Appendix. '$g 



nic acid from gallic acid by working in accordance with his 

 theory, it cannot be ignored. Schiff also traces a very inter- 

 esting correspondence between the astringent acids and other 

 aromatic compounds, in the bright colors which great numbers 

 of them give with ferric salts ; the most familiar instance being 

 that of ink, and instances being familiar to analysts, in the 

 identification of phenol, benzoic, salicylic and cinnamic acids, 

 etc. The wide distribution of the tannins gives great signifi- 

 cance to this insight into their construction. Of the 576 plants 

 in Wittstein's summary, 35, or 6 per cent., are given as contain- 

 ing tannic acids; these plants being found in 17 per cent, of the 

 natural orders. 



The quinones claim attention in this inquiry, for though 

 they are not found in plants they are next steps to plant constit- 

 uents. They hold oxygen atoms united to each other, as before 

 stated. Ordinary quinone, C 6 H 4 (O 2 )", is easily obtained from 

 the quinic acid of the cinchonas and from the allied caffeic acid 

 of coffee, being in each case a means of recognition in analy- 

 sis. Resins, by heat, yield umbelliferone, an isomer of quinone. 



The quinone of anthracene (the triple-hexagon nucleus) is 

 called anthraquinone, C 14 H 8 (O 2 )". From this, by displacing 

 H 2 with fOH) 3 , is now manufactured dioxyanthraquinone, the 

 alizarin of madder, as hereafter to be described. Isomeric with 

 alizarin is the chrysophanic acid found in rhubarb, senna, and 

 the wall lichen (parmelia parietina). Chrysammic acid, which 

 is formed from the aloin of aloes in the common nitric acid test, 

 also from the chrysophanic acid of rhubarb in the same way, has 

 the composition of tetranitra-dioxy-anthraquinone, C 14 H 2 

 (N0 2 )' 4 (OH)' 2 (0 3 )". 



Taking next the acids derived from the benzene nucleus, 

 with their aldehydes and alcohols, we have first benzoic acid and 

 bitter almond oil, the well-known subjects of Liebig and Woh- 

 ler's first advance into the aromatic group. Always classed 

 with these are salicylic, cinnamic, cuminic and anisic acids, 

 aldehydes and alcohols; the aldehydes being essential oils of 

 plants and the acids being the products of the natural oxidation 



