The story of the chemical elements

Preface

I have made an attempt to put forth in some kind of orderly sequence a few of the chief guiding conceptions of chemistry \ endeavouring, on the one hand, to avoid technical details, and, on the other hand, to illustrate these conceptions by describing many common facts. I have tiicd to keep the attention of the reader fixed on the great generalisations of chemistry ; and I have done my best to shew that these generalisations find constant application in the occurrences of everyday life.

M. M. PATTISON MUIR.

Cambridge, October 1896.

Contents

X. INTRODUCTION"

II. THE CHARACTER OF CHEMICAL CHANGE

III. THE CHEMIST’S CLASSIFICATION OF MATERIAL

Introduction

Anyone who observes with some care the material occurrences which are constantly taking place around him must notice, that although these events differ much from one another, very many of them have this in common that in them there is change of substance, or change of form, or change of properties. As a fire burns there is a ohange of coal, or wood, to smoke, flame, and ashes; although we see no new thing produced when coal gas is burning, yet our sense of smell helps our sense of sight, for we know that if the gas were not changed into some other thing when it is burnt we should smell the unchanged gas ; when an oil lamp is burning badly some of the substances that are formed from the oil make known *their presence by unbearable odours. From the dry and winter-stricken trees the return of spring calls forth green buds, and summer changes these to leaves, and autumn dyes those leaves in crimson, purple, and gold ; the blossoms on the fruit-trees that herald the near approach of a milder season change after a time into fruits, and on the surface of these fruits the colour deepens as under the influence of the sun new substances are produced within them ; the fields are ploughed and the seed is sown, and from these seeds corn and other kinds of grain spring up in due time, and then the pale green ears acquire a warmer hue till the waving of the golden grain tells that the time has come for this cycle of changes to be completed. Water changes to ice, and rain to hail and snow ; the mountain side that to day is dry and silent to-morrow is vocal with the sound of dashing brooks ; and the mountains themselves crumble slowly and their rocks are changed to the dust of the plains.

And if we turn to man’s dealings with material nature outside himself we shall find that it is hardly an exaggeration to say that the whole of these dealings consist in taking advantage of changes of substance, properties, or form that occur in material things without his intervention, or in accomplishing novel changes by creating conditions different from those that prevail where he does not interfere.

The timber which is used in making houses, furniture, ships, and many other things that enter into our daily lives, is one product of those complicated changes that are brought about by the growing tree in the food it obtains from the air by its leaves and from the soil by its roots. There are plants which change the substances they absorb by their roots and leaves into sugar, and when these plants are crushed and the liquid

INTRODUCTION.

ipart of the sweet juice which exudes is boiled away ssugar remains. In the living laboratories of other jplants are produced, from materials the same as, (or very like, those that the sugar-cane changes iinto sugar, dye stuffs such as madder and indigo, tor sweet-smelling resins such as frankincense ; and myrrh, or essential oils as cedarwood oil, oil of bergamot, and attar of roses, or gums as : gum tragacanth and gum arabic, or such things as guttapercha and indiarubber, or substances such as quinine, morphine, and salicylic acid that afford some relief to those who suffer pain.

Most of the substances that are used as human food are the products of changes that occur in those living organisms, plants and animals. The plants absorb comparatively simple substances from the air and the soil, and from these they build up more complex things such as starch and sugar ; plants are eaten by animals which carry further the building up processes that the plants began ; and both vegetable and animal substances are consumed by man and are changed into the highly complex materials that form the organism which is for ever synthesising itself from simpler kinds of matter, and is constantly being resolved into less complex forms of substance.

The manufacturing industries are so many examples of the intelligent direction to definite ends of changes in material things. Iron ore is brought in the blast furnace under such conditions that the red earthy stone is converted into lumps of cast iron; and when this iron is melted and air is blown into the fluid mass it undergoes another transmutation into hard, lustrous, madeable steel. Sulphur, or it may be pyrites, is burnt in a stream of air, and the suffocating gas so produced is conducted into large leaden chambers where it mixes with steam and with another reddish coloured gas from which it removes oxygen ; the product of these changes is oil of vitriol, an acrid, corrosive, liquid that is used in almost every manufacturing process.

Common salt is heated with oil of vitriol, and a mixture of the product with coal and chalk is melted in a furnace ; the black solid formed by this operation is lixiviated with water, and when the liquid is evaporated carbonate of soda is obtained. Carbonate of soda is transformed into caustic soda by boiling with milk of lime ; and when caustic soda is heated with fat, olive oil, or cottonseed oil, the products are glycerin and soap. Scrap iron is heated with pearl ash and hoofs, horns, or fragments of hides or leather ; the product is treated with water, and large, yellow, transparent crystals of yellow prussiate of potash are obtained by filtering this liquid and evaporating it. The yellow prussiate is dissolved in water and a solution of iron in an acid is added to this liquid ; the result is the deep blue pigment called Prussian blue. Sand, or finely ground quartz, is mixed with carbonate of soda, or pearlash, and the mixture is melted in pots jilaced in a very hot furnace ; when the melted mass is poured on to a flat metal table a sheet of transparent, colourless, glass is formed.

Coal tar is distilled ; a portion of the colourless liquid which distils over is mixed with aqua, fortis, and the heavy reddish oil, smelling like oil

INTRODUCTION.

oof almonds, which is produced by this treatment iis warmed for some time with iron filings and ^concentrated vinegar, and is then distilled. The (.colourless liquid that distils over is called aniline; ;iand from that liquid is produced, by suitable ttreatment, a vast number of coloured substances 'wherewith cotton, woollen, and other goods may be dyed every shade and variety of colour, both beautiful and crude.

The juice of grapes acquires new properties after being exposed to the air for a time; the i liquid loses some of its sugar, and in place thereof a volatile liquid, endowed with strange powers and potencies, is produced ; the juice of the fruit has changed into “ wine that maketh glad the heart of man.” When barley that has begun to germinate is heated to a proper temperature, and is then mashed with water, and the liquid so produced is mixed with yeast and kept slightly warm, a change occurs similar to that which happens in grape juice exposed to the air; sugar disappears, and alcohol and carbonic acid gas are formed : the decoction of malted barley has been transmuted into beer.

And what is the art of cooking but the intelligent direction of certain possible transmutations in the substance and properties of food-stuff’s so as to produce new materials that nourish the body, please the palate, and enliven the wits of man 1

The story of chemistry is the story of the unravelling of such changes and transmutations of material things as those that have been referred to in the preceding paragraphs.

the story of the

CHEMICAL ELEMENTS.

Jt was supposed in former days that anything might be changed into anything else, provided the proper conditions could be arranged. On this supposition was based the tedious art of alchemy • lor it was not on a vague guess, but on what they took to be a universal law, to wit, the infinite mutability of material things, that the longsunenng, much-enduring, alchemists rested their strange processes. Noticing the profound and unexpected transmutations that occur so frequently m things, the alchemists gave an affirmative answer to the question which these transmutations kept dinning in their ears ;-Can any material thing be changed into any other thing ? And t ion driven to seek for some stable, unchanging reality, by the innate longing of humanity for rest, the alchemists hit upon the cnticirm hypothesis of The One Thing, which they called also the Essence, the Stone of Wisdom, ‘the Blessed W ater, the Philosopher’s Stone, and many other names.

Those early readers of the story of the changes of material nature found that a language had to be constructed wherein they might express their reading of the legend ; and the fundamental conception of their rendering found expression in such sentences as these “ There abides in natuie a certain form of matter which, being discovered and brought by art to perfection* converts to itself, proportionally, all imperfect bodies that it touches.”

... For ’t were absurd To think that nature in the earth bred gold

INTRODUCTION.

Perfect in the instant ; something went before. There must be remote matter.

Nor can this remote matter suddenly Progress so from extreme unto extreme As to grow gold, and leap o’er all the means. Nature doth first beget the imperfect, then Proceeds she to the perfect.”

And, basing their work on this conception of aa perfect matter which was able to convert to i itself all imperfect bodies, the alchemists recognised that much labour was required to gain tthat perfect matter; they recognised, as one of 1 themselves stated, that “Nature moves not by 1 the theorie of men, but by their practice, and : surely wit and reason can perform no miracles unlesse the hands supplie them.” In setting their hands to supply the material conditions favourable to the movement of nature, they were convinced that nature moved in the direction they thought she ought to move in and by ways which they were able to mark out for her progress.

Many centuries passed before the investigators of nature shewed some willingness to accept their true position as parts' of the nature they sought to comprehend. Most of the earlier seekers after a knowledge of nature began by building walls each of which marked off one portion of natural occurrences from the rest. I do not suppose they built these walls consciously, rather they thought they saw walls where no barriers were. The alchemists were very busy within their intellectual sheep-pens, as the chemists of to-day are most active in the larger walled gardens of their intellectual domain ; but the alchemists made fewer breaches in their encircling barriers than we make now in ours. And I think we recognise, what our predecessors could not acknowledge, that the territorial divisions which must be established are of our own making, and are made only for the purpose of helping us to understand the infinitely complex whole.

1 he history of science may be described as the history of the breaking down, and the crumbling away, of artificially constructed barriers. All the great men of science have been famous wallbreakers. The instruments of demolition which these men wielded have been derided by the ignorant wise men who declared the walls would never fall ; the noise of the crashing barriers has travelled slowly to the ears of those who did not wish to hear, and in the vacant places solid constructions have continued to be evident to the eyes which did not desire to see.

It is worthy of remark that the central conception of the alchemists, which, nevertheless, led to their pigeon-holed representation of nature, was the unity of natural phenomena. If their arguments were translated into the language of to-day they would be somewhat as follows — Plants grow from seeds, and the plant is a very different thing from the seed ; animals become larger, stronger, and more complete as they grow older ; the plant may well be called more perfect than the seed, and the full grown animal more perfect than the immature animal ; both plants and animals grow, come to their prime, and decay ; and there are degrees of perfection in

INTRODUCTION.

ne animal and vegetable worlds. Now — we nay suppose the argument of the alchemist to ontinue — nature works in simple ways ; man is hhe crown and glory of creation, and it is foolish o suppose that man cannot understand nature , o preserve the unity of nature it is necessary iihat minerals and metals and all inanimate things hhould grow, and change, from less perfect to more perfect forms ; as there are degrees of perfectness and dignity among living things, so iiaust there be degrees of perfectness and dignity i,mong all things ; some metals disappear in acrid iquids, and these metals are generally easily worn away, they are readily melted and burnt to dross ; but some other metals are not swallowed up by corrosive liquids, nor are they worn away with ease, nor readily changed in the fire ; there ire evidently noble and base metals, perfect and imperfect metals ; and as the less perfect seed under proper conditions produces the more perfect plant, and the plant is rendered yet more rerfect by cultivation, so the imperfect metals fchange slowly into those which are more perfect, and this slow process of change can be hastened by man’s art and device.

The argument from analogy was pushed by the alchemists further than this. What they said umay be rendered somewhat in this way : — It is evident that living things are more perfect than inanimate things; if tin reforo there are changes tfrom less perfect to more perfect forms among living things, much more must changes from immature to mature forms be constantly proceeding among dead things like minerals and

B metals ; and as these minerals and metals are less perfect than plants and animals, it is probable that the plasticity of the minerals and the metals will be greater than the plasticity of living animals and living plants; hence there will not be those marked lines of demarcation in the mineral world which we find in the animal and vegetable worlds ; it will be a comparatively easy thing to grow a noble metal like gold from ignoble metals like lead or copper, although it is an impossible thing to change one kind of animal into another or one sort of plant into another j sort of plant.

A vague conception of the unity of nature of this kind led to little accurate knowledge; the ' conception could not be applied strictly and in detail to natural occurrences ; all that could be . done was to perform a vast number of inaccurate and incomplete experiments, and to state the ] results in the loose and slipshod language of the vague but sonorous hypothesis which prompted the experiments. And so although the hypothesis : postulated the unity of nature there was no unity ' in the experimental results which were collected to support the hypothesis. The resemblances ] and the dissimilarities between natural occurrences are not to be discovered by reasoning about an order of nature which exists only in the brain of the reasoner. A man who sets out to discover what is must endeavour to put aside all his notions of what ought to be ; it is only when he has gained a solid foundation of verified and accurately stated facts that he may venture to make a definite guess concerning the cause of

TIIK CHARACTER OF CHEMICAL CHANGE. 19

ne facts he lias collected, but unless lie makes eearly stated guesses — that is, scientific hypotheses— he will remain a mere collector of half ects and will never become a scientific investiutor.

We shall endeavour in the following chapters > trace the methods which chemists have used i elucidate a certain class of changes that laterial things undergo, and to state and illus- ■ate some of the more important general results aey have attained by the application of these methods.

Chapter II. The Character Of Chemical Change

i AS the changes which material things undergo cere examined with some care, a distinction tame to be made between those changes wherein Ike properties and also the composition of the matter affected are modified, and those wherein he composition of the matter is not altered, Ilthough its properties are changed.

A few simple experiments will illustrate the unore prominent differences between these two cinds of changes.

If a piece of thin, clean, iron wire is held in bhe hot, non-luminous flame of a Bunsen burner,*

* The Bunsen burner is an ordinary gas jet over which its a cylindrical metal tube pierced near the lower end with cwo large holes ; the mixture of air and gas is lighted at the iron glows and emits light. If the wire is removed from the flame after a few seconds, an examination of the wire will show that the iron has not been changed into anything else so far as can be judged by the senses of sight and touch.

When a few chips of wood are placed in a dry test tube which is then gradually heated by a Bunsen burner, the wood soon darkens in colour, and after some minutes moisture is seen forming on the upper parts of the tube, and something is given off with a very decided odour. If the heating is continued for a few minutes, and a lighted taper is then brought to the mouth of the tube, the vapours that are coming off take fire. The senses of sight and smell assure us that the wood has been changed by heating it, into things which are quite different from wood ; and this conclusion is verified by the test of the lighted taper.

If a few small pieces of sugar are heated in a dry test tube, in the same way as the chips of wood were heated in the last experiment, the sugar chars and gives off badly-smelling vapours, which ignite when a lighted taper is brought to the mouth of the tube after the heating has been continued for some minutes. The sugar is evidently destroyed, and things which are not sugar are formed in its stead.

When a few grains of dry salammoniac arc

the top of this tube. A considerable volume of air enters through the holes in the metal tube, and when the mixture of gas and air which issues from the top of the tube is ignited, the whole of the gas is completely burnt and a flame is obtained which is very hot, and is not luminous as it is free from particles of unburnt carbon.

THK CHARACTER OF CHEMICAL CHANGE 21 aaced in a dry test tube, and the lower end of I ee tube is heated very gently in the flame of a mnsen burner, the salammoniac gradually disppears from the heated part of the tube, and a lihite solid slowly forms on the upper, cool part the tube. So far as appearance goes, this lihite solid is the same as the salammoniac that ias heated ; if minute portions of the salamoniac and the white deposit are tasted they eem to be identical ; and if a little of each is mken with water both dissolve easily in the ater; moreover, if both are boiled with a little >da lye, the smell of ammonia (spirits of hartsoorn) is very perceptible in each case. The enses of sight and taste tell us that the salamtoniac was not changed into any new substance vy heating it, although it was transformed from solid to a vapour, which again became a olid when it was cooled ; and this conclusion is trengthened by the results of the tests with vater and soda lye.

So far as they go, these rough experiments ndicate that the iron remained iron when it was iaken out of the flame, and that the salammoniac vas not changed into any new thing by heating r.ntil it became a vapour, and then cooling this rapour : at the same time the iron certainly enquired a new property as long as it was kept in the hot gas-flame, for under these condiions it emitted light; and the salammoniac >assed from the solid to the gaseous state when t was heated. A change of properties was :ffected in each case, but this change was not rermanent, nor did it seem to be accompanied

2- THE 'ST0UY OF THE CHEMICAL ELEMENTS.

!’y i"?. change of composition. On the other land the senses of sight and smell assured us that both wood and sugar were changed into new things with new properties by the action of heat : in these cases change of properties was undoubtedly accompanied by change of composition : and both changes were permanent, fur the lungs produced by heating wood did not change lack into wood, nor were the things formed by heating sugar re-transformed into sugar, when the vessels m which the heatings were conducted were removed from the source of heat.

J he iron seemed to remain iron, and the salammoniac seemed to be still salammoniac But “ thinSs ai'e »ot what they seem ; ” we must have more conclusive proof.

I lie alchemists used to say that during the burning of chalk to lime, an igneous principle, or a fiery essence, passed into the chalk from the fire, and that the caustic properties of burnt lime were due to the presence in it of this igneous Principle. Why should not we also assert that the things formed by boating wood or sugar are produced by the addition to the wood or simar of a calorific principle from the heat, which prniciple remains permanently in the burnt wood or sugar? Why should not we maintain that a fiery essence passes into iron that is placed in a hot flame, but escapes when the iron is removed from the flame.

The balance has forced the chemist to throw aside the alchemical explanation, and it has enabled him to find an explanation more consistent with the facts by revealing facts which

THE CHARACTER OF CHEMICAL CHANGE. 23

were unknown to the alchemist. If any kind of matter is added to chalk during the conversion of chalk into lime in a kiln, the lime must weigh more than the chalk. But when the lime formed oy burning a weighed quantity of chalk is weighed tt is found that instead of weighing more, the lime weighs less, than the chalk from which it has been obtained. If one pound of chalk, for instance, is ■burnt to lime, rather more than half a pound of dime is produced. Some material substance — it may be more than one substance — has been taken away from the chalk in the kiln ; and lime is i chalk deprived of one, or more than one, of its constituents. Or, perhaps, the burning effected tthe removal of something from the chalk and at tthe same time caused the addition of something eelse, the net result of these two occurrences being a loss of weight.

The result of a few experiments on the change that takes place in the lime-kiln, arranged so that determinations are made of the relative ^quantities of matter concerned in this change, is tto present us with a definite subject for further i inquiry. Putting aside speculations about igneous principles and the like — reserving all speculations until we have a fixed basis of accurately ascertained quantitative facts whereon to rest our ttheories — we must seek to solve the questions 'which are directly suggested by the result of our "first application of the instrument of research which the balance-maker has put into our hands.

AY hat did the chalk lose when it was heated 1 We did not see anything leaving the chalk. Well then we must aid our sense of si"ht ; we

O y must try to arrange an experiment in such a way that if anything escapes that something may he caught, weighed, and examined. And we must also make the conditions of our experiment such that if anything combines with the chalk, during the heating of it, we shall be able to detect the removal of this somethb'g from the materials that are in contact with the chalk during the experiment. But to conduct such experiments as these means that we acquaint ourselves with the composition of chalk, and the composition of the air in contact with which the chalk is heated, and that we .know also the composition of the vessel wherein the chalk is exposed to the action of heat. A large inquiry is at once opened ; and that inquiry must lie prosecuted by accurate, that is by quantitative, experiments. We shall have to determine whether chalk has a definite composition, or whether its composition is not always the same , we must resolve chalk and lime into their components, and re-build these substances from those components, and we cannot do this without giving a very definite meaning to the words composition and components.

And as with the chalk so with the wood, the sugar, the salammoniac, and the iron. If the iron was not changed into a new thing when it was heated until it glowed, the weight of the iron before the experiment was made must be the same as the weight of the material when the experiment was finished ; and that we may positively assert that no change of composition accompanied the temporary change of properties from dull iron to a glowing, light-emitting substance,

THE CHARACTER OF CHEMICAL CHANGE. 25

, we must know definitely the composition of the rron before it was heated and after it was heated, and we must determine whether the composition ■t)f the air that surrounded the glowing iron did or did not undergo any change. Similar experiments must be made with salammoniac; the composition of the substance must be determined, and the composition of the white sublimate * which •seemed to be unchanged salammoniac must be compared with that of the salammoniac before nheating ; moreover the loss of weight suffered by the salammoniac must be determined and the vweight of the white sublimate must be found, for iif no change of composition accompanied the cchange from the solid to the gas and back to the -solid these two weights must be the same. 'Methods must also be devised and experiments conducted whereby we shall be able to determine tthc exact compositions of wood and sugar, and the compositions of the things that arc produced when > wood and sugar are heated ; and the experiments imust take into account the possibility of the removal of material things from, or the gain of such things by, the surrounding air and the vessels wherein the experiments are conducted.

It was only as chemists, and naturalists in general, recognised that quantities of matter could be measured by their weights, that they began to find a trustworthy method of examining and disentangling the transformations that matter undergoes. However strange, unexpected, and profound a change in the properties of some mate-

* A solid obtained by cooling the vapour formed by beating a solid is called a sublimate.

•2G THE STORY OE THE CHEMICAL ELEMENTS.

rial substance may be, the balance enables us to find out whether the change has or has not been accompanied by the addition to, or the removal from, the changing substance of some other kind of matter.

Imagine a box with many different things in it : let there be balls of wood of different colours ; lumps of iron, lead, copper, silver, and other metals ; pieces of suet ; parcels of tea, spices, sugar, coffee and such things ; let some of the things in the box be large, and let other things be extremely small. Let it be arranged that nothing is to be taken from the box, nor is anything to lie brought into the box, from outside. Let there be two people. One of these examines an object in the box, say a parcel of tea ; he then turns his back, while the other person either takes out some of the contents of the parcel of tea, or mixes other things with the tea in the parcel, or does both of these, or does not alter the contents of the parcel but dashes a coat of paint over the outside of it ; the first person has then to determine which of the four processes has taken place. It is evident that a couple of weighings would help towards the solution of the problem but would not suffice to solve it. If the parcel weighs the same after the process as before the process, either nothing has been taken out, or if anything has been removed an equal weight of something else (or of some other things) has been put into the parcel. If the parcel weighs less at the end, than it did at the beginning, of the experiment, something has been taken out of it ; but something may also have been put in, pro-