110 



Prof. W. 1ST. Hartley. Notes on the Spark 



and Adeney,* because it was found to be practically a non-conductor 

 of electricity, and no uninterrupted stream of sparks could be obtained 

 from it. A prior publication,! " On Line Spectra of Boron and Silicon," 

 by me, gives descriptions and wave-lengths of lines characteristic of 

 these elements which were observed in solutions of borates and 

 silicates.! 



Having some of the spectra photographed in 1883, I find upon 

 examination of the plates that they were closely investigated at that 

 time. They show no trace of any line of silicon less refrangible than 

 2881-0 (Angstrom's unit). 



There is a line at the less refrangible extremity of the spectrum 

 which, to judge from its position, is yellow or yellowish-green in colour ; 

 but it certainly does not belong to silicon, because solutions of a 

 silicate, and of hydrofluosilicic acid containing 1 per cent., 0*1 per 

 cent., O'Ol per cent., and 0*001 per cent, of silicon, show this line 

 to be stronger in the spectrum given by O'Ol per cent, than in any 

 other of the photographs. It has every appearance of and no doubt 

 is the well-known pair of sodium lines with a mean wave-length of 

 5893. A concentrated solution of sodium silicate gave no stronger 

 indication of this line, and only a feeble representation of the strongest 

 sodium line 3301. This may be accounted for by the remarkable fact 

 referred to in the original paper, that the lines of the metal in borates 

 and silicates seem to be suppressed when the spectra of boron and 

 silicon appear with greatest intensity, but if the quantity of the 

 borate or silicate in the solution is diminished, the sodium lines gain 

 in strength. 



There is, however, a line near a very strong air line seen in the 

 spectrum of a 1 per cent, solution. It continues to increase in length 

 and intensity in other spectra as the proportion of silica diminishes : 

 otherwise it would not be noticeable because it is extremely short, 

 feeble, and enveloped in air lines when photographed from a 1 per 

 cent, solution. A solution equivalent to 0-001 per cent, of silicon 

 yields a spectrum in which this line is about one-fourth of the length 

 of the air lines, and of the seven carbon lines in other parts of the 

 spectrum. 



It is in fact the least refrangible carbon line from the graphite 

 electrodes 1:266-3 (Hartley and Acleney), and is visible and of normal 

 strength and length on photograph No. 10 in the 'Journal of the 

 Chemical Society,' vol. 11, p. 90, 1882. It is one of those lines which 

 is occasionally absent from the carbon spectrum, and it is somewhat 



* ' Phil. Trans.,' 1884, Part 1, p. 63. 



f ' Roy. Soc. Proc.,' 1883, vol. 35, p. 301. 



X Per a list of these lines, see also Watts's 1 Index of Spectra,' p. 127, 1889. In 

 Appendix E, p. 21 of the Index, the same list of lines is headed H. and A., which is 

 erroneous. 



