The absorbance ( 2 . 2 . 2 5 ) of the filtrate , measured at 4 0 5 nm using a mixture of 2 5 mL of a filtered 4 0 g / L suspension of the substance to be examined and 2 mL of a 1 3 per cent V / V solution of sulfuric acid R as the compensation liquid , has a maximum of 0 . 3 5 .