Which compound was discovered by the Bengali chemist Prafulla Chandra Roy?

Acharya Sir Prafulla Chandra Rây CIE (Bengali: প্রফুল্ল চন্দ্র রায়; 2 August 1861 – 16 June 1944)^[1] was a Bengali chemist, educator and entrepreneur

The Royal Society of Chemistry honoured his life and work with the first ever Chemical Landmark Plaque outside Europe. He was the founder of Bengal Chemicals & Pharmaceuticals, India's first pharmaceutical company. In 1896, he published a paper on preparation of a new stable chemical compound: mercurous nitrite.^[4] This work made way for a large number of investigative papers on nitrites and hyponitrites of different metals, and on nitrites of ammonia and organic amines. He started a new Indian School of Chemistry in 1924