JOURNAL 
OF THE 
ROYAL MICROSCOPICAL SOCIETY. 
APRIL 1895. 
TRANSACTIONS OF THE SOCIETY. 
IV . — Monochromatic Violet 
By J. William Gifford, F.R.M.S. 
(. Read 19 th December , 1894.) 
Plate] I. 
Some of the Fellows will perhaps remember that this time last 
year I brought to their notice a malachite-green screen. Since then 
I have been taking photographs of absorption spectra, in the hope of 
being able to construct an equally efficient violet screen. This is 
now accomplished, and the screen has in great measure failed, though 
the failure is not, I venture to think, from any inherent faults of its 
own. But before stating where the fault lies, let me describe this 
screen. 
If the sun’s rays, after passing through a saturated solution of 
methyl- violet, be examined by a small spectroscope, it will be found 
that all rays in the solar spectrum from line B to a position between 
lines F and G have been absorbed. The remaining spectrum consists 
of a narrow red band and a broad violet band. If solutions of ethyl- 
violet and gentian-violet be used much the same effect is obtained ; 
but with the former the violet band extends more into the blue and is 
broader, with the latter it extends less into the blue and is narrower. 
If we impress such a spectrum (methyl- violet) on a photographic 
plate sensitive to all colours, it will be seen that the violet band 
extends into the ultra-violet beyond HxH 2 (plate I. fig. 1). 
On placing a piece of the blue glass known as signal-green 
behind the solution, and again looking through our spectroscope, it 
will be seen that the red band is cut off, and if a photograph be 
taken the invisible violet beyond the H lines also disappears, a band 
of more or less visible violet alone remaining (plate I. fig. 2). 
The solution, made by preference with glycerin and the blue 
glass, may without much trouble be combined in one mount. I have 
adopted this form lately for the malachite-green screen, using the 
blue glass instead of picric acid to get rid of the ultra-violet, for I 
found that sooner or later the picric acid combined with the cement. 
1895 L 
