Uranine A is an organic dye. A dinatrium salt of fluorescein, which has better solubility in water than fluorescein. It is used in heating networks to detect leaks, as well as in hydrology, including karstology to detect the movement of groundwater and underground rivers. Uranine A belongs to the group of triarylmethane (xanthene) dyes. Red-orange or red crystals, which in aqueous solutions are characterized by yellow or bright green fluorescence. For example, when this substance is sewn into a lifejacket, it colors its surface bright green when it enters the water and makes it easy to find a drowning person. It is used to study groundwater pathways, to tint shampoos, foams and bath salts, water in aquariums and ponds, and for other decorative purposes. In analytical chemistry, Uranine A is used as a luminescent acid-base indicator (transition interval – 4.0-5.0). In biochemistry and molecular biology, zothiocyanate derivatives of Uranine A are used as biological dyes for determination of antigens and antibodies. Some halogen-substituted Uranine A derivatives, such as eosins, are also of practical importance. TU 2463-289-00204197-2003 Concentration in relation to the standard sample is not less than 99%.