Title: Calmagite
CAS Registry Number: 3147-14-6
CAS Name: 3-Hydroxy-4-[(2-hydroxy-5-methylphenyl)azo]-1-naphthalenesulfonic acid
Additional Names: 1-(1-hydroxy-4-methyl-2-phenylazo)-2-naphthol-4-sulfonic acid
Molecular Formula: C17H14N2O5S
Molecular Weight: 358.37
Percent Composition: C 56.98%, H 3.94%, N 7.82%, O 22.32%, S 8.95%
Literature References: Prepn from 1-amino-2-naphthol-4-sulfonic acid and p-cresol: Lindstrom, Diehl, Anal. Chem. 32, 1123 (1960).
Properties: Red crystals from acetone. Sol in water. Absorption max (pH 10.10): 610 nm (e 20300). Functions as acid-base indicator: Aq solns are bright red at low pH, red at pH 7.1 to 9.1, blue at pH 9.1 to 11.4. The blue color at pH 10 is changed to red by the addition of calcium or magnesium.
Absorption maximum: Absorption max (pH 10.10): 610 nm (e 20300)
Use: As indicator in titration of Ca or Mg with EDTA.
Calmodulin Calomelol Calotropin Calumba Calusterone

Skeletal formula
Ball-and-stick model
CAS number 3147-14-6
PubChem 5483111
ChemSpider 21159783
Jmol-3D images Image 1
Molecular formula C17H14N2O5S
Molar mass 358.37 g mol−1
Appearance Red to black crystals
Odor Phenolic odor
Melting point 330 °C; 626 °F; 603 K
Main hazards May emit ammonia, oxides of sulfur, oxides of nitrogen, and oxides of carbon.
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Calmagite is a complexometric indicator used in analytical chemistry to identify the presence of metal ions in solution. As with other metal ion indicators calmagite will change color when it is bound to an ion. Calmagite will be wine red when it is bound to a metal ion and may be blue, red, or orange when it is not bound to a metal ion. Calmagite is often used in conjunction with EDTA, a stronger metal binding agent.[2] This chemical is also used in the quantitation of magnesium in the clinical laboratory.