sodium citrate

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A white crystalline or granular compound, Na₃C₆H₅O₇, used in photography and in medicine especially as an anticoagulant of blood stored for transfusion.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun chemistry The salt of sodium and citric acid with the chemical formula Na3C6H5O7 and used primarily as a food additive.