An Introduction to Chemical Science
by
R.P. Williams
Part 1 out of 4
This etext was produced by John Mamoun
with the Online Distributed Proofreading Team of Charles Franks.
An Introduction to Chemical Science
by R.P. Williams, A.M.,
CONTENTS
PREFACE, BY R.P. WILLIAMS
TABLE OF CONTENTS
AN INTRODUCTION TO CHEMICAL SCIENCE
APPENDIX
TEXTBOOK ADVERTISEMENTS THAT APPEARED IN THE ORIGINAL EDITION
INFO ABOUT THIS E-TEXT EDITION
PREFACE, BY R.P. WILLIAMS
The object held constantly in view in writing this book has been to
prepare a suitable text-book in Chemistry for the average High
School,--one that shall be simple, practical, experimental, and
inductive, rather than a cyclopaedia of chemical information.
For the accomplishment of this purpose the author has endeavored
to omit superfluous matter, and give only the most useful and
interesting experiments, facts and theories.
In calling attention, by questions, and otherwise, to the more
important phenomena to be observed and facts to be learned, the
best features of the inductive system have been utilized.
Especially is the writing of equations, which constitute the
multum in parvo of chemical knowledge, insisted upon. As soon as
the pupil has become imbued with the spirit and meaning of
chemical equations, he need have little fear of failing to
understand the rest. To this end Chapters IX., XI., and XVI.
should be studied with great care.
In the early stages of the work the equations may with advantage
be memorized, but this can soon be discontinued. Whenever symbols
are employed, pupils should be required to give the corresponding
chemical names, or, better, both names and symbols.
The classification of chemical substances into acids, bases and
salts, and the distinctions and analogies between each of these
classes, have been brought into especial prominence. The general
relationship between the three classes, and the general
principles prevailing in the preparation of each, must be fully
understood before aught but the merest smattering of chemical
science can be known.
Chapters XV.-XXI. should be mastered as a key to the subsequent
parts of the book.
The mathematical and theoretical parts of Chemistry it has been
thought best to intersperse throughout the book, placing each
where it seemed to be especially needed; in this way, it is hoped
that the tedium which pupils find in studying consecutively many
chapters of theories will be avoided, and that the arrangement
will give an occasional change from the discussion of facts and
experiments to that of principles. In these chapters additional
questions should be given, and the pupil should be particularly
encouraged to make new problems of his own, and to solve theta.
It is needless to say that this treatise is primarily designed to
be used in connection with a laboratory. Like all other text-
books on the subject, it can be studied without such an
accessory; but the author attaches very little value to the study
of Chemistry without experimental work. The required apparatus
and chemicals involve but little expense, and the directions for
experimentation are the result of several years' experience with
classes as large as are to be found in the laboratory of any
school or college in the country.
During the present year the author personally supervises the work
of more than 180 different pupils in chemistry. This enables him
not only to assure himself that the experiments of the book are
practical, but that the directions for performing them are ample.
It is found advisable to perform most of the experiments, with
full explanation, in presence of the class, before requiring the
pupils either to do the work or to recite the lesson. In the
laboratory each pupil has a locker under his table, furnished
with apparatus, as specified in the Appendix. Each has also the
author's "Laboratory Manual," which contains on every left-hand
page full directions for an experiment, with observations to be
made, etc. The right-hand page is blank, and on that the pupil
makes a record of his work. These notes are examined at the time,
or subsequently, by the teacher, and the pupil is not allowed to
take the book from the laboratory; nor can he use any other book
on Chemistry while experimenting. By this means he learns to make
his own observations and inferences.
For the benefit of the science and the added interest in the
study, it is earnestly recommended that teachers encourage pupils
to fit up laboratories of their own at home. This need not at
first entail a large outlay. A small attic room with running
water, a very few chemicals, and a little apparatus, are enough
to begin with; these can be added to from time to time, as new
material is wanted. In this way the student will find his love
for science growing apace.
While endeavoring, by securing an able corps of critics, and in
all other ways possible, to reduce errors to a minimum, the
author disclaims any pretensions to a work entirely free from
mistakes, holding himself alone responsible for any shortcomings,
and trusting to the leniency of teachers and critics.
The manuscript has been read by Prof. Henry Carmichael, Ph.D., of
Boston, and to his broad and accurate scholarship, as well as to
his deep personal interest in the work, the author is indebted
for much valuable and original matter. The following persons have
generously read the proof, as a whole or in part, and made
suggestions regarding it, and to them the author would return his
thanks, as well as acknowledge his obligation: Prof. E. J.
Bartlett, Dartmouth College, N.H.; Prof. F. C. Robinson, Bowdoin
College, Me.; Prof. H. S. Carhart, Michigan University; Prof. B.
D. Halsted, Iowa Agricultural College; Prof. W. T. Sedgwick,
Institute of Technology, Boston; Pres. M. E. Wadsworth, Michigan
Mining School; Prof. George Huntington, Carleton College, Minn.;
Prof. Joseph Torrey, Iowa College; Mr. C. J. Lincoln, East Boston
High.School; Mr. W. H. Sylvester, English High School, Boston;
Mr. F. W. Gilley, Chelsea, Mass., High School; the late D. S.
Lewis, Chemist of the Boston Gas Works, and others.
R. P. W.
BOSTON, January 3, 1888.
TABLE OF CONTENTS
CHAPTER I.
THE METRIC SYSTEM.
Length.--Volume.--Weight
CHAPTER II.
DIVISIBILITY OF MATTER.
Mass.-Molecule.--Atom.--Element.--Compound.--Mixture.--
Analysis.--Synthesis.--Metathesis.--Chemism
CHAPTER III.
MOLECULES AND ATOMS.
Synthesis
CHAPTER IV.
ELEMENTS AND BINARIES.
Symbols.--Names.--Coefficients.--Exponents.--Table of elements
CHAPTER V.
MANIPULATION.
To prepare and cut glass, etc.
CHAPTER VI.
OXYGEN.
Preparation.--Properties.--Combustion of carbon; sulphur;
phosphorus; iron.
Chapter VII
NITROGEN
Separation--Properties
CHAPTER VIII
HYDROGEN
Preparation--Properties--Combustion--Oxy-hydrogen blowpipe
CHAPTER IX
UNION BY WEIGHT
Meaning of equations--Problems
CHAPTER X
CARBON
Preparation--Allotropic forms: diamond, graphite, amorphous
carbon, coke, mineral coal.--Carbon a reducing agent, a
decolorizer, disinfectant, absorber of gases
CHAPTER XI
VALENCE
Poles of attraction--Radicals
CHAPTER XII
ELECTRO-CHEMICAL RELATION OF ELEMENTS
Deposition of silver; copper; lead--Table of metals and non-
metals, and discussion of their differences
CHAPTER XIII.
ELECTROLYSIS.
Decomposition of water and of salts--Conclusions CHAPTER XIV.
UNION BY VOLUME.
Avogadro's law and its applications.
CHAPTER XV.
ACIDS AND BASES.
Characteristics of acids and bases.--Anhydrides.--Naming of
acids.--Alkalies
CHAPTER XVI.
SALTS.
Preparation from acids and bases.--Naming of salts.--Occurrence
CHAPTER XVII
CHLORHYDRIC ACID.
Preparation and tests.--Bromhydric, iodhiydric, and fluorhydric
acids.--Etching glass
CHAPTER XVIII.
NITRIC ACID.
Preparation, properties, tests, and uses.--Aqua regia:
preparation and action
CHAPTER XIX.
SULPHURIC ACID.
Preparation, tests, manufacture, and importance.-Fuming sulphuric
acid
CHAPTER XX.
AMMONIUM HYDRATE.
Preparation of bases.--Formation, preparation, tests, and uses of
ammonia.
Chapter XXI.
SODIUM HYDRATE.
Preparation and properties.--Potassium hydrate and calcium
hydrate
CHAPTER XXII
OXIDES OF NITROGEN.
Nitrogen monoxide, dioxide, trioxide, tetroaide, pentoxide.
CHAPTER XXIII.
LAWS OF DEFINITE AND OF MULTIPLE PROPORTION, and their
application
CHAPTER XXIV.
CARBON PROTOXIDE and water gas.
CHAPTER XXV.
CARBON DIOXIDE.
Preparation and tests.--Oxidation in the human system.--Oxidation
in water.--Deoxidation in plants
CHAPTER XXVI.
OZONE.
Description, preparation, and test
CHAPTER XXVII
CHEMISTRY OF THE ATMOSPHERE.
Constituents of the air.--Air a mixture.--Water, carbon dioxide,
and other ingredients of the atmosphere
CHAPTER XXVIII.
THE CHEMISTRY OF WATER.
Distillation of water.--Three states.--Pure water, sea-water,
river-water, spring-water CHAPTER XXIX.
THE CHEMISTRY OF FLAME.
Candle flame.--Bunsen flame.--Light and heat.--Temperature of
combustion.--Oxidizing and reducing flames.--Combustible and
supporter.--Explosive mixture of gases.--Generalizations
CHAPTER XXX.
CHLORINE.
Preparation.--Chlorine water.--Bleaching properties.--
Disinfecting power.--A supporter of combustion.--Sources and uses
CHAPTER XXXI.
BROMINE.
Preparation.--Tests.--Description.--Uses
CHAPTER XXXII.
IODINE.
Preparation.--Tests.--Iodo-starch paper.--Occurrence.--Uses.--
Fluorine
CHAPTER XXXIII.
THE HALOGENS.
Comparison.--Acids, oxides, and salts
CHAPTER XXXIV.
VAPOR DENSITY AND MOLECULAR WEIGHT.
Gaseous weights and volumes.--Vapor density defined.--Vapor
density of oxygen
CHAPTER XXXV.
ATOMIC WEIGHT.
Definition.--Atomic weight of oxygen.--Molecular symbols.--
Molecular and atomic volumes CHAPTER XXXVI.
DIFFUSION AND CONDENSATION OF GASES.
Diffusion of gases.--Law of diffusion.--Cause.--Liquefaction and
solidification of gases
CHAPTER XXXVIL
SULPHUR.
Separation.--Crystals from fusion.--Allotropy.--Solution.--
Theory of Allotropy.--Occurrence and purification.--Uses.---
Sulphur dioxide
CHAPTER XXXVIII.
HYDROGEN SULPHIDE.
Preparation.--Tests.--Combustion.--Uses.--An analyzer of metals.-
-Occurrence and properties
CHAPTER XXXIX.
PHOSPHORUS.
Solution and combustion.--Combustion under water.--Occurrence.--
Sources.--Preparation of phosphates and phosphorus.---
Properties.--Uses.--Matches.--Red phosphorus.---Phosphene
CHAPTER XL.
ARSENIC.
Separation.--Tests.--Expert analysis.--Properties and
occurrence.-- Atomic volume.--Uses of arsenic trioxide
CHAPTER XLI.
SILICON, SILICA, AND SILICATES.
Comparison of silicon and carbon.--Silica.--Silicates.--Formation
of silica.
Chapter XLII
GLASS AND POTTERY.
Glass an artificial silicate.--Manufacture.--Importance.--
Porcelain and pottery.
CHAPTER XLIII.
METALS AND THEIR ALLOYS.
Comparison of metals and non-metals.--Alloys.--Low fusibility. --
Amalgams
CHAPTER XLIV.
SODIUM AND ITS COMPOUNDS.
Order of derivation.--Occurrence and preparation of sodium
chloride; uses.--Sodium sulphate: manufacture and uses. --Sodium
carbonate: occurrence, manufacture, and uses.-- Sodium:
preparation and uses.--Sodium hydrate: preparation and use.--
Hydrogen sodium carbonate.--Sodium nitrate
CHAPTER XLV.
POTASSIUM AND AMMONIUM.
Occurrence and preparation of potassium.--Potassium chlorate and
cyanide.--Gunpowder.--Ammonium compounds
CHAPTER XLVI.
CALCIUM COMPOUNDS.
Calcium carbonate.--Lime and its uses.--Hard water.--Formation of
caves.--Calcium sulphate
CHAPTER XLVII.
MAGNESIUM, ALUMINIUM, AND ZINC.
Occurrence and preparation of magnesium.--Compounds of aluminium:
reduction; properties, and uses.--Compounds, uses, and reduction
of zinc CHAPTER XLVIII.
IRON AND ITS COMPOUNDS.
Ores of iron.--Pig-iron.--Steel.--Wrought-iron.--Properties. --
Salts of iron.--Change of valence and of color
CHAPTER XLIX.
LEAD AND TIN.
Distribution of lead.--Poisonous properties.--Some lead
compounds.-- Tin
CHAPTER L.
COPPER, MERCURY, AND SILVER.
Occurrence and uses of copper.--Compounds and uses of mercury.--
Occurrence, reduction, and salts of silver
CHAPTER LI.
PHOTOGRAPHY.
Description.
CHAPTER LII.
PLATINUM AND GOLD.
Methods of obtaining, and uses
CHAPTER LIII.
CHEMISTRY OF ROCKS.
Classification.--Composition.--Importance of siliceous rocks.--
Soils.--Minerals.--The earth's interior.--Percentage of elements
CHAPTER LIV.
ORGANIC CHEMISTRY.
Comparison of organic and inorganic compounds.--Molecular
differences.--Synthesis of organic compounds.--Marsh-gas.
series.---Alcohols.--Ethers.--Other substitution products. --
Olefines and other series.
CHAPTER LV.
ILLUMINATING GAS.
Source, preparation, purification, and composition.--Natural gas
CHAPTER LVI.
ALCOHOL.
Fermented and distilled liquors.--Effect on the system.--Affinity
for water.--Purity
CHAPTER LVII
OILS, FATS, AND SOAPS.
Sources and kinds of oils and fats.--Saponification.--Manufacture
and action of soap.--Glycerin, nitro-glycerin, and dynamite. --
Butter and oleomargarine.
CHAPTER LVIII
CARBO-HYDRATES.
Sugars.--Glucose.--Starch.--Cellulose.--Gun-cotton.--Dextrin. --
Zylonite
CHAPTER LIX.
CHEMISTRY OF FERMENTATION.
Ferments.--Alcoholic, acetic, and lactic fermentation.--
Putrefaction.--Infectious diseases
CHAPTER LX.
CHEMISTRY OF LIFE.
Growth of minerals and of organic life.--Food of plants and of
man.--Conservation of energy and of matter
CHAPTER LXI.
THEORIES.
The La Place theory--Theory of evolution--New theory of chemistry
CHAPTER LXII
GAS VOLUMES AND WEIGHTS.
Quantitative experiments with oxygen and hydrogen--Problems
AN INTRODUCTION TO CHEMICAL SCIENCE
CHAPTER I.
THE METRIC SYSTEM.
1. The Metric System is the one here employed. A sufficient
knowledge of it for use in the study of this book may be gained
by means of the following experiments, which should be performed
at the outset by each pupil.
2. Length.
Experiment 1.--Note the length of 10 cm. (centimeters) on a
metric ruler, as shown in Figure 1. Estimate by the eye alone
this distance on the cover of a book, and then verify the result.
Do the same on a t.t. (test-tube). Try this several times on
different objects till you can carry in mind a tolerably accurate
idea of 10 cm. About how many inches is it?
In the same way estimate the length of 1 cm, verifying each
result. How does this compare with the distance between two blue
lines of foolscap? Measure the diameter of the old nickel five-
cent piece.
Next, try in the same way 5 cm. Carry each result in mind, taking
such notes as may be necessary.
(Fig. 1)
3. Capacity.
Experiment 2.--Into a graduate, shown in Figure 2, holding 25 or
50 cc. (cubic centimeters) put 10 cc. of water; then pour this into
a t.t. Note, without marking, what proportion of the latter is
filled; pour out the water, and again put into the t.t. the same
quantity as nearly as can be estimated by the eye. Verify the
result by pouring the water back into the graduate. Repeat
several times until your estimate is quite accurate with a t.t.
of given size. If you wish, try it with other sizes. Now estimate
1 cc. of a liquid in a similar way. Do the same with 5 cc.
A cubic basin 10 cm on a side holds a liter. A liter contains
1,000 cc. If filled with water, it weighs, under standard
conditions, 1,000 grams. Verify by measurement.
4. Weight.
Experiment 3.--Put a small piece of paper on each pan of a pair
of scales. On one place a 10 g. (gram) weight. Balance this by
placing fine salt on the other pan. Note the quantity as nearly
as possible with the eye, then remove. Now put on the paper what
you think is 10 g. of salt. Verify by weighing. Repeat, as before,
several times. Weigh 1 g., and estimate as before. Can 1 g. of
salt be piled on a one-cent coin? Experiment with 5 g.
5. Resume--Lengths are measured in centimeters, liquids in cubic
centimeters, solids in grams. In cases where it is not convenient
to measure a liquid or weigh a solid, the estimates above will be
near enough for most experiments herein given. Different solids
of the same bulk of course differ in weight, but for one gram
what can be piled on a one-cent piece may be called a
sufficiently close estimate. The distance between two lines of
foolscap is very nearly a centimeter. A cubic centimeter is seen
in Figure 1. Temperatures are recorded in the centigrade scale.
CHAPTER II.
WHAT CHEMISTRY IS.
6. Divisibility of Matter.
Experiment 4.--Examine a few crystals of sugar, and crush them
with the fingers. Grind them as fine as convenient, and examine
with a lens. They are still capable of division. Put 3 g. of
sugar into a t.t., pour over it 5 cc. of water, shake well, boil
for a minute, holding the t.t. obliquely in the flame, using for
the purpose a pair of wooden nippers (Fig. 3). If the sugar does
not disappear, add more water. When cool, touch a drop of the
liquid to the tongue. Evidently the sugar remains, though in a
state too finely divided to be seen. This is called a solution,
the sugar is said to be soluble in water, and water to be a
solvent of sugar.
(Fig 3.)
Now fold a filter paper, as in Figure 4, arrange it in a funnel
(Fig. 5), and pour the solution upon it, catching what passes
through, which is called the filtrate, in another t.t. that rests
in a receiver (Fig. 5). After filtering, notice whether any
residue is left on the filter paper. Taste a drop of the
filtrate. Has sugar gone through the filter? If so, what do you
infer of substances in solution passing through a filter? Save
half the filtrate for Experiment 5, and dilute the other half
with two or three times its own volume of water. Shake well, and
taste.
(Fig 4.)
(Fig 5.) We might have diluted the sugar solution many times
more, and still the sweet taste would have remained. Thus the
small quantity of sugar would be distributed through the whole
mass, and be very finely divided.
By other experiments a much finer subdivision can be made. A
solution of.00000002 g. of the red coloring matter, fuchsine, in
1 cc. of alcohol gives a distinct color.
Such experiments would seem to indicate that there is no limit to
the divisibility of matter. But considerations which we cannot
discuss here lead to the belief that such a limit does exist;
that there are particles of sugar, and of all substances, which
are incapable of further division without entirely changing the
nature of the substance. To these smallest particles the name
molecules is given.
A mass is any portion of a substance larger than a molecule; it
is an aggregation of molecules.
A molecule is the smallest particle of a substance that can exist
alone.
A substance in solution may be in a more finely divided state
than otherwise, but it is not necessarily in its ultimate state
of division.
7. A Chemical Change.--Cannot this smallest particle of sugar,
the molecule, be separated into still smaller particles of
something else? May it not be a compound body, and will not some
force separate it into two or more substances? The next
experiment will answer the question.
Experiment 5.--Take the sugar solution saved from Experiment 4,
and add slowly 4 cc.of strong sulphuric acid. Note any change of
color, also the heat of the t.t. Add more acid if needed.
A substance entirely different in color and properties has been
formed. Now either the sugar, the acid, or the water has
undergone a chemical change. It is, in fact, the sugar. But the
molecule is the smallest particle of sugar possible. The acid
must have either added something to the sugar molecules, or
subtracted something from them. It was the latter. Here, then, is
a force entirely different from the one which tends to reduce
masses to molecules. The molecule has the same properties as the
mass. Only a physical force was used in dissolving the sugar, and
no heat was liberated. The acid has changed the sugar into a
black mass, in fact into charcoal or carbon, and water; and heat
has been produced. A chemical change has been brought about.
From this we see that molecules are not the ultimate divisions of
matter. The smallest sugar particles are made up of still smaller
particles of other things which do not resemble sugar, as a word
is composed of letters which alone do not resemble the word. But
can the charcoal itself be resolved into other substances, and
these into still others, and so on? Carbon is one of the
substances from which nothing else has been obtained. There are
about seventy others which have not been resolved. These are
called elements; and out of them are built all the compounds--
mineral, vegetable, and animal--which we know.
8. An element is a chemically indivisible substance, or one from
which nothing else can be extracted.
A compound is a substance which is made up of elements united in
exact proportions by a force called chemism, or chemical
affinity.
A mixture is composed of two or more elements or compounds
blended together, but not held by any chemical attraction.
To which of these three classes does sugar belong? Carbon? The
solution of sugar in water?
Carbon is an element; we call its smallest particle an atom.
An atom is the smallest particle of an element that can enter
into combination. Atoms are indivisible and usually do not exist
alone. Both elements and compounds have molecules.
The molecule of an element usually contains two atoms; that of a
compound may have two, or it may have hundreds. For a given
compound the number is always definite.
Chemism is the force that binds atoms together to form molecules.
The sugar molecule contains atoms, forty-five in all, of three
different elements: carbon, hydrogen, and oxygen. That of salt
has two atoms: one of sodium, one of chlorine. Should we say "an
atom of sugar"? Why? Of what is a mass of sugar made up? A
molecule? A mass of carbon? A molecule? Did the chemical affinity
of the acid break up masses or molecules? In this respect it is a
type of all chemical action. The distinction between physics and
chemistry is here well shown. The molecule is the unit of the
physicist, the atom that of the chemist. However large the masses
changed by chemical action, that action is always on the
individual molecule, the atoms of which are separated. If the
molecule were an indivisible particle, no science of chemistry
would be possible. The physicist finds the properties of masses
of matter and resolves them into molecules, the chemist breaks up
the molecule and from its atoms builds up other compounds.
Analysis is the separation of compounds into their elements.
Synthesis is the building up of compounds from their elements.
Of which is the sugar experiment an example? Metathesis is an
exchange of atoms in two different compounds; it gives rise to
still other compounds.
A chemical change may add something to a substance, or subtract
something from it, or it may both subtract and add, making a new
substance with entirely different properties. Sulphur and carbon
are two stable solids. The chemical union of the two forms a
volatile liquid. A substance may be at one time a solid, at
another a liquid, at another a gas, and yet not undergo any
chemical change, because in each case the chemical composition is
identical.
State which of these are chemical changes: rusting of iron,
falling of rain, radiation of heat, souring of milk, evaporation
of water, decay of vegetation, burning of wood, breaking of iron,
bleaching of cloth. Give any other illustrations that occur to
you.
Chemistry treats of matter in its simplest forms, and of the
various combinations of those simplest forms.
CHAPTER III.
MOLECULES AND ATOMS.
9. Molecules are Extremely Small.--It has been estimated that a
liter of any gas at 0 degrees and 760 mm. pressure contains 10^24
molecules, i.e. one with twenty-four ciphers.
Thomson estimates that if a drop of water were magnified to the
size of the earth, and its molecules increased in the same
proportion, they would be larger than fine shot, but not so large
as cricket balls.
A German has recently obtained a deposit of silver two-millionths
of a millimeter thick, and visible to the naked eye. The computed
diameter of the molecule is only one and a half millionths of a
millimeter.
By a law of chemistry there is the same number of molecules in a
given volume of every gas, if the temperature and pressure are
the same. Hence, all gaseous molecules are of the same size,
including, of course, the surrounding space. They are in rapid
motion, and the lighter the gas the more rapid the motion. This
gives rise to diffusion. See page 114.
10. We Know Nothing Definite of the Form of Molecules.--In this
book they will always be represented as of the same size, that of
two squares. A molecule is itself composed of atoms,--from two to
several hundred. The size of the atom of most elements we
represent by one square.11. Atoms.--If the gaseous molecules be
of the same size, it is clear that either the atoms themselves
must be condensed, or the spaces between them must be smaller
than before. We suppose the latter to be the case, and that they
do not touch one another, the same thing being true of molecules.
Atoms composing sugar must be crowded nearer together than those
of salt. These atoms are probably in constant motion in the
molecule, as the latter is in the mass. If we regard this square
as a mass of matter, the dots may represent molecules; if we call
it a molecule, the dots may be called atoms, though many
molecules have no more than two or three atoms.
The following experiments illustrate the union of atoms to form
molecules, and of elements to form compounds.
12. Union of Atoms.
Experiment 6.--Mix, on a paper, 5 g. of iron turnings, and the
same bulk of powdered sulphur, and transfer them to an ignition
tube, a tube of hard glass for withstanding high temperatures.
Hold the tube in the flame of a burner till the contents have
become red-hot. After a minute break it by holding it under a jet
of water. Put the contents into an evaporating-dish, and look for
any uncombined iron or sulphur. Both iron and sulphur are
elements. Is this an example of synthesis or of analysis? Why? Is
the chemical union between masses of iron and sulphur, or between
molecules, or between atoms? Is the product a compound, an
element, or a mixture?
Experiment 7.--Try the same experiment, using copper instead of
iron. The full explanation of these experiments is given on page
13.
CHAPTER IV.
ELEMENTS AND BINARIES.
13. About Seventy Different Elements are now recognized, half of
which have been discovered within little more than a century.
These differ from one another in (1) atomic weight, (2) physical
and chemical properties, (3) mode of occurrence, etc. Page 12
contains the most important elements.
The symbol of an element is usually the initial letter or letters
of its Latin name, and stands for one atom of the element. C is
the symbol for carbon, and represents one atom of it. O means one
atom of oxygen.[The symbols of elements will also be used in this
book to stand for an indefinite quantity of them; e.g. O will be
used for oxygen in general as well as for one atom. The text will
readily decide when symbols have a definite meaning, and when
they are used in place of words.] Write, explain, and memorize
the symbols of the elements in heavy type.
14. The Atomic Weight of an element is the weight of its atom
compared with that of hydrogen. H is taken as the standard
because it has the least atomic weight. The atomic weight of O is
16, which means that its atom weighs 16 times as much as the H
atom. Every symbol, then, stands for a definite weight of the
element, i.e. its atomic weight, as well as for its atom.
How much bromine by weight does Br stand for? What do these
symbols mean--As, Na, N, P? If O represents one atom, how much
does O2 or 2 O stand for? How much by weight? Most elements have
two atoms in the molecule. How many molecules in 6 H? 10 N? S8?
I20?
The symbol of a compound is formed by writing in succession the
symbols of the elements of which it is composed. How many atoms
in the following molecules, and how many of each element: C2H60?
HNO3? PbSO4? MgCl2? (Hg2(NO3)2?)
15. The Simplest Compounds are Binaries.--A binary is a substance
composed of two elements; e.g. common salt, which is a compound
of sodium and chlorine. Its symbol is NaCl, its chemical name
sodium chloride. The ending ide is applied to the last name of
binaries. How many parts by weight of Na and of Cl in NaCl? What
is the molecular weight, i.e. the weight of its molecule? Name
KCl. How many atoms in its molecule? Parts by weight of each
element? Molecular weight? Does the symbol stand for more than
one molecule? How many molecules in 4 NaCl? How many atoms of Na
and of Cl? Name these: HCl, NaBr, NaI, KBr, AgCl, AgI, HBr, HI,
HF, HgO, ZnO, ZnS, MgO, CaO. Compute the proportion by weight of
each element in the last three.
A coefficient before the symbol of a compound includes all the
elements of the symbol, and shows the number of molecules. How
many in these: 6 KBr? 3 Sn0? 12 NaCl? How many atoms of each
element in the above?
An exponent, always written below, applies only to the element
after which it is written, and shows the number of atoms. Explain
these: AuCl3, ZnCl2, Hg2Cl2.
Write symbols for four molecules of sodium bromide, one of silver
iodide (always omit coefficient one), eight of potassium bromide,
ten of hydrogen chloride; also for one molecule of each of these:
hydrogen fluoride, potassium iodide, silver chloride.
In all the above cases the elements have united atom for atom.
Some elements will not so unite. In CaCl2 how many atoms of each
element? Parts by weight of each? Give molecular weight. Is the
size of the molecule thereby changed? Name these, give the number
of atoms of each element in the molecule, and the proportion by
weight, also their molecular weights: AuCl3, ZnCl2, MnCl2, Na2O,
K2S, H3P, H4C.
Principal Elements.
Name. Sym. At. Wt. Valence. Vap.D. At.Vol. Mol.Vol. State.
Aluminium Al 27. II, IV ... ... ... Solid
Antimony Sb 120. III, V. ... ... ... "
Arsenic As 75. III, V 150. "
Barium Ba 137. II ... ... ... "
Bismuth Bi 210. III, V ... ... ... "
Boron B 11. III ... ... ... "
Bromine Br 80. I, (V) 80. Liquid
Cadmium Cd 112. II 56. Solid
Calcium Ca 40. II ... ... ... "
Carbon C 12. (II), IV ... ... ... "
Chlorine Cl 35.5 I, (V) 35.5 Gas
Chromium Cr 52. (II),IV,VI ... ... ... Solid
Cobalt Co 59. II, IV ... ... ... Gas
Copper Cu 63. I, II ... ... ... "
Fluorine F 19. I, (V) ... ... ... Gas
Gold Au 196. (I), III ... ... ... Solid
Hydrogen H 1. I 1. Gas
Iodine I 127. I, (V) 127. ... ... Solid
Iron Fe 56. II,IV,(VI) ... ... ... "
Lead Pb 206. II, IV ... ... ... "
Lithium Li 7. I ... ... ... "
Magnesium Mg 24. II ... ... ... "
Manganese Mn 55. II, IV, VI ... ... ... "
Mercury Hg 200. I, II 100. Liquid
Nickel Ni 59. II, IV ... ... ... Solid
Nitrogen N 14. (I),III,V 14. Gas
Oxygen O 16. II 16. "
Phosphorus P 31. (I),III, V 62. Solid
Platinum Pt 197. (II), IV ... ... ... "
Potassium K 39. I ... ... ... "
Silicon Si 28. IV ... ... ... "
Silver Ag 108. I ... ... ... "
Sodium Na 23. I ... ... ... "
Strontium Sr 87. II ... ... ... "
Sulphur S 32. II,IV,(VI) 32(96) "
Tin Sn 118. II, IV ... ... ... "
Zinc Zn 65. II 32.5 "
If more than one atom of an element enters into the composition
of a binary, a prefix is often used to denote the number. SO2 is
called sulphur dioxide, to distinguish it from SO3, sulphur
trioxide. Name these: CO2, SiO2, MnO2. The prefixes are: mono or
proto, one; di or bi, two; tri or ter, three; tetra, four; pente,
five; hex, six; etc. Diarsenic pentoxide is written, As2O5.
Symbolize these: carbon protoxide, diphosphorus pentoxide,
diphosphorus trioxide, iron disulphide, iron protosulphide. Often
only the prefix of the last name is used.
16. An Oxide is a Compound of Oxygen and Some Other Element, as
HgO. What is a chloride? Define sulphide, phosphide, arsenide,
carbide, bromide, iodide, fluoride.
In Experiment 6, where S and Fe united, the symbol of the product
was FeS. Name it. How many parts by weight of each element? What
is its molecular weight? To produce FeS a chemical union took
place between each atom of the Fe and of the S. We may express
this reaction, i.e. chemical action, by an equation:--
Iron + Sulphur = Iron Sulphide
Or, using symbols Fe + S = FeS
Using atomic weights, 56 32 = 88.
These equations are explained by saying that 56 parts by weight
of iron unite chemically with 32 parts by weight of sulphur to
produce 88 parts by weight of iron sulphide. This, then,
indicates the proportion of each element which combines, and
which should be taken for the experiment. If 56 g. of Fe be used,
32 g. of S should be taken. If we use more than 56 parts of Fe
with 32 of S, will it all combine? If more than 32 of S with 56
of Fe? There is found to be a definite quantity of each element
in every chemical compound. Symbols would have no meaning if this
were not so.
Write and explain the equation for the experiment with copper and
sulphur, using names, symbols, and weights, as above.
CHAPTER V.
MANIPULATION.
17. To Break Glass Tubing.
Experiment 8.--Lay the tubing on a flat surface, and draw a sharp
three-cornered file two or three times at right angles across it
where it is to be broken, till a scratch is made. Take the tube
in the hands, having the two thumbs nearly opposite the scratch,
and the fingers on the other side. Press outward quickly with the
thumbs, and at the same time pull the hands strongly apart, and
the tubing should break squarely at the scratch.
To break large tubing, or cut off bottles, lamp chimneys, etc.,
first make a scratch as before; then heat the handle of a file,
or a blunt iron--in a blast-lamp flame by preference--till it is
red-hot, and at once press it against the scratch till the glass
begins to crack. The fracture can be led in any direction by
keeping the iron just in front of it. Re-heat the iron as often
as necessary.
18. To Make Ignition-Tubes.
Experiment 9.--Hold the glass tubing between the thumb and
forefinger of each hand, resting it against the second finger.
Heat it in the upper flame, slowly at first, then strongly, but
heat only a very small portion in length, and keep it in constant
rotation with the right hand. Hold it steadily, and avoid
twisting it as the glass softens. The yielding is detected by the
yellow flame above the glass and by an uneven pressure on the
hands. Pull it a little as it yields, then heat a part just at
one side of the most softened portion. Rotate constantly without
twisting, and soon it can be separated into two closed tubes. No
thread should be attached; but if there be one, it can be broken
off and the end welded. The bottom can be made more symmetrical
by heating it red-hot, then blowing, gradually, into the open
end, this being inserted in the mouth. The parts should be
annealed by holding above the flame for a short time, to cool
slowly.
For hard glass--Bohemian--or large tubes, the blast-lamp or
blowpipe is needed. In the blast-lamp air is forced out with
illuminating gas. This gives a high degree of heat. Bulbs can be
made in the same way as ignition-tubes, and thistle-tubes are
made by blowing out the end of a heated bulb, and rounding it
with charcoal.
19. To Bend Glass Tubing.
Experiment 10.--Hold the tube in the upper flame. Rotate it so as
to heat all parts equally, and let the flame spread over 3 or 4
cm. in length. When the glass begins to yield, without removing
from the flame slowly bend it as desired. Avoid twisting, and be
sure to have all parts in the same plane; also avoid bending too
quickly, if you would have a well-rounded joint. Anneal each bend
as made. Heated glass of any kind should never be brought in
contact with a cool body. For making O, H, etc., a glass tube --
delivery-tube--50 cm. long should have three bends, as in Figure
6. The pupil should first experiment with short pieces of glass,
10 or 15 cm. long. An ordinary gas flame is the best for bending
glass.
20. To Cut Glass.
Experiment 11.--Lay the glass plate on a flat surface, and draw a
steel glass-cutter--revolving wheel--over it, holding this
against a ruler for a guide, and pressing down hard enough to
scratch the glass. Then break it by holding between the thumb and
fingers, having the thumbs on the side opposite to the scratch,
and pressing them outward while bending the ends of the glass
inward. The break will follow the scratch.
Holes can be bored through glass and bottles with a broken end of
a round file kept wet with a solution of camphor in oil of
turpentine.
21. To Perforate Corks.
Experiment 12.--First make a small hole in the cork with the
pointed handle of a round--rat-tail--file. Have the hole
perpendicular to the surface of the cork. This can be done by
holding the cork in the left hand and pressing against the larger
surface, or upper part, of the cork, with the file in the right
hand. Only a mere opening is made in this way, which must be
enlarged by the other end of the file. A second or third file of
larger size may be employed, according to the size of the hole to
be made, which must be a little smaller than the tube it is to
receive, and perfectly round.
CHAPTER VI.
OXYGEN.
22. To Obtain Oxygen.
Experiment 13.--Take 5 g. of crystals of potassium chlorate
(KClO3) and, without pulverizing, mix with the same weight of
pure powdered manganese dioxide (MnO2). Put the mixture into a
t.t., and insert a d.t.--delivery-tube--having the cork fit
tightly. Hang it on a r.s.--ring-stand,-- as in Figure 7, having
the other end of the d.t.
(Fig 7.)
under the shelf, in a pneumatic trough, filled with water just
above the shelf. Fill three or more receivers--wide-mouthed
bottles--with water, cover the mouth of each with a glass plate,
invert it with its mouth under water, and put it on the shelf of
the trough, removing the plate. No air should be in the bottles.
Have the end of the d.t. so that the gas will rise through the
orifice. Hold a lighted lamp in the hand, and bring the flame
against the mixture in the t.t. Keep
the lamp slightly in motion, with the hand, so as not to break
the t.t. by over-heating in one place. Heat the mixture strongly,
if necessary. The upper part of the t.t. is filled with air:
allow this to escape for a few seconds; then move a receiver over
the orifice, and fill it with gas. As soon as the lamp is taken
away, remove the d.t. from the water. The gas contracts, on
cooling, and if not removed, water will be drawn over, and the
t.t. will be broken. Let the t.t. hang on the r.s. till cool.
With glass plates take out the receivers, leaving them covered,
mouth upward (Fig. 8), with little or no water inside. When cool,
the t.t. may be cleaned with water, by covering its mouth with
the thumb or hand, and shaking it vigorously.
What elements, and how many, in KClO3? In Mn02? It is evident
that each of these compounds contains O. Why, then, could we not
have taken either separately, instead of mixing the two? This
could have been done at a sufficiently high temperature. Mu02
requires a much higher temperature for dissociation, i.e.
separation into its elements, than KClO3, while a mixture of the
two causes O to come off from KClO3 at a lower temperature than
if alone. It is not known that Mn02 suffers any change.
Each molecule of potassium chlorate undergoes the following
change:--
Potassium Chlorate = Potassium Chloride + Oxygen
KClO3 = KCl + 3 O.
Is this analysis or synthesis? Complete the equation, by using
weights, and explain it. Notice whether the right- hand member of
the equation has the same number of atoms as the left. Has
anything been lost or gained? What element has heat separated?
Does the experiment show whether O is very soluble in water? How
many grams of O are obtainable from 122.58 g. KCIO3? PROPERTIES.
23. Combustion of Carbon.
OXYGEN Experiment 14.--Examine the gas in one of the receivers.
Put a lighted splinter into the receiver, sliding along the glass
cover. Remove it, blow it out, and put in again while glowing. Is
it re-kindled? Repeat till it will no longer burn. Is the gas a
supporter of combustion? How did the combustion compare with that
in air? Is it probable that air is pure O? Why did the flame at
last go out? Has the O been destroyed, or chemically united with
something else?
Wood is in part C. CO2 is formed by the combustion; name it. The
equation is C + 2O = CO2. Affix the names and weights. Is CO2 a
supporter of combustion? Note that when C is burned with plenty
of O, CO2 is always formed, and that no matter how great the
conflagration, the union is atom by atom. Combustion, as here
shown, is only a rapid union of O with some other substance, as C
or H.
24. Combustion of Sulphur.
Experiment 15.--Hollow out one end of a piece of electric-light
pencil, or of crayon, 3 cm. long, and attach it to a Cu wire
(Fig. 9). Put into this a piece of S as large as a pea, ignite it
by holding in the flame, and then hold it in a receiver of O.
Note the color and brightness of the flame, and compare with the
same in the air. Also note the color and odor of the product. The
new gas is SO2. Name it, and write the equation for its
production from S and O. How do you almost daily perform a
similar experiment? Is the product a supporter of combustion?
25. Combustion of Phosphorus.
Experiment 16.--With forceps, which should always be used in
handling this element, put a bit of P, half as large as the S
above,into the crayon, called a deflagrating-spoon. Heat another
wire, touch it to the P, and at once lower the latter into a
receiver of O. Notice the combustion, the color of the flame and
of the product. After removing, be sure to burn every bit of P by
holding it in a flame, as it is liable to take fire if left. The
product of the combustion is a union of what two elements? Is it
an oxide? Its symbol is P2O5. Write the equation, using symbols,
names, and weights. Towards the close of the experiment, when the
O is nearly all combined, P2O3 is formed, as it is also when P
oxidizes at a low temperature. Name it and write the equation.
26. Combustion of Iron.
Experiment 17.--Take in the forceps a piece of iron picture-cord
wire 6 or 8cm long, hold one end in the flame for an instant,
then dip it into some S. Enough S will adhere to be set on fire
by holding it in the flame again. Then at once dip it into a
receiver of O with a little water in the bottom. The iron will
burn with scintillations. Is this analysis or synthesis? What
elements combine? A watch-spring, heated to take out the temper,
may be used, but picture-wire is better.
The product is Fe3O4. Write the equation. How much Fe by weight
in the formula? How much O? What per cent by weight of Fe in the
compound? Multiply the fractional part by 100. What per cent of
0? Whatper cent of C0 .is C? O2? Find the percentage composition
of SO2. P2O5.
From the last five experiments what do you infer of the tendency
of O to unite with other elements?
27. Oxygen is a Gas without Color, Odor, or Taste.
It is chemically a very active element; that is, it unites with
almost everything. Fluorine is the only element with which it
will not combine. When oxygen combines with a single element,
what is the compound called? We have found that O makes up a
certain portion of the air; later, we shall see how large the
proportion is. Its tendency to combine with almost everything is
a reason for the decay, rust, and oxidation of so many
substances, and for conflagrations, great and small. New
compounds are thusformed, of which O constitutes one factor.
Water, H2O, is only a chemical union of O and H. Iron rust, Fe2O3
and H2O, is composed of O, Fe, and water. The burning of wood or
of coal gives rise to carbon dioxide, CO2, and water. Decay of
animal and vegetable matter is hastened by this all-pervading
element. O forms a portion of all animal and vegetable matter, of
almost all rocks and minerals, and of water. It is the most
abundant of all elements, and makes up from one-half to two-
thirds of the earth's surface. Compute the proportion of it, by
weight, in water, H2O. It is the union of O in the air with C and
H in our blood that keeps up the heat of the body and supports
life. See page 81.
There are many ways of preparing this element besides the one
given above. It may be obtained from water (Experiment 38) and
from many other compounds, e.g. by heating mercury oxide,
HgO.
CHAPTER VII.
NITROGEN.
28. Separation.
Experiment 18.--Fasten a piece of electric-light pencil, or of
crayon, to a wire, as in Experiment 15, and bend the wire so it
will reach half-way to the bottom of a receiver. Using forceps,
put into the crayon a small piece of phosphorus. Pass the wire up
through the orifice in the shelf of a p.t. (pneumatic trough),
having water at least l cm. above the shelf. Heat another wire,
touch it to the P, and quickly invert an empty receiver over the
P, having the mouth under water, so as to admit no air (Fig. 10).
Let the P burn as long as it will, then remove the wire and the
crayon, letting in no air. Note the color of the product, and
leave till it is tolerably clear, then remove the receiver with a
glass plate, leaving the water in the bottom.
Do the fumes resemble those of Experiment 16? Does it seem likely
(Fig 10.) that part of the air is O? Why a part only? Find what
proportion of the receiver is filled with water by measuring the
water with a graduate; then fill it with water and measure that;
compute the percentage which the former is of the latter. What
proportion of the air, then, is O? What was the only means of
escape for the P2O6, and P2O2 formed? These products are solids.
Are they soluble in water? Compute the percentage composition,
always by weight, of P2O2 and P2O5.
The gas left in the receiver is evidently not O. Experiment 19
will prove this conclusively, and show the properties of the new
gas.
29. Properties.
Experiment 19.--When the white cloud has disappeared, slide the
plate along, and insert a burning stick; try one that still
glows.
See whether the P and S on the end of a match will burn. Is the
gas a supporter of combustion? Since it does not unite with C,
S, or P, is it an active or a passive element? Compare it with
O. Air is about 14 1/2 times as heavy as H. Which is heavier, air
or N? See page 12. Air or O?
Write out the chief properties, physical and chemical, of N, as
found in this experiment.
30. Inactivity of N.--N will scarcely unite chemically except on
being set free from compounds. It has, however, an intense
affinity for boron, and will even go through a carbon crucible to
unite with it. It is not combined with O in the air; but the two
form a mixture (page 86), of which N makes up four-fifths, its
use being to dilute the O. What would be the effect, in case of a
fire, if air were pure O? What effect on the human system?
Growing plants need a great deal of N, but they are incapable of
making use of that in the air, on account of the chemical
inactivity of the element. Their supply comes from compounds in
earth, water, and air. By reason of its inertness N is very
easily set free from its compounds. For this reason it is a
constituent of most explosives, as gunpowder, nitro-glycerine,
dynamite, etc. These solids, by heat or concussion, are suddenly
changed to gases, which thereby occupy much more space, causing
an explosion.
Nitrogen exists in many compounds, such as the nitrates; but the
great source of it all is the atmosphere. See page 85.
CHAPTER VIII.
HYDROGEN.
31. Preparation.
Experiment 20.--Prepare apparatus as for making O. Be sure that
the cork perfectly fits both d.t. and t.t., or the H will escape.
Cover 5 g. granulated Zn, in the t.t., with 10 cc. H2O, and add 5
cc. chlorhydric acid, HCl. Adjust as for O (Fig. 7), except that
no heat is to be applied. If the action is not brisk enough, add
more HCl. Collect several receivers of the gas over water, adding
small quantities of HCl when necessary. Observe the black
floating residuum; it is carbon, lead, etc. With a glass plate
remove the receivers, keeping them inverted (Fig. 11), or the H
will escape.
32. The Chemical Change is as follows:--
Zinc + hydrogen chloride = zinc chloride + hydrogen.
Zn + 2 HCl = ZnCl2 + 2H.
Complete by adding the weights, and explain. Notice that the
water does not take part in the change; it is added to dissolve
the ZnCl2 formed, and thus keep it from coating the Zn and
preventing further action of the acid. Note also that Zn has
simply changed places with H, one atom of the former having
driven off two atoms of the latter. The H, having nothing to
unite with, is set free as a gas, and collected over water. Of
course Zn must have a stronger chemical affinity for Cl than H
has, or the change could not have taken place. Why one Zn atom
replaces two H atoms will be explained later, asfar as an
explanation is possible. This equation, should be studied
carefully, as a type of all equations. The left-hand member shows
what were taken, i.e. the factors; the right-hand shows what were
obtained, i.e. the products. H2SO4 might have been used instead
of HCl. In that case the reaction, or equation, would have been:
--
Zinc + hydrogen sulphate = zinc sulphate + hydrogen.
Zn + H2SO4 = ZnSO4 + 2H.
Iron might have been used instead of zinc, in which case the
reactions would have been:--
Iron + hydrogen chloride = iron chloride + hydrogen.
Fe + 2 HCl = FeCl2 + 2 H.
Iron + hydrogen sulphate = iron sulphate + hydrogen.
Fe + H2SO4 = FeSO4 + 2 H.
Write the weights and explain the equations. The latter should be
memorized.
33. Properties.
Experiment 21.--Lift with the left hand a receiver of H, still
inverted, and insert a burning splinter with the right (Fig. 12).
Does the splinter continue to burn? Does the gas burn? If so,
where? Is the light brilliant? Note the color of the flame. Is
there any explosion? Try this experiment with several receivers.
Is the gas a supporter of combustion? i.e. will carbon burn in
it? Is it combustible? i.e. does it burn? If so, it unites with
some part of the air. With what part?34. Collecting H by Upward
Displacement.
Experiment 22.--Pass a d.t. from a H generator to the top of a
receiver or t.t. (Fig. 13). The escaping H being so much lighter
than air will force the latter down. To obtain the gas unmixed
with air, the d.t. should tightly fit a cardboard placed under
the mouth of the receiver. When filled, the receiver can be
removed, inverted as usual, and the gas tested. In this and other
experiments for generating H, a thistle-tube, the end of which
dips under the liquid, can be used for pouring in acid, as in
Figure 13.
35. Philosopher's Lamp and Musical Flame.
Experiment 23.--Fit to a cork a piece of glass tubing 10 or 15
cm. long, having the outer end drawn out to a point with a small
opening, and insert it in the H generator. Before igniting the
gas at the end of the tube take the, precaution to collect a t.t.
of it by upward displacement, and bring this in contact with a
flame. If a sharp explosion ensues, air is not wholly expelled
from the generator, and it would be dangerous to light the gas.
When no sound, or very little, follows, light the escaping gas.
The generation of H must not be too rapid, neither should the
t.t. be held under the face, as the cork is liable to be forced
out by the pressure of H. A safety-tube, similar to the thistle-
tube above, will prevent this. This apparatus is called the
"philosopher's lamp." Thrust the flame into a long glass tube 1-
1/2 to 3 cm. in diameter, as shown in Figure 14, and listen for a
musical note.
36. Product of Burning H in Air.
Experiment 24.--Fill a tube 2 or 3 cm. in diameter with calcium
chloride, CaCl2, and connect one end with a generator of H (Fig.
15). At the other end have a philosopher's lamp-tube.Observing
the usual precautions, light the gas and hold over it a receiver,
till quite a quantity of moisture collects. All water was taken
from the gas by the dryer, CaCl2. What is, therefore, the product
of burning H in air? Complete this equation and explain it: 2H +
O = ? Figure 16 shows a drying apparatus arranged to hold CaCl2.
[Fig. 15][Fig. 16]
37. Explosiveness of H.
Experiment 25. -- Fill a soda-water bottle of thick glass with
water, invert it in a pneumatic trough, and collect not over 1/4
full of H. Now remove the bottle, still inverted, letting air in
to fill the other 3/4. Mix the air and H by covering the mouth of
the bottle with the hand, and shaking well; then hold the mouth
of the bottle, slightly inclined, in a flame. Explain the
explosion which follows. If 3/4 was air, what part was O? What
use did the N serve? Note any danger in exploding H mixed with
pure O. What proportions of O and H by volume would be most
dangerously explosive? What proportion by weight?
By the rapid union of the two elements, the high temperature
suddenly expanded the gaseous product, which immediately
contracted; both expansion and contraction produced the noise of
explosion.
38. Pure H Is a Gas without Color, Odor, or Taste.
--It is the lightest of the elements, 14 1/2 times as light
asair. It occurs uncombined in coal-mines, and some other places,
but the readiness with which it unites with other elements,
particularly O, prevents its accumulation in large quantities. It
constitutes two-thirds of the volume of the gases resulting from
the decomposition of water, and one-ninth of the weight. Compute
the latter from its symbol. It is a constituent of plants and
animals, and some rocks. Considering the volume of the ocean, the
total amount of H is large. It can be separated from H2O by
electrolysis, or by C, as in the manufacture of water gas.
When burned with O it forms H2O. Pure O and H when burning give
great heat, but little light. The oxy-hydrogen blow-pipe (Fig.
17) is a device for producing the highest temperatures of
combustion. It has O in the inner tube and H in the outer. Why
would it not be better the other way? These unite at the end, and
are burned, giving great heat. A piece of lime put into the flame
gives the brilliant Drummond or calcium light.
Chapter IX. UNION BY WEIGHT.
39. In the Equation --
Zn + 2 HCl = ZnCl2 + 2 H
65 + 73 = 136 + 2
65 parts by weight of Zn are required to liberate 2 parts by weight of
H; or, by using 65 g Zn with 73 g HCl, we obtain 2 g H. If twice as
much Zn (130 g) were used, 4 g H could be obtained, with, of course,
twice as much HCl. With 260 g. Zn, how much H could be liberated?
A proportion may be made as follows:--
Zn given : Zn required :: H given : H required.
65 : 260 :: 2 : x.
[footnote: Given, as here used, means the weight called for by the
equation; required means that called for by the question.]
Solving, we have 8 g H.
How much H is obtainable by using 5 g Zn, as in the experiment?
To avoid error in solving similar problems, the best plan is as
follows:--
Zn + 2HCl = ZnCl2 + 2 H | 65:5::2:x
65 2 | 65 x = 10
5 x | x = 10/65 = 2/13 Ans. 2/13 g.
The equation should first be written; next, the atomic or molecular
weights which you wish to use, and only those, to avoid confusion;
then, on the third line, the quantity of the substance to be used, with
underneath the substance wanted. The example above will best
how this. This plan will prevent the possibility of error. The proportion
will then be:--
a given : a required :: b given : b required.
How much Zn is required to produce 30 g. H?
Zn + 2HCl = ZnCl2 + 2H | 2:30::65:x
65 2 | 2x = 1950
x 30 | x = 975 Ans. 975 g. Zn.
Solve:--
(1) How much Zn is necessary for 14 g. H?
(2) How many pounds of Zn are necessary for 3 pounds of H?
(3) How many grams of H from 17 g. of Zn?
(4) How many tons of H from 1/2 ton of Zn?
Suppose we wish to find how much chlorhydric acid--pure gas--
will give 12 g. H. The question involves only HCl and H. Arrange
as follows:--
Zn + 2HCl = ZnCl2 + 2 H | H giv. : H req. :: HCl giv. : HCl req.
73 2 | 2 : 12 :: 73 x
x 12 | 2x=876 x=438
Ans. 438 g. HCl.
Solve:--
(1) How much HCl is needed to produce 100 g. H?
(2) How much H in 10 g. HCl?
(3) How much ZnCl2 is formed by using 50 g. HCl? The question
is now between HCl and ZnCl2.
Zn + 2HC1 = ZnCl2 + 2H
73 136 | Arrange the proportion, and solve.
50 x
Suppose we have generated H by using H2S04: the equation is
Zn + H2S04 = ZnSO4 + 2 H. There is the same relation as before
between the quantities of Zn and of H, but the H2S04 and ZnS04 are
different.
How much H2SO4 is needed to generate 12 g. H?
Zn + H2SO4 = ZnS04 + 2 H
98 2 | Make the proportion, and solve
x 12
Solve:--
(1) How much H in 200 g. H2S04?
(2) How much ZnS04 is produced from 200 g. H2S04?
(3) How much H2S04 is needed for 7 1/2 g H?
(4) How much Zn will 40 g. H2SO4 combine with?
(5) How much Fe will 40 g. H2SO4 combine with?
(6) How much H can be obtained by using 75 g Fe?
These principles apply to all reactions. Suppose, for example, we
wish to get l0 g. of O: how much KClO3 will it be necessary to use?
The reaction is:--
KClO3 = KCl + O3 | 48 : 10 :: 122.5 : x
122.5 48 |
x 10 | Ans. 25.5+ g. KClO3.
The pupil should be required to make up problems of his own,
using various reactions, and to solve them.
CHAPTER X.
CARBON.
Examine graphite, anthracite coal, bituminous coal, cannel coal,
wood, gas carbon, coke.
40. Preparation of C.
Experiment 26.--Hold a porcelain dish or a plate in the flame of
a candle, or of a Bunsen burner with the openings at the bottom
closed. After a minute examine the deposit. It is carbon, i.e.
lamp- black or soot, which is a constituent of gas, or of the
candle. Open the valve at the base of the Bunsen burner, and hold
the deposit in the flame. Does the C gradually disappear? If so,
it has been burned to CO2. C + 2 O = CO2. Is C a combustible
element?
Experiment 27.--Ignite a splinter, and observe the combustion and
the smoke, if any. Try to collect some C in the same way as
before.
With plenty of O and high enough temperature, all the C is burned
to CO2, whether in gas, candle, or wood. CO2 is an invisible gas.
The porcelain, when held in the flame, cools the C below the
point at which it burns, called the kindling-point, and hence it
is deposited. The greater part of smoke is unburned carbon.
Experiment 28.--Hold an inverted dry t.t. or receiver over the
flame of a burning candle, and look for any moisture (H2O). What
two elements are shown by these experiments to exist in the
candle? The same two are found in wood and in gas. Experiment
29.--Put into a small Hessian crucible (Fig. 18) some pieces of
wood 2 or 3 cm long, cover with sand, and heat the crucible
strongly. When smoking stops, cool the crucible, remove the
contents, and examine the charcoal. The gases have been driven
off from the wood, and the greater part of what is left is C.
Experiment 30.--Put 1 g. of sugar into a porcelain crucible, and
heat till the sugar is black. C is left. See Experiment 5. Remove
the C with a strong solution of sodium hydrate (page 208).
41. Allotropic Forms.--Carbon is peculiar in that it occurs in at
least three allotropic, i.e. different, forms, all having
different properties. These are diamond, graphite, and amorphous
--not crystalline--carbon. The latter includes charcoal, lamp-
black, bone-black, gas carbon, coke, and mineral coal. All these
forms of C have one property in common; they burn in O at a high
temperature, forming CO2. This proves that each is the element C,
though it is often mixed with some impurities.
Allotropy, or allotropism, is the quality which an element often
has of appearing under various forms, with different properties.
The forms of C are a good illustration.
42. Diamond is the purest C; but even this in burning leaves a
little ash, showing that it is not quite pure. It is a rare
mineral, found in India, South Africa, and Brazil, and is the
hardest and most highly refractive to light of all minerals.
Boron is harder. [Footnote: B, not occurring free, is not a
mineral.] When heated in the electric arc, at very high
temperatures, diamond swells and turns black. 43. Graphite, or
Plumbago, is One of the Softest Minerals.--It is black and
infusible, and oxidizes only at very high temperatures, higher
than the diamond. It contains from 95 to 98 per cent C. Graphite
is found in the oldest rock formations, in the United States and
Siberia. It is artificially formed in the iron furnace. Graphite
is employed for crucibles where great heat is required, for a
lubricant, for making metal castings, and, mixed with clay, for
lead-pencils. It is often called black-lead.
44. Amorphous Carbon comprises the following varieties.
Charcoal is made by heating wood, for a long time, out of contact
with the air. The volatile gases are thus driven off from the
wood; what is left is C, and a small quantity of mineral matter
which remains as ash when the coal is burned.
45. Lamp-black is prepared as in Experiment 26, or by igniting
turpentine (C1OH16), naphtha, and various oils, and collecting
the C of the smoke. It is used for making printers' ink, India
ink, etc. A very pure variety is obtained from natural gas.
Bone-black, or animal charcoal, is obtained by distilling bones,
i.e. by heating them in retorts into which no air is admitted.
The C is the charred residue.
Gas Carbon is formed in the retorts of the gas-house. See page
182. It is used to some extent in electrical work.
46. Coke is the residue left after distilling soft coal. It is
tolerably pure carbon, with some ash and a little volatile
matter. It burns without flame. 47. Mineral Coal is fossilized
wood or other vegetable matter. Millions of years ago trees and
other vegetation covered the earth as they do to-day. In certain
places they slowly sank, together with the land, into the
interior of the earth, were covered with sand, rock, and water,
and heated from the earth's interior. A slow distillation took
place, which drove off some of the gases, and converted vegetable
matter into coal. All the coal dug from the earth represents
vegetable life of a former period. Millions of years were
required for the transformation; but the same change is in
progress now, where peat beds are forming from turf.
Coal is found in all countries, the largest beds being in the
United States. From the nature of its formation, coal varies much
in purity.
Anthracite, or hard coal, is purest in carbon, some varieties
having from 90 to 95 per cent. This represents most complete
distillation in the earth; i.e. the gases have mostly been driven
off. It is much used in New England.
48. Bituminous, or soft coal, crocks the hands, and burns rapidly
with much flame and smoke. The greater part of the coal in the
earth is bituminous. It represents incomplete distillation.
Hence, by artificially distilling it, illuminating gas is made.
See page 180. It is far less pure C than anthracite.
49. Cannel Coal is a variety of bituminous coal which can be
ignited like a candle. This is because so many of the gases are
still left, and it shows cannel to be less pure C than bituminous
coal.
50. Lignite, Peat, Turf, etc., are still less pure varieties of
C. Construct a table of the naturally occurring forms of this
element, in the order of their purity. Carbon forms the basis of
all vegetable and animal life; it is found in many rocks, mineral
oils, asphaltum, natural gas, and in the air as CO2.
51. C a Reducing Agent.
Experiment 31.--Put into a small ignition-tube a mixture of 4 or
5 g. of powdered copper oxide (CuO), with half its bulk of
powdered charcoal. Heat strongly for ten or fifteen minutes.
Examine the contents for metallic copper. With which element of
CuO has C united? The reaction may be written: Cu0 + C = CO + Cu.
Complete and explain.
A Reducing, or Deoxidizing, Agent is a substance which takes away
oxygen from a compound. C is the most common and important
reducing agent, being used for this purpose in smelting iron and
other ores, making water-gas, etc.
An Oxidizing Agent is a substance that gives up its O to a
reducing agent. What oxidizing agent in the above experiment?
52. C a Decolorizer.
Experiment 32.--Put 3 or 4 g. of bone-black into a receiver, and
add 10 or 15 cc.of cochineal solution. Shake this thoroughly,
covering the bottle with the hand. Then pour the whole on a
filter paper, and examine the filtrate. If all the color is not
removed, filter again. What property of C is shown by this
experiment? Any other coloring solution may be tried.
The decolorizing power of charcoal is an important
characteristic. Animal charcoal is used in large quantities for
decolorizing sugar. The coloring matter is taken out mechanically
by the C, there being no chemical action. 53. C a Disinfectant.
Experiment 33.--Repeat the previous experiment, adding a solution
of H2S3 i.e. hydrogen sulphide, in water, instead of cochineal
solution. See page 120. Note whether the bad odor is removed. If
not, repeat.
Charcoal has the property of absorbing large quantities of many
gases. Ill-smelling and noxious gases are condensed in the pores
of the C; O is taken in at the same time from the air, and these
gases are there oxidized and rendered odorless and harmless. For
this reason charcoal is much used in hospitals and sick-rooms, as
a disinfectant. This property of condensing O, as well as other
gases, is shown in the experiment below.
54. C an Absorber of Gases and a Retainer of Heat.
Experiment 34.--Put a piece of phosphorus of the size of a pea,
and well dried, on a thick paper. Cover it well with bone-black,
and look for combustion after a while. O has been condensed from
the air, absorbed by the C, and thus communicated to the P. Burn
all the P at last.
VALENCE.
55. The Symbols NaCl and MgCl2 differ in two ways.--What are
they? Let us see why the atom of Mg unites with two Cl atoms,
while that of Na takes but one. If the atoms of two elements
attract each other, there must be either a general attraction all
over their surfaces, or else some one or more points of
attraction. Suppose the latter to be true, each atom must have
one or more poles or bonds of attraction, like the poles of a
magnet. Different elements differ in their number of bonds. Na
has one, which may be written graphically Na-; Cl has one, -Cl.
When Na unites with Cl, the bonds of each element balance, as
follows: Na-Cl. The element Mg, however, has two such bonds, as
Mg= or -Mg-. When Mg unites with Cl, in order to balance, or
saturate, the bonds, it is evident that two atoms of Cl must be
used, as Cl-Mg-Cl, or MgCl2.
A compound or an element, in order to exist, must have no free
bonds. In organic chemistry the exceptions to this rule are very
numerous, and, in fact, we do not know that atoms have bonds at
all; but we can best explain the phenomena by supposing them, and
for a general statement we may say that there must be no free
bonds. In binaries the bonds of each element must balance.
56. The Valence, Quantivalence, of an Element is its Combining
Power Measured by Bonds.--H, having the least number of bonds,
one, is taken as the unit. Valence has always to be taken into
account in writing the symbol of a compound. It is often written
above and after the elements [i.e. written like an exponent], as
K^I, Mg^II.
An element having a valence of one is a monad; of two, a dyad;
three, a triad; four, tetrad; five, pentad; six, hexad, etc. It
is also said to be monovalent, di- or bivalent, etc. This theory
of bonds shows why an atom cannot exist alone. It would have free
or unused bonds, and hence must combine with its fellow to form a
molecule, in case of an element as well as in that of a compound.
This is illustrated by these graphic symbols in which there are
no free bonds: H-H, O=O, N[3-bond symbol]N, C[4-bond symbol]C. A
graphic symbol shows apparent molecular structure.
After all, how do we know that there are twice as many Cl atoms
in the chloride of magnesium as in that of sodium? The compounds
have been analyzed over and over again, and have been found to
correspond to the symbols MgCl2 and NaCl. This will be better
understood after studying the chapter on atomic weights. In
writing the symbol for the union of H with O, if we take an atom
of each, the bonds do not balance, H-=O, the former having one;
the latter, two. Evidently two atoms of H are needed, as H-O-H,
or
H
= O , or H2O. In the union of Zn and O, each has two bonds;
H
hence they unite atom with atom, Zn = O, or ZnO.
Write the grapbic and the common symbols for the union of H^I and
Cl^I; of K^I and Br^I; Ag^I and O^II; Na^I and S^II; H^I and
P^III. Study valences. It will be seen that some elements have a
variable quantivalence. Sn has either 2 or 4; P has 3 or 5. It
usually varies by two for a given element, as though a pair of
bonds sometimes saturated each other;. e.g. =Sn=, a quantivalence
of 4, and |Sn=, a quantivalence of 2. There are, therefore, two
oxides of tin, SnO and SnO2, or Sn=O and O=Sn=O. Write symbols
for the two chlorides of tin; two oxides of P; two oxides of
arsenic.
The chlorides of iron are FeCl2 and Fe2Cl6. In the latter, it
might be supposed that the quantivalence of Fe is 3, but the
graphic symbol shows it to be 4. It is called a pseudo-triad, or
false triad. Cr and Al are also pseudo-triads.
Cl Cl | | Cl--Fe--Fe--Cl | | Cl Cl
Write formulae for two oxides of iron; the oxide of Al.
57. A Radical is a Group of Elements which has no separate
existence, but enters into combination like a single atom; e.g.
(NO3) in the compounds HNO3 or KNO3; (SO4) in H2SO4. In HNO3 the
radical has a valence of 1, to balance that of H, H-NO3). In
H2SO4, what is the valence of (SO4)? Give it in each of these
radicals, noting first that of the first element: K(NO3),
Na2(SO4), Na2(CO3), K(ClO3), H3(PO4), Ca3(PO4)2, Na4(SiO4).
Suppose we wish to know the symbol for calcium phosphate. Ca and
PO4 are the two parts. In H3(PO4) the radical is a triad, to
balance H3. Ca is a dyad, Ca==(P04). The least common multiple of
the bonds (2 and 3) is 6, which, divided by 2 (no. Ca bonds),
gives 3 (no. Ca atoms to be taken). 6 / 3 (no. (PO4) bonds) gives
2 (no. PO4 radicals to be taken). Hence the symbol Ca3(P04)2.
Verify this by writing graphically.
Write symbols for the union of Mg and (SO4), Na and (PO4), Zn and
(NO3), K and (NO3), K and (SO4), Mg and (PO4), Fe and (SO4) (both
valences of Fe), Fe and (NO3), taking the valences of the
radicals from HNO3, H2SO4, H3PO4.
Chapter XII.
ELECTRO-CHEMICAL RELATION OF ELEMENTS.
58. Examine untarnished pieces of iron, silver, nickel, lead,
etc.; also quartz, resin, silk, wood, paper. Notice that from the
first four light is reflected in a different way from that of the
others. This property of reflecting light is known as luster.
Metals have a metallic luster which is peculiar to themselves;
and this, for the present, may be regarded as their chief
characteristic. Are they at the positive or negative end of the
list? See page 43. How is it with the non-metals? This
arrangement has a significance in chemistry which we must now
examine. The three appended experiments show how one metal can be
withdrawn from solution by a second, this second by a third, the
third by a fourth, and so on. For expedition, three pupils can
work together for the three following experiments, each doing
one, and examining the results of the others.
59. Deposition of Silver.
Experiment 35.--Put a ten-cent Ag coin into an evaporating-dish,
and pour over it a mixture of 5 cc. HNO3 and 10 cc. H2O. Warm
till all, or nearly all, the Ag dissolves. Remove the lamp. 3 Ag
+ 4 HNO3 = 3 AgNO3 + 2 H2O + NO. Then add 10 cc. H2O, and at once
put in a short piece of Cu wire, or a cent. Leave till quite a
deposit appears, then pour off the liquid, wash the deposit
thoroughly, and remove it from the coin. See whether the metal
resembles Ag. 2 AgNO3 + Cu =?60. Deposition of Copper.
Experiment 36.--Dissolve a cent or some Cu turnings in dilute
HNO3, as in Experiment 35, and dilute the solution. 3 Cu + 8 HN09
- 3 Cu (NOA+4 H2O+2 NO.)
Then put in a clean strip of Pb, and set aside as before,
examining the deposit finally. Cu(NO3), + Pb - ?
61. Deposition of Lead.
Experiment 37.--Perform this experiment in the same manner as the
two previous ones, dissolving a small piece of Pb, and using a
strip of Zn to precipitate the Pb. 3 Pb + 8 HNO3 - 3 Pb (NO4)2 +
4 Ha0 + 2 NO. Pb (NO3) 2 + Zn = ? h.
62. Explanation. -These experiments show that Cu will replace Ag
in a solution of AgNO3, that Pb will replace and deposit Cu from
a similar compound, and that Zn will deposit Pb in the same way.
They show that the affinity of Zn for (NO3) is stronger than
either Ag, Cu, or Pb. We. express this affinity by saying that Zn
is the most positive of the four metals, while Ag is the most
nega- tive. Cu is positive to Ag, but negative to Pb and Zn.
Which of the four elements are positive to Pb, and which
negative? Mg would withdraw Zn from a similar solution, and be in
its turn withdrawn by Na. The table on page 43 is founded on this
relation. A given element is positive to every element above it
in the list, and negative to all below it.
Metals are usually classed as positive, non-metals as negative.
Each in union with O and 1=I gives rise to a very important class
of compounds,=--the negative to acids, the positive to bases.
In the following, note whether the positive or the negative
element is written first:--HCl, Na20,-As2S3, -MgBr2, Ag2S. Na2SO4
is made up of two parts, Na2 being positive, the radical SO4
negative. Like elements, radicals are either positive or
negative. In the following, separate the positive element from
the negative radical by a vertical line: Na2CO3, NaNO3, ZnSO4,
KClO3.
The most common positive radical is NH4, ammonium, as in NH4Cl.
It always deports itself as a metal. The commonest radical is the
negative OH, called hydroxyl, from hydrogen- oxygen. Take away H
from the symbol of water, H-O-H, and hydroxyl --(OH) with one
free bond is left. If an element takes the place of H, i.e.
unites with OH, the compound is called a hydrate. KOH is
potassium hydrate. Name NaOH, Ca(OH)2, NH4OH, Zn(OH)2, Al2(OH)6.
Is the first part of each symbol above positive or negative?
H has an intermediate place in the list. It is a constituent of
both acids and bases, and of the neutral substance, water.
ORDER.
--
Negative or Non-Metallic Elements.
Acid-forming with H(usually OH).
Oxygen
Sulphur
Nitrogen
Fluorine
Chlorine
Bromine
Iodine
Phosphorus
Arsenic
Carbon
Silicon
Hydrogen
Positive or Metallic Elements.
Base-forming with OH.
Gold
Platinum
Mercury
Silver
Copper
Tin
Lead
Iron
Zinc
Aluminium
Magnesium
Calcium
Sodium
Potassium
CHAPTER XIII.
ELECTROLYSIS.
The following experiment is to be performed only by the teacher,
but pupils should make drawings and explain.
63. Decomposition of Water.
Experiment 38.--Arrange "in series" two or more cells of a Bunsen
battery (Physics, page 164), [References are made in this book to
Gage's Introduction to Physical Science.] and attach the terminal
wires to an electrolytic apparatus (Fig. 19) filled with water
made slightly acid with H2SO4. Construct a diagram of the
apparatus, marking the Zn in the liquid +, since it is positive,
and the C, or other element, -. Mark the electrode attached to
the Zn -, and that attached to the C +; positive electricity at
one end of a body commonly implies negative at the other.
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