Rapid Testing of Dyes and Pigments
The Journal of Physical Chemistry
The actual testing of dyes and pigments in regard t o their relative permanency t o light is slow work. Of cpurse the time can be cut down somewhat by using a very intense source of light; but this is permissible only in case one is certain that the amount of change is proportional t o the product of the intensity of light into the time of exposure. There is no certainty that that is true in any particular case even when using monochromatic light and it certainly is not the case with an arc
... ase with an arc light. In fact the whole nature of the reaction may change. Methylene blue may be oxidized or reduced. In the immediate neighborhood of a quartz, mercury vapor, lamp, there is enough ozone formed to bleach colors which would ordinarily be perfectly stable. Since most colors are bleached by oxidation, it seemed that it ought to be possible to prepare solutions of oxidizing agents of varying strengths such that one could say that a given dye or pigment was practically fast to light in case it did not bleach perceptibly in agiven solution within a given time. Our experiments are only preliminary ones; but they indicate the possibility of working out a satisfactory method along these lines. Experiments were first made with methylene blue, methyl violet, Victoria green, magenta, azo .red, and eosine, using hydrogen peroxide as oxidizing agent. The concentration of the dyes was 0 . I gram per liter. In the first series, 0, 2, 4, 8, IO cc of a three percent solution of hydrogen peroxide were added respectively t o bottles each containing IO cc of the dye solution. The thirty-six bottles were shaken and then put away in the dark. They were examined every day for about four weeks. The following results were obtained at the end of twenty-seven days.