James Watt
Page 9
Watt’s partnership with Roebuck involved extensive work improving the engine’s design. Its overall form changed extensively; early versions had the steam cylinder turned upside down with the piston rod pointing downwards and arranged to raise and lower a large weight as it operated. This was replaced with a design that had the cylinder standing upright, and which matched more closely the long-established atmospheric engine. The condenser changed as well: from being immersed in a cistern of cold water to condense the steam, to using a jet of water injected inside. The piston design was also modified extensively to ensure that it was a good, close fit inside the cylinder as it moved up and down. The most immediate outcome of this work was that Roebuck was convinced of the ‘justness of the Principles’ of the engine, encouraging him to invest further and, in return for an agreement that he would receive two-thirds of any income derived from the project, he paid for Watt to obtain a patent on the separate condenser. Watt acquired the patent in January 1769, and it became the foundation of his entire future career, thanks to his being persuaded by future business partner Matthew Boulton and his friend William Small that he should patent the condenser’s principles and not the means of applying those principles. A great many practical improvements to the engine by Watt and – controversially – by others would be covered by the terms of his patent, giving him and Roebuck legal domination of state-of-the-art engine design.
With the patent obtained, Watt’s tests on a full-size version of his engine continued at Kinneil until April 1770. They were not as successful as he would have wished, and strained his relationship with Roebuck to breaking point. Roebuck desperately needed a reliable machine to keep his mines dry, but Watt wanted nothing less than perfection. To recall his earlier words to John Robison, he wanted the engine to ‘not waste a particle of steam’. Meeting Watt’s high expectations meant overcoming countless technical problems, but these continually knocked his fragile confidence. In October 1768 he recorded his ‘natural inactivity, want of health & resolution’. Later he claimed to ‘have met with many disappointments . . . I have now brought the engine near a conclusion, yet I am not nearer that rest I wish for than I was 4 years ago . . . Of all things in life, there is nothing more foolish than inventing.’ On 30 October 1768 Roebuck wrote to Watt, ‘You are letting the most active part of your life insensibly glide away. A day, a moment, ought not to be lost.’ It was to no avail: as late as February 1770 Roebuck could complain that ‘a single step has not been advanced towards the engine’.35
As Roebuck’s coal mines filled with water, and his money seeped away, Watt faced a dilemma. The engine offered the chance of long-term success and wealth, if only he could fully comprehend what was going on inside it, so as to perfect its performance. But he also had a growing family to support, and feared ‘growing grey without having any settled way of providing for them’.36 In the nine years from 1765 until 1774, he spent only two periods of three years in total, in 1765–6 and 1768–70, actually working on the engine.37 As we will see, when Watt did grasp the internal workings of the engine, he saw it as a chemical machine. But until this happened, his circumstances forced him to pursue a range of projects that enlarged and exploited his knowledge of chemistry.
The scope of Watt’s chemical interests is indicated by the contents of his workshop, which is a veritable storehouse of practical chemistry. One corner houses 66 chemical storage jars, drawers contain tiny individually wrapped or boxed samples of substances, and upon shelves sit brown paper parcels containing chemicals purchased in bulk, tied with the original string and labelled in Watt’s hand. Fifty different substances comprise ingredients most closely associated with pottery, both the manufacture of glazes and the ceramic bodies they were applied to. Twenty-three, including gamboge, tragacanth, ‘cochenilla’ and turmeric, found use in dyestuffs. Twenty more, including vermillion umber and ‘Precipitate of Prussian Blue’, were employed in artists’ colours. ‘Benzoin’, Epsom salts and ‘Chinese Carthamus’ had medicinal uses, reflecting Watt’s role as family doctor as well as husband and father.38 The range of substances, 140 in all, reflects that Watt cast his net widely depending on what particular projects he had in mind. As early as 1765 he was working with Black to produce alkali from sea salt. In 1784 he was researching the composition of water, while in parallel he was devising a means of chemically copying letters, employing ‘iron cement’ to seal joints in his steam engine and, later, working on plans to bleach textiles with chlorine for the first time in Scotland.39 This was not a systematic but more an opportunistic approach to chemistry.
Watt’s workshop, Birmingham, 1924. Here we can see jars of chemicals, pestles, mortars and bowls, scales for measuring, and even Watt’s apron, hanging on the right.
That is not to say, however, that Watt’s chemical interests were not philosophical. As David Miller has written, ‘the theoretical Watt and the “cookbook chemist” Watt’, as illustrated by the contents of his workshop, ‘were the same person’.40 Similarly, Joseph Black’s lectures were written, according to John Robison, ‘in the clearest, simplest, and most intelligible . . . Language; such that any sensible dyer or Blacksmith or druggist will understand completely’ – yet Black was also regarded as the foremost chemical philosopher of his time.41 Theory and practice enjoyed a close relationship, and Watt soon had the chance to put his knowledge of both to the test in one of chemistry’s most high-profile outputs: in 1768 he became a potter.
The Delftfield Pottery had been established by four business partners in 1748, and was based just west of Glasgow city centre, quite close to the Broomielaw Quay. Its original product was Delftware, clay fired in a kiln at relatively low temperature which was allowed to cool off and then dipped in a glossy white tin glaze. It was dried before having patterns painted on, often in blue – a fashion that had originated in Delft, Holland. But Delftware had a thick, soft body, making it fragile – boiling water could cause cracks – and liable to scratch easily. Even as the Delftfield Pottery was founded, the popularity of Delftware was beginning to wane. If the pottery’s founders, businessmen with little practical pottery experience, appointed Watt to turn its fortunes around, he was quick to realize the importance of making a more durable product, and began to research what this might be and how it could be made.
There were two possible paths that Watt could pursue: to make Chinese porcelain or improve Britain’s existing domestic pottery. Porcelain was immensely sought-after throughout Europe in the eighteenth century, and in 1721 alone, 2 million pieces were imported into Britain.42 Originating in China, porcelain was made from kaolin, a fine, soft white clay. It was mixed with other ingredients which, in England, might include glass or bone ash, from which is derived the term ‘bone china’. When fired at a very high temperature, these ingredients fused together to produce a fine, durable product with a translucent, glass-like finish. Learning the secrets of this manufacturing process was a project played out across Europe: it was first mastered in Dresden in 1709 under conditions of tremendous secrecy, and became a preserve of royal factories making luxurious tablewares for monarchs and their courts. British porcelain makers were established later on, at Bow and Chelsea in London, at Worcester and Derby, among other places. These producers imitated oriental styles in products like tablewares and decorative figures intended not just for the very wealthiest customers, but for those of more modest means as well.
The alternative to a new domestic porcelain industry was to develop the already extant British earthenware trade. The English potteries had long been ‘a more or less rustic art, remarkably skilful but always very near the people, simple . . . and reflecting the country life of the time’.43 Louis Simond wrote of the ‘common-ware’ widely used in France as well as Britain that it was ‘coarse and heavy, with the glaze scaling off, or full of cracks crossing each other in every direction, like lace-work, and retaining in their interstices the various juices of a hundred successive dinners’.44 But earthenwares evolved quickly to ultimately produce a new ware
described by John Aikin in 1795 as ‘the source of a very extensive trade, [which] may be ranked amongst the most important manufactures of the kingdom’: creamware.45
Creamware imitated porcelain in appearance but took advantage of locally available materials and techniques. It was produced by firing ‘ball’ clay mixed with ground flints at a low temperature to produce a light-coloured body that could be coated with lead glaze. After a second firing, this was ‘smoother, warmer in colour, and better adapted for utilitarian purposes’. Production began in Britain in the 1740s, and it proved to be at once durable, cheap and good-looking enough to appeal to a large, discerning market.46 Despite difficulties in obtaining a consistent colour and quality of finish, it gradually usurped the older Delftware, giving rise to a commerce
so active and so universal, that in travelling from Dunkirk to the southern extremity of France, one is served at every inn upon English-ware. Spain, Portugal, and Italy are supplied with it; and vessels are loaded with it for the East-Indies, the West-Indies, and the continent of America.47
The name most closely associated with this new trade was that of Josiah Wedgwood. He devoted enormous efforts to establishing the scientific basis for its manufacture: it took 411 attempts to obtain the perfect chemical recipe for his creamware glaze, for example. But Wedgwood matched patient experimentation with skill in marketing his products: convinced of its ‘real utility & beauty’, in 1766 he sold a cream-coloured table service to Queen Charlotte, naming it ‘Queen’s Ware’ in her honour, a name that was widely adopted.48 In other aspects of his business, a network of agents across Europe drove sales, catalogues and hand bills were used to excite demand, and showrooms in London and Bath presented ‘a thousand lovely forms and images; vases, tea-things, statuettes, medallions, seals, [and] table-ware’.49 But even with his Staffordshire workshops producing over 600,000 pieces of ware yearly, Wedgwood could not keep up with demand – in fact, he found it ‘really amazing how rapidly the use of it has spread allmost over the whole Globe, & how universally it is liked’.50 Although he retained his position as a leader in the pottery industry, over 100 other potteries in Britain also made creamware.51 Included among them was Watt’s Delftfield Pottery.
Watt faced significant barriers in his pottery work. Potters treated the ingredients for their wares as trade secrets, so there was extensive duplication of effort. Watt was also isolated from the main pottery industry in England, explaining that his ‘insulated manufactory has much to struggle with’.52 However, despite a tendency to mix reports of progress with complaints, the company prospered on the back of his chemical work. As early as January 1769, Watt wrote to his friend William Small that ‘Our pottery is doing tolerably . . . I am sick of the people I have to do with. Tho’ not of the business, which I expect will turn out a very good one.’ Almost three years later, he claimed that ‘our pottery does very well tho we make damned bad ware’.53 Some of this bad ware, rejects that would usually have been thrown out, appears to have ended up in Watt’s workshop to store his chemicals in.54 By May 1773 an advertisement in the Glasgow Journal could announce that Delftfield had ‘now learned the art of manufacturing yellow Stone or Cream Coloured Ware . . . They are thereby enabled to serve their customers at lower prices than formerly, and they flatter themselves with better ware.’55 Later, surplus wares found ready buyers in North America, at New York and Charleston.56 Delftfield thus provided Watt with much-needed income – £70 every year (about £5,000 in today’s money) – just when he needed it to support his family.57 The company’s success depended upon Watt’s researches into the composition of the wares and the glazes used.
Watt’s experiments on the bodies of his pottery wares were diverse. Early in his research, he tried replicating porcelain manufacture, writing to Joseph Black in 1768 that ‘I found that [pipe] clay may be burnt as white and hard as any porcelain’, and some of the containers for chemical samples in Watt’s workshop have recipes for soft-paste porcelain written on their lids in Watt’s hand.58 These experiments came alongside development of dense and impermeable new ‘stoneware’ products, and the workshop also contains a whole drawer of small test firings of pieces of cream-coloured clay, accompanied by notes from Watt recording that they were fired ‘by 55 degrees’ and ‘by 80 degrees’ of ‘Wedgwood’s thermometer’.59 In sourcing these materials, Watt’s often peripatetic life, travelling on business, paid dividends: he found good-quality killas clay near Falmouth in 1782, and his workshop contains a wooden box filled with mineral samples, as well as a small amount of ‘Asbestus’ in rock form, and even three human teeth and part of a jawbone, with a note that they were from the battle of ‘Louearly Field fought 1160’.60 While travelling to Birmingham in 1774, Watt also conscientiously noted that the ‘stone grows softer and gravel harder’; he certainly developed a canny eye for potentially useful materials to employ at Delftfield.61
Work on clays was accompanied by research on glazes. Watt began devising mixtures of lead and tin for stonewares, and his investigations of a source of cobalt give us the earliest account of any of his chemical experiments.62 Later, he looked into sought-after creamwares too: the glaze used lead as a primary ingredient, producing a yellow finish. To make it paler, cobalt could be included as well; Watt’s workshop contains a number of samples of this, and the raw materials from which it could be extracted, as well as manganese, used to remove any green tinges from the glazes, all carefully preserved in packets and boxes.63 The success of Watt’s chemical work is suggested by the Scottish potter Robert Muirhead, who described one of his recipes for a fine, white glaze as ‘an entirely new art . . . not discovered & practised by any other persons in Britain’.64
A drawer full of Watt’s experimental ceramic test pieces, 1768–80, preserved in his workshop.
Turning the clay and glaze ingredients into a finished product depended on them being fired in a kiln, and Watt turned his attention to this, too. He found the Delftfield kilns fuelled with wood; the wares within were exposed to the flames and smoke, which often spoiled the glaze with black marks, and the heat from the fire was unevenly distributed, so that wares placed in some parts of the kiln took longer to fire than others. He changed the shape and internal layout of the kilns so they became more evenly heated, replaced wood fuel with cheaper coke or coal, and changed how the kiln’s furnace was stoked with fuel to reduce smoke and prevent ashes contaminating the wares.
Watt’s work on the Delftfield kilns, the better to bake hard the clay wares and finish the glazes, is a reminder that understanding the nature of heat, and how best to manipulate it, was a central concern to all those engaged in chemistry. It was also central to Watt’s developing understanding of the steam engine when he eventually returned to it. Many accounts of the engine point to Watt as a thermodynamicist, pioneering the application of a science of heat that was formalized in the early nineteenth century. However, Watt’s understanding of heat was far different from that of his successors. Rather than being a form of energy, Watt and his colleagues regarded heat as a chemical compound of heat and water. By extension Watt saw the engine as a piece of chemical apparatus where the chemical elasticity of the steam within drove the piston and made the vacuum generated in the separate condenser perform useful work.65
This interpretation of the engine, rather than placing a division between Watt’s work on the engine and, say, his research at the Delftfield pottery, sees them as closely related. Watt was also extremely well-placed to be carrying out that work while in contact with Joseph Black, the foremost researcher on the nature of heat.66 That said, it is difficult to quantify exactly how far Watt’s work at Delftfield was informed by philosophical considerations about heat. Although details of particular experiments can be traced in his correspondence, he did not systematically record his working practices and their outcomes but, as David Miller has commented, ‘it would be surprising if . . . his ideas about heat as a transformative agent were not involved.’67 Certainly, some of what we know about Watt’s pottery
is gleaned from his letters to Black, which is telling in itself. In establishing how different fuels heated the kilns, for example, Black helped Watt with a vivid description: ‘A kiln which is heated with flaming fuel may be said to be heated by means of a torrent of liquid fire which flows through it, but I am persuaded that cokes act mostly by radiation like that of the sun.’68 As for Watt’s detailed ways of working, he wrote of picking up from Black what he called ‘the correct modes of reasoning and of making experiments’.69 And Watt’s personal seal, an emblem of an eye with the initials ‘J.W.’ below, was surmounted by a single, bold word: ‘OBSERVARE’, ‘to observe’, suggesting his skills in methodical observation, measurement and record-keeping.
If Watt’s working practices at Delftfield were informed by strong philosophical elements, as seems likely, then he was not alone. Pottery was recognized as offering excellent opportunities ‘for the exercise of ingenuity and research’ and was an attractive career for ‘persons of observant habits’.70 Simeon Shaw, in his history of the Staffordshire potteries, wrote how Enoch Wood of Burslem ‘had such a judicious arrangement that it presents all the appearances of a most extensive Laboratory and the machinery of an Experimentalist’, and Thomas Minton was ‘possessed of extensive information of the chemical properties of the earths’, for example.71 And the close integration of theory and practice that pottery relied upon suggests the existence of a shared set of practices and concerns for chemists of all backgrounds. A broad framework for this discussion is provided by Joseph Black’s ‘general doctrines of chemistry’, of which ‘the more general or universal effects of heat’ stood out prominently.72
The furnace was at the heart of much activity in philosophical laboratories. It provided the heat to distil liquids inside glass retorts or alembics which sat on top of the fire while resting inside a bath of iron filings, melted tin, lead or even mercury to ensure that even heating took place.73 Some furnaces were brick-built structures not dissimilar to a blacksmith’s hearth, but Joseph Black designed a portable furnace, 22 inches high and 20 in diameter, mounted on castors so that it could easily be moved about. If a specially designed furnace was unavailable, more domestic alternatives would work equally well. One author noted that ‘a complete furnace, capable of being worked in a parlour chimney, may be had, which will create little trouble, and will require no assistance from the bricklayer.’74 Certainly, the stove in Watt’s workshop served as a means of cooking and heating but was also pressed into service for experiments requiring heat; it is accompanied by crucibles to contain liquid substances – some of which still contain the solidified contents of their last experiment – tongs, leather aprons and glass spectacles to protect the eyes.