PART ONE: MATERIALS 182 Apart from the obvious office use of computers for anything from preparing wage statements to scheduling orders so that they go to the works in the most economic way, computers are now being used ‘on-line’, to control actual production processes. A simple example comes from the cutting of billets to suit customers’ orders. Billets of special and very expensive alloy steel have to be cut into many different lengths to suit individual customers. The billets do not come from the mill in exact lengths, and the practice was always for the operator who controlled the billet saw to be given the measured length of each billet as it came to him. He then had to decide the best way to cut it up, according to all the orders he had to satisfy, and set the saw accordingly, so that as little as possible of the expensive material was wasted. However skilled the operator, human error was unavoidable. With computer control the billets are measured automatically as they are rolled and this figure is fed into the computer with details of the customers’ orders. It equates these two sets of information and produces figures for each billet which will use it most economically. There are numerous other examples of computer control in steelmaking and processing, and the trend is increasing. In special and alloy steelmaking there is also a great deal of mechanization and process control is highly instrumented, but the scale of operations is smaller and the range of products wider. Today all alloy and special steels are made in electric furnaces. The old crucible process is extinct, though there is a crucible melting shop preserved in working order at Abbeydale Museum, Sheffield. Electric furnaces can be of two types, arc or induction. In the arc furnace heat is generated by means of an electric arc and metal is melted by this heat in a refractory-lined vessel of drum shape, which can be tilted mechanically to tap the finished steel (see Figure 2.6). Arc furnaces are now of many sizes, holding from a few tonnes to 150 tonnes or more. The induction furnace was invented in Italy in 1877 but the time was not ripe for it to develop and the first one in Britain was installed in 1927. In this furnace there is no arc; an electric current induces a secondary one inside the furnace itself and generates sufficient heat to melt steel. Induction furnaces are generally used for the very special and expensive alloy steels and may range in capacity from a few kilogrammes to 5 tonnes or more. Neither type of electric furnace uses liquid, solid or gas fuel, so the steels made in them cannot be contaminated from these sources, an important consideration in the higher-grade steels. Any contaminant—even in a very small percentage—might be disastrous in a gas-turbine disc, for example, so a very ‘clean’ furnace is highly desirable. Unfortunately, some gases also act as contaminants in steel, and since these gases are present in air it is impossible to avoid their getting into the steel. They must then be removed and there are several ways of doing so. One is vacuum melting. Steel is made as carefully as possible in an ordinary electric furnace and then remelted in an induction furnace which is contained FERROUS METALS 183 in a sealed chamber under a vacuum. As the steel melts, the gases are given off and drawn away by the vacuum pumps. Vacuum furnaces are complicated pieces of machinery, with equipment for taking samples of molten steel, making corrective additions to the melt, and casting the steel into an ingot, all without disturbing the vacuum. They are naturally expensive to buy and they have small outputs, but they are justified when very high quality is essential. Figure 2.6: Model of an electric-arc furnace. PART ONE: MATERIALS 184 Among other methods of cleaning and purifying high-grade steels, is electroslag refining, which is of growing importance. In this process a long bar of steel is made and the end of it is gradually melted off under a pool of molten slag. The slag is specially prepared so that the impurities pass into it; in effect they are ‘washed’ out of the steel. Iron and steelmaking today is a pattern of highly sophisticated and very expensive plant and, for the bulk producers, of very large outputs coming from a few works in coastal areas. The pattern is world-wide; almost every major industrial country is concentrating its bulk steelworks in this way. There are, however, two exceptions to this trend towards ever-increasing size. In the first place the alloy and special steelworks have not followed the pattern and are not likely to. A new giant steelworks could cost £1000 million or more to build today, a cost which could only be justified by the very large outputs achieved for tonnage steels. Alloy steels are not wanted in such great quantities, so the alloy steelworks, though bigger and costing considerably more than they used to, will never reach giant size. In the second place, there is a new type of steelworks, not at all large by modern standards, which is proving very successful. This is the so-called minimill, made economically possible by the electric furnace and continuous casting. There are several in Europe and quite a number in the United States and Japan, where the giant works is often thought to be supreme. One has been built in Britain and others are under construction or planned. A mini-mill is a steelworks based on scrap steel, collected over a fairly small area locally, melted in an electric-arc furnace, cast in a continuous casting machine and then rolled in a mechanized mill. Its products will be few in number; sometimes there will be only one finished product. Concrete reinforcing bars are a typical mini-mill product. The output can range from as little as 50,000 up to about 400,000 or more tonnes a year. The size of a mini-mill is determined by that of the local market and that of the area from which the raw material, scrap, is collected. In the USA, with its great land mass, a market can be a long way—and in terms of transport an expensive way—from the traditional steel-producing areas, so a locally-based works can do well. But even in Japan and Britain, mini-mills can prosper if they get their economics right. The first British mini-mill, at Sheerness in Kent, was designed for expansion from an annual capacity of 180,000 tonnes to 400,000 tonnes. Discounting the possibility that steel may in the foreseeable future be superseded by some other material, it is difficult to imagine any major changes in the metal itself. Specifications will change, new alloys will be developed for new, unforeseeable applications, but steels will still be recognizable as such. It is in the methods of manufacture that the greatest changes are likely. The blast furnace could be the first to face this effect. At present it is the most economic means for converting iron ore to metal. But coke is getting more FERROUS METALS 185 expensive and scarcer: not every type of coal is suitable for making coke and the world’s reserves of those that are are dwindling. There are alternative methods of reducing iron ore. Some modern plants using oil or natural gas as fuel can produce relatively pure iron pellets which are suitable for melting down to make steel. It is also possible to smelt electrically. In a few parts of the world, where coke is too expensive, they are already in use: in Mexico, for example, where there is iron ore, but coke would have to come from the USA and the transport charges alone would make it very expensive. Perhaps the ultimate dream of the steelmaker is the fully-continuous production of steel. Raw materials would come in at one end of the works, flow through the various processes in a continuous line and come out at the other end as finished products. Parts of the production line are already continuous, but there are major technical problems to be solved before truly continuous steelmaking is practicable. But there are quite a lot of people in many countries, trying to fill the gaps between theory and practice and nobody can predict what might happen, or when. The one certainty is that we have not yet heard the last of steel or of its basis, the element iron. 186 3 THE CHEMICAL AND ALLIED INDUSTRIES LANCE DAY INTRODUCTION The chemical industry is that by which various kinds of matter are transformed into other kinds that are needed in manufacturing or in everyday life. Its history falls into two periods. The first, the pre-scientific stage, stretches back into the distant past, to man’s earliest attempts to deal with materials. The second, scientific, period is of quite recent origin, in the late eighteenth century, when chemical science began to be usefully applied to chemical technology. In the earliest period up to the end of the neolithic age, that is around 3000 BC, practice of the chemical arts was restricted almost entirely to the making of fire, alcoholic fermentation and the baking of pottery. This was succeeded in various parts of the world by what are termed the ancient civilizations, such as those of Egypt, Mesopotamia, the Indus Valley and, somewhat later, China. Here city life began, communication, above all writing, developed to make it possible to keep records and disseminate knowledge, and new techniques were developed. Some of these, such as medicine, surveying and astronomical observation, were carried out systematically. At the same time the range of materials available and the processes by which they were treated widened, with the effect of improving the way of life for the citizens. Most important of these materials were the metals, gold and silver, copper and tin, alloyed in bronze, and later iron (see Chapters 1 and 2). Throughout this period, and in the succeeding ages of Greece and Rome, the rise of Islam and on into Western Europe, the extraction and preparation of useful substances was essentially a craft, carried on, like any other, by skilled artisans who learned their trade through apprenticeship and experience and not from a THE CHEMICAL AND ALLIED INDUSTRIES 187 corpus of literature; there was none, and if there had been, very likely they were unable to read. Such accounts as there are of the ancient chemical arts were drawn up by those not engaged in the craft. For example, the encyclopaedic Historia naturalis of the Roman official Pliny has embedded in it many descriptions of chemical processes, some accurate, some less so, for they are based on secondhand reports rather than original observation. Many recipe books survive to give us some idea of what went on, like the chemical tablets of seventh-century BC Assyria, although these are no more than lists of ingredients. With the coming of printing and a mercantile and practical class of reader, a demand developed for clear accounts of the making of various substances. These begin to appear early in the sixteenth century, some being fine examples of the art of book-making. Hieronymus Braunschweig’s books on distilling were printed early in the 1500s and were the first to include illustrations of chemical apparatus. Neri’s sober account of glass-making followed and there were the metallurgical treatises of Vannoccio Biringuccio (1540), Agricola (Georg Bauer) (1556) and Lazarus Ercker (1574). This literature is severely practical and shows little trace either of magical or superstitious elements on the one hand or, on the other, of the current philosophical ideas about the nature of matter. It was the Greek philosophers of the sixth century BC onwards who began to seek an underlying unity in the variety of materials in nature and a few fundamental principles or elements from which this variety could be derived. The explanation that gained widest acceptance was the four-element theory propounded by Aristotle and his followers from the fourth century BC, which held that all materials consisted of varying proportions of the elements fire, air, water and earth. This theory was not seriously criticized until the seventeenth century and fell into disuse during the following century, surviving today only in such phrases as ‘the fury of the elements’. This and certain other ideas about the nature of matter and the ways it could undergo change were applied by the alchemists in the course of their work attempting to make gold. The artisan did not think in philosophical terms because he had not been educated in the schools, and if he had been, it would not have been the slightest help in his craft of making useful materials. The lack of a genuine theoretical understanding was a great handicap particularly in identifying and valuating materials. The glass-maker, for example, did not know that silica, sodium carbonate and lime as such were needed to make glass; the first glass-maker discovered by accident, and his followers knew from experience, that sand melted with the ashes of certain plants would yield glass. They knew that the whiter the sand, the more colourless the glass. Likewise, it had been found from experience that the ash from some maritime plants produced the best glass, but not because they understood that these contained soda, potash and lime and that these were necessary for glass making. Materials were recognized by their look and feel, learned from those who already knew. Knowledge of materials and processes tended to be kept within rather closed communities and not widely PART ONE: MATERIALS 188 disseminated. Communications were difficult enough without the deliberate secrecy that was sometimes practised, as when the earliest Venetian glassmakers sought, albeit vainly, to prevent a knowledge of their art from spreading. Lacking a means of identifying substances correctly, the early chemists could be so confused about them as sometimes to use the same name for different substances, such as ‘nitrum’, which could mean both sodium carbonate and potassium nitrate. On the other hand, different names could unwittingly be used for the same substance: ‘vitriolated tartar’ and ‘vitriolated nitre’ were both used at times for more or less impure potassium sulphate, apparently with no awareness that the substances so designated were essentially the same. Inability to identify materials made it impossible to evaluate them, that is, to determine how much of them was present. Finding out what and how much is the object of chemical analysis and not surprisingly it arose in connection with those materials that could be recognized, namely the metals, particularly gold and silver. The printed books on the assay of metals which began to appear early in the sixteenth century are evidence of a practical tradition in the quantitative evaluation of gold and silver. But for other materials it was hit or miss. The ironworker, for example, had no way of knowing whether he had extracted all the iron from a charge of ore. Very likely more than half would have been left in the refuse or slag, so that later workers often found it worth while to rework them. As for determining the quality of the product, if the customer was satisfied, that was enough; there was no other criterion. Not understanding what was going on, the artisan found it difficult to regulate his processes and distinguish significant from irrelevant factors. Adding a new ingredient one day, or giving the mixture a good stir, might appear to have improved the result and the new procedure would have passed into timehonoured practice until somebody accidentally omitted it without adverse effect. Nobody would have known or even asked why the new procedure seemed to work. There was thus no understanding of the effects of temperature, pressure and all the other conditions that are now known to influence chemical changes. Temperature was in any case difficult to control. The mainly charcoal-fired furnaces were awkward to regulate and things could easily get out of hand, as illustrated by the explosive mishaps that befell the alchemists of Chaucer and Ben Jonson. The poor quality of many of the reaction vessels was also a hindrance and led to much waste. Considering all the handicaps, it is indeed remarkable that such a range of useful materials was produced with an acceptably high quality. It was all achieved by craftsmen relying on skill of eye and hand gained through years of practice and inherited from generations of work in the industries concerned. All this was to change dramatically within a relatively short space of time. The idea of increasing natural knowledge gained from observation and applying it to industry or the useful arts developed during the seventeenth century. The Fellows THE CHEMICAL AND ALLIED INDUSTRIES 189 of the Royal Society, from its foundation in 1662, took a considerable interest in industry and made some useful suggestions for improvements in chemical processes. One of the founder members, the Hon. Robert Boyle, sharply criticized the prevailing ideas in chemistry and urged that it shed its disreputable alchemical connection and apply the concepts of the new mechanical philosophy. This criticism lacked precision, however, and a further century was to elapse before a chemical theory was established which actually corresponded with reality, at the hands of Antoine-Laurent Lavoisier from around 1780. The processes involving oxygen, such as combustion, were correctly explained, the nature of acids, bases and salts was put on a sounder footing, and in particular a clear definition of a chemical element was not only stated but usefully applied to draw up the first list of elements in the modern sense. A beginning was made in chemical analysis and after 1800 great improvements were made in quantitative analysis. Soon after 1800 rules for the way in which elements combined to form compounds were first enunciated, and with the atomic theory of John Dalton, chemists could visualize and explain chemical reactions in terms of the ultimate particles forming the basis of all matter. Early beneficiaries of the chemical revolution were the manufacturers of cheap sulphuric acid, caustic soda, and chlorine for the textile industry. Developments in the industry gathered pace, informed by discoveries on the theoretical side. The nineteenth century was the era of pure and applied chemistry. The pure chemist was concerned to advance chemical knowledge for its own sake, irrespective of its possible practical use. The applied chemist, meanwhile, was employed to improve the processes for producing commercially useful substances, seeking new exploitable materials and, above all, in chemical analysis to monitor processes and the quality of products. Too often the two kinds of chemist worked in isolation from each other, the former being blissfully unaware of the needs of industry and the latter prevented from carrying out research that did not show an obvious profit. This division of role has, however, become increasingly blurred with the growth from the beginning of this century of the great chemical firms: indeed, the terms ‘pure’ and ‘applied’ chemistry can be said to belong to a bygone age. Improved contacts between the universities and industry make the former’s research departments more aware of problems in industry, while much research in industry is in areas wider than those for which there is an immediate cash return. In addition, in most industrialized countries the state sponsors research and itself carries it out, in government laboratories, and without rigidly restricting its attention to problems of public concern. It is a melancholy fact that, in Britain, state, industry and the universities combined to deal with common needs never so effectively as in the two world wars. The production of the first atomic bomb is the prime example of such co-operation on an international scale. By and large the chemical industry in the developed countries has been in the hands of private commercial firms and, however altruistic some of their PART ONE: MATERIALS 190 activities may be at times, the ultimate reason for a process or product to be developed is that it will make a profit. It is worth noting that this profit is the source of funds for research by the state and the universities whether by direct sponsorship or indirectly through taxes. Because of the successful and systematic application of theoretical chemistry, first in inorganic then in organic chemistry and physical chemistry, especially the mechanism of reactions, the range of substances which the chemical industry has produced for man’s use, with ever-improving quality, has been truly remarkable. The comparison with several millennia of near stagnation makes the progress of the last two centuries all the more striking. In 1800 the chemical industry was important, but on a small scale, its products limited to metals, acids, alkalis, pigments, tan-stuffs, medicines and a few other chemicals, some made on a scale not much greater than in the laboratory. Now the scale is vast, yet the industrial chemist exercises a precise control over the processes to yield an exactly predictable result. The source of this progress has been research. Sometimes progress has come by directing research to solving a particular problem, such as making a substance with certain required properties. But the more fruitful source has been to apply discoveries not made with a particular practical end in view. An example of the first is presented by Alfred Nobel and his intention to make nitro-glycerine a safe explosive. In the course of this he invented dynamite and blasting gelatine (see p. 223). But the more remarkable discoveries have been those that were not intended. Thus Perkin, while trying to synthesize quinine lighted on something quite unexpected, the first aniline dye, mauve—which led to a whole new industry (see p. 201). An example of the deliberate application of the results of pure research can be seen in the hydrogenation of oils to make fats like margarine, stemming from the study of the catalytic hydrogenation of unsaturated compounds in the presence of a metallic catalyst by Sabatier and his colleagues around 1900. Until then, the production of margarine, invented in 1869 by the French chemist Hippolyte Mège Mouriès, had been limited by the availability of raw materials, but the hydrogenation process enabled almost unlimited quantities of oils such as cottonseed oil to be converted into solid fats. This chapter follows the history of the making of the more important substances or groups of substances that are a help to man, in one way or another, in his everyday life. POTTERY, CERAMICS, GLASS Pottery and ceramics The hand-forming of plastic clay and changing it by heating into a hard body impermeable to water is a technique that goes back to the dawn of civilization, THE CHEMICAL AND ALLIED INDUSTRIES 191 that is, to before 6000 BC. Indeed, primitive man, whether in prehistoric times or the present, fashions clay by hollowing out a ball and leaving it to dry in the sun or heating it on an open fire. Such simple means can hardly be classed as even primitive industrial chemistry, but with the rise of the ancient civilizations and the settled urban life that made tolerable the fragile nature of pottery, a number of materials began to be used for a variety of decorative effects. Potters learned, too, to control the temperature of their kilns to produce different colours. In modern parlance they employed reducing and oxidizing conditions to achieve various effects, without of course understanding the reason for this. Clays are, chemically speaking, hydrated aluminium silicates with other substances such as alkalis, alkaline earths and iron oxide. It is this last that gives the commonest clay its characteristic red colour. The clays commonly found in nature are plastic when mixed with water and can be formed into a variety of shapes. When left to dry until the water content is 8–15 per cent the clay can still be worked, by scraping or turning, but lacks mechanical strength. After further drying and firing at 450–750°C the chemically-combined water is driven off, the clay can no longer combine with water, and it becomes like moderately hard stone. Firing at a higher temperature eventually causes the clay to vitrify and fuse, but that stage was rarely reached in the ancient world. It is impossible to date the technical advances made during the early civilizations of Egypt, Mesopotamia and the Indus, but the art of throwing pots on the potter’s wheel evolved at this time, as also the firing of the ware in kilns, fuelled with wood or charcoal, in place of the open fire. Temperatures of just over 1000°C could occasionally be reached and much greater control of the draught and therefore the heating conditions was achieved. Pottery could be rendered sufficiently non-porous by burnishing, that is, smoothing the unbaked surface by rubbing, but a better surface could be obtained by dipping the ware in a ‘slip’ or a slurry of fine clay and firing, or by glazing, that is, painting on to the surface a substance which on firing would turn into a thin layer of glass. The Egyptian blue glaze was a notable example. It was made from white sand, natron, limestone and a copper compound, perhaps malachite, which imparted a blue colour to the mixture. This was heated for two days at around 900°C, powdered and applied as a glaze to a siliceous body. The Assyrians, about 700 BC, introduced lead oxide-based glazes, an important development as this was the first glaze that would adhere to a clay base. They were able to obtain a yellow colour by roasting antimony sulphide with lead oxide, and blue and red from copper compounds. The Greeks and Romans made progress in fine workmanship and artistic design rather than in technology. The Greeks, from about 600 BC, did however develop the technique of black and red ware achieved by using reducing and oxidizing conditions to produce two different states of the iron oxide in the red clay. The most interesting development over the next millennium was that of lustre ware. A paste formed from powdered sulphides of copper and silver was . systematically. At the same time the range of materials available and the processes by which they were treated widened, with the effect of improving the way of life for the citizens. Most important of these materials. such phrases as the fury of the elements’. This and certain other ideas about the nature of matter and the ways it could undergo change were applied by the alchemists in the course of their work attempting. first in inorganic then in organic chemistry and physical chemistry, especially the mechanism of reactions, the range of substances which the chemical industry has produced for man’s use, with