ON THE METAL INDIUM. 
3^7 
and among them sulphur and nitrogen, exhibit two distinctly different spectra when the 
temperature is altered, in this respect resembling the metals of the alkaline earths. 
This difference Pliicker ascribes to the existence of these elements in two allotropic con¬ 
ditions. 
A singular relation with regard to what have been termed the carbon lines was ob¬ 
served by the speaker. It has been stated that all the various forms of carbon com¬ 
pounds, "when in the state of incandescent gas, yield identical spectra. This proves not 
to be the case; the spectrum obtained from the flame of olefiant gas is different from 
that obtained by the electric discharge through a vacuum of the same gas ; whilst the 
spark passing through a cyanogen vacuum produces a spectrum identical with that of 
the olefiant gas-flame, and through the carbonic oxide vacuum a spectrum coincident 
with that of the spark through olefiant gas-vacuum. 
As an illustration of the application of abstract scientific principles to useful practical 
purposes, the speaker stated that he had lately applied spectrum analysis to the manu¬ 
facture of steel by the Bessemer process. One of the great drawbacks to the successful 
practical working of Mr. Bessemer’s beautiful process for converting cast-iron directly 
into steel, has been the difficulty of determining the exact point at which the blast of 
air passing through the molten metal is to be stopped. The conversion of five tons of 
cast-iron into cast-steel usually occupies from fifteen to twenty minutes, according to 
the varying conditions of weather, quality of the iron, strength of the blast, etc. If 
the blast be continued for ten seconds after the proper point has been attained, or if it 
be discontinued ten seconds before that point is reached, the charge becomes either so 
viscid that it cannot be poured from the converting vessel into the moulds, or it contains 
so much carbon as to crumble under the hammer. Up to the present time, the manu¬ 
facturer has judged of the condition of the metal by the general appearance of the 
flame which issues from the mouth of the converting vessel. Long experience enables 
the workman thus to detect, with more or less exactitude, the point at which the blast 
must be cut off. It appeared to the speaker that an examination of the spectrum of this 
flame might render it possible to determine this point with scientific accuracy, and that 
thus an insight might be gained into the somewhat complicated chemical changes which 
occur in this conversion of cast-iron into steel. At the request of Messrs. John Brown 
and Co., of the Atlas Works, Sheffield, the speaker investigated the subject, and suc¬ 
ceeded in obtaining very satisfactory and interesting results. The instrument employed 
was an ordinary Steinheil’s spectroscope, furnished with photographic scale and lamp, 
and provided with a convenient arrangement for directing the tube carrying the slit 
towards any wished-for part of the flame, and for clamping the whole instrument in 
the required position. By help of such an arrangement the spectrum of the flame can 
be most readily observed, and the changes which periodically occur can be most accu¬ 
rately noted. 
The light which is given off by the flame in this process is most intense—indeed, a 
more magnificent example of combustion in ox} r gen cannot be imagined ; and a cursory 
examination of the flame spectrum in its various phases reveals complicated masses of 
dark absorption bands and bright lines, showing that a variety of substances are present 
in the flame in the state of incandescent gas. By a simultaneous comparison of these 
lines in the flame-spectrum with the well-known spectra of certain elementary bodies, 
the speaker has succeeded in detecting the presence of the following substances in the 
Bessemer flame :—Sodium, potassium, lithium, iron, carbon, phosphorus, hydrogen, and 
nitrogen. 
A further investigation, with an instrument of higher dispersive and magnifying 
powers than that employed, will doubtless add to the above list; and an accurate and 
prolonged study of this spectrum will probably yield very important information respect¬ 
ing the nature of the reactions occurring within the vessel. Already the investigation 
is so far advanced that the point in the condition of the metal at which it has been 
found necessary to stop the blast can be ascertained with precision; and thus, by the 
application of the principles of Spectrum Analysis, that which previously depended on 
the quickness of vision of a skilled eye has become a matter of exact scientific ob¬ 
servation. 
Another interesting practical application of our knowledge concerning the properties 
•of the kind of light which certain bodies emit when heated, is the employment of the 
light evolved by burning magnesium wire for photographic purposes. The spectrum 
