438 Dr. "Watts on the Spectrum of the Bessemer-flame. 



existence of lines produced by carbon, iron, sodium, lithium, po- 

 tassium, hydrogen, and nitrogen. 



An important practical result of the observations on which 

 these communications were based, was the discovery that the 

 exact point of decarbonization could be determined by means of 

 the spectroscope with much greater exactitude than from the 

 appearance of the flame itself, the change in which indicating 

 the completion of the process is minute and requires a length- 

 ened experience to detect with certainty. This method of deter- 

 mining the point at which it is necessary to stop the blast was 

 indeed at that time (1863) in constant use at Messrs. Brown's 

 works at Sheffield, and has since been introduced with equal 

 success by Mr. Ramsbottom (at the suggestion of Dr. Roscoe) 

 at the London and North-Western Railway Company's steel- 

 works at Crewe. 



I was at that time acting as assistant to Professor Roscoe, and 

 in that capacity conducted a lengthened examination of the Bes- 

 semer spectrum at the works at Crewe. The results of that in- 

 vestigation were not published at the time, on account of their 

 incompleteness ; and I have since then continued in Glasgow the 

 same research, which has now extended itself into an inquiry 

 into the nature of the various spectra produced by the carbon 

 compounds. These experiments are still incomplete ; but under 

 the circumstances, of the publication of Professor Lielegg's papers, 

 I have put together a few of the more important results obtained 

 in the examination of the Bessemer-spectrum. 



The changes which take place in the spectrum from the com- 

 mencement of the " blow " to its termination are extremely in- 

 teresting. When the blast is first turned on, nothing is seen but 

 a continuous spectrum. In three or four minutes the sodium- 

 line appears flashing through the spectrum and then becoming 

 continuously visible; and gradually an immense number of lines 

 become visible, some as fine bright lines, others as intensely dark 

 bands ; and these increase in intensity until the conclusion of the 

 operation. The cessation of the removal of carbon from the iron 

 is strikingly evidenced by the disappearance of nearly all the dark 

 lines and most of the bright ones. 



The spectrum is remarkable from the total absence of lines in 

 the more refrangible portion; it extends scarcely beyond the 

 solar line h. 



Fig. 2 (Plate III.) represents the general appearance of the Bes- 

 semer-spectrum towards the close of the blow, drawn according to 

 the plan proposed by Bunsen (Phil. Mag. vol. xxvi. p. 247). It 

 must be remarked, however, that at the period of greatest inten- 

 sity almost every bright band is seen to be composed of a great 

 number of very fine lines. 



