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Title: An Introduction to Chemical Science
Author: R.P. Williams
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Project Gutenberg Etext of An Introduction to Chemical Science
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This etext was produced by John Mamoun <[email protected]> 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;
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, 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
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
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.
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
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?