COMMON COMMODITIES AND INDUSTRIES SERIES
Each book in crown 8vo, cloth, with many illustrations, charts, etc.,
2/6 net
TEA. By A. Ibbetson
COFFEE. By B. B. Keable
SUGAR. By Geo. Martineau, C.B.
OILS. By C. Ainsworth Mitchell, B.A., F.I.C.
WHEAT. By Andrew Millar
RUBBER. By C. Beadle and H. P. Stevens, M.A., Ph.D., F.I.C.
IRON AND STEEL. By C. Hood
COPPER. By H. K. Picard
COAL. By Francis H. Wilson, M.Inst., M.E.
TIMBER. By W. Bullock
COTTON. By R. J. Peake
SILK. By Luther Hooper
WOOL. By J. A. Hunter
LINEN. By Alfred S. Moore
TOBACCO. By A. E. Tanner
LEATHER. By K. J. Adcock
KNITTED FABRICS. By J. Chamberlain and J. H. Quilter
CLAYS. By Alfred B. Searle
PAPER. By Harry A. Maddox
SOAP. By William A. Simmons, B.Sc. (Lond.), F.C.S.
THE MOTOR INDUSTRY. By Horace Wyatt, B.A.
GLASS AND GLASS MAKING. By Percival Marson
GUMS AND RESINS. By E. J. Parry, B.Sc., F.I.C., F.C.S.
THE BOOT AND SHOE INDUSTRY. By J. S. Harding
GAS AND GAS MAKING. By W. H. Y. Webber
FURNITURE. By H. E. Binstead
COAL TAR. By A. R. Warnes
PETROLEUM. By A. Lidgett
SALT. By A. F. Calvert
ZINC. By T. E. Lones, M.A., LL.D., B.Sc.
PHOTOGRAPHY. By Wm. Gamble
ASBESTOS. By A. Leonard Summers
SILVER. By Benjamin White
CARPETS. By Reginald S. Brinton
PAINTS AND VARNISHES. By A. S. Jennings
CORDAGE AND CORDAGE HEMP AND FIBRES. By T. Woodhouse and P. Kilgour
ACIDS AND ALKALIS. By G. H. J. Adlam
_OTHERS IN PREPARATION_
[Illustration: _Copyright by Messrs Flatters & Garnett, Manchester_
BACTERIA NODULES ON THE ROOT OF LUPIN]
PITMAN’S COMMON COMMODITIES AND INDUSTRIES
ACIDS, ALKALIS AND SALTS
BY
G. H. J. ADLAM,
M.A., B.Sc., F.C.S.
Editor of “The School Science Review”
London
Sir Isaac Pitman & Sons, Ltd., 1 Amen Corner, E.C.4
Bath, Melbourne and New York
Printed by Sir Isaac Pitman & Sons, Ltd., London, Bath, Melbourne and
New York
PREFACE
It has often been said, and still more often implied, that
considerations of utility in education are incompatible with its main
object, which is the training of the mind. Extremely divergent views
have been expressed on this point. Schoolmen have looked askance at some
branches of knowledge because they were supposed to be tainted with the
possibility of usefulness in after life. On the other hand, business men
and others have complained bitterly of the present state of education
because very little that is considered “useful” has up to the present
been taught in schools.
It is possible to err in both directions. A university professor,
lecturing on higher Mathematics, is reported to have told his audience
that it was a source of great satisfaction to him that the theorem which
he was demonstrating could never be applied to anything “useful.” On the
other hand, we have the well-authenticated story of the man who took his
son to the Royal School of Mines to “learn copper,” and not to waste his
time over other parts of Chemistry, because “they would be of no use to
him.”
For narrowness of outlook, there is nothing to choose between the pedant
and the “practical” man. National education would deteriorate if its
control should ever pass into the hands of extremists of either type,
for nothing worthy of the name of education could ever be given or
received in such an irrational spirit.
In dealing with the subject of “Acids, Alkalis, and Salts,” I have
endeavoured to give prominence to the commercial and domestic importance
of the substances dealt with. I thereby hope to gain the interest of the
reader, since interest stands in the same relation to education that
petrol does to the motor-car. It is not education itself, but it is the
source of its motive power. I have also included some considerations of
a theoretical nature which may well be taken as a first step towards the
continuation of the study of Chemistry.
My sincere thanks are offered to my colleagues, F. W. G. Foat, M.A.,
D.Litt., and Mr. I. S. Scarf, F.I.C., for much valuable help and advice;
to Sir Edward Thorpe, C.B., F.R.S., and Messrs. William Collins & Sons
for permission to reproduce Figures 3, 11, and 14; to Messrs. Longmans &
Co. for Figures 4, 5, 9, 12, 13, 16; Messrs. Macmillan & Co., for
Figures 8, 10 and 15. I have also availed myself of the assistance of
several standard works on Chemistry. My acknowledgments in this
direction take the practical form of the short bibliography which
follows—
Lunge, Dr. G.
_The Manufacture of Sulphuric Acid and Alkali._ Vols. I, II, and
III.
Roscoe & Schorlemmer
_Treatise on Chemistry._
Vol. I. The Non-metallic Elements (1911).
Vol. II. The Metals (1913).
Brannt, W. T.
_The Manufacture of Vinegar and Acetates._
Thorp, F. H.
_Outlines of Industrial Chemistry_ (1913).
Thorpe, T. E.
_A Manual of Inorganic Chemistry._
Newth, G. S.
_A Text-book of Inorganic Chemistry._
Mellor, J. W.
_Modern Inorganic Chemistry._
Cohen, J. B.
_Theoretical Organic Chemistry._
G. H. J. A.
City of London School, E.C.
CONTENTS
CHAP. PAGE
PREFACE v
I. INTRODUCTION 1
II. SULPHURIC ACID AND SULPHATES 10
III. NITRIC ACID AND NITRATES 28
IV. THE HALOGEN ACIDS 43
V. CARBONIC ACID AND CARBONATES 49
VI. PHOSPHORIC, BORIC, AND SILICIC ACIDS 56
VII. ORGANIC ACIDS 67
VIII. MILD ALKALI 80
IX. CAUSTIC ALKALIS 95
X. ELECTROLYTIC METHODS 101
INDEX 109
ILLUSTRATIONS
FIG. PAGE
BACTERIA NODULES ON THE ROOT OF LUPIN _Frontispiece_
1. DIAGRAM 7
2. PLAN OF SULPHURIC ACID WORKS 13
3. GENERAL VIEW OF SULPHURIC ACID WORKS 15
4. SULPHUR TRIOXIDE—THE CONTACT PROCESS 19
5. PREPARATION OF NITRIC ACID 30
6. NITROGEN CYCLE (DIAGRAM) 38
7. NITRIC ACID FROM AIR (DIAGRAM) 41
8. PREPARATION OF HYDROCHLORIC ACID 45
9. BORIC ACID 59
10. QUICK VINEGAR PROCESS 71
11. DUTCH PROCESS FOR WHITE LEAD 74
12. SALT CAKE FURNACE 83
13. BLACK ASH FURNACE 85
14. THE SOLVAY PROCESS 89
15. THE ELECTROLYSIS OF SALT SOLUTION 102
16. THE CASTNER PROCESS 105
ACIDS, ALKALIS, AND SALTS
CHAPTER I
INTRODUCTION
Acids. A vague hint from Nature gave mankind the first indication of the
existence of acids. The juice pressed from ripe grapes is a sweetish
liquid. If it is kept for some time, the sweetness goes, and the liquid
acquires a burning taste. If kept still longer, the burning taste is
lost, and in its place a sharp acid flavour, not entirely displeasing to
the palate, is developed. The liquid obtained in this way is now called
wine vinegar; the particular substance which gives it its characteristic
taste is acetic acid.
The strongest vinegar does not contain more than 10 per cent. of acetic
acid, which is itself a comparatively weak acid. It is, therefore, not a
very active solvent. Nevertheless, for metals and for limestone rock,
and other substances of a calcareous nature, its solvent power is
greater than that of any other liquid known at the time of its
discovery. It was this property which seems to have appealed most
strongly to the imagination of the early chemists; and, as is very often
the case, the description of its powers was very much exaggerated. Livy
and Plutarch, who have given us an account of Hannibal’s invasion of
Italy by way of the Alps, both gravely declare that the Carthaginian
leader cleared a passage for his elephants through solid rocks by
pouring vinegar over them!
In the Middle Ages, the study of Chemistry was fostered mainly as a
possible means whereby long life and untold riches might be obtained.
The “Philosopher’s Stone,” by the agency of which the base metals were
to be changed to gold, and the “Elixir of Life,” which was to banish
disease and death, were eagerly sought for. Though these were vain
imaginings according to modern ideas, nevertheless they were powerful
incentives towards experimental work. Many new substances were
discovered in this period, and among these were nitric acid (aqua
fortis), hydrochloric acid (spirit of salt), and sulphuric acid (oil of
vitriol).
Acids were then valued above all other substances. The mediaeval chemist
(or alchemist, as he was called) clearly saw that unless a body could be
dissolved up there was no hope of changing it. Nitric acid, therefore,
which, in conjunction with hydrochloric acid, dissolved even gold
itself, was very highly esteemed. Oil of vitriol also was scarcely less
important, for it was required for the production of other acids.
So far, taste and solvent power were considered to be the characteristic
feature of acids. In the time of Robert Boyle (1627-1691), they were
further distinguished from other substances by the change which they
produced in the colour of certain vegetable extracts. Tincture of red
cabbage was first used, but, as this liquid rapidly deteriorates on
keeping, it was soon replaced by a solution of litmus, a colouring
matter obtained from _Roccella tinctoria_ and other lichens. It imparts
to water a purple colour, which is changed to red by the addition of
acids.
Alkalis. Wood ashes were valued in very early times because they were
found to be good for removing dirt from the skin. Mixed with vegetable
oil or animal fat, they formed a very primitive kind of soap, which was
afterwards much improved by using the aqueous extract instead of the
ashes themselves, and also by the addition of a little caustic lime.
When plant ashes are treated with water, about 10 per cent. dissolves.
If the insoluble matter is then allowed to settle down and the clear
liquid evaporated to dryness, a whitish residue is obtained. The soluble
matter thus extracted from the ashes of plants which grow in or near the
sea is mainly soda; that from land plants, mainly potash. Formerly no
distinction was made, and the general term “alkali” was applied to both.
In order to bring the properties of alkalis into contrast with those of
acids, we cannot do better than make a few simple experiments with a
weak solution of washing soda. Its taste is very different from that of
an acid; it is generally described as caustic. If a little is rubbed
between the fingers, it feels smooth, almost like very thin oil. It does
not dissolve metals or limestone. Its action on vegetable colouring
matter is just as striking as that of acids. Tincture of red cabbage
becomes green; the purple of litmus is changed to a light blue. This
colour change is characteristic of alkalis.
Neutralization. When the colour of litmus solution has been changed to
red by the addition of an acid, the original colour can be restored by
adding an alkali. The change can be repeated as often as desired by
adding acid and alkali alternately. From this we get a distinct
impression of antithesis between the two. In popular language, an alkali
“kills” an acid; in Chemistry, the same idea is expressed by the term
“neutralization.”
Salts. Both “neutralization” and “killing the acid” are modes of
expression which describe the phenomenon fairly well. When an acid is
neutralized, its characteristic taste, its solvent power, and its action
on litmus, are all changed; in fact, the acid as an acid ceases to
exist, and so does the alkali. When the neutral solution is evaporated
to dryness, a residue is found which on examination proves to be neither
the acid nor the alkali, but a compound formed from the two. This
substance is called a salt.
To most people, salt is the name for that particular substance which is
taken as a condiment with food. Its use in this connection dates from
time immemorial. It is distinctly unfortunate that another and very much
wider usage of the term has been introduced into Chemistry. When the
early chemists recognized that other substances, which they vaguely
designated as “saline bodies,” were similar to common salt in
composition, they took the name of the individual and applied it to the
whole class.
OTHER METHODS OF SALT FORMATION
Solution of Metals in Acids. Alkalis are not the only substances which
neutralize acids. Speaking in a broad and general sense, we may say that
an acid is neutralized when a metal is dissolved in it, because, when
the point is reached at which no more metal will dissolve, all the
characteristic properties of the acid are destroyed. A salt is formed in
this case also.
An example will now be given to illustrate this method of salt
formation. Before two pieces of metal can be united by soldering, it is
necessary to clean the surfaces of the metal and the soldering iron. The
liquid used for this purpose is made by adding scraps of zinc to
muriatic acid (hydrochloric acid). The zinc dissolves with
effervescence, which is caused by the escape of hydrogen gas. When
effervescence ceases and no more zinc will dissolve, the liquid is ready
for use. The acid has been “killed” or neutralized by the metal. A salt
called zinc chloride has been formed. This salt can be recovered from
the liquid by evaporation.
Solution of Oxides in Acids. The substances most used in commerce with
the express purpose of destroying acidity are quicklime, washing soda,
and powdered chalk.
Since quicklime is a compound of the metal calcium and the gas oxygen,
its systematic name is calcium oxide; when it neutralizes an acid, it
forms the corresponding calcium salt; for example, if it neutralizes
acetic acid, calcium acetate is formed.
An instance of the neutralization of an acid by an oxide of a metal is
furnished by one method of preparing blue vitriol (copper sulphate).
Copper does not dissolve very quickly in dilute sulphuric acid; hence,
to make blue vitriol from scrap copper, the metal is first heated very
strongly while freely exposed to air. Copper and oxygen of the air
combine to form the brownish black powder, copper oxide, and this
dissolves very readily in sulphuric acid, making the salt, copper
sulphate.
Solution of Carbonates in Acids. Washing soda and chalk belong to a
different class of chemical substances. They are carbonates, that is,
they are salts of carbonic acid. At first it may seem a little
perplexing to the reader to learn that a salt can neutralize an acid to
form a salt. It must be remembered, however, that acids differ from one
another in strength, that is, in chemical activity, and that carbonic
acid is a weak acid. When a salt of carbonic acid—sodium carbonate or
washing soda, for example—is added to a stronger acid such as sulphuric
acid, sodium sulphate is formed and carbon dioxide liberated.
As an example of the neutralization of acids by carbonates, we may
mention here a practical sugar saving device. Unripe fruit is very sour
because it contains certain vegetable acids dissolved in the juice.
These acids are not affected by boiling; and, therefore, to make a dish
of stewed fruit palatable, it is necessary to add sugar in quantity
sufficient to mask the sour taste. If a pinch of bicarbonate of soda is
added to neutralize the acid, far less sugar will be necessary for
sweetening.
Insoluble Salts. The methods given above apply only to those salts which
are soluble in water. Insoluble salts are obtained by mixing two
solutions, the one containing a soluble salt of the metal, and the
other, a soluble salt of the acid or the acid itself.
The formation of an insoluble salt by the interaction of two soluble
substances is well illustrated in the preparation of Burgundy mixture,
the most effectual remedy yet proposed for checking the spread of potato
disease. This mixture contains copper carbonate, that is, the copper
salt of carbonic acid. For its preparation we require copper sulphate
and sodium carbonate (washing soda), a soluble carbonate. When these two
substances, dissolved in separate portions of water, are mixed, copper
carbonate is formed as a pale blue solid which is in such a state of
fine subdivision that it remains suspended in the solution of sodium
sulphate, the other product of the reaction.
The change is represented diagrammatically below. Each circle represents
the atom or a group of atoms named therein. At the moment of mixing,
these groups undergo re-arrangement.
Bordeaux mixture, which some gardeners prefer, is a similar preparation
containing copper hydroxide instead of copper carbonate. It is made by
mixing clear lime water (a soluble hydroxide) with copper sulphate.
[Illustration: Fig. 1]
Elements and Compounds. It is scarcely possible to discuss chemical
processes without having from time to time to use terms which are not in
everyday use. A few preliminary definitions and explanations of terms
which will be frequently used may serve to simplify descriptions, and
render it unnecessary to encumber them with purely explanatory matter.
Among the many different kinds of materials known, which in the
aggregate amount to several hundreds of thousands, there are about
ninety substances which up to the present time have not been broken up
into simpler kinds. These primary materials are called “elements,” the
remainder being known as “compounds.”
The following is a list of the commonest of these elements, together
with the symbols by which they are represented in Chemistry.
METALS
Aluminium Al.
Antimony (_Stibium_) Sb.
Barium Ba.
Bismuth Bi.
Cadmium Cd.
Calcium Ca.
Chromium Cr.
Copper (_Cuprum_) Cu.
Gold (_Aurum_) Au.
Iron (_Ferrum_) Fe.
Lead (_Plumbum_) Pb.
Lithium Li.
Magnesium Mg.
Manganese Mn.
Mercury (_Hydrargyrum_) Hg.
Nickel Ni.
Platinum Pt.
Potassium (_Kalium_) K.
Silver (_Argentum_) Ag.
Sodium (_Natrium_) Na.
Strontium Sr.
Tin (_Stannum_) Sn.
Zinc Zn.
NON-METALS
Boron B.
Bromine Br.
Carbon C.
Chlorine Cl.
Fluorine F.
Hydrogen H.
Iodine I.
Nitrogen N.
Oxygen O.
Phosphorus P.
Silicon Si.
Sulphur S.
The first step in the building-up process consists of the union of a
metallic with a non-metallic element. Such compounds are binary
compounds, and are distinguished by the termination -ide added to the
name of the non-metallic element; for example, copper and oxygen unite
to form copper oxide, sodium and chlorine form sodium chloride, iron and
sulphur form iron sulphide or sulphide of iron.
A compound containing more than two elements is distinguished by the
termination -ate. Most salts fall within this category; thus we speak of
acetate of lead and chlorate of potash, also of sodium sulphate and
copper sulphate, the latter form being the more correct.
A difficulty arises when two bodies are composed of the same elements
combined in different proportions. Then we have to resort to other
distinguishing prefixes or suffixes. For this reason we meet with
sulphur_ous_ acid and sulphur_ic_ acid, the corresponding salts being
sulph_ites_ and sulph_ates_.
Crystals and Water of Crystallization. When a soluble salt is to be
recovered from its solution, the latter is reduced in bulk by
evaporation until, either by experience or by trial, it becomes evident
that the solid will be formed as the liquid cools. In some cases, when
time is not an important factor, evaporation is left to take place
naturally. Under either set of conditions, the substance generally
separates out in particles which have a definite geometrical form. These
are spoken of as crystals.
Crystals often contain a definite percentage of water, called “water of
crystallization.” In washing soda, this combined water forms nearly 63
per cent. of the total weight; in blue vitriol, it is approximately 36
per cent. On being heated to a moderate temperature, the water is
expelled from the solid; the substance which is left behind is called
the anhydrous (that is, the waterless) salt.