of the Solar Spectrum on Vegetable Colours. 113 
refrangible than the fiducial yellow. A slight discoloration is 
perceived in the indigo-blue rays (at about + 30), but the 
green appears quite inactive. 
196. In the case of the purple Iris mentioned above, when 
turned green by the same reagent, the tint is fuller and richer, 
as well as, photographically, more sensitive, and the residual 
yellow less abundant. And in this case the resistance of the 
tint to rays of its own colour is very strongly marked. The 
spectral impression consists, in fact, of two portions clearly 
separated by the whole of the interval occupied by the green 
and greenish blue rays, conformably to the general remark in 
Art. 170. 
197. Sparaxis tricolor ?, var.—Stimulating effect of alkalies. 
—Among a great many hybrid varieties of this genus, lately 
forwarded to me from the Cape, occurred one of a very in- 
tense purplish brown colour, nearly black. The alcoholic 
extract of this flower in its liquid state is rich crimson brown. 
Spread on paper it imparted a dark olive green colour, which 
proved perfectly insensible to very prolonged action, either 
of sunshine or the spectrum. The addition of carbonate of 
soda changed the colour of this tincture to a good green, 
slightly inclining to olive, and which imparted the same tint 
to paper. In this state, to my surprise, it manifested rather 
a high degree of photographic sensibility, and gave very pretty 
pictures with a day or two of exposure to sunshine. When 
prepared with the fresh juice there is hardly any residual 
tint, but if the paper be kept, a great amount of indestructible 
yellow remains outstanding. The action is confined chiefly to 
the negative end of the spectrum, the maximum being at 
— 8-0, and the sensible limits of the impression (corrected for 
semidiameter) being — 11-0 and + 56:4, of which, however, 
all but the first five or six parts beyond the fiducial yellow 
show little more than a trace of action. A photograph im- 
pressed on this paper is reddened by muriatic acid fumes. If 
then transferred to an atmosphere of ammonia, and when 
supersaturated the excess of alkali allowed to exhale, it is 
fixed, and of a dark green colour. Both the tint and sharp- 
ness of the picture, however, suffer in this process. 
198. Red Poppy—Papaver Rheum?.—Among the vege- 
table colours totaily destroyed by light, or which leave no 
residual tint, at least when fresh prepared, perhaps the two 
most rich and beautiful are those of the red poppy, and the 
double purple groundsel (Senecio splendens). The former owes 
its red colour in all probability to free carbonic acid, or some 
other (as the acetic) completely expelled by drying, for the 
Phil. Mag. S. 3. Vol. 22. No.143. Leb. 1843. I 
