OP ARTS AND SCIENCES. 261 



changed by the acid. Several weeks later the purple disappeared, and 

 the insect showed again its proper colors. Carbolic acid, being a 

 comparatively weak acid, is more easily neutralized ; moreover, being 

 volatile, its effects are more transient than those of stronger acids, 

 which change the colors. After such a change alkali only partially 

 restores the proper colors. 



The use of benzine affects mostly yellow and orange wings of Lepi- 

 doptera, changing these colors into isabell. The application of 

 tobacco-smoke changes pink flowers of roses into light-green ones, and 

 its effect on butterflies is visible, but less marked. Light-brown 

 insects preserved in dilute carbolic acid become much daiker, nearly 

 blackish, and they retain this color after having been taken out of the 

 acid. 



By the chemical analysis of chitin a certain part was found appar- 

 ently representing the coloring matter. It was insoluble in water, 

 alcoliol, and ether, amorphous, and probably resinous. This matter 

 can be precijjitated by acids from a solution of potash. 



I was not able to find in the literature sufficient information about 

 the chemical origin and nature of colors. Perhaps some recent pub- 

 lications may throw light upon the subject. Mr. M. Nencki (Bericht. 

 deutsch. chem. Gesell. 1874, vol. vii. p. 1593) stated that indol — 

 the coloring radical of indigo — can be produced through digestion of 

 alliumcn by pancreas juice. The fact was denied by Mr. Kuhne 

 (ibid. 1875 vol. viii. p. 206), in so ffir as the production of indol was 

 affirmed, but he believed it was produced by the fermentation of 

 the juice, or by the numerous bacteria? commonly found in the pan- 

 creas. Mr. M. Nencki reported later (ibid. 1875, vol. viii. p. 336) 

 that he had succeeded in the production of indol from albumen only. 

 The reddish oil — indol-coloring substance — gives with sufficient 

 nitric acid a red color, with less a violet color (ibid. p. 722). Out of 

 the albumen was produced 0.5 per cent nitric acid, nitrosoindol. By 

 boiling the red coloring substance a brown one is produced, which 

 gives in alcoholic solution of kali or natron a green color, with sulphu- 

 ric acid a purple one. 



In 18G8 Messrs. Grabe and Liebermann had shown that madder- 

 lake can be obtained out of anthracen, a kind of coal-camphor. The 

 consequence of this discovery was, that everywhere the culture of 

 madder was given up entirely. Since that time Professor Bayer in 

 Munich has endeavoured to produce an artificial indigo (Nature, 

 vol. viii. p. 251 ; vol. xxiii. p. 390; vol. xxv. p. 593; Kosmos, 1881, 



