The HANNA test kit measures salinity using a fast and efficient titrimetric method. The test requires only a few simple and safe steps to obtain results.  The salinity level in g/kg is determined by a mercuric nitrate titration method. The pH is lowered to approximately 3 by addition of nitric acid. Mercuric ions react with chloride ions to form mercuric chloride. When excessive mercuric ions are present, it complexes with diphenylcarbazone to form a purple solution. The color change from yellow to violet indicates the endpoint.