720 EEPORT— 1893. 



direct heating eflPects of the light. He also made a similar observation in the 

 case of bromine vapour. These statements have been repeatedly called in ques- 

 tion by other observers, who failed to obtain these results on repeating Budde's 

 experiments. 



Experiments made by the author, however, fully confirm Budde's results, and 

 an arrangement is described in which the expansion of chlorine and bromine, as 

 compared with that of air, under the influence of light, can be exhibited as a 

 lecture experiment. 



8. On the Cause of the Red Colouration of Phenol. By Charles A. Kohn, 

 Ph.D., B.Sc, Lecturer on Organic Chemistry, University College, 

 Liverpool. 



The cause of the turning red of phenol has from time to time been the subject 

 of investigation, but the published results are vague and conflicting. That even 

 the purest carbolic acid of commerce becomes coloured on keeping has long been 

 observed, and the general view of the cause of this colouration has been to trace it 

 to some impurity or other contained in the phenol. By some the presence of a 

 metal, especially copper or iron or their salts, has been regarded as the cause of 

 the reddening, by others the colouration has been attributed to alkalis or to cresol, 

 which last in presence of the phenol has been oxidised with the formation of 

 rosolic acid. Fabini, who more recently has investigated the subject, regards the 

 colouration as due to the action of hydrogen peroxide on phenol containing 

 metallic salts in presence of ammonia, the presence of all three reagents being 

 necessary for the production of the colour. 



Since oxidising agents, alkalis — especially ammonia — and metallic salts play 

 an important part in the turning red of phenol, the action of these and similar re- 

 agents on phenol of varying degrees of purity was tried. 



The phenol used was the purest commercial product known as ' absolute phenol,^ 

 and in the later experiments a sample of specially pure phenol, kindly prepared bv 

 0. Lowe, Esq., of Manchester. The original product was repeatedly distilled from 

 glass vessels and the distillates after one, six, nine, and sixteen distillations care- 

 fully tested with ammonia, hydrogen peroxide, caustic potash, mixtures of these 

 reagents, and also with salts of iron and of copper both in the presence and absence 

 of alkalis and of hydrogen peroxide. In all cases characteristic colourations 

 ensue. That with strong ammonia is violet, and those with hydrogen peroxide, 

 caustic potash, dilute ammonia, hydrogen peroxide in presence of caustic alkali, or 

 of ammonia, metals or metallic salts with or without hydrogen peroxide, red or 

 reddish brown. Each of the three reagents which, according to Fabini, must all 

 be present in order to produce a colouration gives marked colourations on 

 its own account. The blue colouration obtained with ammonia is identical with 

 Phipson's * phenol-blue,' and is probably phenol-quinone-imide. Sublimed phenol,, 

 as well as phenol prepared by the saponification and subsequent decomposition of 

 gaultheria oil, behaves similarly. 



Furthermore, all the samples thus prepared, and which were found on testing 

 to be perfectly free from metallic impurities, turned red on exposure to ordinary 

 moist air. Hence it is to be concluded that the purest phenol does redden of its 

 own account, and not on account of the presence of impurities of any kind. This 

 reddening does not take place in the dark, nor is it eflected by the less refrangible 

 rays of light. Phenol exposed in vacuo keeps colourless for months, as it also 

 does when exposed in presence of water in absence of air, or in presence of air when 

 perfectly dry. Both air and moisture are necessary for the colouration to ensue. 

 It has been shown by Dr. Richardson that hydrogen peroxide is produced during 

 the reddening, and to its formation the reddening of phenol when exposed to 

 ordinary moist air is to be traced. The similarity of the colour produced by 

 hydrogen peroxide with that which phenol assumes on exposure supports this 

 statement. The colour is also produced by the electrolysis of phenol in acid solu- 

 tion. The colouring matter is not volatile, and the colouration is always accom- 

 panied by the absorption of moisture. 



