He continued to pursue his experiments in assaying for about two years, during which he had been working entirely after the methods described in books; but, feeling the results still unsatisfactory, he determined to borrow no more from the books, but to work out a system of his own, which should ensure results similar to those produced at the blast-furnace. This he eventually succeeded in effecting by numerous experiments performed in the night; as his time was fully occupied by his office-duties during the day. At length these patient experiments bore their due fruits. David Mushet became the most skilled assayer at the works; and when a difficulty occurred in smelting a quantity of new ironstone which had been contracted for, the manager himself resorted to the bookkeeper for advice and information; and the skill and experience which he had gathered during his nightly labours, enabled him readily and satisfactorily to solve the difficulty and suggest a suitable remedy. His reward for this achievement was the permission, which was immediately granted him by the manager, to make use of his own assay-furnace, in which he thenceforward continued his investigations, at the same time that he instructed the manager's son in the art of assaying. This additional experience proved of great benefit to him; and he continued to prosecute his inquiries with much zeal, sometimes devoting entire nights to experiments in assaying, roasting and cementing iron-ores and ironstone, decarbonating cast-iron for steel and bar-iron, and various like operations. His general practice, however, at that time was, to retire between two and three o'clock in the morning, leaving directions with the engine-man to call him at half-past five, so as to be present in the office at six. But these praiseworthy experiments were brought to a sudden end, as thus described by himself:—
"In the midst of my career of investigation," says he,[6] "and without a cause being assigned, I was stopped short. My furnaces, at the order of the manager, were pulled in pieces, and an edict was passed that they should never be erected again. Thus terminated my researches at the Clyde Iron Works. It happened at a time when I was interested—and I had been two years previously occupied—in an attempt to convert cast-iron into steel, without fusion, by a process of cementation, which had for its object the dispersion or absorption of the superfluous carbon contained in the cast-iron,—an object which at that time appeared to me of so great importance, that, with the consent of a friend, I erected an assay and cementing Furnace at the distance of about two miles from the Clyde Works. Thither I repaired at night, and sometimes at the breakfast and dinner hours during the day. This plan of operation was persevered in for the whole of one summer, but was found too uncertain and laborious to be continued. At the latter end of the year 1798 I left my chambers, and removed from the Clyde Works to the distance of about a mile, where I constructed several furnaces for assaying and cementing, capable of exciting a greater temperature than any to which I before had access; and thus for nearly two years I continued to carry on my investigations connected with iron and the alloys of the metals.
"Though operating in a retired manner, and holding little communication with others, my views and opinions upon the RATIONALE of iron-making spread over the establishment. I was considered forward in affecting to see and explain matters in a different way from others who were much my seniors, and who were content to be satisfied with old methods of explanation, or with no explanation at all….. Notwithstanding these early reproaches, I have lived to see the nomenclature of my youth furnish a vocabulary of terms in the art of iron-making, which is used by many of the ironmasters of the present day with freedom and effect, in communicating with each other on the subject of their respective manufactures. Prejudices seldom outlive the generation to which they belong, when opposed by a more rational system of explanation. In this respect, Time (as my Lord Bacon says) is the greatest of all innovators.
"In a similar manner, Time operated in my favour in respect to the Black Band Ironstone.[7] The discovery of this was made in 1801, when I was engaged in erecting for myself and partners the Calder Iron Works. Great prejudice was excited against me by the ironmasters and others of that day in presuming to class the WILD COALS of the country (as Black Band was called) with ironstone fit and proper for the blast furnace. Yet that discovery has elevated Scotland to a considerable rank among the iron-making nations of Europe, with resources still in store that may be considered inexhaustible. But such are the consolatory effects of Time, that the discoverer of 1801 is no longer considered the intrusive visionary of the laboratory, but the acknowledged benefactor of his country at large, and particularly of an extensive class of coal and mine proprietors and iron masters, who have derived, and are still deriving, great wealth from this important discovery; and who, in the spirit of grateful acknowledgment, have pronounced it worthy of a crown of gold, or a monumental record on the spot where the discovery was first made.
"At an advanced period of life, such considerations are soothing and satisfactory. Many under similar circumstances have not, in their own lifetime, had that measure of justice awarded to them by their country to which they were equally entitled. I accept it, however, as a boon justly due to me, and as an equivalent in some degree for that laborious course of investigation which I had prescribed for myself, and which, in early life, was carried on under circumstances of personal exposure and inconvenience, which nothing but a frame of iron could have supported. They atone also, in part, for that disappointment sustained in early life by the speculative habits of one partner, and the constitutional nervousness of another, which eventually occasioned my separation from the Calder Iron Works, and lost me the possession of extensive tracts of Black Band iron-stone, which I had secured while the value of the discovery was known only to myself."
Mr. Mushet published the results of his laborious investigations in a series of papers in the Philosophical Magazine,—afterwards reprinted in a collected form in 1840 under the title of "Papers on Iron and Steel." These papers are among the most valuable original contributions to the literature of the iron-manufacture that have yet been given to the world. They contain the germs of many inventions and discoveries in iron and steel, some of which were perfected by Mr. Mushet himself, while others were adopted and worked out by different experimenters. In 1798 some of the leading French chemists were endeavouring to prove by experiment that steel could be made by contact of the diamond with bar-iron in the crucible, the carbon of the diamond being liberated and entering into combination with the iron, forming steel. In the animated controversy which occurred on the subject, Mr. Mushet's name was brought into considerable notice; one of the subjects of his published experiments having been the conversion of bar-iron into steel in the crucible by contact with regulated proportions of charcoal. The experiments which he made in connection with this controversy, though in themselves unproductive of results, led to the important discovery by Mr. Mushet of the certain fusibility of malleable iron at a suitable temperature.
Among the other important results of Mr. Mushet's lifelong labours, the following may be summarily mentioned: The preparation of steel from bar-iron by a direct process, combining the iron with carbon; the discovery of the beneficial effects of oxide of manganese on iron and steel; the use of oxides of iron in the puddling-furnace in various modes of appliance; the production of pig-iron from the blast-furnace, suitable for puddling, without the intervention of the refinery; and the application of the hot blast to anthracite coal in iron-smelting. For the process of combining iron with carbon for the production of steel, Mr. Mushet took out a patent in November, 1800; and many years after, when he had discovered the beneficial effects of oxide of manganese on steel, Mr. Josiah Heath founded upon it his celebrated patent for the making of cast-steel, which had the effect of raising the annual production of that metal in Sheffield from 3000 to 100,000 tons. His application of the hot blast to anthracite coal, after a process invented by him and adopted by the Messrs. Hill of the Plymouth Iron Works, South Wales, had the effect of producing savings equal to about 20,000L. a year at those works; and yet, strange to say, Mr. Mushet himself never received any consideration for his invention.
The discovery of Titanium by Mr. Mushet in the hearth of a blast-furnace in 1794 would now be regarded as a mere isolated fact, inasmuch as Titanium was not placed in the list of recognised metals until Dr. Wollaston, many years later, ascertained its qualities. But in connection with the fact, it may be mentioned that Mr. Mushet's youngest son, Robert, reasoning on the peculiar circumstances of the discovery in question, of which ample record is left, has founded upon it his Titanium process, which is expected by him eventually to supersede all other methods of manufacturing steel, and to reduce very materially the cost of its production.
While he lived, Mr. Mushet was a leading authority on all matters connected with Iron and Steel, and he contributed largely to the scientific works of his time. Besides his papers in the Philosophical Journal, he wrote the article "Iron" for Napiers Supplement to the Encyclopaedia Britannica; and the articles "Blast Furnace" and "Blowing Machine" for Rees's Cyclopaedia. The two latter articles had a considerable influence on the opposition to the intended tax upon iron in 1807, and were frequently referred to in the discussions on the subject in Parliament. Mr. Mushet died in 1847.
[1] Dr. Roebuck's grandson, John Arthur Roebuck, by a singular coincidence, at present represents Sheffield in the British Parliament.