on the principle of giving the vapours a
certain amount of resistance in passing through, and of in-
creasing the cooling surface, and thus effecting the condensation
of the higher boiling vapours, whilst the lower boiling vapours
pass on through a Liebig condenser. On a large scale the
principle is exactly the same. The mixture of the liquids which
have to be separated is placed in a still of suitable shape, made
of such material as will not be attacked by the substance which
has to be manipulated. It is sometimes most difficult to find
a suitable substance from which to construct the still, and
the most varied materials are used, including cast-iron,
wrought-iron, copper, silver, lead, enamelled iron, earthen-
ware, and even glass. According to the nature of the sub-
stances and the temperature they require for separation, the
still may be heated by open fire, by steam, or by hot water ;
wherever inflammable liquids have to be treated which give off
vapours at comparatively low temperatures, it is a fixed rule
that no open fire must be used. Fig. 15 shows the general
arrangement of a fractionating plant.

The vapours which come from the still pass through a
separator A, which corresponds to the fractionating tube as used
in the laboratory model. This separator generally consists of a
metal tube A, which may be divided horizontally into a number
of compartments by sieves, as shown in Fig. 16, or by plates
provided with lutes covered by balls, as shown in Fig. 17.
Provision is made at the sides for tubes so that condensed liquid
may run back into the still. The distillation is regulated in
such a manner that if the separator is kept at the proper
temperature, only vapours pass from it into the vessel B above.
This vessel really represents the Liebig condenser of the

ELEMENTS OF CHEMICAL ENGINEERING.

DISTILLING FLASKS, ETC., AND THEIR TECHNICAL EQUIVALENTS. 35

laboratory apparatus, but inverted, so that whatever condenses
in it first goes back in the separator, and the more volatile
constituents pass on into the receiver C, where they are
completely condensed. It may not be unnecessary to point out
that in a system of this kind the distillation and separation of
the constituents take place partly in the still, but to a great
extent in the separator, and that the success of the operation
depends largely upon the proper management of the cooler B,
which regulates the quantity of liquid which runs back into the
separator.

CHAPTER III.

THE AIR-BATH AND ITS TECHNICAL EQUIVALENTS.

THE air-bath is used in the laboratory for drying substances at
different temperatures. It may be heated directly by gas, or
the heat may be transferred to its interior through a water
jacket. The purpose of the drying operation is in most cases to
expel water from solids, though cases occur in which other
liquids have to be separated in this manner from solids, or from
liquids which boil at a higher temperature. As the problem of
expelling superfluous water from solids is the one which most
frequently occurs in practice, we will confine our remarks to
this particular case.

It must be clearly understood that the operation of drying is
not identical with that of ordinary evaporation. In ordinary
evaporation we produce, by the application of heat and by the
evolution of steam, currents which enable the particles of the
liquid to move about freely, and thus to conduct the heat
fairly well. Although, therefore, water, and many compounds
which dissolve in it, are in themselves exceedingly bad con-
ductors of heat, yet in the process of evaporation, as it is
generally understood, the bad conductivity is overcome by the
mobility of the liquids. But whenever the problem before us
consists in drying a mixture of a solid and a liquid, in which
the particles cannot freely move, we have to take into con-
sideration and allow for the fact that the heat has to be
transferred through a bad conductor. We know that without

THE AIR-BATH AND ITS TECHNICAL EQUIVALENTS. 37

special mechanical arrangements 1 pound of coal will evaporate
from 5 to 10 pounds of water from a liquid which remains
such during the process, but it will be impossible to expel any-
thing like that quantity of water from a pasty mass, and the
best mechanical arrangements will not enable us to obtain
results which in ordinary evaporation would be considered
barely satisfactory.

In using the air-bath in the laboratory, we may either use it
with only an opening at the top through which the vapours
evolved may pass, or we may have an opening at the bottom as
well, and thus produce a current of air during the drying
process. If we adopt the latter arrangement, we shall find that
we obtain the desired results in a shorter time, as the moist
substance, instead of being in a stagnant atmosphere saturated
with moisture, will be exposed to a constant current of air,
which not being fully saturated with water, will take up
moisture in its passage. The same applies to work on a large
scale ; but whilst the small quantities manipulated in the
laboratory are generally left undisturbed in the air-bath, the
large quantities dealt with on a manufacturing scale have to be
stirred up by hand or by mechanical means, or they may have
to be moved about and transported from one part of the drying
machine to another.

In the first instance it is necessary to deprive those goods
which have subsequently to be dried by heat of as much
moisture as possible by such means as will be explained in
Chapter VII. Crystals should be drained and, where possible,
dried by a centrifugal machine; precipitates should be deprived
of as much water as possible by means of filter-presses or other
pressing machinery. Only after such preliminary treatment
should the process of drying by heat be resorted to.

As it is often necessary to make use of mechanical arrange-
ments which recur in different forms of drying apparatus, it
may be advisable to give a description of some mechanical

38 ELEMENTS OF CHEMICAL ENGINEERING.

arrangements which we have, so far, not had occasion to consider,
and a study of which will render the subsequent explanations
of drying machinery more lucid and easier to understand.

Supposing we had many tons of crystals which had to be
transported from one end of a room to the other, we could do
so by placing them in a wheelbarrow and wheeling them from
one end to the other ; but the same object could be obtained by
having a roller fixed at either end of the room, over which a
sheet of calico of the width of the rollers was stretched in such
a manner that it would form an endless belt. By turning
the rollers, that endless belt, through friction, would, according
to the speed of the rollers, move at whatever speed we desired
to give it, and any substance placed upon the top part of the
endless belt would travel from one end and be discharged at
the other end. Instead of a belt made of calico, we could use
an arrangement made of metal, consisting of thin metal laths,
wire netting, or similar appliances, to effect the same purpose.
Such an arrangement is largely used for transporting goods in
works, and is known as a carrier conveyor, and shown in Fig. 18.

Another way of effecting the same purpose would be to place
a long Archimedean screw in a trough, when, on turning the
screw, any suitable substances placed in the trough would be
moved in a horizontal direction. Such an arrangement is
known as a screw conveyor, and is shown in Fig. .19. It
works remarkably well with dry or comparatively dry sub-
stances, but is not so efficient in the case of pasty masses, which
are apt to stick. In such contingencies, an arrangement may be
used in which an endless chain travels over sprocket wheels :
bars, which act as scrapers, are fixed to the chain at convenient
intervals, and thus, as the chain revolves, take up and carry
forward any substances which they may meet. An arrangement
of this kind is called a drag plate conveyor, and is represented
by Fig. 20.

The arrangements which we have so far discussed enable us

THE AIR-BATH AND ITS TECHNICAL EQUIVALENTS.

to transport goods in a horizontal or slightly inclined direction.
If it is desirable to transport goods in a vertical direction or at

an obtuse angle, we may make use of an endless chain to which
buckets are attached at convenient intervals. As the chain is
made to revolve, these buckets dip at the lowest point into the

40 ELEMENTS OF CHEMICAL ENGINEERING.

mass which has to be transported from a lower to a higher level,
and get filled. In travelling upwards they will, on passing the
highest point, gradually turn over and discharge the mass which
they contain. Such an arrangement goes by the name of the
bucket elevator, and is shown in Fig. 21.

All these arrangements are largely made use of in the
construction of drying plant, and we may now proceed to
describe some systems in detail.

The nearest approach to the air-bath as used in the laboratory
would be a chamber built of wood, brick, or other suitable
material, well isolated against radiation, through which hot air
was made to circulate. Such an arrangement is frequently
used, and various details of construction are applied to it. The
heating may take place inside the chamber by means of steam
pipes, or the air may be heated before it enters the chamber, or
a mixture of air and the products of combustion from a coke
fire may be passed through the drying chamber in cases where
the presence of carbonic acid would not be injurious. Again,
air may be either drawn through the system or it may be
forced into it. The latter arrangement is the better of the two,
as it prevents cold air from being drawn into the apparatus
if there should be any leakage in it. A number of such
chambers may be placed on the top of each other, forming a
high building, and each story may be heated separately, or may
receive its heat from the story below it. The goods which have
to be dried may be placed on racks or trays which are fixtures
in the drying chambers, or a number of trays may be built up
above each other into a set of shelves, and placed on bogies
so that they may be easily wheeled into or out of the drying
chambers for the purpose of filling and emptying. It is
difficult in these arrangements to obtain an even distribution of
heat, so that the goods in different parts of the system do not
finish drying in the same time.

The simplest form of drying apparatus would appear to be

THE AIR-BATH AND ITS TECHNICAL EQUIVALENTS. 41

FIG. 21.— Bucket Elevator.

42 ELEMENTS OF CHEMICAL ENGINEERING.

one which consisted of a long plate or a shallow pan; and
heated by means of an ordinary fire in such a manner that the
flue gases would pass along channels underneath the plate or
pan. Various metals, enamelled iron, or earthenware tiles
could be used for constructing the drying bed. The heat of
the bed would be greatest near the fireplace, and least at the
end furthest from it, and the material to be dried might be
placed on the cold end and moved gradually by rakes towards
the hottest end. In such an arrangement, however, it would
be impossible to keep the temperature within a narrow range,
and it would be quite impracticable in the case of compounds
which decompose above 100° C. or thereabouts. In such cases
a steam -jacketed shallow pan might be used, care being taken
that the flat bed be made of sufficiently strong material to
stand the pressure of the steam without bulging. Or an
arrangement might be used in which the heat was transmitted
to the bottom of the tray by means of steam pipes. The writer
has found that the efficiency of this construction can be
increased by imbedding the steam pipes in dry iron filings
and placing the bed closely on the top layer. As the iron
filings conduct well, this is a fairly economical way of trans-
mitting the heat of the steam. We may mention that a similar
design also furnishes an excellent sand-bath in laboratories in
which steam is available. Steam coils are placed in a square
box of about 4 inches depth made of wood or sheet iron ; the
box is filled up within half an inch above the coils with dry
iron filings, and a layer of 1 inch of sand is placed on the top
of this.

According to the pressure and temperature of the steam,
which can be regulated at any time by means of a reducing
valve, the sand-bath may be kept at a uniform heat of from
100° C. to 120° C. ; and with superheated steam a temperature
up to 300° C. or more may be obtained. Instead of steam pipes
or steam coils, advantage could be taken of the arrangement

THE AIR-BATH AND ITS TECHNICAL EQUIVALENTS. 43

which we have shown in Fig. 12, p. 18, in which wrought-iron
pipes are cast into iron plates.

In the arrangements described, the air has free access to the
goods which have to be dried. In some cases it may be desir-
able to carry on the drying in a closed system: this could
easily be effected by providing any of the before-mentioned
apparatus with a lid. In that case it will be necessary to
carry off the vapours by means of a mechanical arrangement,
such as a pump, a fan, or an ejector.

From the remarks made at the beginning of this chapter it
will appear that in many cases the drying operation will not
proceed on economical lines unless the mass is frequently
agitated and turned over. In other cases the goods have to
be gradually moved from the coldest to the hottest part of the
system. This, if done by hand, requires constant attention
and labour, and therefore involves extra cost ; wherever it
is practicable, mechanical appliances are therefore employed.
There are many ways in which the work involved in turning
over substances whilst drying can be effected by machinery.
One of the simplest would be to have a shallow trough, at the
bottom of which an endless screw worked, such as we have
described. This could be heated in either of the ways which
we have mentioned, and the speed of the screw could be
arranged in such a manner that the goods were carried from
end to end in the time required to reduce them from the wet
to the dry state. Instead of spiral conveyors, drag plates could
be made to move on a flat plate and thus to carry the substance
forward, but in that case the amount of stirring in many cases
would be inconsiderable, and pasty substances would be liable
to be carried along in almost solid blocks.

Drying apparatus are constructed, and have been found
efficient, consisting of long cylinders in which the material, by
means of large screws, is gradually and slowly moved from
end to end, whilst at the same time little buckets fixed on the

44 ELEMENTS OF CHEMICAL ENGINEERING.

revolving axle lift the stuff from the bottom and in carrying it
round drop it again, thus producing a thorough mixing and
separating. It is evident that here again many ways of heating
the apparatus may be applied ; thus in one arrangement the
coal or coke fire is made to heat the air which is passed
through the drum whilst the products of combustion are taken
round the drum, thus heating it from the outside ; or the drum
may be double-cased and heated by steam, and so on. In
another type of drying machinery, a long chamber provided
with doors at opposite ends may be heated by any of the means
described above. The goods to be dried are placed in little
waggons which run on a tramway along the chamber, and these
little waggons are placed in the chamber by means of long rods,
and left in it for the necessary time. Where space has to be
economised the chamber may be built vertically, and in that
case the little waggons are raised or lowered by means of
chains.

Another arrangement which is largely used consists of a
drying chamber in which carrier conveyors are arranged in such
a manner, one above the other, that the substances which are
fed in at the top pass along the highest band and are made to
drop on the one below, which projects at that end and moves in
an opposite direction, and so on from the higher to the lower
until the goods are discharged at the bottom of the apparatus.
The use of machinery in drying installations to economise hand
labour is not restricted to the drying chamber itself. The wet
stuff or finished material can be moved away or towards the
place by means of bucket elevators, and the other arrangements
mentioned may be used for the same purpose. Economy of
labour and economy of heat are the two main principles which
underlie the construction of such installations. As regards the
former, the problem has been solved very efficiently ; but with
regard to the latter, it is still capable of improvement, and even
with the most perfect designs it has been so far impossible to

THE AIR-BATH AND ITS TECHNICAL EQUIVALENTS. 45

effect the evaporation of more than 5 pounds of water for every
pound of coal used. It need hardly be mentioned that in all
cases where waste steam or waste heat from other sources is
available, this will be used for the purposes of drying.

We will conclude this chapter with an interesting illustration
of how it is possible to get over a difficulty which at one time
seemed almost insurmountable. It is now possible to dry
explosive substances by heat. The manner in which this is
effected is by utilising our knowledge that with a sufficient
vacuum water will boil and evaporate at a low tempera-
ture. The construction which is used consists generally of
a closed metal drying chamber heated by steam, and supplied
with shelves on which the material to be dried is placed. The
chamber is connected with a large explosion chamber fitted
with a great number of safety-valves. If at any time an
explosion should occur, the gases evolved would be drawn into
the explosion chamber, which is always in a state of vacuum,
and any surplus pressure would cause the safety-valves to be
thrown open. When the drying is complete the steam is
turned off, and cold water passed through a system of pipes
conveniently arranged in the chamber, by which the whole
system is cooled ; when the explosive substances are cold they
can be removed without danger. It is obvious that all steam
and water taps are arranged at a distance from the apparatus,
so that they can be regulated without the workmen being
compelled to go near the drying chamber whilst it is in actual
work.

CHAPTER IV.

THE BLOWPIPE AND THE CRUCIBLE, AND THEIR
TECHNICAL EQUIVALENTS.

IN the course of his work in the laboratory the student
of chemistry often has occasion to heat substances to high
temperatures, and he will learn at an early stage that many
different principles are involved in and incidental to that
operation. One of its fundamental conditions is, that the
temperature of the name which we apply should be higher
than the ultimate temperature to which we want to raise
the substance which requires heating; another, that the
volume of the substance to be heated should be proportionate
to the size of the flame, otherwise, if its volume be too great,
loss of heat from radiation and other causes will prevent
it from acquiring a sufficiently high temperature. These
principles are well known to any student who has worked
with the ordinary blowpipe, and has also had an opportunity of
studying the subject by the beautiful method of flame reactions
introduced by Bunsen, by which the ordinary flame of the
Bunsen burner can be made to produce reactions at high
temperatures by the use, in the one case, of a carbonised
wooden match instead of charcoal, or in the other case, of
an extremely thin platinum wire on which a small bead is
formed by borax or other means. The student will also
have learnt that the character of the flame is not the same all
through, and that, if one requires to produce reactions in

BLOWPIPE AND CRUCIBLE, AND THEIR TECHNICAL EQUIVALENTS. 4?

which oxidation may take place, the outer and top part of
the flame are used. If it is necessary to produce reactions
which are of a reducing character, then it will be necessary to
use the blue centre of the flame, which, owing to the absence
of oxygen, has no oxidising properties.

The same principles will hold good where larger quantities
of material are used in the laboratory. For instance, in
analytical work in which crucibles are employed, they are
heated either with the lid cover on, to prevent access of
air, or in a slanting position without the cover, so as to provide
a draught of air through the mass.

If we examine the apparatus which is used in works to
produce results similar to those obtainable in the laboratory,
we find that it is partly constructed on the same principles as
those applied in blowpipe work, partly on the same principles
as those applied in working with a closed or open crucible. A
furnace which is used for operations in imitation of blowpipe
work, that is, for work in which the mass to be heated is
exposed to the direct action of the fire gases, is represented
in Figs. 22 and 23.

It consists of an arched chamber built of bricks and heated
from a grate. The substance to be heated is spread on the
bed of the furnace chamber ; the fire gases pass over it, and are
taken out at the end opposite to the fire grate into the chimney.
It is a matter of course that a furnace of this kind, when
used for operations which require high temperatures, should be
lined inside with fire bricks ; that is to say, that whilst it is
sufficient to build the outside shell of the furnace, which
adds to its stability and prevents radiation, with ordinary
bricks set in mortar, it is necessary to use fire bricks set in
clay, or other heat-resisting material, in those parts which
are exposed to the direct action of the flame. It is evident
that, according to the nature of the operation which is to
take place, it will be necessary to alter the details of construe-

ELEMENTS OF CHEMICAL ENGINEERING.

tion in the furnace. Thus, for instance, if we have to oxidise
copper scale, which chiefly consists of cuprous oxide, to cupric
oxide, the operation involved would be an oxidising operation.
It would be an operation in which the presence of oxygen in the

nil --.!

FIG. 22.— Open Roaster (sectional elevation).

flame would be absolutely necessary. The combustion of the
fuel would therefore be arranged in such a manner that it
will take place in the presence of an excess of air. Such a
flame can be produced by having a number of fire bars set

FIG. 23.— Open Roaster (plan).

widely apart, and by charging the fuel in thin layers. But it
will be necessary to watch the operation carefully, as if too
much air is admitted it would cool the fire gases to such
an extent that more fuel would be consumed than would be
economical ; and where very high temperatures were required,
it would prevent us from obtaining them. A furnace of
this description is called an open roaster.

BLOWPIPE AND CRUCIBLE, AND THEIR TECHNICAL EQUIVALENTS. 49

Whilst we are dealing with this subject, we may point out
that in the case of open roasters it may become necessary to
consider the ingredients which are contained in the fire gases ;
thus, coal which is rich in pyrites would not be suitable in
operations in which the sulphurous acid produced would act on
the substances operated on. Where such is the case, coke as
free from sulphur as possible should be used, or better still a
gaseous fuel. In the latter case the furnace will have to be
constructed in such a manner that, instead of having a fireplace
which is fed with solid fuel, it has a chamber arranged for the
combustion of gas.

If, instead of an oxidising flame, a reducing flame is required,
a similar furnace may be used, which only differs from the one
described above in the arrangement of the fireplace and the
management of the combustion of the fuel. An example of a
reducing operation — with which, no doubt, the student is
familiar, from his study of chemical technology — is that of
producing black ash. In the manufacture of soda by the Le
Blanc process, salt-cake (which is anhydrous sodium sulphate),
coal, and limestone (which is calcium carbonate) are melted
together and produce black ash, a compound of complicated
composition, which, on lixiviating, yields a solution of crude
sodium carbonate. This is distinctly a reducing operation ; and
in order to produce fire gases suitable for it, the fire bars are
placed close together and the fuel is put on the bars in thick
layers ; in this manner no excess of air is drawn through the
bars, and the fire gases, on passing over the mixture of ingredi-
ents which produce the black ash, not only heat them to the
melting point, but also keep them in a reducing atmosphere
and help to further reduce them.

All these furnaces are wasteful in the consumption of fuel,
and wherever it is practicable the waste gases from them are
used for other operations, as, e.g., for boiling down or drying.

In many of the melting operations which are carried on in

50 ELEMENTS OF CHEMICAL ENGINEERING.

open roasters it is necessary to mix the ingredients during the
process, or to rake them up in such a manner as to expose
different surfaces to the fire gases. In order to save the cost of
hand labour, machines have been constructed which enable us
to conduct such mixing operations by mechanical means. Such
a furnace is, for instance, the one which goes by the name of
' the revolver,' and is used for the same purpose as the hand
furnace described above. It consists of a large iron drum
built up in sections, which is lined inside with highly refractory
firebricks of a special kind to resist the action not only of
the heat but of the alkaline black ash. The apparatus is
arranged in such a manner that the drum revolves slowly whilst
the furnace gases supplied from the fireplace attached to it are
made to pass through the revolver, and on leaving it are used
for evaporating and drying purposes. Such an apparatus can
only be used where very large quantities have to be dealt with.
A cylinder of 9 ft. in diameter and of 16 ft. in length would
not be considered a large furnace. To give some idea as to the
work which could be done by such a furnace, we give the
following abstract from Lunge's standard book on sulphuric
acid and alkali: —

"The Widnes Alkali Co., in 1884, had a 'furnace built by
Messrs Cook & Robinson for decomposing 80 or 90 tons of salt-
cake in 24 hours. The fireplace has an area of 17 ft. x 10 ft.,
and consumes 25 cwts. of coal per hour. The same firm erected
in 1887 a black-ash furnace, larger than any known at that date.
The cylinder externally is 30 ft. long and 12 ft. 6 ins. diameter,
internally 28 ft. 6 ins. long and H ft. 4 ins. diameter. The
lining consists of 16,000 firebricks and 120 fireclay blocks,
(' breakers '), weighing each 1| cwts. The bricks weigh about
four tons per thousand. The fireplace has four doors, the
cylinder three manholes. The weight of salt-cake per charge
is 8 tons 12 cwts. For each 100 tons of salt-cake there are
also charged about 110 tons of lime mud and 55 tons of mixing

BLOWPIPE AND CRUCIBLE, AND THEIR TECHNICAL EQUIVALENTS. 51

coal. This is altogether about 25 tons per charge. In a week
of seven days about forty-eight charges are worked through,
equal to a decomposition of 400 tons of salt-cake, yielding 240
tons of 60 per cent, caustic soda. The fuel for firing may be
put down as 200 tons per week, or 10 cwts. per ton of salt-
cake, against 13 cwts. in ordinary revolving black-ash furnaces.
The waste heat of the latter furnaces evaporates sufficient liquor
from 20° to 50° Tw. to keep three self-fired caustic pots working,
which are boiled at a strength of 80° Tw. Were it not for this
evaporation, no less than seven self-fired pots would be required
to do the work, showing a difference of 80 tons of fuel."

Even this enormous machine is not quite the largest that has
been built. Our illustration shows a revolver which was con-
structed by Messrs R. Daglish & Co., Ltd., for Messrs Kurtz &
Co., Ltd., of Sc Helens, and its dimensions are as follows :
diameter 12 ft. 6 ins. and length 30 ft. 0 ins.

Besides the operations which may be carried on in open
furnaces, and which are imitations of the work of the blowpipe,
there are many operations which have to be carried on in closed
vessels, just as crucibles and muffles have to be used in the
laboratory. Although it is found very cumbersome to use
crucibles on a large scale, they are still in ,use in many
operations, such as for melting up the best brands of steel,
copper, and brass. They are made of fireclay or plumbago, or
of steel and other material. In most cases the manner in which
these crucibles are heated is rather primitive. The furnace,
which is provided with a grate at the bottom, represents a
cylindrical or square shaft, in the middle of which the crucible
is placed on a kind of pedestal or on a setting of bricks, and
surrounded with coke, which, on being lit and kept burning
through a powerful draught from a closely adjoining chimney,
produces sufficient heat to melt substances which require
a very high temperature. In this way it is possible to
handle fairly large quantities of metals, on account of their

52 ELEMENTS OF CHEMICAL ENGINEERING.

high specific gravity and the comparatively small bulk which a

-1

considerable weight of them takes up ; but in purely chemical
operations the use of crucibles is limited to work on a com-

BLOWPIPE AND CRUCIBLE, AND THEIR TECHNICAL EQUIVALENTS. 53

paratively small scale. When, therefore, it is necessary to heat
chemicals to a high temperature in such a manner that they are
excluded from contact with the fire gases, a furnace is used
which goes by the name of a closed roaster, and the prototype of
which is the salt-cake furnace, as used in the manufacture of
Leblanc soda.

Figs. 25 and 26 show such a furnace. The closed or blind
roaster consists of an arched muffle built of firebricks set in fire-
clay, and constructed in such a manner that the fire gases pass
underneath the bed of the muffle on their way to the end furthest
from the fireplace. They are then taken over the top of the
arch back to a convenient point near the fireplace, and finally
into the main flue or into the chimney. The bed is generally
made of tiles of suitable size, up to 2 ft. square, which rest on
walls carried along the length of the furnace, and thus provide
channels through which the fire gases pass under the bed. Doors
are provided in suitable positions in front of the furnace through
which the mass can be charged, raked, and discharged. A pipe
is supplied at the top of the muffle through which any gases
evolved during the operation are carried into the condenser.
These furnaces may be made up to 30 ft. in length ; they
cannot conveniently be made much more than 5 ft. in depth, as
otherwise the process of raking up and mixing would become
unmanageable.

Although it is possible to build a muffle with bricks and tiles
in such manner as to make it almost perfectly air-tight, it must
be borne in mind that when it becomes heated up the bricks
and tiles expand and press on the mortar and clay between
them, so that small openings are formed. In the course of time
the muffle will therefore cease to be absolutely air- or gas-tight.
This drawback becomes still more apparent if the furnaces are
worked intermittently, or heated in such a manner that the
temperature varies at different times, within considerable
limits. It has been found by experience that if, for the

ELEMENTS OF CHEMICAL ENGINEERING.

reasons stated above, the muffle ceases to be completely
gas-tight, the gas evolved in the muffle, e.g. hydrochloric acid,

FIG. 25.— Blind Roaster (plan).

is drawn into the flues through which the fire gases pass,
the reason for this being that the pressure of the hydrochloric

FIG. 26.— Blind Roaster (sectional elevation).

acid gas in the muffle is greater than the pressure of the fire
gases in the flues. The fire gases thus become contaminated
with hydrochloric acid and pollute the atmosphere. In order

BLOWPIPE AND CRUCIBLE, AND THEIR~TECHNICAL EQUIVALENTS. 55

to overcome this difficulty a number of devices have been
proposed, all of which are based on the principle of making the
pressure in the supply of the fire gases greater than the pressure
exerted by the evolution of hydrochloric acid in the muffle.
These furnaces are called plus-pressure furnaces, and the
principle on which they are designed should be used wherever
noxious gases are evolved in the muffle. They vary in the
details of construction, but it will be sufficient to describe one
in which the fireplace is built in such a manner that the air
cannot have access to it except by pipes through which the
necessary quantity of air is blown by means of a 'Koots'
blower or other blowing engine. The fire gases travel, as usual,
under and over the muffle, and, before going into the chimney,
are taken through a stack in which are contained a number of
pipes arranged in a similar manner to that shown in the ' Green '
economiser (p. 59). The air which comes from the blowing
engine first passes through these pipes, is heated up by the
waste heat of the furnace, and then passes into the fireplace.

Considerable economy in the consumption of fuel is effected
by heating the air supply, and the best results in that direction
are obtained by the so-called system of regeneration. This
consists in arranging flues in such a manner that the air which
is used for combustion is heated by storing up the heat of
the furnace gases as they pass toward the chimney. In order
to produce this effect two chambers are built side by side and
filled in a honeycomb fashion with bricks. We will call these
chambers A and B, and will now follow an operation in which
they are used. The fire gases, after heating the furnace, are
passed through chamber A. After some time the enormous
quantity of brickwork inside the chamber becomes heated to the
temperature of the flue gases. When this point is reached the
flue gases are diverted from the chamber A, and the flue gases
are made to pass through the chamber B, which in its turn
becomes heated up. At the same time a door or valve in

56 ELEMENTS OF CHEMICAL ENGINEERING.

chamber A is opened so that the air passes through this
heated chamber A, and from there underneath the furnace
in which the coal is being burnt. By thus connecting the
two chambers alternately with the atmosphere and with the
flue it is possible to heat the air supply to a considerable
temperature by the waste flue gases. This principle may be
carried still further in cases where gas is used as fuel, and
the regenerative chambers may be arranged in such a manner
that both the air used for the combustion as well as the gas,
i.e. the fuel, are heated up before combustion. In this manner
great heat can be produced, and great economies in fuel can be
effected.

CHAPTER V.
THE STEAM BOILER AND OTHER SOURCES OF POWER.

WE have had occasion, when discussing the question of drying
apparatus and elsewhere, to refer to mechanical arrangements
which are used in work on a large scale, and which have no
parallel in the work as carried on in the laboratory. These
mechanical arrangements, which are all designed with the view
of saving the cost of labour, may be moved and controlled by
different agencies. Thus, where steam is the controlling power,
the steam will be produced in a boiler and made to drive a
steam engine ; where gas is the controlling power, the gas has
to be produced in one of the many different ways which are
known, and may then be utilised in a gas engine for producing
the power required. Where electricity is the moving power, it
is generated in a dynamo, and this again acts on a motor. But
the three agencies of which we have spoken, that is, steam, gas,
and electricity, obtain their power by means of the combustion
of coal. It is therefore clear that unless sound principles are
applied to the production of power, the application of that
power will not be economical. If, for instance, it would take
2 pounds of coal under a boiler to produce a certain
mechanical effect, and only 1 pound to produce the same
effect by some other means, the cost of work done would
be as two to one.

We will briefly give a description of power-producing
apparatus, with such remarks as will enable the student to

ELEMENTS OF CHEMICAL ENGINEEEING.

understand the principles of their construction, economical
working, and application.

The steam boiler is used for the evaporation of water under
pressure. It consists, in its simplest form, of a cylindrical vessel
made of wrought-iron or steel, two-thirds filled with water, and
heated by means of coal or other combustible matter. But it is
clear that in its simplest form it cannot properly utilise the
heat supplied to it, as we have shown before that in order to

FIG. 27. — The Galloway Steam Boiler and Furnace.

utilise heat to the best advantage it must be taken over the
largest possible surface. For that reason tubes are inserted in
the boiler in the manner shown in the Galloway boiler, Fig. 27.
By doing this one gains as much additional heating surface as is
represented by the tubes. The fire bars are placed between
these tubes, and the fire gases travel along the tubes and
are taken through brick flues which run along each side of
and under the bottom of the boiler, and pass out at the back
into the chimney. The water evaporated is replaced by fresli
water by means of a pump or an injector, and gauge glasses.

THE STEAM BOILER AND OTHEU SOURCES OF POWER.

which are in front of the boiler, always indicate the level at
which the water stands. Pressure gauges indicate the pressure
of the steam ; and a safety-valve, consisting of a lever arrange-
ment, with a corresponding weight for the pressure up to which
one wishes to work, is arranged in such a manner that the valve
automatically opens when
the pressure exceeds that
point and the steam free-
ly escapes. The gases of
combustion which pass
from the boiler into the
chimney still contain heat
which could be utilised.
For that reason, in every
properly designed instal-
lation there is an arrange-
ment for heating the feed
water by means of the
heat which would other-
wise pass from the boiler
into the chimney, and
such an arrangement is
known by the name of an
economises

This consists of a
number of tubes, gener-
ally 96 for one boiler,
encased in brickwork in
such a manner that the gases leaving the boiler have to
pass round the pipes. As a considerable amount of soot
and flue dust, consisting of ashes whicli are mechanically
carried forward, would settle on these tubes, and thus
in time form crusts which would reduce the efficiency of
the apparatus, scrapers are made to travel in a vertical

FKJ. 28. — The Economiser.

60 ELEMENTS OF CHEMICAL ENGINEERING.

direction on the tubes so as to keep them clean. This is
done by means of a little steam engine which works quite
automatically, and reverses its motion when the scrapers have
reached either the top or the bottom of the pipes. The cold
water enters the pipes and circulates through them, and then
passes into the boiler at a temperature of 100° C. or more.
The economy effected in this way is very considerable, and
may amount to 20 per cent, on the fuel or more.

Whilst, years ago, it was considered unusual to work a boiler
at a higher pressure than 50 or 60 pounds to the square inch, the
tendency now is to work at as high a pressure as possible, as it
is far more economical to produce steam of high pressure than
steam of low pressure. Boilers are now constructed to work
at a pressure of 200 pounds or more per square inch, and
with steam at such pressures steam engines have been perfected
in such a manner as to reach a degree of economy never before
attained. It has been found that the flue gases from boilers,
even after heating the feed water, still contained available heat,
that is to say, more heat than would be necessary to produce
sufficient draught in the chimney. This heat is now used in
many cases for converting the saturated steam which comes
from the boiler into superheated steam. Apart from the extra
economy which is thus rendered available in the motive power
of the steam, the great advantage of using superheated steam
lies in the fact that it can be conducted through considerable
lengths of piping without condensation. This fact should make
superheated steam particularly valuable in chemical works,
where heating and boiling apparatus is often a great distance
from the boiler.

There are many other forms of boiler than that of which we
have given an illustration above. They are all based on the
principle of exposing as much heating surface as possible to
the flue gases by increasing the number of tubes and reducing
their diameter.

THE STEAM BOILER AND OTHER SOURCES OF POWER. 61

We need not enter into the description of a steam engine in
detail, as it is too well known, and as the principles on which
it works, and which determine the details of construction,
form part of the course of study in physics. We need only
mention that there are, generally speaking, two kinds of steam
engines — that in which the steam, after going through the
cylinder, passes into the air, and that in which the waste steam
is condensed : they are accordingly classed as non-condensing,

FIG. 29. — Gas Engine (Crossley).

or condensing engines. The same remarks which we have made
on the boiler apply to the engine. In this case the aim should
be to produce the greatest power from a given quantity of steam.
Considerable economy can be effected by using a condensing
engine, but where the waste steam can be used for other purposes,
as for instance boiling or drying, a non-condensing engine may
be found, at a lower cost, quite as economical, and even more so.
Of late years the great improvement which has taken place
in the economical production of gaseous fuel obtained from coal
has produced an equal advance in the construction of ga»

ELEMENTS OF CHEMICAL ENGINEERING.

engines, which now can be obtained up to 1000 horse-power
and more. The principle upon which gas engines work is

fundamentally dif-
ferent from that
upon which the
steam engine
works. In the
steam engine the
piston is moved
by the pressure of
the steam ; in the
gas engine the gas
itself exerts no
pressure upon the
piston, but the
necessary pressure
is produced by the
explosion which is
made to take place
through mixing-
gas with the neces-
sary volume of air
and igniting it.

Figs. 29 and 30
show standard de-
signs of a gas
engine.

The gas used
for these engines
may be either
ordinary coal gas,
a mixture of coal

gas and water gas, or altogether water gas — that is, a mix-
ture of hydrogen, carbonic oxide, and nitrogen. As it is

THE STEAM BOILER AND OTHER SOURCES OF POWER.

possible to produce gas in suitable localities from poor coal
which otherwise could hardly be utilised, and as it is further
possible to separate valuable ammonia and tar products
which in the ordinary combustion of coal are lost, the use of
gas in engines enables us to produce power in a most economical
way.

Although not of much importance to chemical works in this

FIG. 31. — Eight-pole Multipolar Dynamo.

country, we may mention that engines are built on the explosion
principle, in which petroleum or benzine is used as the ordinary
source of fuel. Most of these engines contain an additional
arrangement by which the petroleum or benzine is first heated
so as to convert it into vapour ; the vapour is conducted to the
piston, air mixed with it, and explosion brought about by
ignition, as in the gas engine.

In the steam engine and in the gas engine we convert the

ELEMENTS OF CHEMICAL ENGINEERING.

Fro. 32.— Direct-coupled Steam Engine and Generator.

FIG. 33.— Standard type of Motor.

THE STEAM BOILER AND OTHER SOURCES OF POWER. 65

energy of coal into the energy of steam, or into the energy
produced by the combustion of a mixture of gas and air, and
this directly produces the power of the engine. But it is
sometimes found more economical not to take the power direct
from the engine as produced there, but first to convert it into
electricity by means of a dynamo, and to work a motor from

FIG. 34.— Steel-clad Motor.

the dynamo. It would lead too far to enter into the principles
and details of construction of a dynamo and a motor, and we
therefore only give illustrations of standard types representing
them.

The same may be said about other kinds of motors which are
used in special cases. If, for instance, instead of using steam,

one were to use compressed air or water under pressure in a

66 THE ELEMENTS OF CHEMICAL ENGINEERING.

machine constructed similarly to a steam engine, it would be
possible to transform the energy of the compressed air or water
into power produced by the engine. Such engines are used in
special cases, particularly in small installations in towns where
water is supplied under hydraulic pressure, or in works where
compressed air is used for other purposes, such as for stirring or
for lifting liquids.

CHAPTER VI.

GENERAL REMARKS ON THE APPLICATION OF
HEAT IN CHEMICAL ENGINEERING.

IN the metric system the quantity of heat necessary to be
imparted to one gramme of water to raise its temperature
through one degree Centigrade is termed a heat unit, or calorie.
In technical calculations another heat unit, termed a great
calorie (Cal.), is generally used; it is the quantity of heat
necessary to be imparted to one kilogramme of water to raise its
temperature through 1° C. The British unit of heat, or B.T.U.
(British Thermal Unit), is the amount of heat necessary to raise
1 pound of water through 1° Fahrenheit ; since 1° F. is equal
to 5/9 of a degree C., and '2'2 Ibs. = 1 kilogramme, we have to
divide 5/9 by 2'2 to obtain the ratio between the two units,
which makes one B.T.U. = '252 Calorie.

It has been found that, in order to convert 1 kilogramme of
water of the temperature of 100° C. into steam at the same
temperature and at the ordinary pressure of the atmosphere,
537 Calories are required. As it takes 100 Calories to raise 1
kilogramme of water from 0 to 100°, the total quantity of heat
required in order to convert 1 kilogramme of water at 0° C. to
steam at 100° C. will be 637 Calories. If this process is carried
on in a closed vessel, such as a steam boiler, from which the
steam cannot issue freely, and is therefore subjected to a
pressure of more than 15 Ibs. to the sq. in., which represents
the pressure of the atmosphere (or 1-033 kilogramme to the

THE ELEMENTS OF CHEMICAL ENGINEERING.

sq. cm., which is the equivalent of the atmospheric pressure in
the metric system), the temperature of the steam produced is
higher than 100° C=, and the number of Calories required to
produce the steam at the increased pressure is naturally greater
than 637 Calories. The following table will show the actual
results which have been found : —

Calories per kg.

Weight of

Pressure
in atmo-

Temperature

• op

1 c. metre
Steam in

spheres.

in u.

Heat of
Water.

Heat of

Steam.

Total Heat.

kilo-
grammes.

i-o

100

100-5

536-5

637-0

•60

2-0

120

121-4

521-8

643-2

1-16

3-0

133

134'9

512-2

647-1

1-79

4'0

144

145-4

505-0

650-4

2-23

5-0

152 1537

499-0

6527

275

6-0

159 1609

494-0

654-9

3-26

165 167-2

489-6

656-8

377

8-0

170 173-8

485-6

658-4

4-27

9-0

175

178-0

482-0

660-0

4-77

10-0

180

18-2-7

478-7

661-4

5-27

The steam produced in this manner shows a temperature
corresponding with the pressure. Thus, e.g., steam at one
atmosphere pressure shows a temperature of 120° C. ; at two
atmospheres 133° C., and so on. (The pressure is always
reckoned 'above' that of the atmosphere, hence one atmosphere
pressure as shown on the gauge of a boiler really represents not
15 Ibs. but 30 Ibs. per sq. inch ; but it is always referred to as
' one atmosphere.') If, now, we were to disconnect the steam
from the boiler and to heat a certain volume of it to a higher
temperature than that which belongs to it in its normal state,
we should require more fuel to do so, and we must expect to
get that amount of fuel back in its equivalent of work. As a
matter of fact, we should find that the steam on being heated in
the enclosed space would exert a greater pressure. If, on the

THE APPLICATION OF HEAT IN CHEMICAL ENGINEERING. 69

other hand, whilst heating the steam to a higher temperature,
we were to allow it to expand in such manner as to remain at
the same pressure as in its normal state, we should find that the
temperature of the steam would become higher than it was
before. Taking, for instance, steam at two atmospheres pressure,
we find from the table that its temperature would be 133° C.
If, whilst disconnecting it from the water contained in the
boiler, and without altering its pressure, we were to heat this
steam up to 145°, it would be no longer saturated with water, but
become non-saturated, i.e. superheated steam. It would be
steam that would still have a pressure of two atmospheres; and
if it were allowed to pass through a pipe or other conducting
channel it could not become saturated steam until its
temperature had cooled down to 133°. It therefore follows
that superheated steam can be conducted a distance without
condensation taking place, and this is one of its most valuable
properties.

Another property of superheated steam which in chemical
operations should prove valuable, but which up to the present
has not been utilised to the extent which it deserves, is
that of yielding in proportion to its effectiveness less water
on condensation than saturated steam. If, as is often the case
in chemical operations, we use live steam for heating up a liquid
either to its boiling point or to a point below it, the bulk of
the liquid at the end of the operation will increase by the
amount of steam which becomes condensed : naturally this
amount will be less when we use superheated than when
saturated steam is employed.

If we heat a liquid by means of ' live ' saturated steam the
quantity of heat which the steam will transmit to the liquid
will depend upon the initial temperature of the liquid and the
pressure of the steam. Thus, for instance, if steam were used of
three atmospheres pressure, we find that its total heat amounts
to 0504 Calories. If the liquid which we want to heat is water,

70 THE ELEMENTS OF CHEMICAL ENGINEERING.

and its initial temperature is 15° C., the heat available from
the steam would he 650 — (100 — 15), that is, 565 Calories; in
other words, 1 pound of steam at three atmospheres pressure
would be able to heat up 5 '65 pounds of water to the boiling point.
In practical work this will not be absolutely correct, as more
steam than that calculated will be required. If, instead of
passing the steam into the liquid direct, it is used as ' confined '
steam, that is, if the liquid is heated up by means of a coil or
jacket through which the steam circulates without coming into
contact with the liquid, the efficiency will depend upon several
other factors besides the pressure of the steam. We have then
to take into consideration the property of the material through
which the steam is conveyed in relation to its capacity for
giving off that heat by transmission. Different materials show
considerable differences in their capacity for transmitting heat.
It has been found that copper possesses the highest capacity
of any material applied in practical work ; and putting this down
at 100, we find that that of wrought-iron is about 90, that of
cast-iron about 60, and that of lead about 50. Experience has
shown that it is possible to evaporate 100 litres of water per
hour from 1 square metre of heating surface consisting of
copper. To obtain the same effect by means of steam coils or
jacketed pans made of other materials, it is necessary to increase
the heating surface in the inverse ratios given above.

In connection with this subject it is important to know what
amount of radiation may take place from the vessels which are
used. According to Peclet, the amount of heat (S) expressed in
Calories given off by radiation for every square metre per hour is

8 = 12472 Kxr0077*[l'0077T-l] Calories

in which T is the temperature of the apparatus and t the
temperature of the surrounding atmosphere. The coefficient K
of radiation for different substances may be taken as follows, in
this formula : —

THE APPLICATION OF HEAT IN CHEMICAL ENGINEERING. 71

= Iron 3-17
Brick 3-60

K- Paper
Sand

377
3-62

Wood 3-60

Silver

Copper 16
Brass '26

Wool
Zinc

3-68
•24

Glass 2-91

Tin

•22

In the production of steam in a steam boiler, in the evaporation
of liquids, in the carrying out of melting processes, everything
depends upon the economical utilisation of fuel ; and although, in
practical work, the results obtained are often very different
from those which would be expected from theoretical consider-
ations, yet it is necessary to understand the theory of the
subject. As the chief material used as fuel in this country is
coal, we will confine our remarks to a short consideration of
the utilisation of that material.

The value of coal expressed in calories evolved in its com-
bustion can be ascertained either by calculation or by actual
determination in a calorimeter. The chief constituents of coal
which in combustion evolve heat are carbon and hydrogen.
Those which absorb it during combustion are moisture and the
inorganic matter which remains in the form of ash. Dulong's
formula for calculating the number of calories (V) evolved by
the combustion of 1 kg. of coal is —

V = 8000 C + 29000 H - + 25000 S - 600H0.

If, e.y., we had a coal which in 1 kg. contained
0' -756

H . -051

0 .... -069
S .... -026

N -016

Ash .... -046
Moisture (H20) . . -Q36

1-000

72 THE ELEMENTS OF CHEMICAL ENGINEERING.

we should obtain —

V = 8000 x -756 + 29000p051 - '-9|?1 + 25000 x -026- 600 x

•036 = 7905 Calories,

so that 1 kg. of this coal would yield on combustion 7905
Calories, or 1 Ib. of it would yield -2 = = 14260

B.T.U. On an average the value of coal is 7500 Calories, and
that of coke about 7000 Calories. From these data it would
be expected that 1 Ib. of good coal should be capable of
producing 12 Ibs. of steam. In practical work, except in special
cases, it is impossible to obtain more than 7 or 8 Ibs. of steam
per Ib. of coal. The reason for this discrepancy is due to several
circumstances. Apart from loss of heat through radiation, it is
not possible to regulate the admission of air in such a manner as
to use the theoretical amount which would be necessary for the
complete combustion, and any excess of air which is admitted
into the furnace has to be heated by the fire gases, and therefore
absorbs heat without doing work. A second consideration is this,
that in order to keep the fire burning it is necessary to produce
sufficient draught to take atmospheric air through the system.
Where this is done by means of a chimney it will be necessary
that the flue gases, after having passed through the system, should
still be at about 300° C. in order to produce sufficient draught.
Where other means of producing a draught are available
(commonly expressed by the term ' forced draught,' which
consists of either blowing air through the coal or removing the
exit gases by means of an exhauster), it is possible to carry on
combustion in such a manner that the flue gases on leaving are
below the temperature which would be required if the draught
were produced by a chimney ; but in that case it must not be
forgotten that in order to obtain forced draught power or steam
is required, and as this has to be produced by its equivalent in

THE APPLICATION OF HEAT IN CHEMICAL ENGINEEKING. 73

coal, the saving which is effected by utilising the fuel gases to
greater advantage is partially lost.

The question of utilising coal to the best advantage in
practical work has been most carefully elaborated in the case of
steam-boiler installations. The points which have been
particularly studied are the ratio between the total area and
the space between the bars for the admission of air, the total
area of heating surface, etc. The results obtained are most
important, not only because they are a guidance in the con-
struction of other evaporating plant, but also because they
enable one to apply these results in some measure, however
crude, to installations in which fuel is used for other purposes
than evaporation, for which, except in special isolated cases,
there are at present no data known for the guidance of the
chemical -engineer. We therefore give a few of the results
which are accepted in the setting of steam boilers.

A single-fined or ' Cornish ' boiler, fitted with Galloway
cross tubes, 30 feet long by 7 feet diameter, will evaporate 350
gallons of water per hour for a total heating surface of 730
square feet. A two-nued or * Lancashire ' boiler, with Galloway
tubes, will evaporate 550 gallons of water per hour for a heating
surface of 922 square feet.

A similar ' Galloway ' boiler will evaporate 650 gallons of
water per hour for a heating surface of 970 square feet.

In determining the size of a fire grate it is generally assumed
that 1 Ib. of coal will evaporate from 5 to 7 Ibs. of water, and
1 Ib. of coke from 4J to 6 Ibs. ; on these assumptions the total
grate area should be for every 100 Ibs. of fuel burnt per hour,
in the case of coal, from 7 to 8 square feet, and in the case of
coke, from 8 to 9 square feet. The open spaces between the
bars should be about J to £ of the total grate area. The
total length of the fire grate should not exceed 7 feet. The
sectional area of the flues should be equal to the area repre-
sented by the open spaces between the bars.

74 THE ELEMENTS OF CHEMICAL ENGINEERING.

The theoretical temperature produced by the combustion of
coal or coke can be calculated from well-known thermo-chemical
data ; but it does not agree with the results found in practice.

The chimney required for combustion should have a section
from one-fourth to one-sixth of the sum of the grate areas ; its
height should be from 25 to 50 times its diameter.

CHAPTER VII.

THE FUNNEL AND ITS TECHNICAL EQUIVALENTS.

MANY operations in the laboratory — in fact, nearly all operations
connected with quantitative gravimetric analysis — depend upon
the production of insoluble or sparingly soluble precipitates,
which by various means are separated from the liquid in which
they are suspended. If the precipitate is suspended in a large
amount of liquid, and if it settles well, part of the liquid may
be poured from it. The same would apply on a large scale, only
that in the case where in the laboratory it would be possible to
pour the liquid off, on a large scale taps could be arranged in
cisterns at convenient distances, which, on being opened, would
let off the clear liquid and leave the precipitate undisturbed at
the bottom. When the precipitate is easily disturbed, it is
usual in laboratory work to use a syphon made of glass tubing
for drawing off the clear liquid. On a large scale glass syphons
are only used in special cases. The syphons used are generally
made of lead or copper tubing, according to the nature of
the liquid, and may be constructed to work automatically by
making the short end of the syphon dipping into the liquid of
a flexible material and connecting it to a float, which is
automatically lowered as the level of the liquid descends. In
most cases in the laboratory it will be found more convenient
to effect the separation of the precipitate from the liquid by
filtering the mass through filter paper placed in a funnel. Where
comparatively small quantities have to be dealt with on a large

THE ELEMENTS OF CHEMICAL ENGINEERING.

scale, the filter paper may be replaced by bags made of cotton,
woollen, or linen cloth, the coarseness or fineness of which will
depend upon the nature of the precipitate. The choice of
suitable filter cloth is of great importance, and comparative
tests should be made in the laboratory before deciding which
kind of cloth should be used in the works.

In order to accelerate filtration, the laboratory chemist often
filters under diminished pressure by fixing the funnel into a
flask which is connected with a Bunsen pump, thus drawing the

filtrate into the flask. This
may be done on a large scale
in an apparatus which is shown
in Fig. 35.

The liquid enters the ap-
paratus A at B, 0 being con-
nected with a vacuum pump ;
the space D will become ex-
hausted, and the liquid will
be drawn through the filter

FIG. 35. -Apparatus for Filtering under cl°th which is PlaCed OI1 the

diminished pressure. false bottom E, leaving the

residue on it.

It will occur to the student that this apparatus might be
used in a different way. Suppose, instead of drawing the air
through by creating a partial vacuum, we were to pump air into
the top of the apparatus, we could then force the liquid at
increased pressure through the filter cloth instead of drawing it
through by means of a vacuum. This is an operation which is
not performed in the laboratory, because it would not only be
difficult to construct suitable apparatus, but because it would
not otter any particular advantage over filtering into a vacuum.
On a large scale, however, it is different. Working in a vacuum
means working in a closed system, and thus adding to the
expense of the installation. Moreover, each time the apparatus

THE FUNNEL AND ITS TECHNICAL EQUIVALENTS.

had to be emptied the vacuum would be broken, and a loss in
labour and fuel incurred. It is therefore cheaper to work under
pressure than to work in a vacuum, and for this reason filtering
under pressure has become one of the most important accessories
to chemical work. The apparatus which is used for this purpose
is called a filter press, and consists, broadly speaking, of a set of
chambers, separated by filter cloth. The mixture of liquid and
precipitate is passed, by means of a pump, compressed air, or by
natural gravitation, into the press.

Fiu. 36.— Chamber Filter Press.

There are two kinds of filter presses — chamber presses and
frame presses. In the chamber presses the mixture of liquid
and solid matter is introduced through a channel which runs
through the centre of the press. The filter cloth hangs from
the top of the chamber so as to cover each side of it, and has
an opening cut in its centre so that it can be screwed tight
into the channel of the chamber. On screwing the press
together, it is evident that the two filter cloths will touch each
other, and the chances of obtaining a water-tight system are
therefore increased. The sides of the chambers project in such
manner that the cake of separated solid matter collects in the
space formed by the projections, and on opening the press the
pressed mass falls out automatically. In frame presses the
cake is formed in frames which are separated by filter cloth,

78 THE ELEMENTS OF CHEMICAL ENGINEERING.

in which there are openings at the side, through which the
liquid mixture is introduced. On opening the press, the cake
remains in the frames, which can be lifted out and emptied.
Fig. 36 represents a chamber filter press.

Whatever the construction of the press may be, it is provided
with solid end pieces, one of which is stationary and the other
movable by means of a screw or lever or other mechanical
arrangement. The most usual materials of which presses are
made are iron and wood, but for special purposes they may be
lined in those parts which are exposed to the liquid with lead,
ebonite, or any other resisting material. As stated before,
they may be fed either by natural gravitation or by means of
pumps or compressed air, and arrangements are generally
provided for washing the cakes free from the original liquor.
As the presses may be worked at almost any pressure, it is
evident that care must be taken in ascertaining at what pressure
the substance which one may require to filter works best.
Thus, with very slimy substances great pressure would only
have the effect of depositing a thin film on the filter cloth ;
it would become stopped up, and further filtration would cease.

The manufacture of filter presses has become a speciality with
several well-known firms of engineers, who construct them in
many varieties, to suit special purposes. They may be obtained
capable of dealing with substances which either have, during
filtration, to be kept at a raised temperature so as not to
crystallise out, or which may have to be kept at a low tempera-
ture so as not to melt. These purposes are generally effected
by channels being provided in the chambers through which
steam, hot or cold water may be passed.

Besides being used for filtering purposes, a funnel is often
used in the laboratory for draining crystals or similar sub-
stances free from part of their moisture or mother-liquor. Some-
times the student in the laboratory will effect this purpose
more quickly by putting the crystals into a little bag attached

THE FUNNEL AND ITS TECHNICAL EQUIVALENTS.

to a string and swinging the bag round for some time. In
doing this he practically does what a centrifugal machine does
on a large scale. It is well known that when a body is com-
pelled to move in a curved line, say a circle, it has a tendency
to relinquish the curved line and proceed at a tangent, that is,
to get away from the centre of curvature. The natural conse-
quence is that it presses against the sides of the body in which
it is made to move, and is thereby prevented from going into
space. This tendency, known as centrifugal force, is pro-
portionate to the square of the
velocity.

A centrifugal machine, or a
hydro-extractor, as it is often
termed, based on this principle, and
represented in Fig. 37, consists of
a cage A, which is made to revolve
at great velocity inside a solid
frame B, supplied with an aperture
C through which any liquid may
drain. The cage is made of sheet
copper or iron, perforated with
holes or with slits. A centrifugal
machine may be over-driven or
under-driven, that is, the arrange-
ment by which it is coupled up to the engine may be placed either
below or above the cage. If crystals containing moisture are
placed in the cage and the machine is set in motion, the
crystals are thrown against the sides of the cage and the water
forced through the openings, so as to leave the crystals com-
paratively dry. When the mass which is to be dried is of a
very fine texture, so that it would go through the openings in
the cage, it is necessary to place a filter bag in the cage on which
the crystals or other materials are deposited. In that case it
is particularly necessary to bear in mind that with double

FIG. 37.— Centrifugal Hydro-
Extractor.

80 THE ELEMENTS OF CHEMICAL ENGINEERING

velocity the pressure against the sides becomes four times, with
triple, nine times, and so on, what it had been before, so that
it is quite possible that with a centrifugal machine revolving at
a great speed one might get worse results than with a machine
revolving at a lower speed, as then the centrifugal force becomes
too great, and the filter cloth or the interstices of the cage
may become stopped up. The fact that the centrifugal power
increases proportionately to the square of velocity adds to the
danger of the machine. Care must be taken that the mass in
the cage is evenly distributed. Hydro-extractors are made which
are provided with an arrangement by which any unevenness of
distribution is automatically counterbalanced.

It follows, of course, that the centrifugal machine can also be
used for filtering or drying precipitates, but in most cases it will
be found that a filter press is more suitable for that purpose, as
in this case it is easier to wash the precipitate with a minimum
quantity of water or liquid than in a centrifugal machine. In
the case of precipitates it is always necessary to use a filter
cloth in the centrifugal machine, and it is then particularly
necessary to see that the velocity at which it works is suited
to the material, and is not so great that it stops up the
pores of the filter.

It is often found necessary in the laboratory to filter sub-
stances through sand, asbestos, glass, or similar material, which
in that case is placed at the bottom of the funnel. On a large
scale similar arrangements are frequently used, particularly for
clearing water or trade effluents, and in sewage works. In such
installations, generally, large cisterns are built in the ground
with brick, concrete, or similar material. These may contain
false bottoms, or may be simply provided at the bottom with
channels for letting off the clear filtered liquor. They often also
have arrangements for distributing the original liquor evenly over
the top of the tank. These cisterns are partially or wholly
filled with sand, coke, coal, broken bricks, or similar material.

THE FUNNEL AND ITS TECHNICAL EQUIVALENTS. 81

The processes of filtering are of great importance, and require
considerable practical experience. They belong unfortunately
to those parts of chemical engineering in which theory can be
of but little use to the student, except in those points which we
have indicated. They present, however, an interesting example
of processes which, though impracticable in the laboratory, can
be carried out successfully on a large scale.

CHAPTER VIII.

THE MORTAR AND ITS TECHNICAL EQUIVALENTS.

IN order to produce chemical reactions it is necessary that the
substances should be brought into as intimate contact as possible.
Liquid substances may be made to react without preliminary
mechanical treatment, but where we have to deal with solids it
is well known that the finer they are powdered and the more
intimately they are mixed the easier it will be to obtain the
reaction desired. In the laboratory we may use a hammer in
order to break up large pieces of mineral matter, then we may
put the smaller pieces thus obtained into an iron or porcelain
mortar and powder them finer, or we may pass them into an
agate mortar and grind them there to the finest powder which
we can obtain. It will be noticed that in working on a small
scale we are restricted to the force which our arms or wrists
can exert, aided to some extent by any leverage which we might
obtain, as in the case of using a longer or shorter handle with
the hammer. But in working on a large scale, obtaining our
power from an engine, the force which we can exert is almost
unlimited, so that in manufacturing work we can produce effects
in crushing and grinding by means which we cannot apply in
the laboratory. It naturally follows that in the construction of
the apparatus we need not adhere to the means which are at
our disposal in the laboratory, but may adopt constructions in
which we can make use of the greater force which is at our
command.

THE MORTAR AND ITS TECHNICAL EQUIVALENTS.

Thus, in breaking up large stones into smaller fragments we
may make use of the forces which are obtained by a cutting or
crushing motion. Fig. 38 represents a stonebreaker in which
the jaw A is made to move backwards and forwards in a
horizontal direction against a fixed plate or wedge, so that any
large pieces of ore which are placed between are crushed into
smaller pieces. The width between the two crushing parts

FIG. 38.— Stonebreaker.

may be regulated so as to produce larger or smaller frag-
ments. The same effect may be produced by passing the
large pieces of ore through grooved crushing rollers. Stone-
breaking machines are made in different sizes, according to the
hardness of material and the quantity which they have to deal
with, and the power required varies accordingly, — a few cwts. to
ten tons per hour, and from half a horse-power to twelve horse-
power and more.

84 THE ELEMENTS OF CHEMICAL ENGINEERING.

The pieces which we have obtained in the crusher may vary
in size, and it is practicable to obtain them as small as nuts.
The next step would be to reduce these nuts to powder, and this
may be done in many different ways. Where a hard ore has to
be further reduced in size, an apparatus may be used which
resembles a mortar in its appearance and action. If we wish to
imitate the pounding action of a mortar on a large scale we
could construct a mortar itself in cast-steel ; we could further
have a heavy pestle of the same material, to which we could fix
a rod with a short piece at the top projecting at a right angle.
If we now had a shaft carrying a curved piece of steel revolving
near the pestle in such a manner that the curved piece caught
the projection of the pestle at each revolution, it would lift the
pestle up, and the latter falling by its own gravity would crush
the ore. An arrangement of a number of pestles working side
by side is largely used in the preparation of ores, and is
represented in Fig. 39.

In like manner, as explained in the stonebreakers, the ore
may also be further reduced in fineness by passing it through
steel or iron rollers, which may be either grooved or smooth ;
or soft materials, such as coke and similar substances, may be
crushed by being made to pass between two cogwheels fixed on
two shafts which revolve in the same or in opposite direc-
tions. Where plain or grooved rollers are used, there may be a
number of them arranged vertically in such a manner that the
material is first reduced to a certain fineness, then passed
through into a second set of rollers below the first set, where it
is still further reduced, and so on, so that one may commence
with coarse material at the top, and draw from the bottom in
one and the same machine a product of almost any fineness
which may be required.

Where it is necessary to obtain hard ores in the finest state
of division, that object is often attained by levigation. The
substance is finely ground in the dry state, mixed with a large

THE MOETAR AND ITS TECHNICAL EQUIVALENTS. 85

FIG. 39.— Ore-crushing Machine (Stamp Mill).

86 THE ELEMENTS OF CHEMICAL ENGINEERING.

quantity of water, and run into a series of tanks in such a
manner that it first enters one tank and is left there for a
certain period, then taken into a second tank, and so on. It
follows that the coarsest material will settle out in the first
tank, somewhat finer in the second tank, and that in the last
tank the very finest material will be obtained. Instead of first
grinding the material in the dry state and then mixing it with
water, it may from the start be mixed with water in the grind-
ing mill. The apparatus used for this purpose resembles in its
appearance and principle a mortar mill, such as can be seen
wherever building operations on a large scale take place. As
is well known, the mortar mill consists of a plate on which
heavy rollers, generally two, revolve. If, instead of a shallow
plate, a deep trough is arranged, the bottom of which may be
made of chilled steel, and the sides of which may be built of
bricks, and if the rollers are also made of steel, we have a
machine which in principle represents a wet grinding mill.
Mills which are built on the principle of mortar mills are
generally termed edge-roller mills, and they may be used for
dry grinding as well, in which case the trough we have described
is replaced by a shallow pan, generally made of cast-iron or
steel. It is, however, often inadmissible to grind substances in
iron, as they become more or less contaminated with that im-
purity. Edge-roller mills are therefore sometimes made in
granite, both as regards the bed and the runners ; and all parts
which are liable to be touched by the material which has to be
ground are arranged in such a manner that no iron or other
objectionable material enters into their construction.

Owing to the great variety which we find in the hardness of
different substances and in other properties, such as their
tendency to cake together, designs of mills are exceedingly
numerous. To go back again to the ordinary mortar, we can
imagine that the mortar, instead of having a solid bottom, had
that part cut out conically, and in its place had fitted into it a

THE MORTAR AND ITS TECHNICAL EQUIVALENTS.

grooved cone. If the bottom of the hollow part of the mortar
from which the cone was cut contained a number of teeth, or
were also grooved, it would follow that if the bottom cone were
made to revolve, anything falling between the ridges of the
bottom cone and the grooves of the hollow part of the mortar

FIG. 40. — Disintegrator.

would become crushed, and on this principle a number of
machines are constructed which are useful for grinding soft
materials, such as soda-ash and similar chemicals. Very useful
machines for grinding are those which are known by the
name of disintegrators, as it is possible by their help to grind
materials of very varied hardness. Fig. 40 represents one of
these machines.

88 THE ELEMENTS OF CHEMICAL ENGINEERING.

The disintegrator consists of a number of steel bars, which
are fitted into two or three concentric circles or drums round
the driving shaft, and joined to two cages by upright wrought-
iron discs and rings. The cages are fixed on horizontal shafts,
and fit into one another in such a way that the drum of one
cage can turn in the circular space between the two drums of
the other cage. Pulleys on the shafts on which these are
fixed are arranged in such a manner that the two cages rotate
in opposite directions. The cages are enclosed in a casing of
sheet iron (which can be easily removed), with which is
connected a hopper for feeding the machine. The material
to be ground is fed into the innermost drum, and is thrown
outward by centrifugal force through the spaces between the
bars, which are revolving in opposite directions. The material
is thus subjected to a great number of blows, and is ground
to a considerable degree of fineness. As the disintegrators
revolve at great speed, a thousand revolutions per minute and
more, and as they work on the centrifugal principle, any
obstruction which may occur in these machines will produce
serious consequences ; they therefore require careful attention.

Another construction which is frequently used for grinding
materials of moderate hardness is one in which the grinding
is effected by the weights of iron rollers. The mill consists
of a cylindrical vessel (Fig. 41), commonly called a mill barrel,
in which are placed a number of solid cast-iron rollers. There
is a manhole at the top or sides of the barrel, with an arrange-
ment by which it can be easily opened and closed, through
which the material to be ground is charged, and ultimately dis-
charged. These mills are either driven from a pulley fixed on
the centre shaft or from gearing working into a spur wheel fixed
round the outside centre of the barrel. Instead of using rollers
for grinding, a number of cannon balls may be used for the
same purpose. Both this mill and the one next to be
described may be used for grinding materials both in the dry

THE MOKTAR AND ITS TECHNICAL EQUIVALENTS.

90 THE ELEMENTS OF CHEMICAL ENGINEERING.

and in the wet state, and it is possible to obtain a very finely
ground mass by their means. Instead of a cylindrical barrel, a
spherical vessel is frequently used, which rotates at an angle to
the plane. The grinding in this mill is effected with the aid of
cannon balls.

Where an extreme degree of fineness is required, and it is not
practicable to use iron or steel machinery, the well-known
mills which have been used for many years for grinding corn
are still applied. In these mills the material is ground
between two circular stone slabs into which grooves are cut,
and which rotate against each other.

We have only enumerated a few of the many designs in the
market. In choosing a mill for a special purpose, it is essential
to consider the particular requirements for which it is wanted.
Thus, if we can set aside a mill for a special purpose, so as to
always grind the same material in it, it is not very essential that
one should be able to take the mill quickly to pieces for clean-
ing purposes. If, however, a mill is required to grind alternately
several kinds of materials, so that it has to be carefully cleaned
out between changes, one will have to lay particular stress on
choosing one of such construction as will allow the cleaning to
be done in the shortest time. In all cases it is necessary to
make sure that any broken parts can be easily replaced, and it
will be even necessary to consider local conditions, as in some
constructions of mills, such as the stamps, the noise produced
is such that they would be considered a nuisance in densely
populated parts.

Although every maker of grinding machinery will undertake
to work samples through his machines, and recommend such
machines amongst those which he makes which would meet the
requirements of the case best, it is not always possible, particu-
larly in new installations, to provide sufficient material for the
purpose. To get a thorough knowledge of the machines used
in chemical technology, it is necessary that one should see

THE MORTAR AND ITS TECHNICAL EQUIVALENTS.

them at work, and every opportunity should be taken of
obtaining such practical demonstration.

The material, after leaving the grinding mills, is not of uniform
fineness. It is therefore often necessary to separate the finest
part from the grit, and for that purpose sieves, made either in

FIG. 42. — Machine for Mixing dry Materials.

metal wire or in silk mesh, are used. This mesh, in the case of-
metal, is classified according to the number of openings in the
linear inch, and is accordingly given as 20, 40, 60, 80, or 90 mesh.
Everyone is familiar with the ordinary sieve, which consists of
a shallow drum, into which a sheet of copper, brass, or silk
mesh is fitted ; it may be used where not very large quantities

THE ELEMENTS OF CHEMICAL ENGINEERING.

have to be dealt with, and a number of such sieves may be
placed on a table and suitably fastened to it whilst the table is
made to revolve at a fair speed, in such a manner that it
occasionally receives a knock which throws it violently up.
Where large quantities have to be sieved, an oblong sieve may

FIG. 43. — Machine for incorporating Liquids and finely-ground Solids.

be used, arranged in such a manner that it has a quick, horizon-
tal, oscillating movement, and occasionally receives a knock
throwing it up in a vertical direction. As the material moves
along in the sieve, the finest part will fall through into a box
underneath, and the coarser part can be made to travel into
another receptacle, from which it is taken back to the mill
to be ground finer. Another construction is one in which the

THE MORTAR AND ITS TECHNICAL EQUIVALENTS. 93

mesh is placed outside a frame, and forms either a circular or
an octagonal long tube, which is made to revolve by means of
a centre shaft.

Besides being used for grinding materials, the mortar is
frequently used as in the laboratory for mixing ground sub-
stances together, or for incorporating finely ground solids with
liquids. The same operations have frequently to be carried out
on a large scale, and a convenient arrangement for mixing
dry materials is that shown in Fig. 42, which consists of an iron
drum, fixed obliquely on a horizontal axle. Through the
rotation of the drum the various materials inside are thrown
against one another, and in a short time become thoroughly
mixed. When it is desirable to incorporate liquids and finely
ground solids, many of the mills which we have discussed could
be used, particularly edge-runner and roller mills. In many
cases special apparatus designed for the purpose will, however, be
found more suitable. One of these is shown in Fig. 43, and
consists of a mixing trough, in which rotate blades of special
construction. A machine of this description may be obtained
in different sizes, and capable of dealing with small or large
quantities.

CHAPTER IX.

MEASURING INSTRUMENTS AND THEIR TECHNICAL
EQUIVALENTS.

AMONGST the most important operations carried on in the
laboratory are those relating to measurements. They are of
manifold kinds, and are applied for the determination of the
weight of solids, the volume of liquids and gases, the
temperature, the pressure in relation to that of the ordinary
atmosphere, etc. As the quantities to be dealt with, and the
circumstances under which operations are carried on, are
different in works, it is evident that although the principles
upon which apparatus is constructed for use in large installa-
tions are substantially identical with those used in the
construction of laboratory apparatus, yet the details and
dimensions will not be the same.

Taking as an instance the balances which are used in the
laboratory, we find that they depend upon the principle of an
oscillating beam, in which the position of the centre of gravity
determines the sensitiveness of the instrument ; and in practical
work ordinary beam scales are frequently used in sizes which
render it possible to determine weights up to 1 ton and more.
Fitted with knife-edge centres and bearings, they can be made
extremely sensitive, and are therefore particularly useful in
the handling of expensive goods. A more convenient system is
represented by a platform weighing-machine, which may be made
either on the principle of the above-mentioned scales or on the

MEASURING INSTRUMENTS AND THEIR EQUIVALENTS.

principle of decimal or centesimal leverage. Such a machine is
shown in Fig. 44, where a platform by a system of levers is con-
nected with the indicating apparatus which carries the weights.
The levers are adjusted in such a manner that the actual
weight placed on the platform requires only one-tenth or one-
hundredth of that weight to be balanced. The indicating arrange-

FIG. 44.— Platform Weighing-Machine.

ment consists of a steelyard with division-marks representing
pounds and fractions of pounds, and having at its extreme point
an arrangement for carrying weights representing cwts. and frac-
tions of cwts. The pounds and fractions of a pound are, as with
a rider on a chemical balance, recorded by a running weight
which moves on the divisions on the steelyard. These weighing-
machines can be made to carry weights up to 8, 10, or more

96 THE ELEMENTS OF CHEMICAL ENGINEERING.

tons. Some weighing-machines are constructed in such a
manner that they require no weights, but indicate the- result on
a dial; others may be made to weigh definite quantities of
powdery substances automatically by a system of shutters acted
on by levers.

The measurement of liquids, where the same quantities are
often used, is generally performed in vessels of convenient
(preferably rectangular) shape. The contents of these may be
found either by calculation, or by filling them with water to the
required level and ascertaining the volume by calculation from
the weight obtained. As one cubic foot of water weighs 62*5
pounds (equal to 6'25 gallons), it is easy to calculate from the
weight in pounds how many cubic feet or how many gallons a
vessel will hold. In like manner, when it is desirable to
ascertain the volume of a liquid other than water, this can be
easily ascertained by weighing the liquid and dividing the
weight thus obtained by 6'25 times, the specific gravity, when
the result will give the capacity in gallons.

In the laboratory the determination of the specific gravity of
a liquid as performed in a pycnometer is somewhat tedious, but
in a works, the areometer, which is used for the purpose, enables
one to obtain the result almost instantly. This consists of a
bulbous body and a thin stem. The former is filled with shot
or mercury, and its total weight adjusted in such manner that
when it is placed in a liquid it will sink deeper or be raised
higher according to the specific gravity of the liquid. The stem
is divided in such a manner that the scale marked on it
indicates the specific gravity of a liquid at the point to which
the stem sinks into it, either by giving the figures for the
specific gravity direct, or on a scale which can be easily converted
into it. In this country the areometer generally used is that
constructed by Twaddell ; each degree corresponds to an addi-
tion of '005 to the specific gravity of water; so that if, for instance,
the instrument indicates 6° Twaddell, it means that the specific

MEASURING INSTRUMENTS AND THEIR EQUIVALENTS. 97

gravity is 1 + (6 x -005), that is, 1*03. If the instrument indicates
53° Twaddell, it means that the specific gravity is 1 +(53 x '005),
that is, 1-265. On the Continent there are several other
aerometers used, and the table which is given below will enable
the student to convert statements expressed by these arbitrary
scales approximately into specific gravities, or, with a slight
calculation, specific gravities into these scales.

If d be the specific gravity of a liquid as compared with
water = 1, and n the variable showing the degree on the
respective scale, then we have for the different scales —

For liquids heavier than water:

145-9

Baume d =

Cartier . . . . . d =
Beck d =

Brix . . . . . . d =

200
Balling d =

145-9-Ti
136-8

126-1 -ra
170

170-w
400

Gay-Lussac . . . . d =

200^71

100

100-71

Twaddell d =

i+lQO

For liquids lighter than water:

145'9

Bai d -

135-9 + rc

136-8
Cartier d =

1261+7*

98 ELEMENTS OF CHEMICAL ENGINEERING.

170

Beck . . d =

Brix , d =

170+n

400

400 + n
Balling . . . . . d =

100
G-ay-Lussac . . . . d =

Before leaving the subject of weights and measures as far as
solids and liquids are concerned, it may be useful to point out
that there are certain coincidences which enable one to convert
English weights and measures into the metrical system without
tedious calculations, and sufficiently near for ordinary work.
Thus, for instance, as an English ton contains 2240 Ibs., and
as 1 kilogramme is equal to 2 -2 Ibs., for purposes of quick
calculation it may be taken that 1000 kilogrammes are nearly
equal to 1 ton, or that 50 kilogrammes are equal to 1 cwt. As
1 cubic foot of water weighs 997'14 ozs., which is very nearly
1000 ozs., and as 1 litre weighs 1000 grammes, it follows that
results expressed in grammes per litre also represent the same
result expressed as ozs. per cubic foot. Thus, for instance, if an
analysis were to give us 55*5 grammes per litre of salt, we could
say straight away that that represented 55'5 ozs., which is
347 Ibs. of salt, per cubic foot. Again, as one gallon weighs
10 Ibs., the grammes per litre divided by 100 are equal to Ibs.
per gallon. Also, as 1 gallon weighs 70,000 grains, any results
which are found as grammes per litre multiplied by 70 will
give the result in grains per gallon.

Where it is necessary to measure a quantity of gas in motion,
an apparatus of a similar kind to that used for the measurement
of coal gas by means of ordinary gas meters is used. Where
this is not practicable, the speed with which the gases travel is
determined. Suppose we wanted to determine the amount of

MEASURING INSTRUMENTS AND THEIR EQUIVALENTS. 99

sulphurous acid passing into the atmosphere from a chimney,
we could easily get at the amount of sulphurous acid per cubic
foot by aspirating that amount or a multiple of that quantity
through a standard iodine solution. By ascertaining from
drawings or by measuring the sectional area of the chimney at
the point at which we took the sample, we could ascertain the
number of cubic feet of gas which passed through the chimney
in a certain time if we knew the speed at which the gases
travel. The apparatus which is used for determining the speed
is called an anemometer, and is based upon the movement of a
column of ether in a tube when under the influence of a current
of gas.

The measurement of temperatures in the laboratory is nearly
always performed by means of an ordinary mercury thermometer,
and, where this is feasible, the same means are used on a large
scale, as for accuracy, and the ease with which the latter can
be verified, the mercury thermometer is the best. But it must
be borne in mind that the ordinary thermometer is only reliable
within points which are neither too near the freezing nor the
boiling point of mercury. For temperatures higher than 320°
or 330° Centigrade it is now possible to use specially constructed
mercury thermometers, which, being filled up with nitrogen or
carbon dioxide gas under pressure, and made of refractory glass,
will indicate temperatures up to 550° C. A serious objection to
glass thermometers is that they are liable to be broken. That
objection can to some extent be got over by encasing them in
suitable metal cases, leaving that part of the scale uncovered by
metal on which the reading is observed. In order to meet
different requirements, thermometers are constructed of all
sizes and shapes up to 3 feet and more in length, bent at right
angles or in other ways, and constructed in such a manner that
the scale is only uncovered for that range of degrees which it is
desired to observe. For temperatures above 550° C. instruments
are used which are termed pyrometers, the construction of

100 ELEMENTS OF CHEMICAL ENGINEERING.

which is based on different principles. One class of construction
depends upon the fact that metals expand with a rise of
temperature, and the increase in length in the metal, which may
be in the shape of a bar or a spiral, is transferred by a lever
arrangement to a scale and indicated by a pointer. Pyrometers
have also been constructed which depend upon the principle of
the expansion of air, the heat being indicated on a dial in a
similar manner. It may be stated here, as a rule which applies
to all measuring instruments for heat, that it is necessary to
check them from time to time, and this applies not only to
pyrometers, but also to thermometers, which, as is well known,
change in the course of time.

One of the simplest and, if properly conducted, one of the
most reliable ways of determining high temperatures is by
means of the calorimeter. The calorimeter is based on the fact
that if a substance of known specific heat, and of known
weight, heated to a certain point, is dropped into a known
quantity of water of known temperature, it will cause that
quantity of water to rise in temperature by a definite amount.
If, therefore, the weight of the substance used and the specific
heat of it be known, and a definite quantity of water be taken
for the purpose of the experiment, it will be possible from the
rise of temperature in the quantity of water taken to determine
the heat to which the original substance was raised. The
apparatus consists of a metal box, generally made of sheet
copper, which is placed in a wooden box, the space between the
two being filled with a bad conductor, such as wool or similar
substances. The copper box is covered with a lid which is
provided with two holes, one to allow a thermometer graduated
in tenths of degrees to pass through, the other to enable one to
drop in the heated mass of metal which is used for ascertaining
the temperature. A stirrer is fixed in such manner that the
water in the calorimeter can be mixed to equalise the tempera-
ture. The metal cylinder may be made of wrought-iron,

MEASURING INSTRUMENTS Al^«iiSJiHfe^UIVALENTS. 101

copper, nickel, or platinum. In order to carry out the test, the
apparatus is two-thirds filled with an accurately measured
quantity of water, the metal cylinder is placed in a metal spoon
fixed on a sufficiently long rod and passed into the flue or
furnace, the temperature of which has to be determined. It is
left there for a sufficient time, twenty minutes or half an hour,
and then quickly removed and dropped into the calorimeter.
The temperature of the water in the calorimeter is taken
immediately before the metal cylinder is dropped into it and
shortly after. If the original temperature of the water be 1°
and the maximum temperature after inserting the heated
cylinder be tl ; if the weight of the metal cylinder be p and the
specific heat of the metal of which it is made be c, the weight
of the water added to the water weight of the copper vessel and
stirrer pl, then the temperature T of the hot cylinder is

T pi(^o)
pc

The water weight means the actual weight of the copper vessel
multiplied by the specific heat of copper. It must not be
forgotten that the specific heat of metals varies with the
temperature, and this fact should be taken into consideration.

A very convenient form of measuring temperatures is now
at our disposal in the form of electrical thermometers. These
are of twofold construction ; they may be either resistance or
contact thermometers. In the resistance thermometers, use is
made of the fact that the resistance of a metal to the passage
of a current depends upon the temperature, so that if, for
instance, a platinum wire is exposed to the heat of a furnace
and a weak current is passed through it, that current will affect
the needle of a galvanometer according to the temperature of
the wire. The contact thermometer, on the other hand, depends
upon the fact that if two pieces of different metals, as, for
instance, an iridium and a platinum wire, are placed in contact,

102 ELEMENTS OF CHEMICAL ENGINEERING.

an electric current is produced which varies with the tempera-
ture to which the contact place is exposed; and this current
can also be measured by means of a galvanometer, which may
be adjusted to a scale in such a manner that the degrees
Centigrade or Fahrenheit are shown on a scale direct. These
instruments are extremely useful, particularly as they can
be used in places and in apparatus in which it would be
difficult to introduce other kinds of thermometers; but it is
important here, as in every other case, to check the instruments
from time to time.

Another kind of thermometer much used now is the
Thalpotassimeter. This instrument works on the principle
that liquids exposed to different temperatures in a closed space
will, according to the temperature, produce a pressure which
can be read off on a convenient scale. The liquids used for the
purpose vary according to the temperatures which are required
to be measured. For low temperatures, such as required in a
vacuum apparatus, etc., they may be ether or alcohol ; for higher
temperatures, mercury or other liquids. A peculiar system of
determining temperatures is often used in furnaces in the
manufacture of pottery and similar ware, and consists of little
cones made of glazing material having different degrees of
fusibility. The approximate melting point of these cones is
known, and by placing a number of them in the furnace it can
be easily ascertained which of them is first affected by the heat.
The actual temperature at which the furnace is working will lie
between the fusing point of this and that of the cone having
the next higher fusing point which is not affected.

For quick determinations, which may be left to the workman,
it is sometimes convenient to make use of the known
temperatures at which certain metals or compounds melt.
Thus, for instance, potassium nitrate melts at 329° 0., and
bismuth at 264° C. If we introduce these two in a little spoon
fixed on a long handle into the furnace to be tested for heat,

MEASURING INSTRUMENTS AND THEIR EQUIVALENTS. 103

and if we find that the bismuth melts and that the potassium
nitrate does not, then we may take it that the real temperature
is between the two melting points.

The instruments designed for ascertaining in the laboratory
the composition of mixtures of gases constitute one of the
triumphs of scientific accuracy. In work on a large scale,
where absolute precision is not required, and where approximate
results are satisfactory, so long as they can be obtained with
the least expenditure of time, the apparatus which is used for a
similar purpose is naturally constructed on different lines to
that used in the laboratory.

The main difference in the construction of the apparatus
consists in the substitution of water and similar liquids for
mercury, not only because mercury is an expensive material,
but also because its high specific weight renders work with
large quantities extremely cumbersome. To carry about an
apparatus filled with mercury, of sufficient size to allow of
measurements being made on such large quantities that slight
differences in the volume would still show, would be impracticable ;
yet it is often necessary to perform tests on the spot, without first
transferring the gas samples to the laboratory. Although it is
over thirty years since technical gas analysis was introduced
into chemical works, its importance, not only to chemical works
but to other branches, is hardly yet sufficiently recognised, and
for that reason we may dwell on this point a little longer. One
of the first uses to which gas analysis was put in chemical works
was that in which the amount of oxygen was determined in the
gases leading from sulphur or pyrites burners. It is well
known that for the manufacture of sulphuric acid, sulphur or
pyrites is burnt in kilns by means of air. If too much air is
added, the gases become too dilute, and the chambers in which
the sulphuric acid forms do not work to the best advantage.
If the quantity of air admitted is too small, there are losses in
the quantity of nitre required. It is therefore necessary, in

104 ELEMENTS OF CHEMICAL ENGINEERING.

order to properly regulate the admission of air to the kilns, to
ascertain whether too much or too little air is introduced, and
this knowledge is gained by drawing samples at intervals from
the gases leaving the burners or kilns, and determining the
quantity of oxygen which is left in them. This may be done
by means of a simple apparatus which is known as a Bunte
burette, in which the gases, after the sulphurous acid has
been removed, are passed into a eudiometer and shaken up
with an alkaline solution of pyrogallic acid. The free oxygen
present is thus absorbed, and determined in quantity by
difference from the volume of the remaining nitrogen. Apart,
however, from the use of gas analysis in specifically chemical
operations, there are other processes in which it is important to
determine the composition of gaseous constituents which are
formed, and the most important are those which relate to the
combustion of coal and other kinds of fuel.

We have in previous chapters frequently had occasion to
point out that the commercial success of many operations
depends upon the economical utilisation of heat. If we leave
out of consideration the power of wind and water, which is at
present, and particularly in this country, not much utilised, we
find that the results of chemical reactions and of physical
processes, as conducted in chemical works, are only due to the
conversion of the energy stored up in coal into other kinds of
energy. It is therefore of the greatest importance that we
should obtain the utmost yield from the latent energy of fuel.
In many cases an examination of the products of combustion
will enable us to approach that point more closely, and for that
reason we should be in a position to analyse the products of
combustion quickly and with sufficient accuracy.

The well-known apparatus which is used for the determina-
tion of gases of combustion is called an ' Orsat/ and enables
one in a very short time to determine the amount of carbon
dioxide, carbon monoxide, and oxygen, and. by difference, also

MEASURING INSTRUMENTS AND THEIR EQUIVALENTS. 105

nitrogen, in the products of combustion. Apparatus has also
been constructed to show automatically at any time the amount
of carbon dioxide which is present in flue gases. One consists
of two delicately balanced glass spheres, of which one is
surrounded by air and the other by the flue gas which is to be
tested, the difference in weight, as indicated by the beam on
which these spheres are balanced, showing the difference in the
specific gravity between the air and the gas to be tested, from
which the percentage of carbon dioxide can be calculated.
Another kind of apparatus is constructed, on purely mechanical
principles, in such a manner that the machine itself performs
the function of the determination of carbon dioxide by absorp-
tion in caustic potash, and records the results automatically.

CHAPTER X.

MATERIALS USED IN CHEMICAL ENGINEERING, AND
THEIR MODE OF APPLICATION.

APART from a sound knowledge of physics and chemistry, the
successful designing of apparatus used on a large scale depends
upon a knowledge of the details of construction, and this again
requires a knowledge of the details of such other trades as
enter into chemical engineering. It is impossible to design a
plant, or even to understand the construction of a plant pro-
perly, without being to some extent acquainted with the
principles of iron-founding, the coupling of pipes, bricksetting,
carpentering, joinering, etc. It must be understood that it
would be impossible to have such a knowledge of all these
branches as would enable one to do the practical work ; but
with a general knowledge of the principles which underlie the
work in different trades, and by carefully watching work in
progress, a great deal of useful knowledge can be obtained.
Another important point gained will be this, that in construct-
ing new designs we shall understand whether the whole and
its details can be readily executed, and if so, which will be
the most economical way.

As this is a subject of great importance, we will consider a
few of the principal trades, which enter into the construction
of chemical plant in this chapter.

It may be safely stated, that although everyone has had
ample opportunity of watching bricksetters at their work, few

106

MATERIALS USED IN CHEMICAL ENGINEERING. 107

will have exercised their powers of observation sufficiently to
know exactly how the work should be and is done. The
main object in building with bricks is to arrange the different
courses in themselves and amongst each other in such manner
as to produce a homogeneously interlaced mass. There are
many possible ways of attaining that object, but we shall only
mention a few of the most important.

The average standard brick is supposed to be 9 ins. long,
4 1 ins. wide, and 3 ins. in thickness. It is usual in building to
express the thickness of walls not in inches, but in the number
of bricks. Thus a wall 4J ins. thick would be termed half
brick; one 9 ins., one brick ; one 14 ins., one and a half bricks
thick. Strictly speaking, bricks are not made exactly to the
above sizes, but about £ in. less in each direction, so that when
the interstices between them are filled with the binding material,
their dimensions are represented by the above integers without
fractions. The width of the binding material between the
bricks should be about f in. A standard brick weighs approxi-
mately 7 Ibs., and a thousand of them, termed a load, from 61
to 63 cwts. In measuring brickwork it is usual to reduce it
to a thickness of 14 ins. and express the quantities in ' rods.'
One rod of brickwork = 272 superficial feet 1£ bricks thick.
It is made up of 235 feet of bricks and 71 of mortar,
and requires 4300 standard bricks. It is generally stated
that a bricklayer and his labourer can set about 800 bricks in
a day's work ; but in work requiring careful handling, such as
furnace-building or boiler-setting, the quantity achieved per
day will be much less.

The chief aim in bricksetting is that of obtaining a good bond ;
and the principal point which has to be considered on that
score consists in arranging the courses in such a manner that
the bricks in one course cover the joints between the bricks in
the course below. The two chief methods used are the English
and the Flemish bond. The former gives the best results, and

108

ELEMENTS OF CHEMICAL ENGINEERING.

is preferable to the latter where strength and durability are re-
quired. Fig. 45 shows the difference between the two sufficiently
clearly without further explanation ; tigs. 46 and 47 demonstrate
the means adopted for obtaining a good bond in building corners.
In work which is not exposed to great heat, ordinary bricks

I 1 1

1 1 1

1 1

FIG. 45.— English and Flemish Bond.

made of impure coloured clay, more or less mixed with sand,
are used, and ordinary mortar is used for binding the bricks
together. The latter is made by mixing slaked burnt lime
with sand. One cubic yard of lime takes from 4 to 6 cubic
yards of sand, and yields 4 to 6 cubic yards of mortar. But if

FIG. 46.— Bond.

the finished brickwork is exposed to damp, or if it is re-
quired to hold or store water, it is necessary to use cement,
of which the Portland brand is considered to be most suitable.
Generally speaking, cements are silicates of lime and alumina
which have been strongly ignited, and are placed on the market
in the form of fine powder. It must be borne in mind that
whereas ordinary mortar shrinks on setting, cement expands.

MATERIALS USED IN CHEMICAL ENGINEERING.

109

But it is not usual to use cement by itself except in special
cases; it is generally used mixed either with sand or with
mortar.

In works in general, bricks set in cement or in cement
mortar are usually applied for foundations for buildings, for
water-tanks, and for foundations for engines. In the latter
application, it is sometimes overlooked that under the con-
tinuous action of oil, cement becomes disintegrated ; it is there-
fore advisable, apart from the fact that every apparatus, and

FIG. 47.— Bond.

particularly engines, should be kept clean, to make such arrange-
ments for oiling purposes as to prevent the oil from oozing into
the ground.

In chemical works cement is found to be particularly useful,
as it resists the action of alkalies, acids, and many chemicals to
a remarkable degree. It lias, moreover, the useful property of
being able to stand a considerable degree of heat, safely up to
200° C., and even higher, and to be equally unaffected by opera-
tions which require a temperature below freezing point.

Where brickwork is exposed to great heat it is necessary to
use special bricks, called firebricks ; they are made of a purer

110 ELEMENTS OF CHEMICAL ENGINEERING.

clay than the ordinary building bricks, and are set in ground
clay. They are made in standard sizes, similar to ordinary bricks,
and may be obtained in almost any shape to suit different con-
structions. As they are about five times as expensive as ordinary
bricks, they are sparingly used, and only where it is absolutely
necessary. In drawing a plan of a furnace or similar structure,
it is therefore necessary to specially indicate where either kind
of bricks should be placed. This is generally done by colouring
those parts which are to be built in firebrick and clay yellow.

Besides firebricks, tiles made of similar refractory material
are frequently used in furnaces and similar constructive work.
They are particularly useful for covering spans of more than
6 inches, such as occur in flues and small fireplaces. Thus we
have seen in Chapter IV. that the bed of a 'blind' roaster
is made of tiles, the reason for this being that we are thus
enabled to make the flues wider. If we were to use ordinary or
fire bricks for the purpose, we could not place the side walls
forming the flue more than 5 or 6 inches apart, otherwise
the 9-inch brick would not rest on them securely. By using
tiles we can therefore span distances which are too large to be
covered by brick, and too small to be covered by arches, or
where, for other reasons, it would be inconvenient to use an arch.

In parts which are exposed to great heat, spans of more
than 15 inches should be covered by arches. These are
built up in the form of a segment of a circle, which should
have sufficient 'spring' to be stable. Although in former times
it was usual for the bricksetter to cut his ordinary bricks into
suitable shape for the arch, it is better to order specially shaped
bricks for that kind of work. It may be laid down as a general
rule, that in designing a furnace or other brick apparatus every
detail should be worked out in such a manner that no cutting
of bricks by the bricksetter is required. Bricks may be ob-
tained from the makers of almost any size and shape, and in
such intermediate sizes as will represent a brick cut into half

MATERIALS USED IN CHEMICAL ENGINEERING. Ill

or into a quarter of its original size. In all work exposed to
heat it is particularly necessary to set the bricks and tiles in
such a manner as to allow for the expansion which will take
place, otherwise the structure will soon crack in many places
and become leaky and unsafe.

On starting a new furnace it is necessary to heat it slowly and
gradually, and according to its size and the temperature which
is to be maintained. It may take from three days to a month
to bring it up to working heat. In like manner, when a
furnace has to be stopped, it has to be cooled down very
gradually ; this is done by letting the fires down slowly, and
then closing the dampers so as to prevent cold air from passing
through.

Apart from its use in the construction of buildings and roofs,
into which we need not enter more particularly, timber is
employed in the construction of tanks, casks, and barrels, and is
manipulated by the carpenter, joiner, or cooper. The different
pine woods are mostly used for chemical purposes, though other
kinds of timber will be found sufficiently strong arid durable
for many purposes. Most kinds of timber will stand the action
of liquids as long as they are not too strongly acid, but alkaline
solutions will act injuriously on them. Certain solutions, with-
out being either acid or alkaline, have a peculiar disintegrat-
ing influence on woods, and will in time ooze through the pores
and leak away; some calcium and magnesium salts show
particularly this objectionable property. Wooden structures,
such as tanks or barrels, which have been used for the storage
of liquids, should not be allowed to stand dry for any length of
time. If not in use they should be filled to their full capacity
with water, otherwise they will cease to be liquid- or water-tight.
In constructing them it is necessary to see that no material
is used which would act or be acted upon by the liquid
which the tanks or barrels are to hold. It would, e.g., be out
of the question to use iron nails in the construction of a tank

112 ELEMENTS OF CHEMICAL ENGINEERING.

intended to hold a solution of pure aluminium sulphate.
Many tanks are built up of staves in a manner similar to that
in which barrels are made. They are slightly wider at the
bottom than at the top, so that the hoops which are used for
pressing the staves together can be easily tightened by being
moved towards a part of greater circumference. It is often
required to know approximately the contents of a barrel. A
simple formula for calculating it is

in which D is the diameter at the widest point, d the diameter
of the lid or bottom, and h the height of the barrel.

Wherever there is any doubt as to what kind of timber
would be most suitable for the construction of tanks, it is
necessary to immerse in the laboratory samples of different
kinds of woods in the liquid which the tanks are destined to
hold, and under the same conditions with regard to heat as will
prevail in actual work.

The most important of all materials which enter into the
construction of chemical apparatus is iron. It is usual to
distinguish three kinds which are used in the arts and manu-
factures, viz., cast-iron, wrought-iron, and steel. But in order
to obtain the best technical effects from them it is necessary to
make further distinctions, and to consider their properties more
in detail, particularly when they have to be used for special
purposes. Ordinary grey cast-iron, as it comes from the blast
furnace, contains from 2J to 4^ per cent, of carbon, mostly in
the form of graphite, and also silicon; in white cast-iron the
carbon is chemically combined with the iron. It may contain
manganese in varying quantities, from 1 to over 20 per cent.
In steel, the quantity of carbon is more than | per cent. ; in
wrought-iron, less.

It is impossible to give an adequate description of the process
of iron-founding. The different stages of it, the making of the

MATERIALS USED IN CHEMICAL ENGINEERING 113

patterns, the manner of moulding, and other details, must be
seen to be clearly understood. At the same time, it is of the
greatest importance that the student should be acquainted with
the details of this kind of work, and that he should take an
opportunity of watching the different processes in a foundry.
The explanation of this and similar processes might be greatly
advanced if cinematographs were used as an aid to the lectures.
Within the walls of the college or technical school it would be pos-
sible to demonstrate to the student in a most instructive manner
the work of the bricksetter, the pattern-maker, the moulder, the
iron-founder, the turner, and many other craftsmen ; and any
points which were not clear to him could be easily demonstrated
by reproducing the picture on the screen, and stopping it at
such intervals as might be required for explanations.

A little instance will show the importance of being acquainted
with the details of different trades. I found that castings
which I used for work with corrosive substances became
corroded and gave way in odd places in a manner which I
could not account for. It occurred to me that this might be
due to the fact that the studs which are used for supporting the
core of a mould were made of wrought-iron, and remained in the
finished casting. The casting therefore consisted in those parts
in which the studs were left of wrought-iron, and not of cast-
iron. It is well known that different chemicals have a different
action on cast-iron as compared with wrought-iron; in many
cases wrought-iron is more easily attacked than cast-iron.
Apart from this, it is well known that wherever two metals are
joined, probably owing to an electric current which is set up,
the corrosive action is increased. I have therefore lately made
it a point in all specifications for chemical work to insist upon
cast-iron studs being used, with results which confirm the
correctness of my views.

Going further into such details as can be explained in
writing, it must be noted that the patterns which are made for

114 ELEMENTS OF CHEMICAL ENGINEERING.

castings must be larger than the actual size shown in the
drawing. Koughly speaking, it may be taken that on cooling
down, the molten metal shrinks to the extent of J to ^Q of an
inch for every lineal foot, and an allowance for this is always
made in preparing the patterns and laying out the moulds into
which the iron is cast.

If we, further, consider the manner in which iron is prepared
for casting, we will find that it is melted with the addition of
such substances as will produce a slag. The slag will rise to
the top in the cupola, but some of it will still be left in the
molten iron, or formed during the time of transferring the
molten mass to the place in which it has to be cast into form,
and will rise to the top of the finished casting. It is therefore
necessary to arrange the mould in such a manner that the
weakest part of the apparatus is at the top. If, for instance,
we require a pipe which is to be heated at one end, it would be
necessary to cast this pipe in a vertical position, and in such a
manner that the part which is to be exposed to heat would be
at the bottom of the mould. By casting it a little longer than
required and cutting the superfluous end-piece off, we should
obtain a pipe which would be perfectly sound all through, and
particularly strong at the bottom part.

By mixing different grades of metal in the cupola, different
makers produce cast-iron vessels which resist the action of
special chemicals particularly well. The manipulation of cast-
iron in the cupola to produce castings which have specific
resisting properties in relation to different chemicals is a matter
which has not yet received the attention it deserves. That the
properties of cast-iron are largely influenced by admixtures
with other elements is well established ; and it is possible that
when our knowledge has become more complete, we shall be
able to use iron vessels in operations for which at present they
are not suitable. It may be generally said that cast-iron will
withstand the action of alkalies when they are in solution and

MATERIALS USED IN CHEMICAL ENGINEERING. 115

when melted ; that it is hardly attacked by strong acids, but
easily by weak acids ; that many neutral salts can be safely
manipulated in it, whereas others cannot. The probability is
that dissociation is the fundamental cause why neutral salts act
on iron. Thus, for instance, ammonium chloride, which is a
typical representative of the action of dissociation, acts strongly
on iron on boiling down. Under ordinary circumstances and in
a dry atmosphere iron does not change, but in moist air or in
contact with water it soon becomes oxidised and rusts.
Wrought-iron exhibits this property in a more pronounced
manner than cast-iron. It is wrell known that by coating iron
vessels with a thin layer of a material which will prevent access
of air, such as paint or varnish, it can be preserved indefinitely.
Where iron vessels have to be bedded-in, one must be careful to
choose the substance in which they are to be imbedded in such
a manner that it may not act on the iron. It has been found
that iron which has been bedded in lime or plaster of Paris
rusts very rapidly, whereas if bedded in cement or in tarry
matters, such as asphalt, it remains unaltered. These are only
a few of the details which have to be considered in chemical
engineering in the use and application of iron. They will show
that in that branch of knowledge no detail can be too small to
receive due consideration.

As regards wrought-iron, the principal point which has to be
considered when it is used in conjunction with cast-iron, as
frequently occurs in constructive work, is that its coefficient of
expansion is greater than that of cast-iron. Wherever a doubt
exists whether cast-iron, wrought-iron, or steel should be used
for a special purpose, it is always advisable to try in the
laboratory the action which the substance which has to be
manipulated exerts on these materials, and to do so as nearly
as possible under the same conditions as will prevail in the
works.

Next in importance to cast-iron, as far as its application

116 ELEMENTS OF CHEMICAL ENGINEERING.

in chemical industries is concerned, comes lead. Its most
valuable property is that of not being attacked by hot or cold
sulphuric acid as long as the strength of the latter is under
140° Twaddell. As this acid enters into a great many opera-
tions, it is natural that the vessels in which such operations are
performed should either be made of, or coated with, lead. It is
now possible to obtain cast-iron vessels of almost any size
coated with lead, which has been fixed on the iron by a special
process of casting or plating. Apparatus of the most varied
description is made on this principle, and lead-coated or lead-
lined boiling and evaporating pots, autoclaves, hydro-extractors,
perforated plates, tubes and pipes are in the market.

As regards the use of sheet lead, we have in the first chapter
explained that it is usual to distinguish the different thicknesses
in terms of weight per square foot. The annexed table gives
the standard weights in pounds, and the corresponding thickness
in decimals of an inch : —

3 Ibs. per sq. ft. ='051 in. thickness

4 „ „ =-068 „

5 „ „ =-085 „

6 „ „ =102 „ ,-

7 H » =-'119 „

8 „ „ =136 „

— from which the weight of sheets of greater thickness can be
easily calculated by simple proportion.

Lead pipes are made in standard lengths of 15, 12, and 10
feet : their thickness varies between ^ and \ of an inch, and
their weight can be approximately calculated by the formula
l5'5l7t(D + t) Ibs. per foot, where D is the internal diameter
and t the thickness in inches.

We have pointed out before that in constructing chemical
apparatus from lead sheets (and the same applies to lead pipes)
the edges are joined together by means of a strip of lead which

MATERIALS USED IN CHEMICAL ENGINEERING. 117

is melted on to the edges. The heat required for the purpose
is obtained from a small portable apparatus in which hydrogen
is evolved from zinc and dilute sulphuric acid. By means of a
long india-rubber pipe the gas is conducted into a burner which
is arranged on the same principle as the burner which is used
in the laboratory for glassblowing, and the necessary air is
supplied from a hand blower, which is generally manipulated
by the plumber's apprentice. The zinc and acid used for the
evolution of hydrogen should be free from arsenic, so as to
avoid the formation of the highly poisonous arseniuretted
hydrogen.

It is a peculiar property of lead that whilst it expands in
the usual way under the influence of heat, it does not contract in
the same ratio on cooling ; allowance for this must therefore be
made where necessary, so as to avoid bulging. The chemical
properties which determine its use should be familiar to the
student. It stands the action of dry or moist air ; it is little
affected by chlorine, but is acted upon by hydrochloric acid ;
ammonium sulphate is almost without action on it, whereas the
chloride, especially on heating, dissolves it readily. Organic
acids and many inorganic salts in solution, such as chlorides,
nitrates, nitrites, etc., attack lead and bring it into solution.
It is also necessary to remember that if lead is in contact with
other metals, as, e.g., iron, copper, or the like, galvanic action
may be set up and reactions produced which may be injurious
to the leaden vessels. Leaden vessels must, moreover, never be
bedded in cement, as direct contact with the latter makes them
brittle.

The use of copper is restricted on account of its being easily
attacked by many acids, and by ammonia. But as it is a good
conductor of heat, and as its great tensile strength allows of its
being used in thin sheets for the construction of chemical
apparatus and of tubes, it is still largely used in chemical
engineering. Generally speaking, it is used more in organic

118 ELEMENTS OF CHEMICAL ENGINEERING.

than in inorganic chemical industries, most extensively in
brewing, in distilling apparatus for alcohol and other organic
inert volatile compounds, in sugar-refining, etc. Where two or
more sheets have to be joined together, this may be done either
by riveting or by brazing, and for the latter purpose different
solders are used, which, according to their higher or lower
melting point, are termed ' hard ' or ' soft ' solder.

Of other metals, gold and silver are only used for special
apparatus in isolated cases ; platinum, for concentrating sul-
phuric acid ; zinc for vessels for storing, and for scoops and similar
vessels used in handling dry goods ; and tin, almost exclusively
in the form of tubes. Mckel and aluminium are also now
largely used in the construction of apparatus for chemical
works, and will no doubt be used more frequently in the future
as the prices for these goods become further reduced.

Of equal importance to the metals are the different alloys
which are obtained by fusing together certain metals in certain
proportions. In this manner substances of metallic appearance
are obtained which in many cases exhibit properties different
to either of their constituents. The best known amongst them
is brass, which in its usual form contains about 70 per cent, of
copper and 30 per cent, of zinc. By increasing the quantity of
copper to 80 per cent, or even more, the colour of the resulting
alloy passes from yellow to reddish, and it becomes softer and
more tenacious. Some makers add a little tin to the mixture ; if
the quantity of the latter is increased, whilst the amount of the
zinc is reduced, the alloy is classed amongst the bronzes ; these
are harder and resist acid better than brass ; by the addition of
phosphorus these properties are still further emphasised.

Aluminium forms alloys of valuable properties, that with
copper being known as aluminium bronze ; with magnesium, as
magnalium; the former resists the action of many salts in
solution, such as alkali chlorides, ammonia compounds, caustic,
etc. ; the latter has great tensile strength and can be soldered.

MATERIALS USED IN CHEMICAL ENGINEERING.

119

Of the lead alloys, the one with antimony is best known ; it
is harder than lead, but retains its acid-resisting properties,
and is largely used for taps.

Metal sheets, tubes, and wires, with the exception of lead, are
generally specified by gauges. These are ascertained by means
of a steel plate with incisions of different widths, against which
the arbitrary numbers of the respective gauges are marked. By
ascertaining into which of these incisions the wire or plate will
fit, and noting the number marked against that point, the
gauge can be accurately ascertained. In the English standard
gauge, 0,000,000 represents a thickness of half an inch, No. 1
three tenths of an inch, and so on down to No. 50 with the
corresponding thickness of one thousandth of an inch. Un-
fortunately this is not the only gauge in use, and this should be
borne in mind to avoid mistakes. As it may be useful to the
student in future work, and is an item which might be trouble-
some to find, we insert here particulars of the German gauge.
There are 25 numbers, and the thickness is expressed in milli-
metres : —

No.

mm.

No. inin.

No.

mm.

No.

mm.

No.

mm.

5-50

6 375

2'50

1-375

0750

5-00

7 3-50

2-25

1-250

0 625

4-50

8 3-25

2-00

1-125

0-562

4-25

9 3-00

175

1-000

0-500

4-00

10 275

1-50

20 0-875

0-438

Notwithstanding the wide range of useful properties which
the metals and their alloys possess, there are special occasions
in which they cannot be used in contact with certain chemicals,
and in such cases it is necessary to employ glass, porcelain,
earthenware, rubber, or ebonite. Thus large glass vessels are
used in the concentration of sulphuric acid ; glass pipes have
been and are used for conducting hydrochloric acid gas from

120 ELEMENTS OF CHEMICAL ENGINEERING.

the furnace to the condensers ; whilst earthenware pipes are
used for the same purpose in conveying nitric acid gas in the
manufacture of the liquid acid. The larger the apparatus made
of these materials is, the more costly it becomes, not only on
account of its original price, but also on account of the greater
difficulty in its handling, and the greater risk and liability of its
becoming damaged.

Earthenware goods are glazed, and their durability and
resistance to the action of chemicals depend largely on the
quality of the glaze. Badly glazed vessels absorb the liquids
which are stirred or heated in them, and soon become useless.
It is hardly necessary to mention that earthenware apparatus
should never be placed suddenly on hard, unyielding supports ;
they should not be exposed to sudden wide changes of temper-
ature, nor to violent shocks. When heated in a water, sand, or
oil bath, the level of the liquid which they contain should be
kept above the level of the bath, so that the expansion of the
earthenware may be more gradual.

A highly important material for the construction of chemical
apparatus is enamelled iron,, as it combines the good qualities
of earthenware with the durability of iron. A good enamel,
besides being able to resist the action of the chemical which is
to come in contact with it, should have the same coefficient of
expansion as the iron on which it is coated. Unless this is the
case, it will soon crack and the corrosive liquid will find its way
to the iron, with the result that the enamel will peel off.

The problem of always applying the most suitable material
in the construction of chemical apparatus is one of the greatest
importance to the chemical engineer and manufacturer.
Closely connected with it in the building up of installations is
the art of connecting the different parts of apparatus in such a
manner as to produce a machine which as a whole shall be
water or gas tight. According to the materials used, different
ways may be adopted to attain this purpose, and we will in the

MATERIALS USED IN CHEMICAL ENGINEERING. 121

following consider a few of those which are most commonly
employed.

Suppose we have to construct an apparatus in which a gas
has to be evolved and conducted to another apparatus a
considerable distance away. The materials of which the pipes
would have to be made would depend upon the properties of the
gas, and might be any of the metals, alloys, or other substances
discussed above. But the manner of joining the pipes would
not only depend upon the chemical properties of the gas, but
also on the material of the pipes and the pressure of the gas.

It is evident that wherever it is feasible we should use cast-
or wrought-iron pipes as being the cheapest and most durable
material. The former are mostly joined together by flanges,
which contain a number of corresponding holes through which
the screw bolts are passed. A ring made of compressible
material and constituting the packing is inserted between the
flanges, and by tightening the bolts a perfectly secure joint
is obtained. This should never be done by first tightening
one screw as far as it will go, and then another, and so on ;
but we first give one screw a few turns, then bring the
opposite screw to the same tightness; then proceed in the
same way with the other screws, and repeat the process until
the flanges are uniformly pressed together. In the case of iron
pipes not exposed to the action of corrosive gases or liquids,
the choice of packing chiefly depends upon the temperature
which it may have to stand. For ordinary temperatures, rings
made of woven or compressed yarn or of india-rubber may be
used ; for higher temperatures, asbestos rings, or solid or hollow
metal rings. But as flange joints are the safest and most
convenient means of joining surfaces together, it frequently
happens that they are used in cases where highly corrosive
substances have to be conveyed, and with pipes made of lead,
copper, or earthenware. In such cases it is clear that the
material of which the flange is made is not of such importance

122 ELEMENTS OF CHEMICAL ENGINEERING.

as the material of which the packing consists, for the latter is
directly exposed to the corrosive action, whereas the flange is
protected from it. Suitable packing can be made with the
following materials : india-rubber, asbestos covered with white
or red lead, graphite, or mixtures of graphite and oil, asphalt,
lead (sheet or pipe), copper (sheet or pipe), millboard, etc.

Wrought-iron pipes may also be joined together by means of
flanges, but the most usual way is to join them by means of
screw couplings. We have on previous occasions mentioned
other forms of joints and the different cements which are used
for the purpose. In these matters a knowledge of chemistry and
physics, combined with common-sense, will enable the student
to avoid mistakes which are frequently made by those who
only follow to the letter prescriptions found in books. Taking,
for instance, the case of connecting pipes, it will always be
necessary to consider the conditions under which the pipes are
worked. Thus, if there is a great length of piping liable to
get hot, it follows that provision must be made to allow for
expansion ; and it is clear that this could be done in several
ways, such as by joining a few of the pipes in stuffing-box
fashion, or using elastic metal tubing as packing between
flanges, or occasional lengths of flexible metal tubing instead of
rigid pipe, etc. It is also clear that, where necessary, loss of
heat should be prevented by covering the pipes with some
non-conducting material.

CHAPTER XL

TECHNICAL RESEARCH AND THE DESIGNING OF
PLANT.

THE purpose of the preceding chapters has been to introduce
the student to a subject which, as a separate course of study, is
unfortunately neglected at our universities and technical
schools.

The first object of the study of chemical engineering should
be to enable the student to more easily grasp the details of
such technical processes as are taught in books and lectures.

The present system of teaching chemical technology is such
as to render its study unnecessarily difficult. Too many types
of machinery and plant are placed before the student at once,
just as they occur in connection with certain industries which
are brought to his notice. Take, for instance, the Leblanc soda
industry, a favourite course of lectures in chemical technology ;
nearly every mechanical process is here represented which
occurs in practical work, including apparatus for grinding,
stonebreaking, evaporating, crystallising, filtering, melting, etc.
etc. Whilst the student has to wade through this bewildering
mass of what is to him new matter, he is likely to miss the
essential principles which underlie both the chemical and
engineering problems of the manufacture. To teach technical
chemistry on these lines is tantamount to teaching such chapters
in physics as statics or dynamics to students who have no
knowledge of mathematics, trusting that they may obtain the

123

124 ELEMENTS OF CHEMICAL ENGINEERING.

necessary knowledge of mathematical problems involved by
reading them up at the time they occur. It is universally
recognised that a course of mathematics should precede that
of physics ; it should also be recognised that chemical engineer-
ing occupies a similar relation to technical chemistry, and
should precede the courses of chemical technology. The result
of study on these lines will be, that the student will be able
to assimilate the principles of technical work and apply them
successfully to problems which may present themselves in
branches of chemistry which have not been specially taught
him. If our technical chemists of this and the next generation
are to hold their own, it will be necessary that the universities
and colleges should recognise this ; but particularly, also, that
it is not their province to turn out specialists in one or other
of the countless fields of chemical technology, but men equipped
with a sound general knowledge, and who have been trained to
use their knowledge. To achieve this, the course of study
should be thoroughly systematic.

The second object of a knowledge of chemical engineering
should be to enable the student to design plant required for the
carrying out of new processes which he has worked out him-
self. As the subject of technical research work is an unknown
quantity at our universities and colleges, it is no wonder that
the designing of plant has received no attention. The two
should go hand in hand, for without adequate plant the best
chemical process cannot succeed.

The ideal course of technical study would be one in which the
student could devote the first two years entirely to theory,
to lectures on higher mathematics, physics, and theoretical
chemistry, and to work in the laboratory on analytical methods
and preparations. After that he should pass to the technical
side of the institution, which should be equipped with workshops
containing all the standard apparatus used in chemical work,
and on such a scale that work with several cwts. of material

TECHNICAL RESEARCH AND THE DESIGNING OF PLANT. 125

could be carried on in them. There should be laboratories and
drawing-offices, and the student should attend lectures on
chemical engineering, chemical technology, and such other
subjects as will be of practical use, as, e.g., mechanical drawing,
patent law, calculations of cost, etc., supplemented by practical
demonstrations in the workshop and visits to works. In the
fourth year he should be put on to some simple technical research,
and after working it out in the laboratory, should be made to
work his process in the workshop on a large scale. The design-
ing of plant for this or other special purposes would conclude
his course.

Although the subject of technical research does not, strictly
speaking, come within the province of this book, it is so closely
connected with chemical engineering that a brief outline of its
scope may be found useful, and I will therefore attempt in the
following pages to demonstrate on simple examples the principles
which govern it, the lines on which it may be carried out, and
the manner in which the knowledge gained by chemical work
will influence the application of chemical engineering in the
construction of plant.

The primary object which the technical chemist has before
him is to produce on a manufacturing scale an article cheaper
or better than has been done before, to utilise waste products
to advantage, and to avoid or abate such effluents, whether
gaseous, liquid, or solid, as may create a nuisance. He must
therefore accustom himself to deal with large quantities, or, as
it has been aptly expressed, to think in tons. To this should
be added, that he must think, not only in equivalents, but in
pounds, shillings, and pence, and to realise that he should be
careful to attach the proper meaning to the term ' equivalent '
when used in technical language.

To the laboratory student, e.g., barium carbonate is BaCO3,
sulphuric acid is H2S04, hydrochloric acid is HC1, and their
equivalents are respectively 197, 98, and 2x36'5 = 73. In

126 ELEMENTS OF CHEMICAL ENGINEERING.

order to neutralise 197 Ibs. of barium carbonate it will therefore
require the number of pounds of sulphuric acid or hydrochloric
acid expressed by their equivalents. But in technical work we
do not deal with pure substances, and therefore the equivalents
have to be modified in the ratio of the impurities contained in
the materials used. Thus, if we should have to operate on a
native barium carbonate, and found that it contained only 95
per cent, of actual barium carbonate, if our sulphuric acid con-
tained only 80 per cent, of actual sulphuric acid H2S04, and if
our hydrochloric acid contained only 30 per cent, of actual
HC1, then the proportions of materials which would be
equivalent to each other would be as

: :. = 207-4: 122-5: 243.3.

And if the prices for these articles were £5 per ton of crude
barium carbonate 95 per cent., 30s. per ton of sulphuric acid
80 per cent., and 25s. per ton of hydrochloric acid 30 per cent.,
we should have to divide these prices by the same factors which
we have used for their equivalents, and should then obtain the
prices of the actual effective matter contained in them. We
should then find that we have to pay £5, 5s. 6d. per ton for
actual BaC03, 37s. 6d. per ton for actual H2S04, and 83s. 4d. per
ton for actual HC1. This point will become clearer if we compare
the prices of the same article in different degrees of purity or
concentration. On page 142 we find the price for pure sulphuric
monohydrate is £5, 10s. ; that of ordinary 168° Tw. = 98 per
cent. H2S04 is £3, 5s., and that of 150° Tw. = 80 per cent, is
£1, 12s. 6d. per ton. We should thus have to pay per ton of
H2S04 as follows: — in the monohydrate £5, 10s.; for acid

q.o?;

of 168° Tw. -^- = £3, 6s. 4d., and for 150° Tw.- - £2, Os. 7d. ;
'yo 'oil

so that by neglecting to choose the cheapest acid we might pay
from £1, 5s. 8d. to £3, 9s. 5d. too much per ton of H2S04 if

TECHNICAL RESEARCH AND THE DESIGNING OF PLANT. 127

it were immaterial for our purposes at what degree of purity or
concentration we used our acid.

These considerations are important when the question arises
as to which of several qualities of the same material at our
disposal will be relatively the cheapest. But the lowest-priced
goods are not always the cheapest ; there may be impurities in
the cheaper quality which in subsequent operations it might be
found more costly to remove than if one had started from
a purer though more expensive article. Ordinary hydrochloric
acid, for instance, contains a considerable amount of iron and
sulphuric acid, and in working it up these impurities may
be more expensive to remove than if one had used pure
hydrochloric acid at more than double the cost from the outset.
As a practical instance we may mention the manufacture of
aniline hydrochloride ; here it is necessary to use a pure
hydrochloric acid, as the crude article would yield an unsaleable
product. Another instance is that of nitrate of soda in
connection with the manufacture of nitric acid. For many
purposes it is necessary to obtain a nitric acid as free as possible
from chlorine compounds, and in these cases such parcels of
nitrate are picked out as contain the least amount of sodium
chloride, even though the price may be higher than that of a
lower grade nitrate.

We may now proceed to the further question as to what it
would cost to produce 1 ton of barium sulphate and of barium
chloride from the materials we have mentioned above. Having
regard only to the quantities of the chemicals which we use
and their prices, without reference to what we might call
mechanical expenses, that is, labour, plant, etc., we know that
theoretically it takes 197 tons of carbonate of baryta to produce
233 tons of barium sulphate, but we have also found that with
the barium carbonate at our disposal it will take 207'4 tons to
produce 233 tons of sulphate of baryta of 100 per cent.

If the price of carbonate of baryta 95 per cent, is taken at

128 ELEMENTS OF CHEMICAL ENGINEERING.

£5 per ton, it would cost 5x207 '4, that is, £1037 to produce
233 tons of barium sulphate, that is, £4*45 per ton. In the
same way we find that it would take, not 98 tons of sulphuric
acid, but 122*5 tons of our acid of 80 per cent, to produce 233
tons of barium sulphate, so that the cost of sulphuric acid per
ton of barium sulphate produced, taking the sulphuric acid at
£1, 12s. 6d. per ton, would be 122-5 x 1-625 -f 233, i.e. £-854
per ton of sulphate of baryta produced. If we now add
up the cost of barium carbonate and sulphuric acid, that
is, £4 -45 + £'854, we get £5'304 as the cost of chemicals,
of the quality and prices indicated above, necessary to produce
1 ton of barium sulphate. This calculation can be simplified,
as it is not necessary to calculate the cost of each item separ-
ately, and in its simplified form it would stand as follows : —

Barium carbonate 95 per cent. = 207*4 tons
@£5 . ... £1037

Sulphuric acid 80 per cent. = 122-5 tons

@ £1-625 . . 199

£1236

i.e. 1236-0-^233 = £5-304 is the cost for chemicals per ton of
barium sulphate. The calculation of cost for barium chloride
with two equivalents of water of crystallisation, and having the
formula BaCl2-|-2H20 = 244, will be easily understood from the
following calculation : —

Barium carbonate 95 per cent, = 207'4

tons @ £5 £1037-0

Hydrochloric acid 30 per cent. = 243-3

tons @ £1, 10s. . . . 364-95

£1401-95

1401'95

i.e. —oTT" =£5'745 is the cost for chemicals per ton of crystal-
lised barium chloride.

TECHNICAL RESEARCH AND THE DESIGNING OF PLANT. 129

If the points to be considered in technical research were
only those which have been given above, the matter would be
extremely simple ; but there are other factors which have not
been touched upon so far, and which play a most important
part in technical research. For it is not only necessary to
consider the quantity of the impurities which the materials
we are using contain, but it is even more essential that we
should know exactly the nature of these impurities, and how
far they will influence the quality and cost of the final product.

In order to show this, and in general to explain the course
of a technical investigation, we will follow an extremely simple
case of technical research through the laboratory experiments
to its application on a large scale. The case we have taken
is a purely hypothetical one, and the figures are arbitrarily
chosen, so that the student may for himself obtain correct
data by repeating the experiments on these lines.

We will assume that we have a source of cheap barium
carbonate guaranteed to contain 95 per cent, of BaC03 delivered
to us finely ground at £2, 10s. per ton. We will further
assume that we can buy sufficient quantities of muriatic acid at
£1, 10s. per ton delivered at the works, and that we are up to
the present buying barium chloride at the rate of £6, 10s. per
ton delivered at our works, of which we use 10 tons per week
in another branch of our works. What will it cost to pro-
duce that quantity, and will it be cheaper to continue buying
barium chloride or to make the article ourselves ?

In taking up a problem involving technical research, a
thorough knowledge of the general properties of the sub-
stances used and produced, and in particular a knowledge of
the composition of these substances, is required. The former
may be obtained from books, the latter can only become known
by analysis. Further data will be necessary, which can only be
ascertained by experiment, and it is these data which constitute
the actual technical research. It is hardly necessary to state

130 ELEMENTS OF CHEMICAL ENGINEERING.

that they vary in each case, and the example which we are
giving is only intended to show the general principles which
should guide us in the right direction, as applied to this
particular example.

We will suppose that we have acquired such a knowledge of
the properties of barium carbonate, hydrochloric acid, and
barium chloride, by previous experience and by a careful study of
the literature, as would justify us to proceed further in the
matter. The first step in our research will then be to ascertain
the exact qualities of the substances at our disposal. We should
commence by analysing a fair average sample of our barium
carbonate, and we might find that it contained — •

BaC03 ...... 95-0 per cent.

CaCOs ...... 5-0 „

100-0 „

On analysing our hydrochloric acid we will assume that we
find it stands 30° Tw. = 1*15 sp. gr. and contains per litre —

HC1 ........ 290-0 grms.

H2S04 . .... 5-0 „

Fe2016 1-0 „

296-0 „

For every ton of our carbonate of baryta we shall require
the following quantities of HC1 : —

'95 x 73
To saturate '95 ton of BaC0 -' ='352 ton HC1.

.f)K v 70

To saturate '05 ton of CaC03 U* =-00365 „

Total . . -35565 „ „

Our hydrochloric acid contains sulphuric acid which will
neutralise a certain quantity of barium and calcium carbonate :

TECHNICAL RESEARCH AND THE DESIGNING OF PLANT. 131

as a matter of fact, whichever of the two constituents it may
attack first, it will ultimately yield barium sulphate. The

5 x 73

equivalent of 5 grms. of H2S04 is = 372 grins. HC1,

y o

so that, calculated on its neutralising properties, our hydro-
chloric acid contains 290 + 372 = 29372 parts HC1 in
every 1150 parts by weight. It will therefore require

1150 x -35565

- = 1-392 tons hydrochloric acid to neutralise one
''

ton of our barium carbonate. We will now examine the result
after neutralisation. Of the 1'392 tons of hydrochloric acid

we find that -|yr?r — '435 per cent, is there as H2S04, i.e.

•0061 ton H2S04: this is equivalent to 197*Q°°61= -Q122 ton

y o

BaC03. We therefore have the following data. For every
ton of barium carbonate used we have available for conversion
into barium chloride '95 -'0122 ton = '9378 ton BaC03, which
will require T392 tons of our hydrochloric acid, and should

244 x '9378
yield the theoretical quantity of : -- = 1162 tons of

BaCl2 + 2H20.

We may now make a preliminary calculation as to the cost
of chemicals in the process :—

1 ton barium carbonate at £2, 10s. . . £2'500
1-392 tons hydrochloric acid at £1, 10s. . 2'088

£4-588
i.e. £4-588 -f 1162 = £3, 19s. per ton BaCl2 + 2H20. ,

Besides barium chloride we obtain barium sulphate as an
insoluble precipitate and calcium chloride in solution. We
have now ascertained that, assuming that we had to pay £6, 10s.
per ton for barium chloride, there would be a margin of £2, 11s.

132 ELEMENTS OF CHEMICAL ENGINEERING.

per ton between the cost of chemicals and further expenses if
we made it ourselves, and we might consider it worth our while
to pursue the matter further.

In that case we should begin a series of experiments made
on the actual products, and produce barium chloride from our
raw materials in the laboratory. We should remember, first
of all, that barium chloride is but slightly soluble in hydro-
chloric acid, and that we should, therefore, at no time have a
large excess of acid present ; further, that there is a hydrate of
hydrochloric acid which contains 20*18 per cent, of HC1, and
distils over as such at 110° 0. ; so that if we wish to avoid loss
of HC1, we should always have less than 20 per cent, of it
present and keep the temperature below 110° C. ; and, lastly,
that a saturated solution of barium chloride holds about 40
per cent, of the salt in solution, and that it will therefore be
useless to try to obtain a stronger solution. But it might also
occur to us whether it might not be possible to utilise the
property of hydrochloric acid to throw down barium chloride
from its aqueous solution, and whether we might not at some
time find it advantageous to make our own hydrochloric acid
and use it in the form of gas, for the double purpose of pre-
cipitating the barium chloride and leaving a solution containing
sufficient HC1 to serve for a further neutralising operation.
This is a matter on which we cannot enter more fully here, but
we mention it incidentally to show that it is not out of the
question that reactions which sometimes appear to stand in the
way of successful work may be turned to advantageous use, and
should always receive due thought by being considered from
every point of view.

We might now proceed to make a few experiments somewhat
on the following lines : —

Experiment 1. — We should weigh into a basin 100 grammes
of barium carbonate, and gradually add to it as much water as
will ultimately produce, with the addition of hydrochloric acid,

TECHNICAL RESEARCH AND THE DESIGNING OF PLANT. 133

a saturated solution of barium chloride. 100 grammes of
barium carbonate will produce 116'2 grammes of BaCl2+2H20;
and as we know from text-books that 100 parts of water at
100° C. will dissolve 72 parts of BaCl2 + 2H20, it follows that
116 grammes of BaCl2 + 2H20 will require for solution 162
grammes of water. We have found that 100 grammes of our
barium carbonate will require 139 grammes of our hydro-
chloric acid, which contains actual HC1 35 '6 grammes and
139 — 35 '6 — 103*4 grammes of water. Of this water there will

be required - - =17'1 grammes to provide for the water

of crystallisation, so that we have left available water for
dissolving the barium chloride 1034 — 17'1 = 86*3 grammes.
As we require altogether 162 c.c. H20 for our purpose, we must
mix our barium carbonate with 162 — 86'3 = 757 grammes of
water before adding the hydrochloric acid.

We therefore add to the 100 grammes of our barium carbonate
about 80 c.c. of water and heat up to about 100° C. We then
add gradually 139 grammes, or by measure 120 c.c., of our
hydrochloric acid, and carry on this operation until no more
C02 is evolved, noting the time it takes to do so and how far
the froth rises at its maximum. The point which we now have
to determine is how to deal with the iron, which, being contained
in the hydrochloric acid, might contaminate our finished product.
We have two courses open to us. We may either use an excess
of acid, and thus keep the iron in solution ; in that case it would
gradually accumulate in subsequent operations, and ultimately
adhere in objectionable quantities to the crystals of barium
chloride. The other course, and the preferable one, would be
to try to eliminate it altogether. This might be done in many
ways, by adding ammonia, or caustic soda, or ferrocyanide of
potassium or sodium, but the use of either of these substances
would introduce further foreign matters. We might, however,
remember that barium carbonate precipitates ferric hydrate

134 ELEMENTS OF CHEMICAL ENGINEERING.

from its soluble compounds, and we shall probably find that if
we add an excess of barium carbonate, we may neglect this small
excess of barium carbonate in our calculations, as it would yield
its equivalent as barium chloride, which is of greater commercial
value.

We have now obtained a nearly saturated hot solution of
barium chloride, which we filter through a hot funnel, leaving
the filtrate to crystallise. We finally collect, drain, and weigh
the crystals of barium chloride, measure the mother-liquor, and
determine its specific gravity.

Experiment 2. — In order to explain another point of interest,
we will assume that the mother-liquor from the first experiment
measures 160 c.c. This mother-liquor will contain a certain
amount of calcium chloride, say 8*5 grammes, besides a con-
sirable amount of barium chloride. By boiling it down, we
should arrive at a point at which the maximum quantity of the
latter would crystallise out. But in order to save fuel when
applying our experiments to work on a large scale, we might use
half the mother-liquor, i.e. 80 c.c., instead of water, to mix with
the next lot of barium carbonate, and add the hydrochloric acid
to that mixture. After filtering and crystallising we should
again obtain 160 c.c. of mother-liquor, which would now contain
8'5 + 4'25 = 12'75 grammes CaCl2. It can be easily seen that
however long we continue this proceeding our mother-liquor
could never contain more than twice the original quantity of
CaCl2 = 17 grammes in the 160 c.c., for here we have a

geometrical progression 8'5(l + -~ + o2+ • • • 5*) which adds

up to 2 x 8*5. If we therefore ascertained by a separate
experiment that the presence of that quantity of calcium
chloride had no detrimental effect on the quality of the barium
chloride produced, we could save half the cost of evaporation by
using half the mother-liquor as described above in the mixing
operation in the place of water.

TECHNICAL RESEARCH AND THE DESIGNING OF PLANT. 135

Making a series of experiments on these lines, we shall arrive
at such data as will give us a fair idea as to what will be the
actual yield in practice of barium chloride. We will assume
that we find it 95 per cent, of the yield which we calculated.
In order not to complicate matters, we will also assume that we
do not take into consideration the final mother-liquors, which
still contain some barium chloride and considerable quantities
of calcium chloride. We may now consider what plant we shall
require on a large scale in order to carry out the different
operations.

For a production of 10 tons per week we must produce 2
tons of barium chloride per day ; 1-162 tons of barium chloride is
equal to 1 ton of our carbonate of baryta, or, taking off 5 per
cent, for loss in working, 1104 tons barium chloride will be
obtained for every ton of barium carbonate, and for every 1*392
tons of hydrochloric acid used. We require, therefore, for every
2 tons of barium chloride —

Barium carbonate . . . . 1 '8 12 tons
Hydrochloric acid .... 2*521 „

The 2-521 tons of hydrochloric acid equal 5649 Ibs. at 1*15 sp. gr.
= 491*2 gallons. We found in Experiment 1 that we had to
add 757 grammes water extra for every gramme of barium
carbonate ; this, calculated on 1*812 tons or 4059 Ibs., comes to
3073 Ibs. = 307 gallons of water. The final bulk of our liquor
will therefore come to nearly 800 gallons; and, allowing for froth-
ing, we should require a vessel to hold at least 1200 gallons if
we wanted to mix each day's work in one batch. We have
calculated these quantities so as to show how to perform these
calculations ; the safest and most reliable way will, however, be
to take the actual quantities as obtained in Experiment 1, and
calculate them on the basis of 2 tons barium chloride per day.
We will assume that the two sets of figures agree, and we shall
next have to settle the question as to the means by which we

136 ELEMENTS OF CHEMICAL ENGINEERING.

are going to heat up the mixture of hydrochloric acid and
barium carbonate, and of what material we shall have to make
the vessel in which this is done.

Without taking into consideration the initial temperature
and specific heat of the solid and liquid matter, radiation and

other points, we should require about 979" — 368,200

Calories in order to heat 800 gallons of water to 100° C.
Taking the heating power of good coal at about 7000 Calories,
we should only want 52*6 kgs. = 115 Ibs. of coal for this purpose.
Although the operation might only take six hours, a labourer
would have to attend to the fires long before the work could be
started properly, as the flues would cool down considerably in
the interval between two operations. It will probably save
labour and be more advantageous in other respects if in this
instance we use steam instead of an open fire, especially if there
should be waste steam from an engine or from other sources
at our disposal.

Having decided on the use of steam, the next question to be
decided will be whether to use live or confined steam ? Here,
again, we have to consider that, on account of the frothing
caused by the evolution of C02, we must take our time over the
mixing operation. We shall therefore have considerable loss of
heat due to radiation, so that we shall require far more steam
for heating than the theoretical calculation will show, and
therefore have a corresponding excess of condensed steam, i.e.
in the last instance of mother-liquor, to deal with. We may
therefore be justified in assuming that confined steam will
probably be the most economical way of applying heat in the
mixing operation.

Although, by taking care that we always have an excess of
barium carbonate present, we might use an iron coil for convey-
ing heat to the mixing operation, yet the slightest shortage
would cause the iron to be attacked by the acid. We should

TECHNICAL RESEARCH AND THE DESIGNING OF PLANT. 137

run far less risk if we made the coil of lead, and an experiment
should now be made to ascertain whether it would be safe to
use lead in the construction of this apparatus,' by- conducting an
operation in the laboratory similar to the one described in
Experiment 1, bi*t having several pieces of lead at the bottom
of the basin whilst neutralising. The acid should be run to the
top of the mixture, so as to be nearly neutralised when it
reaches the bottom of the dish. We will assume that the
experiment turned out satisfactorily, and that we decided,
subject to further experiments to be considered later on, to
adopt the use of a lead coil for heating.

We have, roughly speaking, about 400 gallons of liquor to
commence with, which, in the course of an operation lasting
about six hours, will be increased to 800 gallons. We shall
require the preliminary heating up of 400 gallons of liquid, to
be performed as quickly as possible, say in an hour ; therefore
the dimensions of the lead coil will be calculated on that basis,
taking also into account the heat required for the heating up of
the 4059 Ibs. of barium carbonate. To obtain the latter item
we shall have to determine the specific heat of BaC03, and
will assume it to be '2, in which case it would require as much
heat as 80 gallons of water. We have then 480 gallons = 2177
litres, which we assume have to be heated up from 0° to 100° C.,
and which will require 217,700 Calories. It is known that
1 square metre of copper tubing will transmit from 1000 to
1500 Calories per hour for every degree rise in temperature.
Taking the average at 1200 Calories, we should require for a rise
of 100° say about 1/8 square metres of copper pipe. For lead
pipe, in such conditions as we have here, the effect would only
be about one-third, so that we should want 5'4 sq. m. Assuming
the diameter of our pipe to be 6 centimetres, its length would
be 29 metres ; or, in other words, for a lead coil of 2| inches
diameter, we should require piping amounting to 95 feet in
length.

138 ELEMENTS OF CHEMICAL ENGINEERING.

The size of the mixing vessel must be such as to allow for
frothing ; if 7 feet in height, 3 feet of this should be allowed
for frothing and the space taken up by the coil, so that we
have to calculate what cylindrical vessel 4 feet high will hold
800 gallons, or 128 '3 cub. ft. If we place these figures in the

formula for the volume of a cylinder we have d = x /- — — = 6 -4

7 7T

feet. We shall therefore have for the dimensions of the
mixing vessel 6 ft. 5 ins. in diameter and 7 ft. in height, and
with these dimensions the 95 ft. of lead pipe would give us
nearly five windings in the coil. This vessel might be made of
lead, wood, or enamelled iron, or might be built in brick. The
objection to lead would be, that it might be attacked at the top,
where the strong acid could come in contact with it ; the
objection to wood, that the calcium chloride in the liquors might
ooze through it ; and to enamelled iron, that the enamel might
chip off'. The ultimate choice would lie between wood and brick,
and the question which to choose could only be satisfactorily
determined by an experiment on a small works scale. It is at
this stage that the student will miss the workshop, in which he
could make such an experiment.

We will assume that we had made these experiments in the
workshop ; that we had found that bricks set in good Portland
cement would withstand the action of our liquids, and that we
decided to build a tank 6 ft. 5 ins. in diameter and 7 ft. high.
We have from the outset assumed that the tank must be
circular, because we had in our minds that we should have to
provide it with an agitator. We should now draw a complete
plan of the apparatus for mixing, including wooden agitator,
how it is fixed, how geared, showing the steam coil with steam
trap, the running-off tap, the supply of hydrochloric acid, and
means of carrying off the poisonous vapours of C02, — in fact,
everything that would be necessary to conduct the operations
safely, economically, and efficiently.

TECHNICAL RESEARCH AND THE DESIGNING OF PLANT. 139

We shall have, in like manner, to consider the construction of
each apparatus that will be used in the further stages of manu-
facture. But it would exceed the purpose and limit of this
book to go further into the details of the many points which
have to be taken into account, and in which the student should
be guided and checked by a master who combines the necessary
knowledge with practical experience. It must suffice to indicate
that the plant for each operation has to be drawn to scale,
including filtering apparatus, boiling-down plant, storage vessels
for mother-liquors, crystallising vessels, etc. In each case the
material of which the vessel or apparatus has to be made will
have to be carefully chosen, and its suitability, where necessary,
must be ascertained by experiment in the laboratory. When
all the details have been worked out, a general plan of the
manner in which the apparatus is to be arranged is to be drawn
on lines which involve the least amount of cost in shifting the
solids and liquids, making use, wherever possible, of natural
gravitation. The connections with the boiler, with shafting,
etc., will have to be drawn in ; and where a certain piece of
ground is given in which the work is to be performed, the plant
has to be adapted to its size and shape. If a building has to
be erected for the housing of a plant, it must be designed so as
to suit the ground and the plant. Finally, an estimate of the
cost of plant must be made, and specifications of work and
materials required written out.

We have taken pains to find one of the simplest instances of
technical research as an example, and yet it will be seen that
there is a very large amount of thought and work involved in
carrying it through. In order to simplify our explanations, we
have not even taken into consideration that use might be made
of the carbonic acid evolved, and that the final mother-liquor
and the barium sulphate formed must be dealt with. Even as
far as we have gone we have not completed our work, for only
after getting all our data together are we able to calculate

140 ELEMENTS OF CHEMICAL ENGINEERING.

approximately what it will actually cost to produce 10 tons of

barium chloride per week.

We will assume that the plant required will cost £1000, and

that it will depreciate to the extent of 10 per cent, per annum ;

in that case we have to distribute £100, over 500 tons of barium

chloride = 4s. per ton. In like manner we should deal with

the other items, and might obtain a weekly estimate somewhat

as follows : —

Depreciation on plant 10 per cent. . .£200
Labour, three men at 25s. . . . 3 15 0
Coal (total, including steam) . . .200

Water 030

Gas 020

Office expenses (apportioned) . . .100

Laboratory 0 10 0

Sundries 0 10 0

£10 0 0
So that we should have to add to the cost of chemicals, £1 per

£3 19s
ton, the total cost being thus brought to ' ' + £1 = £5, 3s. 2d.

per ton of barium chloride. Other charges of purely financial
and commercial items should be added to this, but it would lead
too far to discuss them here.

Many simple examples of technical research could be found
which, treated in a similar manner, would be instructive. Other
never-failing sources of themes are supplied by the patent liter-
ature, and many interesting investigations could be submitted
to students if they were taught to carry out the process as
described in the patent specifications ; and a student who, under
a competent master, had carried on technical research of this
kind for twelve months, or even less, should, after leaving college,
gain as much experience in one year's work in a factory as it
would otherwise take him five years or more to acquire.

TECHNICAL RESEARCH AND THE DESIGNING OF PLANT. 141

CONCLUSION.

To keep within the limits of an elementary book, it has been
necessary to touch only lightly on many important subjects and
to omit others, a knowledge of which would be useful to
advanced students. Apart from intentional omissions (such as,
for instance, the subject of electro-chemical technics, of which
only a few special branches are sufficiently known, and in
which it would be too early to generalise), there will, no doubt,
be noticed omissions, due to this being a first attempt at
representing the subject in a somewhat novel form. The
author will be grateful for suggestions as to how this book may
be improved.

The measurements have, as far as practicable, been given in
the metric system, which all students of chemistry should be
familiar with. Where it was necessary to state the ultimate
results in English measurements, we have purposely made the
preliminary calculations in the metric system, and converted
the final results into English measurements.

The calculations incidental to the text have been made by
means of Fuller's ingenious slide rule, which, being equal to an
ordinary slide rule of 41 ft. 8 ins. in length, gives accurate results
with a great saving of time. In some cases Boucher's calcu-
lating circle with a dial of 5 inches diameter has been used,
which is even more convenient than, though not as accurate as,
Fuller's instrument. In the author's opinion, every student
should at an early stage be accustomed to work with these
instruments ; if he can only save half an hour a day by using
them, he will, apart from being able to utilise the time thus
saved, be induced to make calculations which, on account of
their tediousness, he would not otherwise perform.

Tables of prices of chemicals and of a few materials have
been added, but it will be clearly understood that the figures
given must not be taken as absolute. The values of chemicals

142 ELEMENTS OF CHEMICAL ENGINEERING.

and other commodities are liable to frequent fluctuations ; still,
with the reservations expressed here, it will be better that the
student should have some idea of prices than none at all.

CURRENT PRICES OF CHEMICALS
AND MATERIALS.

£ s. d.

Acid, Acetic, 25 per cent. . . . per cwt. 069

„ ,, 40 per cent. . . „ „ 093

glacial „ „ 1116

Arsenic, S.G. 2'000 . . . „ „ 100

Benzoic, ex gum . . . ,, Ib. 029

Boracic ,, cwt. 22 / to 24/

Butyric, pure concentrated 50 per cent. „ Ib. 014

80 per cent. „ „ 01 10

,, ,, absolute . . . . ., ,, 030

„ Carbolic, crude 60° . . . . „ „ 0 1 10

„ „ crystallised 40° . . „ „ 00 6-J

„ liquid 95/97 per cent. . „ gall. 009

„ Formic, 40 per cent. . ,, cwt. 176

65 per cent. . . . „ „ 200

90 per cent. . . „ „ 2 10 0

Gallic, pure crystals . . „ Ib. 0 1 11

Hydrofluoric ., „ 0 0 3f

Muriatic (Tower Salts), 30° Tw. per bot. (1 cwt.) 1/6 to 1/9

(Cylinder), 30° Tw. „ 030

Nitric, 80° Tw perlb. 0 0

Nitrous „ „ 001-

Oxalic „ „ 0 0 2

Picric „ „ 0 0 11

Phosphoric, 1'750 . „ „ 0 0 9

Salicylic, powder . . . . „ „ /10J to 1/2

„ crystals . . . „ „ 1/0 J to 1/4

Sulphuric (fuming 50 per cent.) . ,, ton 15 10 0

„ (monohydrate) . . . ,, „ 5 10 0

(Pyrites, 168° Tw.) . . „ ,, 350

„ ( „ 150° Tw.) . o . „ „ 1 12 6

,, (free from arsenic, 145° Tw.) ,, ,, 1 15 0

Sulphurous (solution) S.G. 1-025 „ „ 300

CURRENT PRICES OF CHEMICALS AND MATERIALS.

143

Acid, Tannic, commercial I.

„ pure
Tartaric .
Valerian ic, tr
„ m

Aldehyde, 75 per cent.
Alizarine, 20 per cent.
Alum, loose lump
Alumina Sulphate (pure)

„ Hydrate,
Alumino-ferric cake
Aluminium (ingot
Ammonia, Anhydrous
•880 = 28° B

= 24°

,, Carbonate
„ Fluoride
,, Muriate
,, „ (s

„ Nitrate

,, Oxalate

„ Phosphate

„ Sulphate (

., Vanadate
Arnyl Acetate, pure
Aniline Oil, (pure)

„ Salt .
Anthracene, 30 per c
Antimony Metal

„ Bifluoride, 66

„ Oxide, white
Antimony (Tartar Emetic) .

,, Sulphide
Arsenic, red .

,, white powdered
Barium, Chloride calcined

,, Carbona
,, Hydrate

<£

rcial I. ... per cwt.

II. , „ „

, Ib.

yd rated „

lohyd rated . . ,,

Lt. . . . . j.

3£

„ ton

ure) . . . . „ „

„ cwt.

„ ton

Btal, 98/991 per cent.) „ „

148

3 . . . . , Ib.

B ....,„

B . , ,,

• . j jj

• • • j j>

, tOTl

sal-ammoniac) 1st . , cwt.

2nd . , „

, ton

, Ib.

j jj

grey), London . . ,, ton

Hull . „ „

. . . . „ Ib.

jj ^

• . . . . j j j j

. • . • j > jj

ent. per unit . . ,, ,,

„ ton

per cent. Oxide Antimony Ib.

cwt.

netic) .... Ib.

•

cwt.

red .... ton

cined . . . cwt.

stals .... „

mtive), 92/94 per cent. ton

cwt.

10/

LI/

144

ELEMENTS OF CHEMICAL "ENGINEERING.

Barium, Nitrate . . .
,, Peroxide, 80/85 per cent.
,, Sulphate (native levigated) .
„ Sulphide .

Benzol, 90's "

„ 50/90

Bisulphide of Carbon

Birch Oil

Bleaching Powder, 35 per cent. .

„ Liquor, 7 per cent.
Borax ......

Butyl, Acetate . . .

„ Benzoate .

„ Butyrate .

,, • Valerianate .

Calcium Chloride .

,, Oxide from marble
„ Sulphite .
Chalk, precipitated .
China Clay (at Runcorn), in bulk
Chloral, Chloroform .

,, Hydrate, tablets .
„ „ crystals .

Chromium Acetate (crystal)
Copper ......

,, Oxide (copper scales)
,, Sulphate .
Creosote (ordinary), naked

,, (filtered for Lucigen light) .
„ from beech wood tar
Formaldehyde, 40 per cent.
Glucose Chips ....

Glycerine (crude), 80 per cent. .
(distilled, S.G. 1260) .
Grease Oils, 18° Tw. .
Iodine .....

Iron Chloride ....

„ Sulphate (Copperas) .

,, Sulphide ....

Lead (sheet) . . . ' .
,, Acetate (white, ex ship)

(brown, „ ) .

£ 8. d.

per cwt.

0 17 6

5' 55

200

„ ton

40/ to 60/

„ cwt.

050

„ gall. -

0 0 11

5) 55

0 0 10

ton

17 10 0

Ib.

0 0 2|

ton

676

3 10 0

cwt.

0 13 0

Ib.

026

070

066

060

ton

2 17 6

cwt.

0 10 0

1 0 0

090

ton

20 / to 27/6

Ib.

026

0 1 7

0 1 10

0 0 6J

ton

48 10 0

5 t

50 0 0

18 15 0

gall.
ts

0 0 H
0 0 21

Ib.

024

cwt.

2 12 6

5 J

0 13 0

ton

28 0 0

60 0 0

300

oz.

006

cwt.

0 19 0

ton

1 15 0

3 10 0

12 15 0

24 10 0

16 0 0

CURRENT PRICES OF CHEMICALS AND MATERIALS.

145

£ s.

Lead, Borate ......

per cwt.

3 13

, Carbonate (white lead), pure

„ ton

19 10

, cwt.

2 3

, Litharge Flake (ex ship) .

„ ton .

14 0

, Nitrate . . . .

,, ,,

22 0

, Peroxide .....

JJ J»

2 5

Resinate ......

JJ JJ

19/ to

30/

, White

JJ •?

0 16

Lime Acetate (brown, ev ship) .

>J JJ

5 5

j> jj (grey ,, )

JJ )J

7 2

Magenta . . . . . .

,, lb.

0 2

Magnesium (ribbon and wire)

„ oz.

0 1

,, Chloride ....

„ ton

3 5

,, Carbonate ....

, cwt.

1 17,

„ Calcined Magnesia

, ton

15 10

Magnesium Sulphate (Epsom Salts) .

j ?j

3 2

Manganese Ore, 70 per cent.

j jj

3 10

„ Borate

, cwt.

2 0

., Oxide, black ....

J '5

0 6

, Peroxide, pure artific.

, lb.

0 2

, Resinate, fused

, cwt.

0 19

, ,, precipitated

JJ >J

1 10

, Sulphate, 95 per cent.

„ ton

18 0

, ,, technical powder

,, cwt.

0 16

Methyl Benzoate

JJ JJ

0 3

,, Butyrate ....

JJ J'

0 4

„ Salicylate .....

»J »J

0 3

,, Valerianate .....

J J J J

0 6

Methylated Spirit, 61° O.P.

„ gall.

0 2

Naphtha (crude), from coal tar, 30 per cent.

at 120° C

jj j>

0 0

„ solvent, from coal tar, 90 per cent.

at 160° ....

jj jj

0 1

„ (wood), solvent ....

5 J JJ

0 2

„ „ miscible, 60° O.P. .

JJ JJ

0 3

Nickel Sulphate ...

,, cwt.

2 8

,, „ and Ammonia .

JJ J)

2 2

Oil, Cotton seed .....

„ ton

24 5

,, Linseed ......

31 0

,, Stearine ......

j j jj

28 0

Paraklehyde ......

jj *"•

0 4

Pepsin, Porci, B.P. . ,

jj j»

0 18

146

ELEMENTS OF CHEMICAL ENGINEERING.

. d.

Phosphorus (red) ..... per Ib.

, ,

(yellow) ...

Pitch

))

ton

Potassium Bicarbonate ....

cwt.

Bichromate ....

Ib.

Bisulphite, 50/55 per cent.

cwt.

Carbonate, 90 per cent, (ex ship)

ton

Chlorate .....

Ib.

Cyanide, 98 per cent.

Fluoride, neutral

3.3

bi .

Hydrate (caustic potash), 90 p. cent.

ton

3 3

75/80 p. cent.

»J

Potash Hydrate, liquid, 50 p. cent.

3 3

Muriate, 80 per cent, (ex ship) .

Nitrate (refined)

Oxalate, neutral

Ib.

Permanganate (small crystals) .

cwt.

33 33 ••

,, (large crystals) .

Prussiate (yellow)

)

Ib.

Sulphate, 90 per cent, (ex ship)

ton

„ (Kainit)

Pumice

Powder

cwt.

Silver (metal) ......

))

oz.

1T9_

Sodium

(metal) .....

Ib.

Acetate (ex ship) ....

ton

Arseniate, 45 per cent. .

Benzoate .....

Ib.

+-t

Bicarbonate (cwt. kegs)

ton

1:3

Bichromate ...

Ib.

) )

Bisulphite, powder

cwt.

,, crystals

3»

Borate, free from silver

Ib.

2/6

,, (borax) crystals

•3

ton

Garb, (alkali), 58 per cent, (bags) .

,, (caustic soda-ash), 48 p. cent.

3»

„ (refined „ ), ,,

,, (soda crystals)

Chlorate

Ib.

Fluoride .... 7

to 6d.

Bifluoride, ,

CURRENT PRICES OF CHEMICALS AND MATERIALS.

14?

Sodium Hydrate (60 per cent, caustic soda)
,, ,, (70 per cent, caustic soda)

(f.o.b.1) .
,, „ (74 per cent, caustic soda)

(f.o.b.) . .
„ ,, \7Q per cent, caustic soda)

(f.o.b.) . .

„ ,, 77 to 78 per cent, powdered

(99 p. cent, hydrate)
,, „ (pure liquor, 90° Tw.)

„ Hyposulphite ....
,, Manganate, 25 per cent.
,, Nitrate (95 p. cent, ex ship, Liverpool)
„ Nitrite, 98 per cent.
,, Phosphate .....
„ Prussiate ( r1 errocyanide)
„ Salicylate, powder.
„ „ crystals

Silicate (glass) ....

(liquid, 100° Tw.) .
Stannate, 40 per cent. .
Sulphate (salt-cake)

,, (Glauber's salts)
Sulphide (crystals)
Sulphite .....
Strontium Hydrate, 100 per cent.
Sulphocyanide Ammonium, 95 per cent.
,, Barium, 95 per cent.

,, Potassium ....

Sulphur, Brimstone, best quality

,, Flowers .....
„ (Roll Brimstone) •
Superphosphate of Lime (26 per cent.)
Tallow . . . . " .
Tin Crystals ....

,, English, ingots ....
Vermilion .......

Zinc (Spelter)

„ Chloride (solution, 100° Tw.) .

„ Sulphate, crystals ....

1 Free on board.

per ton

£ s. d.

8 15 0

9 15 0
10 5 0
10 10 0

)' 55

5 0

5 55

0 0

5 55

10 0

5 55

10 0

, cwt.

9 9

, ton

15 0

5 55

12 6

, Ib.

0 4J

5 5>

1 2

1 55

1 4

, ton

15 0

55 ;>

15 0

, cwt.

15 0

, ton

6 0

5 55

7 6

>5 55

5 0

11 5>

10 0

J J5

10 0

, Ib.

0 6

) 5.5

0 4

5 55

0 7J

, ton

0 0

5 55

10 0

J 55

0 0

5 55

5 0

5 55

0 0

, Ib.

0 7J

, ton

110

10 0

, Ib.

2 1J

, ton

15 0

5 55

0 0

5 )J

0 0

148

ELEMENTS OF CHEMICAL ENGINEERING.

Materials used in Construction.

per ton from

Cast-Iron, crude, pig, fluctuating
,, „ ordinary large castings
,, ,, small castings and compli-
cated patterns
„ ,, enamelled

Copper, crude, varies

,, to the market price add for plates
„ „ „ ,, tubes

Lead, crude .....
,, sheet .....

Tin, fluctuates much

Lime ......

Cement ......

Ericks ......

Firebricks .....

Coal . . .

Coke

about

»
from

£2 10 0
£5 to £7

£7 to £20
£20 to £30
£40 to £80
£15 0 0
£30 0 0
£11 0 0
£14 to £16
£110 to £150

about

1000

ton about

12/to 16/
£200

20/ to 25/
£400
10/ to 15/
£0 12 0

INDEX.

ACID, mixing of, 4.
Airbath,36.
Alloys, 118.

Aluminium bronze, 118.
Ammonia, recovery of, 63.
Ammonium nitrate, 1.
Analysis of flue-gases, 105.

,, ,, gases, 103.
Anemometer, 99.
Antimony, 119.
Apparatus for drying, 36.
Application of heat, 67.
Arches, 110.
Areometers, 97.

BALL mill, 88.
Barium chloride, 125.
Barium sulphate, 126.
Barrels, volume of, 112.
Basin, 3.
Beaker, 3.
Black ash, 49.
Blind roaster, 53
Bio \\pipe, 46.
Boiler, Cornish, 73.

,, Galloway, 58.

,, pressure in, 60.

,, steam, 57.
Boilers, setting of, 73.
Bond, English, 107.

,, Flemish, 107.
Bonds in bricksetting, 107.
Boucher's calculator, 141.
Brass, 118.
Bricks, fire, 110.
Bricksetting, 107.

,, bonds in, 107.

Brickwork, measurements of, 107.
British Thermal Unit, 67.

Bronzes, 118.
Bucket elevator, 39.
Bunsen's flame reactions, 46.
Bunsen pump, 76.

CALCULATION of cost, 123
Calculator, Boucher's, 141.
Calorie, 67.
Calorimeter, 100.
Carpenter's work, 111.
Carrier conveyor, 38.
Casks, volume of, 112.
Casting iron, 113.
Cement, 108.

,, properties of, 109.
Centrifugal machine, 79.
Chamber press, 77.
Chambers, drying, 40.
Chemicals, prices of, 142.
Chimney draught, 72, 74.
Chimney gases, determination of

sulphurous acid in, 99.
Chloride of barium, 126.
Circular sieve, 93.
Closed roaster, 53.
Coal, composition of, 71.

,, value in calories, 71.
Coils, steam, heating by, 19.
Composition of coal, 71.
Compressed-air engine, 66.
Conclusion, 141.
Cones, fusible, determination of heat

by, 102.
Conveyor, carrier, 38.

,, drag plate, 38.
,, screw, 38.
Cooper's work, 111.
Copper, 117.
Cornish boiler, 73.

149

150

INDEX.

Corn mill, 90.
Cost, calculation of, 123.
Couplings, 122.
Crossley's gas engine, 61.
Crucible, 46.
Crushing rollers, 83.

DESIGNING of plant, 123.
Disintegrator, 87.

Distillation, 21, 27.

,, fractionating, 32.
Drag plate conveyor, 38.
Draught, forced, 72.
Draught of chimney, 72, 74.
Drying apparatus, 36.

,, chambers, 40.

,, in a vacuum, 45.

,, ,, wagons, 44.

,, of explosives, 45.
Dry mixer, 93.
Dynamo, multipolar, 63.

EARTHENWARE, 120.
Ebonite, 119.
Economise!-, Green's, 59.
Edge roller mills, 86.
Electrical thermometers, 101.
Electric motor, 64, 65.
Elevator, bucket, 39.
Enamelled iron, 120.
Engine, compressed-air, 66.

„ gas, 62.

,, hydraulic, 66.

,, steam, 61.
English bond, 108.

,, measurements, conversion into

metric system, 98.
Evaporating pan, 12.
Evaporation in a vacuum, 23

,, multiple, 26.

Explosives, drying of, 45.

FILTERING tanks, 80.
Filter presses, 77.

,, vacuum, 76.

Filtration of slimy substances, 78.
Firebricks, 110.
Fire grate, dimensions of, 73.
Flame reactions, Bunsen's, 46.
Flame, reducing, 49.

,, oxidizing, 48.
Flange joints, 121.
Flemish bond, 108.

Flue-gases, analysis of, 105.

,, determination of sulphurous

acid in, 99.
Forced draught, 72.
Fractionating distillation, 32.
Frame press, 77

Fuel-gases, sulphurous acid in, 49.
Fuller's slide rule, 141.
Funnel, 75.
Furnace, 47.

muffle, 53.

,, plus pressure, 55.
Furnaces, starting of, 111.

GALLOWAY boiler, 58.

Gas analysis, 103.

Gas engine, Crossley's, 61.

„ ,, Mather & Platt's, 62.
Gases, measurement of, 99.
Gauge, German, 119.
Gauges, 119.
German gauge, 119.
Green's Economise!1, 59.
Grinding, wet, 86.

HEAT, application of, 67.
, , determination of, 99.

,, radiation of, 70.

,, transmission of, 70.
Heating by open tire, 10.

,, ,, steam, 17.
Heating- surface, 73.
Hydraulic engine, 66.
Hydro-extractor, 79.

INSTRUMENTS, measuring, 94.
Iron, casting, 113.

,, ,, studs in, 113.

,. enamelled, 120.

,, leadcoated, 116.

,, properties of, 112.

JOINTS for flanges, 121.

,, pipes, 121.
Joints, lead, 117.

,, packing for, 121.

KNEADING machine, 93.

LBAD, properties of, 116-117.
„ sheet, 116.

fusible
cones. 102.

INDEX.

151

Lead-coating on iron, 116.
,, joints, 117.
,, pipes, weight of, 116.
Levigation, 84.
Liquids, determination of specific

gravity of, 96.
, , measurement of, 96.

,, mixing of, 3.

MACHINE, centrifugal, 79.
Magnalium, 118.
Materials, prices of, 142.
Mather & Platt's gas engine, 62.
Measurement of gases, 99.

,, ,, liquids, 96.

Measurements, conversion of metric

into English, 98.
, , of brickwork ,107.

Measuring instruments, 94.
Mechanical raking, 50.
,, sieves, 92.
Mesh of sieves, 91.
Metric system, conversion into

English measurements, 98.
Mill, corn, 90.

,, mortar, 86.

,, stamp, 84.
Mills, ball, 88.

, , edge roller, 86.

,, roller, 88.
Mixer, dry, 93

,, kneading, 93.
Mixing acid, 4.

,, liquids, 3.
Mortar, 82, 108.
„ mill, 86.
Motor, electric, 64, 65.
Muffle furnace, 53.
Multiple evaporation, 26.
Multipolar dynamo, 63.

NITRATE of ammonia, 1.
Nitric acid, condensation of, 31.
,, ,, manufacture of, 27.
,, plant, 28.

Oi'EN roaster, 48.

Orsat, 104.

Oxidising flame, 48.

Oxygen, determination of, 104.

PACKING for joints, 121.
Pan for evaporating, 12.

Patternmaking, 114.

Pipe joints, 121.

Plant, designing of, 123.

Platform weighing machine, 95.

Plus-pressure furnace, 55.

Porion evaporator, 16.

Press, chamber, 77.

,, frame, 77.
Pressure filter, 76.

,, in boilers, 60.
Prices of chemicals, 142.

,, ,, materials, 148.
Properties of iron, 112, 115.

„ „ lead, 116.
Pump, Bunsen's, 76.
Pyrometers, 99.

RADIATION of heat, 70.
Raking, mechanical, 50.
Recovery of ammonia, 63.

„ tar, 63.

Reducing flame, 49.
Regeneration, 55.
Research, technical, 123.
Revolver, 50.
Revolving stirrer, 6.
Roaster, blind, 53.
closed, 53.
,, open, 48.
Roller mill, 88.
Rollers, crushing, 83.

SCALES, 94.

Screw, Archimedean, stirring by, 7.

Screw conveyor, 38

Separator, 33.

Setting of boilers, 73.

,, ,, steam-boilers, 73.
Sheet-lead, weight of, 116.
Sieve, circular, 93.
Sieves, 91.

,, mechanical, 92.

,, mesh of, 91.
Slide rule, Fuller's, 141.
Slimy substances, filtration of, 78.
Soda ash, dissolving of, 5.
Specific gravity of liquids, determina-
tion of. 96.
Stamp mill, 84.
Steam-boiler, 57.

,, boilers, setting of, 73.

,, coils, heating by, 19.

,, engine, 61.

,, jacket pan, 17, 18.

152

INDEX.

Steam, heating by, 17, 18.

,, superheated, 60, 68.

,, tables giving pressure, tempera-
ture, calories and weight of, 68.
Steel, 113-115.
Stirrer, revolving, 6.
Stirring, by Archimedean screw, 7.
Stonebreaker, 83.
Studs in castings, 113.
Sulphate, barium, 127.
Sulphurous acid, determination of, in

flue-gases, 99.

Sulphurous acid in fuel gases, 49.
Superheated steam, 60, 68.
Surface heating, 73.
Syphon, 75.

TABLES, steam, 68.
Tanks for filtering, 80.
Tar recovery, 63.
Technical research, 123.
Temperature, determination of, 99.

Thalpotassimeter, 102.
Thelen pan, 14.
Thermal unit, 67.
Thermometers, 99.

,, electrical, 101.

mercury, 100.
Tiles, 110.
Transmission of heat, 70.

UNIT, thermal, 67.

VACUUM filter, 76.

,, evaporation in a, 23.
Volume of casks, 112.

WAGGONS, drying in, 44.
Weighing machines; 95.
Weight of lead pipes, 116.
,, ., sheet lead, 116.
Wet grinding, 86.
Wheel flue, 11.
Wrought-iron, 113-115.

PRINTED BY NEILL AND CO., LTD., EDINBURGH.

THIS BOOK IS DUE ON THE LAST DATE
STAMPED BELOW

AN INITIAL FINE OF 25 CENTS

WILL BE ASSESSED FOR FAILURE TO RETURN
THIS BOOK ON THE DATE DUE. THE PENALTY
WILL INCREASE TO SO CENTS ON THE FOURTH
DAY AND TO $1.OO ON THE SEVENTH DAY
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FEl

'UJ

LD 21-100m-7,'33

YC 18716

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