In Duma’s method of estimation of nitrogen 0.35 of an organic compound gave 55 mL of nitrogen collected at 300 K temperature and 715 mm pressure. The percentage composition of nitrogen in the compound would be:
(Aqueous tension at 300K= 15 mm)

The Lassaigne’s extract is boiled with conc. ${\mathrm{HNO}}_3$ while testing for halogens, because it:

1. Helps in the precipitation of $\mathrm{AgCl}$
2. Increases the solubility product of $\mathrm{AgCl}$
3. Increases the concentration of ${\mathrm{NO}}_3^{-}$ ions
4. Decomposes ${\mathrm{Na}}_2\mathrm{S}$ and $\mathrm{NaCN}$, if formed