58 -Appendix. 



The phenols are formed by substitution of OH for H at- 



tached directly to the C of the ring. The first phenol, known 



...... . as purest grade of carbolic acid, is obtained 



by gentle decomposition of many plant con- 

 '; stituents. Cymophenol, C 10 Hi ;} OH, is 



found in the oil of thyme, from the Gym- 

 nospermse. Of the diatomic phenols, pyro- 

 catechin, C 6 H 4 (OH) 2 , is readily obtained 

 from tannins by distillation and exists ready 

 '' OH formed in Ampelopsis Hederacea. Creo- 



sote, obtained by destructive distillation of many bodies, con- 

 tains two homologous phenols, diatomic and triatomic, each 

 bearing methyl : 



Guaiacol, C 7 H 8 O S = C.H 4 



CH, 

 Creosol, C 8 H 10 O 3 = C 6 H 3 O. CH 8 



' OH 



Pyrogallol (pyrogallic acid, largely used as a deoxidizing agent 

 by photographers) is a triatomic phenol, C 6 H 8 (OH) 8 , and is 

 readily formed from tannins and from gallic acid ; while its 

 isomer, phloroglucin, is obtained from resins and from glucos- 

 ides by heating with potassa. 



The orcins, isomers of C 7 H 8 O 2 , substitutions of two mole- 

 cules of hydroxyl and one of methyl for three atoms of hydro- 

 gen in benzene, are found ready formed in lichens. The dyes 

 archyl, cudbear and persio contain orcins, as also litmus, from 

 Leconora Tartarea. Aloes, treated with potassa, yields orcins. 



And now, in 1872, Schiff ascribes to gallic acid, C 7 H 6 O 5 , a 



rational formula consisting of the introduc- fr-JO 



I 1 OH 



tion of one carboxyl and three hydroxyl _ u I 



(^ B HL g s 

 molecules in place of four of the hydrogen i 



atoms of benzene. 9 Farther, he presents and OH 



maintains a rational formula for fermentable tannic acids, the 

 natural source of gallic acid. 10 Having at last synthesized tan- 



(9) Ann. Chem. Phar., clxiii,209; Jour. Cfiem. Hoc., 1872, 820. 



(10) Jour. Chem. Soc., 1872, 245, 1019, 1098,;' 1874, 2d7. 



