MICR CHE MIS TRY. 8 ? 



with a large drop of concentrated sulphuric acid. If vanillin 

 be present, the section at once becomes colored deep car- 

 mine-red throughout its whole extent. If phloroglucin is 

 used in the same way, a brick-red color is instantly ob- 

 tained with sulphuric acid ; but the color produced by orcia 

 is even more striking. 



4. Quinones. 



138. The quinones are characterized by the fact that the 

 two para-atoms of hydrogen in the benzol molecule are re- 

 placed by two atoms of oxygen which are either united 

 together by their second valence, or to the carbon atoms 

 concerned by both valences. They are mostly colored deep 

 yellow. It is not very probable, from the investigations 

 already made, that they play a very important role in the 

 chemistry of the plant. Nucin, emodin, and chrysophanic 

 acid have been recognized microchemically. 



a. Juglon, Nucin, Oxynaphtoquinone, C 10 H B O 2 .OH. 



139. Nucin has been recognized in the cell-sap of the 

 parenchyma of the outer husk (pericarp) of the fruit of Jug- 

 lans regia by O. Herrmann (I, 183). He used for this pur- 

 pose a solution of ammonia, or better, the fumes of ammo- 

 nia, which at first color the nucin a brilliant purple ; but 

 this color gradually passes into brown. 



b. Emodin, Trioxymethylanthraquinone, C 14 H 4 O 2 .CH 3 .(OH) 3 . 



140. Bachmann (I) observed in the lichen Nephroma lusi- 

 tanica that small yellow crystalline granules adhere t6 the 

 exterior of the hyphae of the pith, which agree in their 

 microchemical reactions with the emodin previously pro- 

 duced macrochemically only from the rhubarb root and 

 the fruits of Rhamnus frangula. They are dissolved, like 

 chrysophanic acid, by caustic potash and soda solutions with 

 a red color. Lime and baryta waters color them dark red 

 but do not dissolve them. But they are distinguished from 

 chrysophanic acid by being readily soluble in alcohol, glacial 



