William Henry Fox Talbot and the foundations of spectrochemical analysis

Talbot is one of the early researchers into the field of spectral analysis. Between 1826 and 1836 he made several significant contributions and deserves recognition as one of the founders of modern spectrochemical analysis. William Henry Fox Talbot is generally…

Talbot is one of the early researchers into the field of spectral analysis. Between 1826 and 1836 he made several significant
contributions and deserves recognition as one of the founders of modern spectrochemical analysis. William Henry Fox Talbot is generally regarded as one of the founders of modern photography. Of two biographical encyclopedias
of science consulted, only one contains an entry but makes no mention of any contributions to spectroscopy (1). The internet
sites are scarcely better (2,3). However, some older texts on spectroscopy do note his experiments with flame spectra (4–6)
and the latter two considered him the founder of spectrochemisty, a title traditionally reserved for Kirchhoff and Bunsen.
One such claim might well be dismissed, but two would seem to demand further investigation. English classical scholar, mathematician, scientist, and inventor William Henry Fox Talbot was born on February 11, 1800,
in Melbury, Dorset, England. He was the son of William Davenport Talbot, an officer in the Dragoons, and Lady Elizabeth Fox
Stangeways, daughter of the second Earl of Ilchester. His father died when he was but five months old. However, to his good
fortune, his stepfather — his mother remarried in 1804 — treated him with love (3). Talbot entered Trinity College in Cambridge, England, in 1817 where he won prizes in Greek verse. He graduated with classical
honors in 1921 and was 12th in his class in mathematics (3). Spectroscopic Investigations In 1826 Talbot published a paper entitled “Some Experiments on Coloured Flames.” He described using an alcohol burner and
simple spectroscope to observe the flames produced by salts of sodium, potassium, and strontium. Discussing the red line observed
with the flame of niter or of a chlorate of potash, Talbot wrote The red ray appears to possess a definite refrangibility and to be characteristic of the salts of potash, as the yellow ray
is to the salts of soda. . . . If this should be admitted I would further suggest that whenever the prism shows a homogeneous
ray of any colour to exist in a flame, this ray indicates the formation or the presence of a definite chemical compound. In 1834, in a paper entitled “Facts Relating to Optical Science,” Talbot noted that the flame spectra of strontium and lithium
salts were visually indistinguishable. He wrote The strontia flame exhibits a great number of red rays well separated from each other by dark intervals. . . . The lithia
exhibits one single red ray. Hence I hesitate not to say that optical analysis can distinguish the minutest portions of these
two substances from each other with as much certainty, if not more, than any other known method. It is for this statement that Twyman (6) considers Talbot to be the discoverer of spectrochemical analysis. In 1835 Talbot wrote on the nature of the continuous spectrum, which he correctly attributed to the heating of matter: In short, we see that the mere presence of the lime in a heated state is the cause of the light . . . the emission of intense
light by a particle of lime in this experiment without the loss of any portion of its own substance, arises from the cause
above referred to — namely that the heat throws the molecules of lime into a state of such rapid vibration that they become
capable of influencing the surrounding aetherial medium and producing in it the undulations of light. Later in the same paper he comments on the dark lines in the spectrum produced by iodine vapor: “I have found by careful observation
that they are not equidistant, but that they become gradually more crowded towards the blue end of the spectrum. This . .
. seems a consequence of some simple general law.” Still later he notes, : . . . I have advanced the hypothesis that the vibrations of light and those of material molecules are capable of mutually
influencing each other. It remains to be seen whether the same hypothesis does not afford a clue to the explanation of this
apparently complex phenomenon of absorption. . . . Let us suppose that iodine vapour is so constituted that its molecules
are disposed to vibrate with a rapidity not altogether dissimilar to that of light. Now, if the different coloured rays differ
also (as is probable) in rapidity of vibration, some of them will vibrate in accordance and others in discordance, with the
vibrations of the iodine gas, and these accordances will succeed each other in regular order from the red end of the spectrum
to the violet end; each discordance marked by a dark line or deficiency in the spectrum, because the corresponding ray is
not able to vibrate through the medium but is arrested by it and absorbed. The quotations above are all from Frank Twyman (6), managing director of Hilger Ltd. for many years, who was a significant
player in the development of spectroscopic instrumentation in the early decades of the 20th century. Inasmuch as this author
has no access to the originals, the papers quoted by Twyman are as follows: Brewster J. Sci. 5, 77 (1826); Phil. Mag. 3(4), 112–114, (1834); Phil. Mag. 3(7), 113 (1834).