This foundational experiment introduces the two-stage standardisation protocol that underpins all secondary-standard work in the manual. In the first stage, a primary standard solution of oxalic acid (H2C2O4·2H2O, E = 63.04 g/equiv) is prepared by accurate weighing and used to determine the exact normality of an approximately 0.1 N NaOH solution. NaOH is a secondary standard — it absorbs both moisture and CO2 from the atmosphere, making direct preparation of an accurately-known concentration impossible. In the second stage, the standardised NaOH is used as the titrant to determine the unknown normality and strength (g/L) of a given HCl solution, exploiting the 1:1 molar ratio of the neutralisation reaction (NaOH + HCl → NaCl + H2O). Phenolphthalein is the indicator of choice throughout; the chapter explains in detail why methyl orange is inappropriate for these titrations. The experiment produces three inter-related results: the exact normality of oxalic acid, the standardised normality of NaOH, and the normality and strength of HCl. Sources of systematic error — CO2 absorption, parallax at the burette, wet pipette, indicator excess — are analysed and corrective measures prescribed.