Working standard solution: This was prepared by taking 0.1, 0.2, 0.3… 0.9 and 1 ml of stock ascorbic acid solution and making up each to 1 ml with 0.4% oxalic acid solution. These solutions numbered 1 to 10 (in test tubes) contain 2, 4, 6, 8… 18 and 20 mg ascorbic acid per 100 ml, respectively