I have acquired an old bottle with Guaiac reagent which was evaporated in its reagent bottle (10-15 mls). I added alcohol and the reagent dissolved forming a brown solution without precipitate. I don't know if this solution is working (reacting) well or if it has 'expired', hence how can I test it at home pls? Like I am asking how can I test for Lugol's iodine and the reply would be try it on starch or paper and if it turns blackish-blue it is working fine. Thanks
take some Blackening Russula (Schwärztäubling), e. g. Russula nigricans or Russula adusta, or White Russula (Weißtäubling), e. g. Russula delica, and apply the fluid on the stem margin. When the colour immediately (within two seconds) changes to bluish black, your fluid works. When it lasts five seconds or even longer, the fluid does not work correctly.
We don't have those Russulas 😭😭😭 Can I apply to some chemical or compound instead? Or fabric or ironmongery material.