The fundamental principles of chemistry : practically taught, by a new method

Front matter

(itoxmll ^Ettibersits iLitratg.

THE GIFT OF

LONGMANS, GREEN & CO.,

Chapter I

MATTER — STATE OF AGGREGATION OF BODIES — PHYSICAL PROPERTIES OF BODIES — EXPERIMENTS — MOLECULAR FORCES — COLLECTING AND STORING GASES— FITTING UP CHEMICAL APPARATUS — QUESTIONS.

I. Those who take up this book with the intention of studying it, will, no doubt, have heard the word matter employed in conversation, and they will also have without doubt met with it in some of the books they have read ; and most probably they themselves will have used it both in conversation and in writing ; they must therefore have attached some meaning to this important word, for it is a very important word, especially for what it signifies in Natural Science. I wish those studying this book to reflect for a few moments before going further as to the meaning they attached to it when they or others employed it. Like many other words it is employed both in ordinary and scientific language. The following are a few of its meanings in ordinary language, and they are given in order to impress on the young student, that whilst a word has many different significations in ordinary language, it has one, and only one, in the particular department of science in which it is employed as a scientific term ; hence one word cannot be substituted for another in scientific, as it frequently can in ordinary, language to convey the same idea ; just as, for instance, if we speak of any tool, say a spade, hammer, &c., we cannot substitute any other word for the word spade or hammer,

B as no other word would convey to other minds the particular tool we meant. The student will, we hope, gather from these marks the imperative necessity of learning, in order to become acquainted with a science, the exact and precise meaning of every scientific word and phrase employed.

2. The following are a few of the meanings of the word ' matter' as given in dictionaries : —

I. The contents of any speech or writing; the thing said ; the meaning ; sense. (2) Good sense ; substance, as opposed to empty verbosity or frivolous jesting. 'To speak all mirth and no matter.' (3) Subject; thing treated ; that about which we write or speak. (4) Affair ; business ; event; course of things; as 'Mattershave succeeded well thus far'; 'Observe how matters stand ' ; ' Thus the matter rests at present ' ; ' Thus the matter ended.' (5) In logic that which forms the subject of any mental operation, as distinguished from the form. (6) Body ; substance extended ; anything perceptible by any of the senses ; that of which the whole sensible universe is composed.

3. The last meaning is the only one in which it is used in Natural Science, or, in other words, when its meaning is confined to the Material World. For when employed in Natural Science it includes, but is restricted to, everything which possesses weight and occupies space ; these are termed the essential properties of matter, since they suffice to define it.

4. A young child knows from observation that all matter is not of the same kind, but that there are many different kinds; there are, for example, gold, silver, iron, copper, sulphur, common salt, chalk, and a very large number of other kinds of matter. Now each of these different kinds of matter is termed a substance or body ; and each substance exists in one or other of the three states of aggregation in which matter can exist, viz. the solid, the liquid, and the gaseous state ; some substances exist naturally in only one of these states, as, for example, gold, silvfer, or iron in the solid state ; but most of them, and perhaps all of them, can be made to pass into one or both of the other states in which they do not naturally exist, by the application of heat, cold (diminution of heat), or pressure ; or by a combination of pressure and one of the other two agents, as we shall learn further on. Water, for example, exists naturally in all the three states ; in all climates it exists in the liquid state ; and in all climates it exists in the gaseous or vaporous state in the air ; and in the Arctic regions, and in temperate climates

Law of Gravitation 3

in winter, it exists in the solid state as ice and snow. Some of the water in the gaseous state in the air passes, or becomes converted, into one of the other two states of aggregation, owing to a diminution of temperature in the atmosphere; it then appears in the form of dew, or comes down to the earth in the form of rain — the liquid state, or of hail or snow — the solid state.

5. It has already been stated that all substances, whether existing in the solid, the liquid, or the gaseous state, occupy a certain space ; the amount of space a substance occupies is termed its volume.

6. Every particle of matter attracts every other particle of matter, whether the matter exists in the solid, the liquid, or the gaseous state, not only in the world we dwell in, but throughout the entire universe ; this attraction is called the Law of Gravitation. This force or attraction operates at the greatest conceivable distances, and is common, as we have stated, to the three forms of matter, and as each particle attracts, the mass containing the greatest number of particles must consequently exert the greatest attractive force ; hence it is that all bodies, with the exception of the celestial ones, when at some distance from the earth's surface and unsupported, fall or descend to it. One of the effects of this attraction is the downward pressure which substances exert on whatever supports or prevents them from falling to the earth ; this pressure is termed their ■weight.

7. The word ' particle ' which has been employed has several different meanings in ordinary language, but it is only necessary to give the one which corresponds with its scientific meaning, viz. 'a minute part or portion of matter, the aggregation of which parts constitutes the whole mass ; ' this corresponds with its scientific meaning, for the smallest portion of matter which is mechanically divisible is termed a particle. But it is believed by scientific men that there are more minute portions of matter than particles ; these minute portions are indivisible ; the largest of these mechanically indivisible portions are termed molecules ; the molecules are chemically divisible; the still smaller portions, which are both mechanically and chemically indivisible, are termed atoms.

8. Before going further we must inform the student that the terms particle and molecule have been used indiscriminately, and in some scientific works at the present time the word particle is sometimes used in place of the word molecule ; but in this work the two words have separate and distinct meanings; particle being employed to signify the smallest portion of matter that is mechanically divisible ; molecule the smallest 'portion which can exist in the free slate, and which is mechanically indivisible but chemically divisible.

9. It will be evident to the student from what has been stated that the minutest particle is an aggregation of molecules, as a mass of matter is an aggregation of particles. Science cannot at present inform us how many molecules are required to form the minutest particle ; but, to form an idea of the size of molecules, Sir William Thompson gives this illustration. Imagine a drop of rain, or a glass sphere the size of a pea, magnified to the size of the earth, the molecules in it being increased in the same proportion ; the magnified structure would be coarser-grained than a heap of small shot, but probably less coarse-grained than a heap of cricket-balls. The number of molecules of gas in a cubic centimetre (0-06103 cubic inch) of air is calculated at twenty-one trillions. Molecules and atoms are treated of in a subsequent chapter.

10. We will here cite a few examples to show to what an almost incredible extent matter admits of being subdivided ; and the minuteness of some organised bodies.

1. ' WoUaston succeeded in obtaining threads of platinum of a diameter not exceeding 3pn^,)„„ of an inch. The method which he employed for preparing them consisted in drawing a silver wire with a platinum core, and dissolving the shell of silver in nitric acid. In this way threads can be obtained so fine that they are actually invisible to direct view ; their existence can only be detected by the aid of certain special optical phenomena. In the art of beating gold, leaves are obtained whose thickness cannot exceed 55^55 of an inch. A square inch of this leaf would weigh less than the jjjljg of an ounce, and as a square whose side is jL of an inch is visible to the naked eye, it follows that this square inch of leaf contains more than 60,000 visible parts.'

2. ' According to Biot, the thread by which a spider lets itself down is composed of more than 6,000 single threads. But more surprising than all is the microcosm of organised nature in the infusoria. Of these creatures, which for the most part we can see only by the aid of the microscope, there exist many species so small that millions piled on each other would not equal a single grain of sand, and thousands might swim at once through the

Divisibility of Matter 5

eye of the finest needle. The coats-of-mail and shells of these animalcules exist in such prodigious quantities on our earth that, according to Ehrenberg's investigations, pretty extensive strata of rocks, as, for instance, the smooth slate near Belin, in Bohemia, consist almost entirely of them. By microscopic measurements, one cubic inch of this slate contains about 41,000 millions of these animals. Since a cubic inch of this slate weighs 220 grains, 187 millions of these shells must go to a grain, each of which would consequently weigh about the j|ymillionth part of a grain. Conceive further that each of these animalcules, as microscopic investigations have proved, has its limbs, entrails, etc. , the possibility vanishes of our forming the most remote conception of the dimensions of these organic forms.

3. 'The two following examples show that when substances evade the perception of our sight and touch, our olfactory nerves frequently detect the presence of matter in the atmosphere, of which no chemical analysis could afford us the slightest intimation.

4. ' It is well known that a grain of musk will continue for years to supply the air, which is continually being renewed around it, with a sufficient number of particles to communicate to it its odour ; and papers laid near musk may be conveyed to the East Indies and back without losing the smell. The mind cannot form an idea of the number of f articles which must volatilise from the musk every second, in order to render the scent perceptible in all directions ; and not only of their number, but also of their minuteness. In like manner a single drop of oil of lavender evaporated in a spoon over a lamp, fills a large room with its fragrance for a length of time. '

11. These and numerous other examples, which might be given, would, if there were no opposing facts, lead us to believe that matter can be infinitely divided ; but our present interpretation of chemical phenomena leads us to assume that there is a limit, as we have previously stated, and shall more fully explain further on, to the division of matter.

12. When particles cohere together then, as has been stated, a mass of matter is formed ; and the more numerous the particles cohering, the larger, of course, the volume of the mass ; a piece of lump sugar, for example, is an aggregation of a number of particles of that substance. In some substances the particles are, as it were, indiscriminately united ; in other substances they are arranged in a crystalline form, as seen in sugar, alum, epsom salts, &c.

13. The particles cohere together in different solid substances with very different degrees of attractive force ; some solids, for instance, are very easily pulverised, that is their particles are very easily separated ; other solids, on the contrary, resist pulverisation by ordinary means. The particles of the substances employed as building materials, as stone, iron, &c., are united very firmly together ; hence the great strength of these substances ; and this is the case with all solids whose particles are, like the solids named, firmly bound together. We may here state, what has already been implied, that each particle of a pulverised body possesses the same properties or qualities as the entire mass did before pulverisation.

14. In some cases if the parts of the same substance which have been divided are brought into very intimate contact they will unite ; thus on pressing together two clean, smooth, and freshly cut surfaces of lead, they cohere, and a force of some pounds is required to separate them. In the same way, two perfectly polished plates of glass cohere, sometimes so completely that they may be cut and worked as a single piece. This has not unfrequently happened in plate-glass manufactories. No doubt two pieces of all substances might be made to cohere, as lead does, if they could be brought into sufficiently intimate contact. When it is desired to unite two pieces of a metal like iron, which cannot be made to unite by simply pressing them together, the cohesion between the particles of each piece is first weakened by heating them ; the consequence is they become quite soft, and can be readily bent ; when they are pressed or hammered together in this state they cohere and form one piece ; this operation is termed ■welding.

15. However compact a substance in the solid state may appear, its molecules are not in actual contact, there are spaces or pores, as the spaces are termed, between the molecules. The Florentine Academicians in 166 1 proved the existence of pores between the molecules of so compact a solid as gold ; they proved this by filling a thiri globe of gold with water, and after hermetically sealing its orifice subjected the globe to pressure ; the result was, that the water was forced through the pores of the gold, and appeared in the form of dew, on the outer surface of the globe. In the building of the Britannia bridge it was also found that the water used in the enormous hydrostatic presses employed to raise the tube, was freely forced through the pores of the thick iron cylinders of the press. '

I ' No decisive proof of the porosity of vitreous bodies, such as glass, seems yet to have been obtained. That they form almost a solitary class of excep-

■Experiments on Porosity 7

16. There are two kinds of pores, viz., sensible pores and physical pores ; the sensible pores are apparent to the eye, either alone or aided by the microscope. Filtration is an application or utilisation of the porosity of certain substances, as paper, woven fabrics, stones, &c. ; the sensible pores of these substances are sufficiently large to allow liquids to pass through them, but small enough to arrest the passage of solid particles which may be suspended in the liquid.

17. The physical pores are not apparent to the sight, and are the spaces or intervals between the molecules.

18. The space between the molecules can be diminished to a greater or less extent, in other words the molecules can be forced nearer to each other by the action of external pressure. This property is called compressibility, and is both a consequence and a proof of their porosity.

Experiments on Porosity.

1. Immerse a piece of chalk in water, air-bubbles will at once begin to ascend to the surface of the liquid, in consequence of the water displacing the air in the pores of the chalk.

2. Pour some water on a piece of marble ; the water will rest on the surface, it will not enter into the pores, unless great pressure is used and for a sufficient length of time. Yet chalk and marble are formed of the same constituents ; they differ only in their physical properties ; and this difference is chiefly, if not entirely, due to the cohesiveness being less between the particles of the chalk than between the particles of the marble, and therefore the greater porosity of the former than of the latter substance.

19. Different liquids possess different degrees of facility for penetrating the pores of solid bodies ; for instance, if pohshed marble is wetted with water very little, if any, enters its pores, while oil, on the contrary, is rapidly absorbed by it ; and a bag of cambric or gauze, whose pores are visible to the eye, holds mercury securely, until sufficient pressure is applied to force out the liquid.

20. As filtration is in constant use in chemical laboratories, and as it is also a utilisation of the porosity of substances, we will now describe the operation, and illustrate it with experiments. Filtration is employed for separating liquids from

tions to an otherwise general rule seems highly, improbable. It is most likely that vitreous bodies have not yet been proved to be porous only because we have not yet discovered the proper mode of testing them for this property.

solids, and usually is accomplished by passing the mixture of solid and liquid matter through filtering paper (a paper made for the purpose) of proper size and shape, supported in a funnel. The pores of the paper permit the fluid, and the solids dissolved in it, to pass, whilst the undissolved solid matter being unable to pass through the pores, remains behind on the filter. Sometimes, however, the undissolved solid matter is in such a finely divided state that the filter does not at first intercept all the solid particles, some portion passing through the pores of the filter ; in such cases the imperfectly filtered portion must be returned to the filter until it becomes perfectly bright and clear.

21. If any coloured solid dissolves in the liquid the liquid, even when perfectly filtered, will not be colourless, but coloured.

22. To prepare a filter, cut the filtering paper in circular form, and fold it so as to form a half-circle, and then again fold it at right angles to the first fold (fig. i) ; the paper ought to fall wholly within the funnel (fig. 2). The paper, when placed within the funnel, must be mois-

FlG. I.

tened with water, and then the liquid to be' filtered must be gradually poured on. The funnel is supported in one of the rings of the retort-stand (fig. 2).

23. The liquid which passes through the filter is called the filtrate. When the solid particles are very heavy, the supernatant liquid can be separated from the solid, without passing it through a filter. This is accomplished by simply inclining the

COHBSIOM 9

vessel, so as to allow the fluid to pass away unattended by the ' undissolved solid '; this is called decantation; or the fluid may be removed by a syphon.

Experiments on Filtration.

3. Mix some powdered chalk with water ; then pass the mixture through a filter ; if the filtrate comes through turbid at Srst (not clear), return it to the filter as often as is necessary to obtain it perfectly clear and bright.

4. Mix some soil with water ; a portion of the soil will dissolve in the water, and a portion will remain undissolved ; subsequently filter the solution ; the filtrate will most probably be coloured, on account of some of the coloured components of the soil having dissolved in the water.

24. We have yet to mention a remarkable class of illustrations proving the porosity of solid bodies. Not only can gases pass through unglazed pottery, but hydrogen, the lightest of known gases, can pass through platinum and iron when they are red-hot ; but we must reserve any further remarks on the passage of gases through metallic and non-metallic septa until we treat on the motion of gases in Part II.

25. The cohesive attraction between the molecules of substanfces varies not only in different substances, that is in substances of unlike constituents, but also, as shown by Expt. 2, in some substances composed of- the same constituents ; and an alteration in the molecular attraction can in some solids be produced by artificial means, the difference in the mechanical properties of tempered and untempered steel, for example, is owing to the difference in the molecular attractions produced by the tempering.

26. It is owing to a natural difference in the molecular attraction in some solids, and to the alteration which can be effected in the molecular arrangement in others by the action of physical agents, that solids vary, or can be made to vary, in the properties of hardness, tenacity, ductility, and malleability. Silver, gold, and platinum, which are the most ductile and malleable of the metals, can be drawn out into the form of wire, or beaten out in the form of thin leaves to an almost inconceivable extent without any rupture or breach of continuity between the molecules taking place. Platinum, which is the most ductile of metals, has been drawn out into wire so fine that it was only o'oooo3 of an inch in diameter ; and gold, lo Fundamental Principles of Chemistry

which is the most malleable of metals, has been beaten into leaves so fine that they were only about jj^^th of an inch thick.

27. Ductility and malleability are not the same property or quality ; for the same metals are not always both ductile and malleable, or do not at least possess these properties in an equal degree. Iron possesses ductility in a much greater degree than it possesses malleability ; for it admits of being drawn into extremely fine wire, though it cannot be beaten into extremely thin plates. Tin and lead, on the other hand, are highly malleable ; they can be beaten into extremely thin leaves ; but they are not ductile, since they cannot be drawn into fine wire.

28. A property the very opposite of malleability and ductility is brittleness ; the molecules of brittle substances do not, as in malleable and ductile solids, admit of any very considerable displacement without losing their cohesiveness ; in other words a brittle substance cannot be nmch altered in form without breaking.

29. We must now explain the meaning of the word properties we have been employing. By the term properties, as applied to bodies, we understand the different ways in which bodies present themselves to our senses, and we distinguish general from specific properties. The former are shared by all bodies, and among the most important are impenetrability, extension, divisibility, porosity, compressibility, elasticity, mobility, and inertia.

30. Specific properties are such as are observed in certain bodies only, or in certain states of these bodies ; such are solidity, fluidity, tenacity, ductility, malleability, hardness, transparency, colour, &'c.

31. We have so far, in speaking of the cohesion of the molecules of bodies, confined and limited our descriptions and illustrations to solid bodies ; we have now to notice how far this attraction between the molecules of the same substances operates in bodies that are liquid, and in bodies thait are gaseous at ordinary temperatures.

32. As regards the particles of liquids, they have, as compared with those of solids, no fixed position, on account of the less cohesive attraction between them ; hence they glide or pass over each other with the greatest ease, being displaced by

Cohesion i i

the slightest force ; liquid bodies on this account are capable of assuming the shape of any vessel in which they are placed. But there is nevertheless a greater or less cohesion between the molecules of liquids, which causes them to be more or less viscous. But the cohesive power between the molecules of liquids is more strikingly shown in the rounded form assumed by detached drops ; this is very beautifully exemplified in raindrops as they fall through the air, and in drops of dew ; in these small masses, water, as is seen, assumes the spheroidal shape.

33. The difference in the form assumed by large and small masses of liquids is thus explained — in large masses the force of gravity overcomes the cohesive force ; hence liquids acted upon by the former force have no specia.1 shape ; they take that of the vessel in which they are contained ; and the free surface of the liquid is a horizontal plane perpendicular to the force of gravity. But in smaller masses cohesion overcomes the force of gravity, and therefore in minute masses liquids assume the spherical or globular form.

Experunents Illustrating the Tendency of Liquids in Small Masses to Assume the Spherical Form.

5. Introduce by means of a pipette (fig. 3) a drop of oil into the middle of some alcohol which has been diluted with water to precisely the same specific gravity as the oil ; the two liquids will not mix with or dissolve each other, but the oil will remain suspended in the diluted alcohol in the form of a perfectly spherical mass.

6. Pour into a narrow-necked bottle a saturated solution of zinc sulphate, add a few drops of carbon disulphide, coloured by some iodine dissolved, which will float on the surface of the zinc solution.. Then carefully add some distilled water so as to make it rest on the surface of the zinc solution and not mix with it ; the carbon disulphide will, if these conditions have been obtained, collect in the form of a flattened spheroid, presenting the appearance of blown coloured glass, and will be larger than the neck of the bottle if a sufficient quantity of the carbon compound has been employed.

34. The Florentine Academicians made the experiment which has already been described (par. 15) not for ascertaining whether solids were or were not porous ; but whether liquids were or were not compressible; the liquid they operated upon, as already

stated, was water. As the globe was completely filled with water, any pressure on it they expected would, by altering its shape and diminishing its capacity, either compress the liquid, if it were compressible, or, if it were incompressible, would burst the globe. Neither of these expected results occurred ; but, contrary to the expectations of the experimenters, the experiment proved that gold was porous.

35. The Academicians inferred, from the results of the experiment, that water was not compressible, and this opinion was accepted as correct for some time afterwards ; but later researches have proved that all liquids are compressible, but only to a slight degree as compared with either solids or gases. Thus, for a pressure equal to that of the atmosphere — 15 lbs. per square inch— mercury experiences a compression of o'ooooog part of its original volume, water a compression of 0-00005, and ether a compression of 0-000133. The compressibihty of Hquids is, however, greater the higher their temperature ; thus that of ether at 14 °C. is one-fourth greater than its compressibility at 0° C. The apparatus employed for measuring the compressibility of liquid is named the piezometer, the term being derived from two Greek words, one signifying ' I compress,' and the other 'measure.'

36. As liquids are compressible their molecules, as in the case of solids, are not in actual contact, but are separated by spaces termed pores. The pores in liquids are not so obvious as they are in many solids, but it is none the less certain that they exist in liquids as in solids ; this is proved not only from their being compressible ; but also from the fact that two liquids that can mix together will, when added together, ■ often occupy a less volume than the two occupied before being mixed.

Experiment on the Porosity of Liquids.

7. Half-fill with water a glass bottle, in shape like the specific gravity bottle (fig. 47), and fitted with a ground stopper, then pour some alcohol carefully down the inside of the vessel, so as not to mix the two liquids. The bottle should be so filled that a few drops of alcohol are pushed out when the stopper is inserted ; this must be done in such a careful manner that no air-bubbles enter the bottle. Raise the bottle between the thumb and fingers, press the forefinger firmly on the stopper, and then invert the bottle several times so as to mix the two liquids together. When they are thoroughly mixed, it will be seen, on placing the bottle on the table, that

Elasticity, Ductility, and Malleability 13

the volume of the mixed liquids is less than they occupied before they were mixed, hence proving their porosity. The same phenomenon may be observed in mixing many other liquids. If the water is coloured red with a solution of aniline-red (magenta), it will be seen whether the alcohol has been successfully introduced into the bottle.

37. When the external compressing force is removed, liquids always regain exactly their original volume. Bodies which recover their original form perfectly on the removal of the external pressure are said to be perfectly elastic under compression ; if they only partially recover their original shape, their elasticity is said to be imperfect, and they remain distorted permanently. All liquids and gases are perfectly elastic, but no solid is perfectly elastic, this property being always confined in sohds within certain limits. Imperfect elasticity gives rise to the remarkable properties of ductility and malleability in some solids, properties we have already noticed.