Bromthymol blue, 125ml (4 oz.) for sale. Buy from The Science Company.

This 0.1% aqueous bromthymol blue solution (sometimes incorrectly spelled bromothymol blue) is a commonly used pH indicator. Bromthymol blue changes color over a pH range from 6.0 (yellow) to 7.6 (blue). It is a good indicator of dissolved carbon dioxide (CO2) and other weakly acidic solutions.

Despite its name, bromthymol blue solution may sometimes appear yellow or reddish depending on the pH of the stock water used to prepare this pH indicator solution.

Low levels of CO2 or acid in solution with bromthymol blue indicator will appear blue. As the level of CO2 or acid increases, the solution will gradually take on a yellow tint. This makes bromthymol blue ideal for biology experiments to indicate photosynthetic activity (solution turns blue as plants use up CO2) or respiratory activity (solution turns yellow as CO2 content increases).

Comes packed in convenient squeeze bottle for dispensing by the drop.