of nine John became first a bobbin-winder, and then a hand-loom weaver. At ten a workman in a print-works taught him reading, writing, and arithmetic. He also learnt to play on several instruments, and gave much time to music, to which he remained keenly sensitive through life. When he served as a militiaman, a few years later, he was known as ‘Awkward John,’ and he was transferred to the band. In 1807 his future career was decided by seeing on his infant half-brother a dress of an orange-colour, which ‘set him all on fire to learn dyeing.’ He straightway bought all the dyeing materials he could procure, and, having by a long series of experiments learnt to dye in most colours, he set up in partnership with a man who had suitable premises, and they ‘dyed for Great Harwood and the surrounding country;’ the material operated on consisting chiefly of the remnants which were at that time the perquisites of the hand-loom weavers. In September 1809 Mercer gave up this business, despite its success, to become an apprentice in the colour-shop of the Oakenshaw print-works on the invitation of the owners, Messrs. Fort Bros. But the jealousy of a foreman prevented him from acquiring any real knowledge of the processes employed; and he therefore, in the following year, accepted the surrender of his indentures offered by his masters, who were forced by commercial distress, due to the Berlin decrees, to reduce their staff. Mercer again became a hand-loom weaver, and invented many ingenious designs in weaving. He also gave much attention to the study of mathematics, in which he was helped by an excise surveyor named Lightfoot. In 1813 he became deeply religious and joined the Wesleyans. In the same year he became engaged to Mary Wolstenholme, whom he married on 17 April 1814.
In 1813 Mercer had resumed work as a dyer, while still continuing to weave, and in 1814 his attention was directed towards chemistry by the ‘Chemical Pocket-Book’ of James Parkinson, which ‘introduced him [he writes] into a new world.’ It was this book which led him to his first discovery of importance, a method of fixing orange sulphide of antimony on cotton-cloth; no good orange dye suitable for calico-printing having been previously known. The details of the process were communicated to a firm of printers, and successfully applied, but Mercer received no reward for his services. In 1818 Messrs. Fort Bros. re-engaged Mercer, this time as a chemist in their colour-shop, at a salary of thirty shillings a week. In 1823 Mercer rediscovered and introduced into England a method of applying to cotton-cloth lead chromate, a yellow dye of great importance, originally discovered in France by D. Koechlin, whose patterns had been shown to him. He also discovered the use of certain manganese compounds, which still have considerable importance as bronze dyes, greatly improved the methods of printing indigo, and made many other minor inventions. In 1825 Mercer was taken into partnership by Messrs. Fort Bros., and continued a partner of the firm until its dissolution in 1848. During this period Mercer showed great mental activity, technical discoveries of more or less importance following each other in quick succession from his laboratory.
Mercer took a keen interest in theoretical chemistry, and this interest was greatly stimulated and strengthened by the influence of Dr. Lyon (now Baron) Playfair. The two men became friends in 1841, Playfair being then one of the chemists at Messrs. Thompson's works at Clitheroe. Playfair and a few scientific friends met once a week at Whalley to discuss scientific matters; and it was at one of the Whalley meetings that Mercer propounded the first rational theory of the so-called ‘catalytic’ action. He read a paper on the subject at the Manchester meeting of the British Association in 1842; and the theory was more fully developed and illustrated by Playfair (Mem. Chem. Soc. iii. 348). Certain observations of his made in 1843, and discussed at the Whalley meetings, led Playfair to the discovery of a new class of compounds, the nitro-prussides. In 1847 Mercer joined the Chemical Society (ib. iii. 315). In 1848 the Oakenshaw firm decided to dissolve partnership and retire, rather than face the severe competition which had arisen among calico-printers—their determination proceeding chiefly from an unwillingness to manufacture goods of an inferior quality at a cheaper rate. The profits of the undertaking had been considerable, and Mercer was now free to pursue researches sketched out during the busy years. He undertook an investigation on the action of caustic soda, sulphuric acid, and zinc chloride on cotton-cloth, paper, and other materials made from vegetable fibre. These experiments (which were carried out in commercial partnership with Robert Hargreaves of Broadoak, near Accrington, and at his works) led to the discovery of the process known as ‘mercerising,’ and to the preparation of parchment paper, patented by Mercer in 1850. By treating cotton-cloth with any one of the reagents mentioned, in a solution of a certain concentration, the individual cotton fibres become thicker and shorter, and the
