Principles of estimation
(1) Estimation of halogens by Carius method : Upon heating an organic compound with fuming HNO3 in the presence of AgNO3, the halogen present in the compound forms the corresponding silver halide which is collected filtered; washed, dried and weighed. This is the amount of halogen present in the compound.
Let the mass of organic compound taken = m g
Mass of AgX formed = m1 g
1 mol of AgX contains 1 mol of X
Mass of halogen in m1 g of AgX =

atomic‌mass‌of‌X×m1g

molecular‌mass‌of‌AgX

Percentage of halogen =

atomic‌mass‌of‌X×m1×100

molecular‌mass‌of‌AgX×m

(2) Estimation of sulphur : An organic compound containing sulphur is heated with fuming nitric acid. This oxidises the sulphur to sulphuric acid which is precipitated as BaSO4 upon reaction with Ba(OH)2. The mass of BaSO4 tells the % of sulphur present in the compound.
Let the mass of organic compound taken = m g
and the mass of barium sulphate formed = m1 g
1 mol of BaSO4 = 233 g BaSO4 = 32 g sulphur
m1 g BaSO4 contains

32×m1

233

g sulphur , % of sulphur =

32×m1×100

233×m

(3) Estimation of phosphorus : A known mass of an organic compound is heated with fuming nitric acid whereupon phosphorus present in the compound is oxidised to phosphoric acid. It is precipitated as ammonium phosphomolybdate, (NH4)3PO4.12MoO3, by adding ammonia and ammonium molybdate. Alternatively, phosphoric acid may be precipitated as MgNH4PO4 by adding magnesia mixture which on ignition yields Mg2P2O7.
Let the mass of organic compound taken = m g
and mass of ammonium phosphomolybdate = m1 g

Mg2P2O7

222g

=

2P

62g

Percentage of phosphorus =

62×m1×100

222×m