Discoveries and Inventions of the Nineteenth Century

by Robert Routledge

“Iron and coal,” it has been well said, “are kings of the earth”; and this is true to such an extent that there is scarcely an invention claiming the reader’s attention in this book but what involves the indispensable use of these materials. Again, in their production on the large scale it will be seen that there is a mutual dependence, and that this is made possible only by means of the invention we have begun with; for without the steam engine the deep coal mines could not have the water pumped out of them,—it was indeed for this very purpose that the steam engine was originally contrived,—nor could the coal be efficiently raised without steam power. Before the steam engine came into use iron could not be produced or worked to anything like the extent attained even in the middle of the nineteenth century, for only by steam power could the blast be made effective and the rolling mill do its work. On the other hand, the steam engine required iron for its own construction, and this at once caused a notable increase in the demand for the metal. Once more, the engine itself supplies no force; for without the fuel which raises steam from the water in the boiler it is motionless and powerless, and that fuel is practically coal. In consequence of thus providing power, and also of supplying a requisite for the production of iron, coal has acquired supreme industrial importance, so that all our great trades and places of densest population are situated in or near coal-fields. But what we have further to say about coal may be conveniently deferred to a subsequent article, while we proceed to treat of iron, and of the contrivances in which it plays an essential part.

Iron has also been called “the mainspring of civilization,” and the significance of the phrase is obvious enough when we consider the enormous number and infinite variety of the things that are made of it: the sword and the ploughshare; all our weapons of war and all our implements of peace; the slender needle and the girders that span wide rivers; the delicate hair-spring of the tiny watch and the most tenacious of cables; the common utensils of domestic life and the huge battle-ships of our fleets; the smoothest roads, the loftiest towers, the most spacious pleasure palaces. Such extensive applications of iron for purposes so diverse have been rendered possible only by the greater facility and cheapness of production, together with the better knowledge of the properties of the substance and increased skill in its treatment, that have particularly distinguished our century. Apart again from the constructive uses of iron, it enters essentially into another class of inventions of which the age is justly proud, namely, those which utilize electricity in the production of light, mechanical power, and chemical action; for it is on a quality possessed by iron, and by iron alone, that the generation of current by the electric dynamo ultimately depends. This peculiar property of iron, which was first announced by Arago in 1820, and has since proved so fertile in practical applications, is that a bar of the metal can, under suitable conditions, be instantly converted into the most powerful of magnets, and as quickly demagnetized. What these conditions are will be explained when we come to treat of electricity.

Fig. 16.—Aerolite in the British Museum.

Besides the unique property of iron just referred to, and its superlative utility in arts and industries, there are other circumstances that give a peculiar interest to this metal. It is the chief constituent of many minerals, and traces or small quantities are found in most of the materials that make up the crust of the earth; it is present also in the organic kingdoms, being especially notable in the blood of vertebrate (back-boned) animals, of which it is an essential component. Notwithstanding its wide diffusion, iron is not found native, that is, as metal, but has to be extracted from its ores, which are usually dull stony-looking substances, as unlike the metal as can be conceived. In this respect it differs from gold, which is not met in any other than the metallic state, in the form of nuggets, minute crystals or branching filaments, and from metals such as silver, copper, and a few others which also are occasionally found native. It is true that rarely small quantities of metallic iron have been met with in the form of minute grains disseminated in volcanic rocks; but in contrast with the practical absence of metallic iron from terrestrial accessible materials is the fact that masses of iron, sometimes of nearly pure metal, occasionally descend upon the earth from interplanetary space. These are aerolites, of which there are several varieties, some consisting only of crystalline minerals without any metallic iron, others of a mixture of minerals and metals, but the most common are of iron, always alloyed with a small quantity of nickel, and usually containing also traces more or less of a few other metals and known chemical elements. The iron in some specimens has been found to amount to 93 per cent. of the whole. These aerolites, or meteorites, as they are also called, are of irregular shape and vary greatly in size, which however is sometimes very considerable: one found in South America was calculated to weigh 14 tons, another discovered in Mexico, 20 tons. There is in the British Museum a good specimen of an iron meteorite, which is represented in Fig. [16], where it will be observed that a portion has been cut off to form a plane surface, which when polished and etched by an acid, reveals a crystalline structure quite peculiar and distinctive, so that such meteorites can be recognized with certainty, even if they did not possess surface characters which are easily observed and identified when once a specimen has been examined. The fall of meteorites to the surface of the earth is comparatively rare, but it has been witnessed by even scientific observers; as when Gassendi, the French astronomer, saw in Provence the fall of a meteorite weighing 59 lbs. In the Transactions of the Royal Society for 1802 may be found a detailed account of an instance in England of the fall which took place in Yorkshire, on the 13th December 1795, of a stone 56 lbs. in weight. Aerolites become ignited or incandescent by reason of the great velocity with which they pass through the atmosphere, whereby the air in front of them is condensed and heated, the heat often being sufficient to liquefy or even vaporize the solid matter. The so-called shooting stars are with good reason believed to be nothing but such incandescent aerolites, and the aerolites themselves are regarded as small asteroids, or scattered planetary dust, portions of which occasionally coming within the sphere of the earth’s attraction are drawn to its surface. Meteoric iron is too rare to be of any value as a source of iron, but certain specimens have been found in which the metal was malleable and of excellent quality. From such meteorites the natives of India and other places have, it is said, sometimes forged weapons of wonderful temper and keenness, and we may well imagine that when such weapons have been made from iron that had actually been observed to fall from the sky, they would be regarded as endowed with magical powers, so that we may perhaps ascribe to such circumstances the origin of some of the legends about enchanted swords, etc. It is significant also that in some Egyptian inscriptions of the very highest antiquity, the word indicating iron has for its literal meaning stone of the sky.

But as nature has hardly provided man with the metal iron, he has been obliged to find the art of extracting it from substances which are utterly unlike the metal itself. In this case, as in many others, the art has been discovered and practised ages before any scientific knowledge of the nature of the processes employed had been acquired. The idea prevails that there are such difficulties in extracting this metal; that elaborate and complex appliances, not unlike those in use in modern times, were requisite for the purpose; and therefore that the use of iron is compatible only with a somewhat late period in man’s history, and implies a comparatively advanced stage of civilization. Now there undoubtedly are facts which tend to confirm this view; for instance, the Spaniards who first colonized North America found the natives perfectly familiar with the use of copper, but without any acquaintance with iron, although the region abounded with the finest ferruginous minerals; and, again, the archæologists who have examined the relics of ancient civilizations and of pre-historic peoples about the shores of the Mediterranean, find in the earliest of these relics weapons and implements of rudely chipped stones, followed later by the use of better-shaped and polished stones; hence the periods represented by these, they have respectively designated by the terms palæolithic and neolithic—the old and the new stone ages. At some later time the stone of these implements was gradually replaced by bronze, which is a mixture of copper and tin, while as yet iron does not occur in any form among the remains. In the latest layers, however, articles of iron are found, and it is inferred that this metal came into use only after bronze had been known for an indefinite period; hence these later pre-historic periods have come to be respectively called the bronze age and the iron age. No doubt this succession really occurred in the localities where the observations were made, but it would not be justifiable to assume that the same was the case in every part of the world, for much would depend on such circumstances as the presence or absence of the essential minerals. We may also set against the supposed difficulty of obtaining iron from the ores, the still greater complexity of the methods required for the production of copper and of tin. Besides this is the fact that the ores of tin are found but in very few places in the world, and of these only the Cornwall mines, so well known in ancient times, would be likely to furnish a supply to the places where pre-historic bronzes are found; this implies that navigation and commerce must have already made considerable progress. On the other hand, iron has been produced and worked for untold ages by the negro races all over Central Africa, and the method of treating the ore has no doubt been that which is there still practised by certain scarcely civilized tribes, and it is as simple as any metallurgical operation can possibly be, requiring merely a hole dug in a clay bank, wherein the fuel and minerals are piled up, and the mere wind supplies sufficient blast to urge the fire to the needful temperature, or air is blown in from rude bellows made of a pair of skins alternately raised and compressed. These very primitive furnaces have in some places developed into permanent clay structures, seven or eight feet in height. The natives of Central Africa have therefore long known the method of extracting iron, as well as of forging and casting it.

The nature and value of what has been done during the century in the treatment of iron would not be intelligible without some description of the ordinary processes of extracting the metal from the ores; and a scientific understanding of these implies some acquaintance with chemistry. Not because metallurgy has been developed from chemistry, for the fact is rather the reverse; indeed, as we have seen, the art of extracting iron from its ores was practised ages before chemistry as a science was dreamt of. Although we may assume that many of our readers have sufficient knowledge of chemistry to attach distinct ideas to such few chemical terms as we shall have occasion to use, yet it may be of advantage to others to have some preliminary notes of the character of the chemical actions, and of some properties of the substances that will have to be referred to. It is certainly the case that people in general, and even people very well informed in other subjects, have but the vaguest notions of the nature of chemical actions, and of the meaning of the terms belonging to that science. For example, one of our most popular and justly esteemed writers, treating of the very subject of iron extraction, calls the ore a matrix, thereby implying that the iron as metal is disseminated in detached fragments throughout the mass, which is a conception inconsistent with the facts. The reader will be in a more advantageous position for understanding the relation of the ores of iron to the metal, if he will follow in imagination, or still better in reality, a few observations and experiments like the following—of which, however, he is recommended not to attempt the chemical part unless he is himself practically familiar with the performance of chemical operations, or can obtain the personal assistance of someone who is. Taking, say, a few common iron nails, let him note some obvious properties they possess: they have weight—are hard and tough so that they cannot be crushed in a mortar—are opaque to light—if a smooth surface be produced on any part, it will show that peculiar shiny appearance which is called metallic lustre, in this case without any decided colour—they are not dissolved by water as sugar or salt is—and are attracted by a magnet. If several of the nails be heated to bright redness they may be hammered on an anvil into one mass, and this may be flattened out into a thin plate, or it may be shaped into a slender rod and then drawn out into wire; or otherwise the nails may be converted into the small fragments called iron filings. In these several forms the nails, as nails, will have ceased to exist; but the material of which they were formed will remain unchanged, and each and every part of it however large or small will continue to exhibit all the properties noted above as belonging to the substance of the nails, which in the cases supposed has undergone merely physical change of shape. Treating our nails in yet another way, we may proceed to subject them to a chemical change, by an experiment very simple in itself, but involving certain precautions, by neglect of which the tyro in chemical operations would incur some personal risks; these might however be obviated by using only very small quantities of the materials (a mere pinch of iron filings and a few drops of sulphuric acid), when the results would still be sufficiently observable. A few of the iron nails having been placed in a flask of thin glass, we pour upon them a mixture of oil of vitriol (sulphuric acid) and water, which has previously been prepared by gradually adding 1 measure of the acid to 5 measures of water. The action that takes place is greatly accelerated by heat, and indeed the contents should be heated to boiling by standing the flask on a layer of fine sand spread on an iron plate and gently heated from below. The nails will soon disappear, being completely dissolved by the acid liquid, and the turbid solution should be filtered through filtering paper as rapidly as possible and while still hot. This turbid and dirty looking condition is due to foreign matters in the nails, for these never consist of pure iron. The filtered liquid is set aside to cool in a closed vessel, in which after a time will be found a deposit of crystals of a pale bluish-green colour. The liquor above these having been poured off, the crystals are to be rinsed with a very small quantity of cold water, and then dried between folds of blotting-paper, after which they are ready for examination. The quantity of the diluted acid put into the flask should have a certain proportion to the weight of the nails; about 5 fluid ounces to 1 ounce of iron will be found convenient, for if less is used the nails will not be entirely dissolved, and an excess will tend to keep the crystals in solution instead of depositing them when cold. The nails—as such—will now have passed out of existence: can we say that the iron that formed them exists in the crystals? Certainly not as the metal iron, for every property of the metal will have disappeared. The crystals are brittle, can be crushed in a mortar—they are translucent—they show no metallic lustre, but only glassy surfaces—they are readily dissolved by water—they are not attracted by a magnet. The most powerful lens will fail to show the least particle of iron in them; they have in their properties no assignable relation to the metal of the nails, but are matter of quite another sort; and be it noted that this entire otherness is the special and characteristic sign of chemical change. So complete is the transformation in the case we have been considering that it would never have been said that iron was contained in these crystals, but rather that the metal had for ever passed out of existence, but for one circumstance; and that is, that by subjecting the crystals to certain processes of chemical analysis we can again obtain from them the iron in metallic state. Nay more, we should find the weight of metal so obtained to be exactly equal to that of the pure iron dissolved from the original nails, supposing of course that we operated upon the whole of the crystalline matter so produced. The inference therefore is that although every property of the iron appeared to be absent from the crystals, the iron entering in them retained there its original weight, and the correct statement of the change would be, that in the crystals the iron had lost all its original properties SAVE ONE, namely, its weight, or gravitating force, if we choose to call it so, a property belonging to it in common with every material substance. Chemical analysis can also separate from the crystals their other constituents and weigh them apart—so much water and so much sulphuric acid—and when to these weights that of the iron is added, the sum exactly makes up the weight of the crystals.

A still simpler experiment, which may be performed by anyone with the greatest ease, may serve as a further illustration of the profound nature of the change in the properties of bodies brought about by chemical combination, and it will also serve as the occasion of directing attention to a remarkable circumstance that invariably characterizes such changes, and one that should always be present in our minds when we are considering them. A yard of flat magnesium wire can be bought for a few pence, and after its metallic character has been observed in the silvery lustre disclosed by scraping the dull white surface, a few inches is to be held vertically by a pair of tongs, or by inserting one extremity in a cleft at the end of a stick, then the lower part is brought into contact with a candle or gas flame. The metal will instantly burn with a dazzlingly brilliant light, and some white smoke (really fine white solid particles) will float into the air; but if a plate be held under the burning metal, some of the smoke will settle upon it, together with white fragments that have preserved some shape of the metallic ribbon, but which a touch will reduce into a fine white powder, identical with the well-known domestic medicine called “calcined magnesia”—a substance totally different from the metal magnesium. The reader will scarcely require to be told that in this burning the metal is entering into combination with the oxygen of the air—by which that invisible gas somehow becomes fixed in these solid white particles, so entirely unlike itself. But this experiment might be so arranged that the quantities of magnesium and oxygen entering into the magnesia could be weighed. For this purpose special appliances would be required in order to ensure complete combustion of the metal, for in the experiment as just described some small particles are liable to be shielded from the oxygen by a covering of magnesia, and the arrangement would have to be such that the whole of the white powder could be gathered up and weighed. In the absence of such appliances, and of a delicate balance, together with the skill requisite for their use, the reader must for the time be contented to take our word for what would be the result. In every experiment the magnesia would be found heavier than the metal burned in the proportion of 5 to 3; in other words, magnesia always contains (so the phrase runs) 3 parts of magnesium combined with 2 of oxygen: never more nor less. A definite proportion between the weights of the constituent substances characterizes every chemical combination, and when this is once determined in a single sample of the compound, it is determined for every portion of the same, wherever found or however produced. But each compound has its own particular proportion, that is, the quantitative relations are different for each. For example, the two constituents of water, hydrogen and oxygen, are combined in the ratio of 1 to 8, etc.; and oxygen combines with metals in a ratio different in each case. Then occasionally the same ratio of constituents occurs in compounds of different composition. The elementary student is apt to suppose that this is because of the law which he finds stated, probably in almost the first page of his text-book: “Every compound contains its elements in definite and invariable proportions”; and even well-educated people entertain the idea of the fact being “governed by” or “obeying” the law just quoted,—a misconception arising from the other use of the word “law,” as signifying an enactment. The real case however is the converse; namely, that a multitude of facts like that above stated have governed the law, and caused it to be what it is—the general statement of many observed facts.

We have assumed that the reader’s chemical knowledge had already made him aware that in every case of ordinary combustion the oxygen of the atmosphere is in the act of entering into combination with the burning body: as with the magnesium, so with a coal fire, a gas flame, or a burning candle; only in these last cases the products of the combustion pass away invisibly. The candle by burning disappears from sight, but its matter is not lost, and as in the case of magnesium, the compounds it forms weigh more than the unburnt candle. The experiment is commonly shown in courses of elementary lectures on chemistry, of so burning a candle that the invisible products are retained in the apparatus, instead of being dissipated in the atmosphere, and the increase of weight of the burnt candle over the original one is demonstrated by the balance. Important as is the part played by oxygen in all chemical actions on the earth, the composition of the atmosphere was not understood until the end of the eighteenth century, and it was well on into the nineteenth before the quantities of its constituents were accurately determined. Now everyone knows that air is mainly made up of a mixture of the two gases oxygen and nitrogen. A mixture of two or more things is very different from a chemical combination of them; for in the former each ingredient retains its own properties. (See Air in Index.) Nitrogen being an inert gas that takes no part in combustion, or in the ordinary chemical actions of the air, acts therein simply as a diluent of the oxygen. It is necessary in relation to our present subject to bear this in mind, as well as the relative quantities of the two gases in air. For our immediate purpose we may neglect the minor constituents of air—such as watery vapour, carbonic acid, etc., of which the total weight does not exceed one hundredth part of the whole—and consider air as a mixture of 23 parts by weight of oxygen with 77 of nitrogen, or calculated in volumes, 21 measures of oxygen with 79 of nitrogen. Compounds of oxygen with nearly every one of the other seventy or more chemical elements are known, and these compounds, which are called oxides, are arranged by chemists under five or six classes, forming as they do basic radicles, acid radicles, saline oxides, etc. With some of these compounds belonging to different classes, we must make acquaintance after noticing the elementary substance with which the oxygen is united.

We begin with carbon, which forms the chief constituent of all our combustibles. Some specimens of graphite, plumbago, or “blacklead” consist of almost pure carbon (98 per cent.), and some varieties of wood charcoal exceptionally contain 96 per cent.; but in ordinary charcoal the percentage is much less. Coal, the most familiar of our solid fuels, varies greatly in composition, carbon being the predominating constituent, in amount from 57 to 93 per cent. Coke, another fuel much used in metallurgical operations, is made by heating coal without access of air, when a large quantity of gaseous substances is expelled. Coke burns with an intense and steady heat without emitting any visible smoke, but it does not ignite as readily as coal. Carbon forms two different compounds with oxygen: both are invisible gases, but they differ in the proportions of the constituents, and present different properties. When carbon (coal, coke, or charcoal) is completely burnt, that is, with an abundant supply of air, the product is carbonic acid gas, in which 3 parts of carbon are combined with 8 of oxygen: when, on the other hand, the carbon is burnt with a sufficiently restricted access of air, the result is carbonic oxide gas, in which 3 parts of carbon are united with only 4 of oxygen. The reader will here observe that the former contains just twice as much oxygen as the latter for the same quantity of carbon. This fact and numberless others like it are expressed or summed up by another law of chemical combination which states that when two elements combine in several different proportions these are invariably such that the ratios in the several compounds will be found to have exact and simple numerical relations; that is, such as may, when reduced to their lowest terms, be expressed by the simple integers 1, 2, 3, etc., as 1 : 2, 3 : 2; ... 8 : 9, etc. It comes to the same thing if we compare together the weights A and A´ which are united in each compound with any one identical weight of B, giving of course the ratio A : B ÷ A´ : B. For instance, in the case just given, of carbon and oxygen, 3 : 4 ÷ 3 : 8 = 2 : 1. This, which is simply stating the facts, is called the law of multiple proportions. On a later page will be found another illustration (see Index, Nitrogen and Oxygen Compounds), and its expression in terms of the atomic theory, which goes behind the facts (so to speak), but is extremely useful by comprehending many other groups of facts in chemistry and in other sciences. Carbonic acid gas is of course incombustible, but carbonic oxide gas burns by uniting with the additional proportion of oxygen and becoming carbonic acid. On the other hand, carbonic acid gas passing over red-hot coals takes up from them the additional proportion of carbon, and is, we may say, unburnt into carbonic oxide. When we see a pale blue flame flickering over the bright embers in a fire grate, it is carbonic oxide burning back again by taking more oxygen from the air above the coals. Carbonic oxide combines directly with two or three of the metals, as, for instance, it forms a volatile compound with nickel, at a certain temperature, and this is decomposed again at a higher temperature. The like takes place with iron, although in very small quantities, but the observation throws some light on the processes of reduction. Carbonic oxide is neither acid nor basic, but carbonic acid is an acid oxide, and as such unites with oxides of the basic class to form another range of compounds. Thus, for example, the oxide of the metal calcium is quicklime, which is strongly basic, and this directly combines with carbonic acid, forming a neutral substance called in systematic chemistry calcium carbonate, or more commonly but less correctly, carbonate of lime, familiar to everyone in the compact state as limestone, and marble, and in a more or less pulverent condition as chalk. When any of these is heated to redness, carbonic acid is expelled and quicklime remains. Like most oxides, quicklime forms a compound with water, the combination being attended with the extrication of much heat, the compact quicklime swelling and crumbling into slaked lime. The chemist’s term for a compound of a basic oxide with water is hydrate, while that of an acid oxide with water is for him properly an acid, or in order to particularly distinguish this class, an oxy-acid. It was however the older practice to give the name of acid to the oxide alone, and this naming having found its way into popular language is much more familiar to the non-scientific reader. The systematic names of the two compounds of carbon and oxygen are carbon monoxide and carbon dioxide, but we shall use here the more familiar terms carbonic oxide and carbonic acid.