338 REPORT—1899. 
With 4 mm. the absorption band has disappeared, and the spectrum 
extends to !/A 4660. 
Para-toluidine Hydrochloride. 
1435 gram salt in 40 c.c. alcohol. 
With 10, 8 and 6 mm. an absorption band appears from 1/X 3647 to 
4253. With 4 mm. the absorption band has disappeared, and the 
pectrum extends to !/\ 4474-2. 
Let us deal now with organic colouring matters, a class of substances 
which have naturally been more generally studied, but by observations 
made over a restricted range of spectrum lying between \ 7500 and 
r 4000. 
‘Ueber Absorption des Lichts durch Gemische von farbigen Fliissigheiten.’ 
By F. E. Me.pe.! 
Melde chiefly addressed himself to the following inquiries :— 
Do the absorption bands which a coloured substance exhibits remain 
if the liquid be mixed with one or more other coloured solutions, without 
any chemical interaction taking place? Is it possible for the change of 
temperature in a liquid which exhibits selective absorption to cause a 
shifting of the absorption bands? His results showed that there was an 
alteration which was believed to be of a physical character. H. Burger? 
was strengthened in the belief that the changes observed by Melde were 
not merely physical, but partly chemical, taking into account the work of 
Magnus and H. W. Vogel.? 
The subject was investigated very carefully by J. Landauer,‘ chiefly 
as a contribution towards a settlement of the question whether every 
chemical compound had its own absorption spectrum.? He under- 
took the spectral analytical examination of saffranin and its salts, since 
it has the very peculiar property of changing colour on the addition of 
concentrated acids in varying proportions to the red solution.® It became 
evident that each of the colours had its own spectrum. The green solu- 
tions extinguished the violet, the blue, and the red; the blue-green 
behaved in similar manner until there was a portion of the red rays 
remaining which were not absorbed ; the blue solution took away merely 
the yellow rays, and the more the colour was changed to violet and red 
by addition of water, the more the spectrum went over to the green part. 
Drawings of the spectra of thick and thin layers of liquid show the 
movement of the absorption band from the red and yellow towards the 
green and blue, while a second absorption band about F and G moves 
into the more refrangible region, and goes, no doubt, into the ultra- 
violet. The change is caused by the formation of different hydrates in 
solution, which are capable of being carried possibly as far as complete 
dehydration. The addition of water of course reverses the change. 
1 Pogg. Ann. vol. exxiv. p. 91, and vol. cxxvi. p. 264. 
2 « Spectroscopische: Untersuchungen tiber die Constitution von Lisungen,’ Ber, 
vol. ii. pp. 1876-78, 1878. ant 
8 Praktische Spectralanalyse irdischer Stoffe, pp. 123 and 212. 
4 ‘Zur Kenniniss der Absorptionsspectra,’ Ber. vol. ii. p. 1772. 
5 Moser, Pogg. Ann. vol. clx. p. 177, and Ber. vol, xi. p. 1416, 
6 Hofmann and Geyger, Ber. vol. v. p. 631. sue 5 
