A sample of $0.441\ \text{g}$ of potassium dichromate, $294\ \text{g/mol}$, is dissolved in acid with an excess of potassium iodide. The iodine that forms is titrated with $0.144\ \text{mol/L}$ sodium thiosulphate. The reactions are $\text{Cr}_2\text{O}_7^{2-} + 6\text{I}^- + 14\text{H}^+ \rightarrow 2\text{Cr}^{3+} + 3\text{I}_2 + 7\text{H}_2\text{O}$ and $\text{I}_2 + 2\text{S}_2\text{O}_3^{2-} \rightarrow 2\text{I}^- + \text{S}_4\text{O}_6^{2-}$. What volume of thiosulphate is needed?