Lassaigne's test gives presence of chlorine and nitrogen in organic compound by fusion of organic compound in the presence of sodium. The fused products in this case are:
${\mathrm{CH}}_3{\mathrm{NH}}_2.\mathrm{HCl}\underset{\mathrm{fusion}}{\overset{\mathrm{Na}}{\to }}\mathrm{NaCN} \mathrm{and} \mathrm{NaCl}$

$\mathrm{NaCN}$ gives +ve test for nitrogen and $\mathrm{NaCl}$ gives +ve test for halogen.