In a recent communication (Proc. Roy. Soc. Edin., 1914–15, vol. xxxv, p. 22) measurements of the optical rotation and cryoscopic behaviour of the following sugars, viz. β-l-arabinose, l-xylose, α-d-glucose, α-d-galactose, d-mannose, d-fructose, α- and β-lactose, dissolved in (α) formamide, (b) water, were described. The investigation has been carried a step further by the addition of β-d-ghicose, β-d-galactose and maltose to the above list. Thus the change in rotation or mutarotation in formamide solution has now been measured, starting from both the α and β-form of d-glucose, d-galactose and lactose. As in the case of the water solutions of these sugars, the constant rotation shown when there is equilibrium between the two modifications is found to be the same whether the startine-point be the α- or the β-modification.