Thanks for your news of my dear friend. I have been very remiss in not writing to him. Tell him so, please; and ask him to send me the first proof-sheets of his “Filtration” paper for me to translate; unless, indeed, you do it yourself, as I am sure you can perfectly well. Give B[unsen] my kindest regards, and say that I will write to him soon.
Part II of “Researches on Vanadium,” dealing with the chlorides VCl₄, VCl₃, and VCl₂, and metallic vanadium, which he obtained by heating the dichloride in hydrogen, was presented to the Royal Society on June 16, 1869,[18] and his last memoir, treating of the bromides, and of certain of the metallic vanadates, including vanadinite which he prepared artificially, on April 7, 1870.[19]
With the mention of a short communication, “On Two New Vanadium Minerals,” to the Proceedings of the Royal Society for 1876,[20] and of a lecture on “Recent Discoveries about Vanadium” at the Royal Institution, the foregoing statement includes all Roscoe’s published contributions to the history of vanadium. As regards original work, he handed over the subject to his senior students, and under his inspiration and direction a considerable number of communications from the Owens College Laboratory were made to the Chemical Society from Crow (1876), Bedson (1876), H. Baker (1878), Kay (1880), Brierley (1886), Hall (1887), and published in the Transactions of the Chemical Society.
Other noteworthy contributions by Roscoe to inorganic chemistry are his study of tungsten compounds, in which he describes for the first time the existence of the pentachloride WCl₅ and the corresponding pentabromide WBr₅,[21] and his discovery of uranium pentachloride, UCl₅.[22]
These compounds are of considerable theoretical interest on account of their “anomalous” character. He also discovered columbium trichloride, CbCl₃, which he found to have the remarkable property of decomposing carbon dioxide when heated in that gas with the formation of columbium oxychloride, CbOCl₃, and carbon monoxide—a reaction not exhibited by any other metallic chloride (Chem. Soc. Abstracts, 1878, 272), and he determined the vapour densities of the chlorides of lead and thallium which he showed to be normal.[23]
An examination of the earth metals contained in samarskite proved that the rare earth-metal announced by Delafontaine under the name of “philippium” was a mixture of yttrium and terbium.[24]
The spark spectrum of terbium was at the same time mapped by him and Schuster. An examination of a specimen of oxide which ought to contain “philippium” in large quantities if that chemical element existed showed no conclusive evidence of any other metals than yttrium or terbium.[25]
In 1882 he sent to the French Academy a note on a re-determination of the atomic weight of carbon by the method of Dumas and Stas, using Cape diamonds, and obtained the value 12·002 (O = 16) as the mean of six experiments (Chem. Soc. Abstracts, 1882, 724). He also showed, with the assistance of Schuster, that the spectrum of the carbon dioxide furnished by the South African diamond was identical with that furnished by other forms of carbon.
So long as he remained in Manchester Roscoe was in the habit of making occasional contributions to the meetings of the Literary and Philosophical Society on general or local interest. Among these communications were papers on arsenic-eating in Styria; on a crystallizable carbon compound in the Alais meteorite; on the amount of carbonic acid in Manchester air; on the corrosion of leaden hot-water cisterns; Dalton’s first table of Atomic Weights, etc.—all of which are printed in the Proceedings or Memoirs of the Society.