Warming a salt solution with ammonium molybdate in the presence of concentrated nitric acid gives a canary-yellow precipitate. The anion tested is

Phosphate forms ammonium phosphomolybdate, $(\mathrm{NH}{}_4){}_3[\mathrm{P}(\mathrm{Mo}{}_3\mathrm{O}{}_{10}){}_4]$, a canary-yellow precipitate, on warming with ammonium molybdate and concentrated $\mathrm{HNO}{}_3$. Borate, sulphate and nitrate do not give it.