These investigations were carried on for more than two years, concurrently with the technical and outside work required. During this time purification works had been established at Crossness and Barking outfalls, a sludge ship had been provided for the disposal of the sewage sludge at sea, and the effect of the discharge had been studied in the lower reaches and estuary of the Thames, and a chemical survey of the condition of the foreshores had been completed. But the formation of the London County Council, with Lord Rosebery as the first Chairman, involved new arrangements. This circumstance, combined with the death of Sir Joseph Bazalgette, the Chief Engineer, and the opposition of the Labour Party, resulted in Roscoe resigning his post as Scientific Adviser.
Mr. Lunt transferred his services to the British Institute of Preventive Medicine, but Roscoe continued to carry on his laboratory with the assistance of Mr. Frank Scudder until 1898. During this period he acted as chemical adviser to sanitary authorities all over the country on questions of sewage purification and water-supply; and was frequently consulted by manufacturers on works-processes, and on legal, patent, and trade-mark cases, and in connection with parliamentary inquiries, e.g. humidity and purity of air in textile mills, flashpoint of paraffin oils, etc. He was further concerned in the promotion of Bills for the creation of rivers boards, as, for example, those of the Mersey and Irwell and West Riding. He gave considerable attention to the question of the manufacture and use of water gas (“carburetted” and “blue” gas), and inspected most of the water-gas plants then in operation in England and on the Continent, sending Mr. Scudder to visit and report on the installations in the principal cities of America. In 1898 they both gave evidence before a Parliamentary Committee on the question of restricting the amount of the poisonous carbonic oxide in town gas.
In 1891 Roscoe’s services were retained by the Mersey and Irwell Joint Committee to report on the influence of the various manufacturing works in the Mersey and Irwell basins in polluting the streams, and as to the best means of preventing it. In 1893 the Committee made the position of Scientific Adviser a permanent appointment, and established a properly equipped laboratory in Manchester in connection with its work. Roscoe retained the appointment until 1905, when the frequent journeys to attend the meetings of the Joint Committee began to tell upon his health, and at his suggestion Mr. Scudder was appointed to succeed him. The London laboratory was given up in 1908.