128 
Transactions of the 
[Monthly Microscopical 
Journal, Sept. 1, 1869. 
meut of transmitted or reflected light produces a marked change in 
the spectrum of this substance, as well as in that of many others. 
A very large number of the petals of flowers yield solutions 
closely resembling the dilute solutions of alkanet in spirit, so that 
in the ordinary way it is difficult to determine the difference between 
them. The spectrum of alkanet-root at once removes a doubt ; but 
so much cannot be said for a number of other red or crimson solu- 
tions. The brilhant damask rose, when immersed in water, loses 
all its colour ; which is at once restored on adding a drop of sul- 
phuric acid. A fine pink is obtained, which is permanent, by 
diluting with glycerine and spirit. This heightens the red end of 
the spectrum, producing a brilliant halo of red light ; the rest 
of the spectrum is absorbed ; or, if a paler solution is used for 
examination, a broad absorption band occupies the green, and the 
blue of the spectrum is deepened. The crimson purple-coloured 
petals of fuschia lose colour by immersion in water or spirit and 
water, but a drop of acid at once restores the brilliant colour of the 
flower, and the solutions produce the same reaction on the spectrum 
as the red rose. From another variety of the fuschia, bearing white 
and red coloured flowers, a paler solution is obtained, which a drop 
of acid converts into a pink ; but if an alkali be added the colour 
changes to a yellow, and no reaction is observed in the spectrum. 
Nasturtium petals produce a fine amber red, which changes into a 
crimson on the addition of an acid ; and its reaction on the spectrum 
is the same as that of the damask rose. Cactus speciosa petals yield 
a fine crimson-coloured solution. Acid only very slightly deepens 
the solution, which augments the red ; and a broad dark band 
occupies the yellow and green, while the blue becomes more 
intense. From the juicy leaf or stem of the Oj)untia cochinil- 
Ufera, upon which the cochineal insects feed, chlorophyll cannot be 
obtained in sufficient quantity to produce any reaction on the 
spectrum. A fine crimson colour is, however, extracted on digest- 
ing the Coccus cacti (cochineal insect) in distilled water, which 
produces a general absorption of the green, blue, and violet ; but 
upon adding a small quantity of ammonia to the solution, the 
colour is changed to a lake or reddish purple, when two sharp 
bands appear in the yellow and green, and one in the blue ; the 
violet is intensified. "When liquor calcis is added to another 
portion of the solution it nearly approaches a violet, and produces 
a similar series of bands ; on adding an excess of alum, the colour 
changes to a yellow, which absorbs the greater part of the green 
and blue. 
The deep crimson colour obtained from the Pseony produces 
general absorjjtion below the red ; when a small quantity of Hquor 
potassse is added to the solution, this red colour is converted into a 
green, and characteristic bands appear in the yellow and green 
part of the spectrum ; if the solution be pale enough, another line is 
