Per Cent. Per Cent. Phloroglucinol 2.4002 100 ... Hydroquinone 2.3716 100 ... " 2.0542 100 ... Pyrogallol 2.5150 100 ... " 2.7940 100 ... Pyrocatechol 2.9805 100 ... " 2.9574 100 ... Resorcinol 2.9954 100 ... " 2.9725 100 ... Gallic acid 2.0706 78.84 21.16 " 1.2240 83.18 16.82 " 1.1405 59.94 41.06 [Greek: b]-Resorcylic acid 2.1040 51.08 48.92 " " 2.2008 47.12 52.88 Protocatechuic acid ... ... ... " " ... ... ... Vanillic acid ... ... ... Tannin 2.0599 ... Nearly all sol. Digallic acid 2.1042 80.16 19.84 Leucodigallic acid 2.0041 1.94 98.06 With the introduction of the carboxylic group the tendency of condensation to diphenylmethane derivatives is lessened; by protocatechuic acid the tendency is nil. Nierenstein considers this reaction analogous to the formation of cork, to the genetic relation of which with the diphenylmethane formation Drabble and Nierenstein have referred in an earlier publication. [Footnote: _Biochemical Jour._., 1907, 2, 96.] It is hence possible that the plants may employ formaldehyde as a methylation medium, and produce these insoluble condensation products for the purpose of ridding themselves of the poisonous phenols and aromatic hydroxy acids (and tannins), in addition to oxidising processes whereby phlobaphenes, ellagic acid, etc., are formed. The reaction between phenols and aldehydes has been further studied by Michael, [Footnote: _Amer.Jour_., 5, 338; 9, 130.] who prepared a condensation product from phenol and resorcinol with benzaldehyde, and Russanow, [Footnote: _Ber_.9 1889, 22, 1944.] who also employed benzaldehyde and phenol. Lipp [Footnote: Diss., Bern., 1905.] investigated the action of benzaldehyde and piperonal on phenols, anisoles, cresols, cresylic ether, resorcinol, and the ether of the latter and phenol, and showed that when free phenols are condensed with benzaldehyde the hydroxyls occupy the same position as by the interaction between benzaldehyde and the corresponding phenolic ethers. The resulting dihydroxytriphenylmethane derivatives form beautiful crystals, which on oxidation are converted into benzaurines, the constitution of the latter probably being--