proved insufficiently elastic for new developments, and has not been generally adopted.
Frankland in 1865 was asked to continue Hofmann's monthly analyses of metropolitan drinking water, and he continued to do this for the registrar-general and for the local government board, improving the methods and extending the scope of his investigation down to his death. Together with his pupil, Professor Henry Edward Armstrong, he devised new methods of water analysis, which he embodied in a book on the subject, 'Water Analysis for Sanitary Purposes,' published in 1880.
In 1868 a second royal commission on rivers pollution, consisting of Major-general Sir William Thomas Denison [q. v.], Mr. John Chalmers Morton [see under Morton, John, 1781-1864], and Frankland, was appointed to complete the labours of the first commission (1865-8), and to extend them to Scotland. The new commission set up a laboratory under the direction of Frankland, and issued six annual reports, 1868-74, dealing with the pollution of rivers, the purification of sewage, and the domestic water supply. An immense amount of work was done on the river basins of England and Scotland, and the work has served as a foundation for subsequent investigations of problems still not satisfactorily solved. Frankland recognised the great superiority over other processes of intermittent downward filtration through land as a means of sewage purification. His investigations form the basis of the bacteriological process of purification now extensively employed. The work on water analysis finally absorbed nearly the whole of Frankland's time not devoted to teaching.
In 1885 he resigned his professorship at the Royal School of Mines, and went to live at his house, The Yews, at Reigate. After his retirement he worked at the chemistry of storage batteries (Proc. Roy. Soc. 1883, xxxv. 67, and 1889, xlvi. 304), and fitted his house with a battery devised on a system of his own. Frankland died on 9 Aug. 1899, after a short illness, at Golaa, Gudbrandsdalen, in Norway, where for many years he had spent his summer holiday in his favourite pursuit of salmon fishing.
The Royal Society's Catalogue (carried down to 1884) includes sixty-three papers by Frankland alone, two in collaboration with Kolbe, fifteen with B. F. Duppa, one with H. E. Armstrong, three with J. Norman Lockyer, and ten with other chemists. In 1877 he published, with a dedication to Bunsen, a volume of 'Experimental Researches in Pure, Applied, and Physical Chemistry,' which includes the papers published down to that date. He also published the following books: 1. 'How to teach Chemistry,' 1875 (six lectures delivered in 1872 and summarised by G. Chaloner). 2. 'Chemical Lecture Notes,' 1st edit. 1866; 2nd edit. 1870-2; 3rd edit. 1881 (in collaboration with F. R. Japp). 3. ' Inorganic Chemistry,' with F. R. Japp, 1884. 4. 'A Course of Lectures on Gas-lighting' (delivered at the Royal Institution in March 1867, and originally published in the 'Journal of Gas-lighting'). He also contributed articles on chemistry to the 'English Cyclopaedia,' and he gave a number of lectures before the Chemical Society and at the Royal Institution.
Besides the memoirs alluded to in detail above, Frankland published an important thermo-chemical investigation in connection with the well-known 'Faulhorn' experiment of his brother-in-law, A. Fick, and J. Wislicenus, on the 'Origin of Muscular Power' (Philosophical Mag.  xxxi. 485, xxxii. 182), which they attributed mainly to the combustion of carbohydrates, and not to that of muscle-substance, a result which has been generally confirmed. He devised, with W. J. Ward, certain improvements in methods of gas-analysis. He wrote several papers on meteorology (especially Alpine) and the glacial epoch, and he suggested that the persistency of town-fog is due to a film of coal-oil on the surface of the minute globules of water of which it is formed.
Frankland was an exceptionally brilliant and accomplished man of science. In nearly every fresh research he broke new ground, and laid the foundations for important work in the future. It is by his suggestion of the notion of valency, and by the great contributions to organic chemistry enumerated above, that he will be chiefly remembered. Frankland's memoirs are markedly clear in general plan and in expression. He had great manipulative skill in the laboratory.
Frankland was twice married; first, on 27 Feb. 1851, to Sophie, daughter of F. W. Fick, chief engineer to the electorate of Hesse-Cassel (d. 7 Jan. 1874), by whom he had three sons, Frederick William (b. 18 April 1854), sometime chief commissioner of government insurance in New Zealand, and Percy Faraday (b. 3 Oct. 1858), now professor of chemistry in the university of Birmingham, the third dying in infancy, and two surviving daughters; and secondly, in 1875, to Ellen (d. 20 Jan. 1899), daughter of C. K. Grenside of the Inner Temple, by whom he left two daughters.
A marble medallion of Frankland, by John