IN RELATION TO QUANTITATIVE CHEMICAL ANALYSIS. 
57 
it is easy to see that the absence of these lines may be accounted for by the small 
quantity of metal in the spark. 
When zinc electrodes are moistened these very short lines become somewhat 
lengthened. 
When aluminium electrodes were employed to obtain a photograph of its spectrum 
(Journal of the Chemical Society, vol. xli,, p. 90), a number of short lines were 
exhibited which did not appear in the spectra of solutions of the chloride. The wave¬ 
lengths of the aluminium lines as seen in solutions are the following: 3960-9, 
3943-4, 3612-7, 360f2, 3584'5, 3092-2, 3081-5, 3056’8 (faintly), 2615-6, 2659 8, 
2651"7, 263P0 (a group of five lines), and lastly 2567"5. 
Nearly all the remaining short lines are caused by the presence of iron, a fact 
which may be easily ascertained by prolonging the exposure of the photographic plate. 
Commercial aluminium may contain as much as 2 per cent, of iron, and as the iron 
lines are strong, this quantity modifies the appearance of the spectrum to such a 
degree as to give it a considerable resemblance to that of iron, but there is the widest 
possible difference between the spectra of the two metals. J. L. Schonn, who 
examined the ultra-violet spectra of several metals with Iceland spar prisms and a 
fluorescent eye-piece, has remarked on what he believes to be a similarity between 
the aluminium and iron spectra (Wiedemann’s Annalen, vol. ix., p. 4S3 ; vol. x., 
p. 143). It is possible that the likelihood of iron being contained in the aluminium 
had escaped his notice, or that he was not prepared to recognise the iron lines when 
they were somewhat altered in appearance by the metal being present in small 
quantities. 
Mr. J. Norman Lookyer, referring to the differences in the appearances of the 
spectrum of the same element under different conditions, has shown that by diminution 
of pressure under which the spark is taken, certain short lines disappear, while longer 
lines remain. Further, he states in reference to the spectra of chemical compounds : 
“ It was found in all cases that the difference between the spectrum of the chloride 
and the spectrum of the metal was :— That under the same spark conditions the short 
lines were obliterated, while the air lines remained unchanged in thickness ” (Phil. 
Trans., clxiii., p. 253, 1873). 
It is obvious that this statement cannot be applied to solutions of chlorides examined 
in the manner described in the preceding pages, and the reasons for our different 
conclusions are the following. The short lines are not visible in the spectra of dry 
metallic chlorides, because the quantity of metal present in the spark is too small. 
Thus the spark does not pass from the chloride because it is a very bad conductor, or 
through it because it does not form a continuous and homogeneous covering to the 
metallic electrode, but only past or between the particles of the salt from the 
surface of which portions are volatilised. The conditions are quite different when 
metallic solutions are used; the salt is equally diffused throughout the liquid, which 
forms a continuous coating to the electrode through which the spark must pass, and 
MDCCCLXXXIV. T 
