Glycerol is an trihydric alcohol whose IUPAC name is propane-$1, 2,3$ -triol. It gives different oxidation products depending on the nature of oxidizing agent. With bismuth nitrate, it gives mailnly mesooxalic acid $COOH - CO - COOH$
Oxidation with bismuth nitrate-
$(CH_2OH)_2CHOH \to (COOH)_2CO$