170 BRITISH APHIDES. 



This fine purple colour is produced in the largest 

 quantity by warming the bruised mass of Aphides with 

 dilute potash or ammonia. 



The chief difference between the solutions of brown 

 and green Aphides consists in an alkali changing the 

 latter into a gamboge-yellow instead of a purple. 



These experiments lead rather to the conclusion 

 that the colouring matter of Aphides partakes more of 

 the nature of chlorophyl or its derivatives than of the 

 derivatives of carminic acid. 



It is worthy of note that in the generality of cases 

 colouring matters, such as indigo, Indian yellow, 

 madder lake, and the like, do not separately exist in 

 the substance of vegetables, but the pigments are 

 disengaged through fermentation or oxygenation. 

 Again, alizarin is itself a reddish-yellow, but alkaline 

 solutions strike it a rich violet, just as we find them 

 act towards the substance Mr. Sorby calls Aphidi- 

 lutein. 



This able experimenter has, as before stated, 

 brought the spectroscope to bear on the solutions of 

 Aphis colouring matter, and particularly he examined 

 that obtained from bruised masses of Scliizoneura 

 lanigera. This tinctorial matter he likewise collected 

 by agitation with carbon disulphide.* 



Such a solution, viewed through a prism, was found 

 to give a broad absorption from the yellow, over the 

 green, to the centre of the blue, without, however, 

 bringing into view any very well marked narrow bands. 

 This colouring matter, which he calls Aphidein, is 

 affected by several chemical agents. It is changed 

 to yellow by citric and other acids, but the colour is 

 restored by the addition of excess of ammonia. 



The changes efiected by the oxydation of Aphideine 

 are very rapid in some cases, and they are accom- 

 panied by a gradation of hues, the reds passing into 

 yellow Aphidilutein, and back again by dioxydation. 



* Sorby " On the Colouring Matter of some Aphides," ' Quart, 

 Journ. Mic. Soc.,' xi, p. 352. 



