What does A. R. in A. R. sodium nitrite mean? 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 &quot;Ar&quot; means aromatic ring. Is that the same thing?
But I've also seen &quot;Sodium Nitrite, Granular, AR®&quot; 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?
I don't know if I have completely answered, but here's my go:
AR : (ANALYTICAL REAGENT) : Reagents essential for analytical purpose and research work having high purity. If reagent meets the requirements of the American Chemical Society Committee on Analytical Reagents, it will be denoted as an AR (ACS) reagent.
Also see:

https://www.researchlab.in/?product-details/grade-of-purity/
https://www.avantorsciences.com/pages/en/grade-definitions#:~:text=AR%E2%80%94The%20standard%20Macron%20Fine,an%20AR%20(ACS)%20reagent.

EDIT:And note that it isn't a Analytical ring