通过该方法测定的游离酸度包括可被水萃取的酸度和由于直接连接到醋酸纤维素的酸性基团（例如羧基）而产生的酸度。本方法不适用于含有任何可能影响试验的添加剂的醋酸纤维素。其原理是用水处理醋酸纤维素的试验部分，并用氢氧化钠溶液滴定所得溶液。游离酸度计算为醋酸纤维素中游离醋酸的质量百分比。第二版取消并取代第一版ISO 1061: 1975年，它构成了一个小的技术修订。

The free acidity determined by this method includes acidity extractable by water and acidity due to acidic groups directly attached to the cellulose acetate, e.g. carboxyl groups. This method is not suitable for cellulose acetate containing any additives which may affect the test. The principle consists in treating a test portion of cellulose acetate with water and titrating the resultant solution with sodium hydroxide solution. The free acidity is calculated as the percentage, by mass, of free acetic acid in the cellulose acetate. This second edition cancels and replaces the first edition ISO 1061:1975, of which it constitutes a minor technical revision.