73 
1908-9.] A Question in Absorption Spectroscopy. 
in the same way as the other double cells, and the compartments had the 
same internal dimensions. Each cell consisted, in addition to the frame, of 
five pieces of glass, three plates and two pieces of square tubing with the top 
side ground off. They were satisfactory, but had to be put together with 
very great care. The effect of the cement on the dyes does not seem to 
have been mentioned by other workers, and may explain some effects 
observed in the photometry of the aniline colouring matters. 
In the article cited, Formanek gives five cases where on mixing dyes 
the bands affect one another. In his book he gives the sources from which 
his dyes were obtained, but we were able only to obtain those necessary for 
four of these cases. These cases are as follows : — 
(1) The bands of malachite green and brilliant green in water (6183, 
6255) run together on mixing. A new band is formed which lies between 
6183 and 6255. 
(2) If a little malachite green (band at 6183) be added to a suitably 
diluted solution of methylene blue (chief band at 6678, subsidiary band 
at 6081) in water, the subsidiary band of the methylene blue at 6081 runs 
together with the band of malachite green, and in the spectrum we see only 
the chief band of methylene blue in its original position and the band of 
malachite green somewhat displaced. If malachite green be added until the 
proportions of both colouring matters are about the same, the absorption 
band of malachite green returns to its original place. 
(3) If Nile blue A (band at 6448) and methylene blue are mixed in 
water, we obtain only one band which lies near the position of the Nile 
blue band. 
(4) On mixing methylene blue and methyl violet 6 B, which has a band 
at 5935, the methyl violet band is displaced towards the red. 
We first of all examined these cases spectroscopically taking different 
strengths. In no case did we see the slightest displacement as a result of 
mixing nor coidd any alteration of intensity be detected. The spectro- 
photometric method was then employed, one critical point in the spectrum 
being taken for each case, e.g., a point was taken between the bands if they 
were expected to move together on mixing. In the second case only could 
a small change of intensity be detected, which was not very consistent ; as 
it was about -^th of the intensity it was too small to be investigated. It 
could not in any case be detected by the spectroscopic method, which was 
the method employed by Formanek. 
Formanek seems to have used only test-tubes for the liquids under exam- 
ination, and we are forced to the conclusion that the shift he observed is 
merely an apparent one caused by the one maximum being on the slope of 
