I'm reading about a reaction from a 1970s organic chemistry book. It references A. R. sodium nitrite. What does the A. R. mean?
I see from online that "Ar" means aromatic ring. Is that the same thing?
But I've also seen "Sodium Nitrite, Granular, AR®" with a registered trademark, implying it might be a specific brand of Sodium Nitrite, but that didn't make sense. https://www.chemical.net/sodium-nitrite-acs
Are there different types of sodium nitrite?