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_.

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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.

Roscoe was largely instrumental in making spectrum analysis first known to British men of science and the British public generally. Almost immediately after the publication of Bunsen and Kirchhoff’s classical paper in _Poggendorff’s Annalen_, he translated it for the _Philosophical Magazine_. He also gave many public lectures on the subject, beginning with that at the Royal Institution on March 1, 1861—one of the most successful of the many he delivered there. Indeed, there were few of our larger towns in which he was not invited at one time or other during the sixties and early seventies to lecture on that astonishing development of nineteenth-century science. These lectures involved no inconsiderable effort. They necessitated much bulky and fragile apparatus difficult to transport. Some of the illustrations could only be shown to a large audience by means of the electric lantern, and this, in those days, needed the provision of a large battery of Groves’s cells; electricity “laid-on” by a public authority was not then, as now, almost everywhere available.

One of these courses of six lectures given to the Society of Apothecaries of London in 1868 was subsequently published, with additions, in an admirably illustrated volume which had a considerable measure of success—a second edition, still more largely augmented owing to the extraordinary rapidity with which knowledge on celestial chemistry increased, being called for within a year. In the preparation of a third and fourth edition he was assisted by his friend Dr. Schuster. As the successive editions show, the rate at which literature accumulated round the subject was altogether unprecedented in the history of scientific discovery.

Roscoe made an attempt to apply the spectroscope to the Bessemer process of steel manufacture, and for this purpose caused a long series of observations to be made, first at Brown’s Atlas works in Sheffield, and then at the Crewe works of the L. & N.W. Railway Company, when a considerable amount of information concerning the peculiarities of the spectrum of the converter-flame was gained, mainly by the observations of Dr. W. Marshall Watts, a former student and one of his assistants, who took over the subsequent conduct of the inquiry.

Considering his interest in the subject, comparatively little original work on spectroscopy was published by Roscoe.

The following is a list of the inquiries with which he was concerned:

“On the Effect of Increased Temperature upon the Nature of the Light Emitted by the Vapour of Certain Metals on Metallic Compounds.” By H. E. Roscoe and R. B. Clifton. _Manchester Phil. Soc. Proc._ II. (1860-1862), pp. 227-230.

“Note on the Absorption-spectra of Potassium and Sodium at Low Temperatures.” By H. E. Roscoe and A. Schuster. _Roy. Soc. Proc._ XXII. (1874), pp. 362-364.

“On the Absorption-spectra of Bromine and Iodine Monochloride.” By H. E. Roscoe and T. E. Thorpe. _Phil. Trans._ CLXVII. (1878), pp. 207-212.

“Note on the Identity of the Spectra Obtained from the Different Allotropic Forms of Carbon.” By H. E. Roscoe and A. Schuster. _Manchester Lit. Phil. Soc. Proc._ XIX. (1880), pp. 46-49.

“The Spectrum of Terbium.” By H. E. Roscoe and A. Schuster. _Chem. Soc. Jour._ XLI. (1882), pp. 283-287.

The only attempt he was able to make to contribute to our knowledge of the chemistry of the sun by spectroscopic observations had an unlucky ending. He formed one of the members of the Government expedition sent to Sicily to observe the total solar eclipse of December 22, 1870. The following letters refer to this subject:

VICTORIA PARK, MANCHESTER, _November 2, 1870_.

Lockyer has asked me to go with him in the American Eclipse Expedition. I have a good mind to do so, but I have written to say that I was not sure that I could make the observations alone (!), and that it would be very desirable that you should go too! So we shall see what comes of it.

I am unfortunately laid up with an attack of gout, which quite disables me and reduces me to the level of the beasts that perish. However, I hope soon to be all right again.

I will write to Francis about the Lisbon paper, which ought certainly to be out.…

Did Schorlemmer write to you about your attacking the Germans for attacking the French? He was quite wild, and came up to me in such a state of excitement that I could scarcely understand what he said. However, under the influence of cigars and a bottle of sherry he cooled down again and perhaps has buried his resentment.

Huxley comes for the first of the Science Lectures on Friday.

I am delighted to hear of your numbers of evening students, and was much pleased by your Introductory. I have no doubt that the laboratory will fill too. You must have patience.

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OWENS COLLEGE, MANCHESTER, _November 19, 1870_.

_Of course_ you come to Sicily.… Lockyer thinks of going on December 8th. Perhaps I may go a day earlier—with you if you can come—and spend twenty-four hours in Heidelberg.

I send box, stand, papers, and all I can find—except insolation affairs which cannot yet be got out of H⸺’s hands. He shall have no peace till they are ready, and they shall then be sent at once to you. _You_ will be responsible for the whole apparatus being in order. Look them over carefully.… You know what is wanted.

Unfortunately H.M.S. _Psyche_, the vessel conveying the party from Naples, was wrecked off Aci Reale, about a couple of miles to the north of the classic Cyclops rocks, and under the shadow of Etna, by striking a submerged and uncharted rock. The ship was badly holed, and rapidly began to fill, but fortunately the weather was fine and the sea calm, and all were got safely on shore. The cliffs were scarcely 200 yards away, but the landing was difficult, the jagged reefs of lava seeming to afford no sure footing. Eventually all the instrumental equipment was also landed, in a more or less damaged condition, but much of the personal baggage was lost. A letter written by one of the members of the expedition which found its way into a Manchester newspaper thus describes the event:

We formed ourselves into a line to pass the things along the rocks to the prominence which we had mounted.… Everybody worked with a will, and laboured like galley-slaves. The ship had now settled down considerably; the water was up to her quarter, and the boats pushed off in the expectation that she would roll off the reef. By this time we had almost stripped the ship of everything easily movable, and we prepared to get it to a secure place. The nearest point habitable was Catania, seven miles to the south, and we got the boats ready to take ourselves and our things thither.… Roscoe assumed command of our expedition. Everybody seemed to look to him instinctively. I shall never forget the sight of him, standing, with his legs apart to steady himself on a narrow piece of the lava rock, with his arm stretched out, giving his orders with the authority of one who seemed born to command. As the gig was about to push off I saw him look round, and when he saw me he motioned for me to get into it.… In a few hours the remainder of the party arrived, and shortly afterwards the luggage and apparatus.

It was arranged that Roscoe, assisted by the late Sir George Darwin and Mr. Bowen of Harrow School, should make observations on the spectrum of the corona from a position on Mount Etna as high as the snow would permit. On the day before that of the eclipse the party had toiled up more than 5,000 feet of the mountain with their instruments strapped on the backs of half a dozen mules, to a deserted hut on the side of the volcano. The night was spent in a storm of rain and snow, and next morning, in a piercing wind, the instruments were put together with benumbed fingers. As the sun was gradually covered, the sky became clouded over and the upper part of Etna was completely enveloped in fog, and during the minute of totality a violent hailstorm broke over the party, rendering all observations impossible.

A number of measurements of the chemical intensity of daylight during the progress of the eclipse were, however, made by the writer at Catania, some little distance away, by the method described by Roscoe in the Bakerian Lecture for 1865. These showed that the diminution in the total chemical intensity of the sun’s light during an eclipse is directly proportional to the magnitude of the obscuration of the solar disc.[26]

This matter is referred to in the following letter.

_June 11, 1871._

The results are very interesting, and you have worked them out in an _admirable_ manner. I had no idea that so much could be made out.

I am writing at once to Airy and Lockyer to ask them whether we may not send the paper to the Royal Society (last meeting on _Thursday next_) so as to have it in series with our other papers.

I have just heard from Wild, the director of all the Russian observatories, that he is anxious to adopt the plan over all the Russias, and wants an automatic arrangement. So I am going in for it and hope to get a machine made before long. It is really too important to be delayed.

You deserve great credit for your labours, and by rights the paper should be _yours alone_, but perhaps we [had] better keep together. We can do the automatic affair also together if you like.

The automatic arrangement alluded to has already been mentioned. It was not proceeded with.