Thymol blue (CAS 76-61-9): storage and disposal

Since thymol blue turns red in strong acid, a leaking acid bottle on the next shelf can turn a stock solution red, and alkali can turn it blue, so keep it apart from both. A closed bottle on a general shelf is the usual place, with dropper bottles upright in a tray, and many prep rooms keep it in an indicator set with others whose colours look similar. Because several indicators are red, yellow or blue, labelling matters more than position. Put the opening date on the solution and keep the powder away from food supplies. University stores often hold small amounts for specialist titrations, which are used rarely.

The label and the container say most about an old bottle. A smudged or colour-stained label, dye on the thread and a cap that has stuck are the usual signs, and the shelf below often shows a coloured ring from drips. The solution can lose level through a loose cap and leave a dried crust at the neck. Because the dye has two colour changes, the colour of the stock is a useful clue: a red, yellow or blue tint that differs from what was supplied suggests contamination from a neighbouring acid or alkali. Powder should be loose, and damp or caked powder shows moisture has entered. A bottle without a receipt date is awkward to describe.

By specialist collection only. It never goes down the drain or into general waste. It is normally packed in a non-regulated or low hazard laboratory pack with compatible chemicals.

Pouring leftovers away to clear a shelf is not the route for any indicator, even one that is not classified as hazardous on the sources we checked. Thymol blue remains a chemical waste, so it travels on a waste transfer note under code 16 05 09, and it must be described accurately by form, strength and volume. Powder and solution are listed separately, and sealed bottles are packed upright into a lab pack with compatible items. A sink or drain is never the answer, and nobody should try to alter the colour to see if it can be reused.

Usually held as: solid, solution.

Part-used bottles and full containers are both fine. Tell us the size and how many, and an estimate is enough for a first price.