42 ROYAL SOCIETY OF CANADA 



mucih mare intense. On cooling to — 80° C, the colour disappears, but 

 reappears on warming to the room temperature. At a low temperature 

 an abnormally large amount of alkali must be used in order to bring 

 out the red colour — a fact which may be explained by the decreased 

 dissociation of salts in alcoholic solution. I am not aware of any 

 experiments on the change of dissociation of salts dissolved in alcohol 

 at low temperatures, but it seems unlikely that dissociation plays a 

 prominent rôle here. The phenol-phthalein probably exists as a lactone 

 at low temperatures ; and on heating ^ is changed into an acid. 



Phenol-phthalein dissolves in the liquefied halide-acids to form 

 strongly coloured, conducting solutions. Carboxyl acids do not con- 

 duct, as a general rule, in these acids, and it seems probable that the 

 phenol-phthalein has the lactone formula. If so, in order to conduct 

 the current the phenol-phthalein must be ionized, and the presence of 

 the negative ion is indicated, according to Ostwald's theory, by the 

 beautiful red colour. A similar experiment can be shown with 

 liquefied ammonia. In all cases the phenol-phthalein is not per- 

 manently changed, but appears quite sensitive after this treatment. 



If alkaline phenol-phthalein be placed in U tubes and covered over 

 with dilute alkali and a current be passed through the solution, the 

 red colour moves, apparently, to the anode. These experiments were 

 not always satisfactory, but seemed in the majority of cases to indicate 

 that the red colour is due to a negatively charged ion. 



* Compare with acid solutions of tetra-m«thyl-diamido-triphenyl-carblnol. 



