Page:Dictionary of National Biography, Third Supplement.djvu/544

 sons and a daughter, who survived him. He died of heart-failure on 14 December 1913, while staying at a London hotel, and was buried at Sonning.

 SWAN, JOSEPH WILSON (1828–1914), chemist and electrical inventor, the second son of John Swan, by his wife, Isabella Cameron, was born at Sunderland 31 October 1828, and educated at Hendon Lodge and Hylton Castle, near Sunderland, under the Rev. John Wood, who interested him in science and encouraged him to study such scientific books as were then available. At the age of fourteen he was apprenticed to a firm of chemists and druggists at Sunderland, where he obtained considerable experience in operative and experimental chemistry. Before the end of his apprenticeship he joined the business of John Mawson, a chemist of Newcastle, and, encouraged by Mawson's kindly interest, he continued his experimental researches, and later became a partner in the business.

Swan was interested in photography, and, on the invention of the collodion process by Frederick Scott Archer [q.v.] in 1851, turned his attention to improvements in the manufacture of collodion; his firm soon after brought out a preparation of collodion for photographic use which has never been excelled. The experiments of W. H. Fox Talbot [q.v.] and Farguier had shown the possibility of a photographic printing process based on the hardening action of light on bichromated gelatine, but the methods were uncertain and of little practical use until Swan in 1864 patented the ‘carbon process’ (afterwards known as ‘autotype’), which by the use of the methods of single and double transfer rendered the production of permanent prints a matter of ease and certainty. The carbon process was also used for the production of a variable resist to the etching solution in photogravure and became the basis of that widely-used form of photo-engraving. The variation of relief in a carbon print suggested to Swan the making of an electro-type matrix from which prints were mechanically produced by casting with a gelatinous pigment, and the process of ‘photo-mezzotint’, patented in 1865, led to the stannotype and Woodburytype methods of printing. The chrome tanning of leather was also one of the results of Swan's study of the reactions of chromic acid and gelatine. During the next fifteen years Swan experimented on the production of typographic half-tone blocks and patented the use of line screens in such work.

In 1871 Swan's attention was attracted to the improvement of the gelatino-bromide of silver emulsion invented by Dr. R. L. Maddox, and he discovered that the sensitiveness depended on the temperature at which the emulsion was formed, and also on its being subjected for some time to a somewhat high temperature. This was the real starting-point of the manufacture of rapid dry plates, and the gelatine-silver bromide plates of Mawson and Swan soon became famous. Two years later the same methods were employed in the preparation of bromide paper, the forerunner of the development papers afterwards so widely used.

Swan's name is more widely known in connexion with the development of incandescent electric lighting. Arc lights, run from primary batteries, had been in use for some time, but the subdivision of the electric light was the great difficulty, and to this Swan turned his attention. At a lecture given by W. E. Staite he had been much interested by the light given off by a fine platinum-iridium wire rendered incandescent by a battery current, and he considered that in this direction lay the solution of the problem of subdivision. T. A. Edison had already patented a lamp in which a carbon high resistance filament was heated to incandescence in a vacuous globe, but owing to the difficulty of preparing the filaments and of obtaining a good vacuum in the globe, the lamps were short-lived and of little practical use. Swan, however, succeeded in producing fine carbon filaments by squirting a solution of dissolved cellulose (‘viscose’) through fine apertures into a coagulating solution, and the filaments so obtained, after drying and carbonization, were mounted to the conducting ‘leads’ by short-circuiting under a solution of benzol and aniline, while the application of the Sprengel air-pump secured the necessary vacuum in the globe. His first lamp was shown at the Newcastle Literary and Philosophical Society in February 1879, and in that year his own house and that of (Sir) William Crookes [q.v.] were lit by these lamps. Swan's improvements in Edison's invention were a complete success, and the Edison-Swan lamp solved the problem.

In other branches of electrical science Swan made important advances. His  518