a white precipitate In the Lassaigne’s test for halogens in an organic compound, the sodium fusion extract is acidified with nitric acid and then treated with silver nitrate. If nitrogen and sulphur both are present in the organic compound, then the Lassaigne’s extract is boiled to expel nitrogen and sulphur, which would otherwise interfere in the test for halogens.
Halogen tests is given in the above figure. From this, it is clear that in the Lassigne’s test for chlorine if the organic compound contains nitrogen but not chlorine we would get white precipitate.