100 REPORT— 1902. 



(5) phloroglucinol tricarboxylic ester. As the melting-point of phloro- 

 glucinol is variously stated at temperatures ranging from 210-217°, we 

 made a careful comparison of all our pure preparations with the view of 

 determining whether specimens obtained from different sources really 

 differ from one another as regards this property, or whether the diffei'ences 

 observed are merely due, as stated by Baeyer,' to the various determina- 

 tions not having been made under the same conditions. We first com- 

 pared several specimens of phloroglucinol from kino which had been 

 carefully purified by recrystallisation, and found that when slowly heated 

 side by side they melted at 210°, and when quickly heated at 217°. All 

 the other specimens when heated side by side with the specimens from 

 kino behaved in the same way. 



The absorption spectra of aqueous solutions of all the five specimens 

 vrere photographed, and the curves on comparison were found to be 

 practically identical. It may therefore be regarded as definitely estab- 

 lished that phloroglucinol from whatever source obtained has always the 

 same structure. 



On comparing the spectra of phloroglucinol with those of the trim ethyl 

 ether, M.P. 52°, the resemblance between them was found to be so close as 

 to leave no doubt as to the enolic structure of phloroglucinol, assuming 

 that the ether itself possesses this structui-e. 



Furthermore, the resemblance is so close that it is impossible to 

 suppose that the phloroglucinol contains any appreciable quantity of sub- 

 stance with a ketonic structure.- 



Both phloroglucinol and its trimethyl ether show a selective absorp- 

 tion, the absorption band, however, not being strongly mai-ked. If phloro- 

 glucinol possessed the ketonic structure the absorption band would be 

 entirely absent since diketohexamethylene, a substance of similar structure 

 to the ketonic derivatives of phloroglucinol, shows only general absorption.-^ 



CO 



HoC 



CR.2 

 CH, 



CO 



Diketohesameth)'lene. 



On the other hand, the presence of an absorption band is characteristic 

 of substances having the true benzenoid structure ; confirmation of this 

 conclusion is aftbrded by the great similarity which exists between the 

 spectra of phloroglucinol and those of pyrogallol, a substance which 

 exhibits no ketonic reactions.^ The spectra of pyrogallol were described 

 by Hartley and Huntington,'' but as the method of representation 

 employed at that time was different from that now adopted, we have 

 rephotographed the spectra and redrawn the curve to facilitate comparison 

 with phloroglucinol. For the same reason we include in this paper an 

 account of the re-examination of the absorption spectra of phenol.^ 



' Jier., 19, 218C. 



' Chem. Soo. Trans., 1899, 75, 640; 1900, 77, 830. 



3 Ibid., 1898. 73, .598. 



* Baeyer, Ber., 19, 163. 



5 Hartley and Huntington, PMl. Trans., Part I., 1879, 257, 



" Hartley and Huntington, he. cit. 



