Citric Acid is a weak organic acid used as an acidifier in dyeing.
It will alter the pH level of the dye bath and is an odourless alternative to white vinegar when immersion dyeing with acid dyes (for a pH of 4.0 use 5g in 1 litre of dye bath water, or 25g = 1oz in 5 litres = 1 gallon approx).
If you are painting or printing with Acid dyes, or using Procion MX dyes as an acid dye and wish to steam or microwave set the dyes, the fabric should first be pre-soaked in a solution of Citric Acid mixed as above and allowed to dry before painting.