1 gm sample+25 ml UP water titrate with N/50 ml NaOH till pH 3.56...

%Free Sulphuric Acid= 0.09808*B.R./weight

then add 10 ml acetone and set pH 5.6 by adding N/2 NaOH

& Purity of Hydroxyamine Sulphate = 4.1035*B.R*Factor of NaOH/weight

continue in this solution add formaldehyde of 8.3 pH containing and set pH 8.3 of solution by adding N/50 NaOH..

%AS = 0.132*B.R./weight@stefano salvatori