Sodium tartrate (Na<sub>2</sub>C<sub>4</sub>H<sub>4</sub>O<sub>6</sub>) is a salt used as an emulsifier and a binding agent in food products such as jellies, margarine, and sausage casings. As a food additive, it is known by the E number E335.
It is made by the combination reaction of baking soda/sodium bicarbonate (NaHCO<sub>3</sub>) with tartaric acid.
Because its crystal structure captures a very precise amount of water, it is also a common primary standard for Karl Fischer titration, a common technique to assay water content.