Studies on Polychrome Methylene Blue III. Alkali Methods of Polychroming

Studies were made on the influence of time and temperature, of free access of air, of pH, of salt concentration, of evaporation and of various alkali salts as polychroming agents in the conversion of methylene blue into azures and other decomposition products. Extended spectrophotometric studies were made as a means of evaluating the rate of change and nature of final products, and staining tests were made as indicated.

Alkali polychroming of methylene blue proceeds equally well in the presence or absence of external oxygen. It is attended by a slow, continuous evolution of formaldehyde. It is accelerated by increase in concentration of alkali, by evaporation, by increase in pH, and by higher temperatures, but even the low pH levels and low alkali concentrations yield the same products if the process be continued long enough. This contrasts with the cessation of the polychroming on exhaustion of the oxidizing agent in the acid polychroming processes.

It is found that close control of pH, temperature, time, evaporation, access of air, and alkali concentration will enable the production on repeated trial of polychrome methylene blues which are spectroscopically and tinctorially closely similar. Nevertheless, spectroscopic control would appear to be indicated in manufacture.