381 
lately been described by Dr. Thudichum 1 under the general 
name of leuteine. I think that this new name can only be 
looked upon as something like the old term xanthophyll, as 
hitherto inaccurately employed for a whole series of yellow 
colours, some of which correspond with some of those in- 
cluded under leuteine. If it were thought desirable to have 
a generic name, the term leuteine might indeed be employed ; 
but I must protest against the idea that the substances 
described as such by Dr. Thudichum are one single colouring 
matter. Some of their properties are indeed very similar, but 
that is often the case with those substances which give closely 
connected spectra, even when other facts show that they are 
entirely distinct, for there seems to be a sort of correlation 
between optical characters and chemical reactions ; but this 
is no reason why we should confound together substances 
giving absorption-bands in distinctly different positions in 
similar solutions. 
The adulteration of saffron with the sliced petals of the 
yellow crocus could easily be detected, even in a solution, by 
means of the remarkable spectrum of the latter, when the 
product of the action of bromine is deoxidized by sulphite or 
hyposulphite of soda. To the alcoholic solution of the colours 
soluble in water an aqueous solution of bromine should be 
added very gradually, until, after having become quite pale, 
it is made slightly yellow by the addition of more. Excess 
of ammonia and a little sulphite of soda should then be 
added. In the case of pure saffron the liquid remains almost 
or quite colourless, whereas ammonia first turns the colouring 
matter of the crocus to a red, which soon becomes yellow, and 
then sulphite of soda changes it to a remarkably fine red, 
which is highly fluorescent of red-orange colour, the spectrum 
showing a bright narrow band at about 3^-. That of the 
transmitted light is very characteristic, and shows an excel- 
lent absorption-band at . On adding citric acid the colour 
becomes red-pink ; it is still highly fluorescent, but of more 
yellow tint than before, the bright band being raised to about 
4, and the absorption-band in the spectrum of the transmitted 
light is raised to 5-A- ; but the addition of hydrochloric acid 
destroys both the fluorescence and the absorption-band. The 
only colour that I have met with analogous to this is one 
which occurs in the yellow flowers of several plants allied to 
the common wallflower ( Cherianthus Cheiri), but the bands 
1 ‘ Proceedings of the Royal Society,’ vol. xvii, p. 253, January, 1869. 
