Congo red

American  

noun

Chemistry.

1. a water-soluble powder, C 32 H 22 O 6 N 6 S 2 Na 2 , one of the Congo colors that is not acid-fast or lightfast: used chiefly as a dye, biological stain, and chemical indicator.

---

Congo red British  

noun

1. a brownish-red soluble powder, used as a dye, a diagnostic indicator, a biological stain, and a chemical indicator. Formula: C 32 H 22 N 6 O 6 S 2 Na 2

---

Etymology

Origin of Congo red

First recorded in 1880–85

Example Sentences

The leak turned a tributary of the River Congo red and killed huge numbers of fish, which some people ate, said Environment Minister Eve Bazaiba.

From BBC • Sep. 3, 2021

Amyloid is defined pathologically by the demonstration of green birefringence on binding of the dye Congo red and biophysically by a cross-β fibre diffraction pattern. b, Models of recombinant PrP fibrils and ex vivo prions.

From Nature • Nov. 8, 2016

As defined by pathologists1 who document amyloids in numerous diseases, the fibrils must be deposited in body tissues and fluoresce a green–yellow colour when stained with the dye Congo red and viewed between crossed polarizers.

From Nature • Nov. 8, 2016

Amyloid is defined pathologically by the demonstration of green birefringence on binding of the dye Congo red and biophysically by a cross-β fibre diffraction pattern. b, Models of recombinant PrP fibrils and ex vivo prions.

From Nature • Nov. 8, 2016

A weak solution of Congo red or methyl orange may be used.

From Nitro-Explosives: A Practical Treatise by Sanford, P. Gerald (Percy Gerald)