The Platinum Process

It may be wondered why Knight should then turn his mind to the problem of producing the hitherto intractable metal platinum in malleable form, but the potential value of the metal had formed the subject of a number of papers and articles in the scientific periodicals that had now begun to be published in London, these following upon several reports of but indifferent progress made by workers in Sweden, Germany, France and Spain (10). The Repertory of Arts and Manufactures, for example, founded in 1794, reproduced in 1797 the classic paper, “Observations on Platina”, read by Lavoisier to the Académie des Sciences some seven years earlier in which he described Janety’s process using arsenic (11) while John Aikin’s newly established Monthly Magazine reprinted in March 1798 an account of the researches of the Russian metallurgist Count Mussin-Pushkin in compressing a mixture of platinum and mercury and forging it at a white heat (12). In the October and November of the same year Tilloch’s Philosophical Magazine carried a translation of the paper by the Abbé Rochon, “Observations on Platinum and its Utility in the Arts”, from the Journal de Physique (13). Earlier sources of information available to Knight would have included William Lewis’ “Commercium Philosophico-Technicum” published in parts between 1763 and 1765 and including some 170 pages on platinum, as well of course as Macquer’s “Dictionnaire de Chymie” that had been translated into English by James Keir in 1777, while Priestley’s own “Heads of Lectures on a Course of Experimental Philosophy”, published just prior to his departure for America in 1794, also included two pages on platinum. (Priestley was also sufficiently interested in platinum to purchase a modest amount; his claim for compensation after the destruction of his house and laboratory on July 14, 1791 includes the item “Half a pound of platinum £2.8.0”).

Thus the problem of the infusibility of platinum and the numerous attempts to overcome this was much in the air at this time, there was considerable interest in finding a reliable method of rendering it workable, and it was clearly the prospect of commercial success that motivated Knight. His paper opens:

The earlier chemical part of his process, dissolution in aqua regia and precipitation with sal ammoniac, was not new, but his important innovation was the much more forcible hot compression of his precipitate in a hollow inverted refractory cone to a compact mass that could then be forged into an ingot of malleable metal. This process had the principal advantage of avoiding contact between the platinum and red hot iron that had readily introduced contamination in the hands of other workers, but rather curiously there is no indication that he made much practical use of his process or that he made more than one or two articles from his platinum. In fact, in February 1801, scarcely more than a year after his paper was presented, he disposed of the considerable quantity of 800 ounces of native platinum to Wollaston at four shillings an ounce, half of the cost being met by Smithson Tennant (14). His acquaintance with Wollaston undoubtedly arose from the close proximity of the Foster Lane premises to the Church of St. Vedast, exactly opposite and only a few feet away across this narrow lane, where the rector, from 1779 until his death in 1815, was the Rev. Francis Wollaston—father of the scientist—and where members of Knight’s family had attended and had been buried. Why Knight abandoned his platinum work we shall never know, but possibly he foresaw that greater success might be achieved in the hands of a more professional scientist. This purchase was only the second of many such transactions made by Wollaston in the early days of his extensive researches.

Although Knight claimed a high degree of purity for his product it must be remembered that the other five members of the platinum group were then unknown. A recent study by Professor M. C. Usselman and his colleagues, who reproduced Knight’s process starting with native platinum from Colombia provided by Johnson Matthey Inc., has shown that the product would have contained only 94 per cent of platinum with 2 per cent of iron, 2 per cent iridium and small amounts of palladium, rhodium and lead (15). These impurities could have caused problems for Knight in the fabrication of his few products.

In the meantime Richard’s father William Knight had died in January 1799 and he became the sole owner of the business, being joined two years later by his younger brother George, the firm then becoming known as R. and G. Knight and continuing in this style until 1838. It was now that, with a secure basis for expansion, Richard turned from ironmongery to the devising of apparatus and equipment, an activity in which he progressed and prospered for the remainder of his life, serving his fellow scientists with their needs in the rapidly developing technology of the period.

The isolation of sodium and potassium by Humphry Davy in 1807, employing a rather crude assembly of a platinum spoon to hold the caustic soda and caustic potash and bringing them into contact with a platinum wire connected to the negative pole of a battery, aroused of course, considerable excitement in scientific circles, and this classic experiment was repeated on numerous occasions, first before the Askesian Society and the British Mineralogical Society by William Allen and William Hasledine Pepys using a more sophisticated platinum apparatus designed by Pepys and made in several versions by Knight (16).

A little earlier Humphry Davy, in one of his lectures for the Board of Agriculture on the analysis of soils, recommended a chemical chest supplied by Knight (17).

By 1811 Knight was able to publish an extensive catalogue of “Apparatus and Instruments for Philosophical, Experimental and Commercial Chemistry” this including furnaces, retorts, stills, blow pipes, electric batteries, thermometers and a range of platinum apparatus.

The British Mineralogical Society was discontinued in 1805, most of the members including Knight then becoming proprietors of the new London Institution, while in 1807 he was one of the eleven founder members of the Geological Society, being chosen as a member of their Committee for Chemical Analysis.

Richard Knight retired in 1838 at the age of seventy, the business being carried on by his brother George and later by the latter’s two sons George and Richard. He had moved from Clapton in 1830 to a house in Tavistock Square where he died on February 21, 1844, leaving a thriving business and the very considerable sum of £35,000 to his five daughters, his wife having pre-deceased him by eight months (18). He was buried in the grounds of the New Gravel Pit Chapel in Hackney where he had been for so long a leading member and for some years a trustee.

An obituary notice written by his life long friend William Hasledine Pepys appeared in the journal associated with the Unitarian movement (19), but otherwise this industrious chemist, mineralogist and instrument designer, despite his friendship with so many scientists of his time, seems to have left but little record of his achievements other than a brief account of an early method of producing platinum in usable form.