Henry Enfield Roscoe to Faraday   26 April 1860

Owens College, | Manchester, | April 26th 1860

My dear Mr. Faraday

You will I know be interested to hear that Bunsen has discovered a new alkaline metal1 - discovered it by a method which, it seems to me, is for our Science of Chemistry what Adams’s2 & Leverrier’s3 discovery of the planet Neptune is in Astronomy4.

I believe I mentioned to you, when I saw you last, that Bunsen and Kirchoff are engaged at present upon what they term “Spectral Analysis” ie, the identification of the constituents of a body by means of the various colours which these constituents impart to the flame.

You will probably have read a short notice given by Stokes in the Phil: Mag: a month or two ago of Kirchoff’s5 most interesting and important discovery of the cause of the Fraunhofers6 lines in the Solar Spectrum7.

Making use of this important discovery, Bunsen finds that every (or almost every) elementary body or its compounds imparts to a colourless flame light of a definite degree of refrangibility - soda for example giving a spectrum consisting of two narrow bright bands corresponding exactly in refrangibility to the dark line D in the Sun’s spectrum. In this way, if a mixture of the Salts of Ba. Sr. Ca. Mg. Li. K. Na be made - & if 1/10 of a milligramme in weight of such a mixture be placed in a colorless flame (of Hydrogen - or Coal gas & air) and if the resulting coloured rays be allowed to pass through a prism, the spectrum thus formed will show bands of light in different positions, each one of which corresponds to, & is produced by one of the constituents of the mixture. Thus at one glance the presence of each of these substances - in a mere trace of such a mixture - may in one moment with certainty be detected.

Bunsen has found Lithium in all the potashes which he has examined, also in 20 grammes of Sea-water!

Now examining in this way the alkalies he has found a substance which in its spectral relations is different from any of the 3 known fixed alkalies (K.Na.Li) - but up to the present time he has not found it in quantities sufficient to enable him to isolate it or to obtain the Chemical analogies of its salts.-

I need not insist on the immense importance of these investigations & the new & vast areas they open out -

I intend going to Heidelberg in the summer, & on my return I should be glad, if you think it adviseable, to give an account of these experiments on one of your Friday Evenings in the spring8.

Ever my dear Mr. Faraday truly yours | Henry E. Roscoe

Prof Faraday.

1
This was caesium. On Bunsen’s discovery see James (1983a), 43.
2
John Couch Adams (1819-1892, ODNB). Astronomer and Fellow of Pembroke College, Cambridge, 1853 to 1892.
3
Urbain Jean Joseph Leverrier (1811-1877, DSB). Director of the Paris Observatory, 1854-1870.
4
Neptune was discovered in 1846. On this see Grosser (1962).
5
Gustav Robert Kirchhoff (1824-1887, DSB). Professor of Physics at Heidelberg, 1854-1875.
6
Joseph Fraunhofer (1787-1826, DSB). Bavarian glassmaker and discoverer of the eponymous lines in the solar spectrum.
7
Stokes (1860).
8
Roscoe (1861), Friday Evening Discourse of 1 March 1861.

Bibliography

GROSSER, Morton (1962): The Discovery of Neptune, Cambridge, MA.

JAMES, Frank A.J.L. (1983a): “The Establishment of Spectro-Chemical Analysis as a Practical Method of Qualitative Analysis, 1854-1861,” Ambix, 30: 30-53.

ROSCOE, Henry Enfield (1861): “On Bunsen and Kirchhoff's Spectrum Observations”, Proc. Roy. Inst., 3: 323-8.

STOKES, George Gabriel (1860): “On the Simultaneous Emission and Absorption of Rays of the same definite Refrangibility; being a translation of a portion of a paper by M. Léon Foucault, and of a paper by Professor Kirchhoff”, Phil. Mag., 19: 193-7.

Please cite as “Faraday3768,” in Ɛpsilon: The Michael Faraday Collection accessed on 30 April 2024, https://epsilon.ac.uk/view/faraday/letters/Faraday3768