procurement of ferric alum to be used in pre-treatment plant of wtp of 2x250mw htps kasimpur , ferric alum grade-ii conforming to is: 299/1989 ( 4th revision or as per latest amendment , if any ) having following specification . a . aluminum sulphate octadecahydrate . it shall be in the form of slab of 20kg ( approx ) . b . insoluble . 0 . 5% by mass ( max ) c . soluble iron compound ( as fe ) : 0 . 7% by mass ( max ) . d . water soluble aluminum compound as al2o3: 15% by mass ( min ) . e . lead ( as pb ) : 30ppm ( max ) . f . arsenic ( as as2o3 ) : 6ppm ( max ) g . ph of 5% aq . soln . : 2 . 7 ( min ) h . acidity ( as h2so4 ) 0 . 5% by mass ( max )