supply of caustic soda lye grade on 48 percent concentration basis as per is 252 1991 with latest amendment if any for ptep panki kanpur. , caustic soda lye grade on 48% concentration basis as per is: 252: 1991 (with latest amendment if any technical specifications are as follows: - sodium carbonate (as na2co3) -0.40% (max) by mass. sodium hydroxide (as naoh) - 47.50% (min) by mass. chloride (as nacl)- 0.10% (max) by mass. sulphate (as na2so4) - 0.10% (max) by mass. silicates (as sio2)- 0.02%(max) by mass. iron (as fe) ppm, max. 20.00 copper (as cu) ppm, max 2.00 manganese (as mn) ppm, max. 1.00 matter insoluble in water. nil specific gravity: 2.13