Determination of Distribution of Water in Wheat Grains by Interference Microscopy

Abstract

IT is of interest, especially in milling, to know the water content of different parts of grains, such as wheat. This communication describes a new method which permits the measurement of the water content with relatively high accuracy in every point of a microscopic section. The method is based on changes in refractive index of the tissue by water. The section is immersed in indane, a liquid with refractive index (n_D=1.537) similar to that of the dry tissue (n_D=1.53) and photographed in an interference microscope (Leitz) adjusted to give fringes in the field. Afterwards, the preparation is completely dried in vacuo (0.1 mm mercury, 96° C, 3 h), re-immersed in the liquid and photographed again in the interference microscope. The shift of the interference fringes (Fig. 1) between the two photographs, ϕ₁–ϕ₂ (where ϕ, the optical retardation, = fringe distance × wave-length), enables the calculation of the water content in the following way: the amount of water per unit area m_w is given by m_w=d·ρ, where d is the optical path length of water and ρ its density (1.00), so that m_w=d. Since the shift of the fringes: where n_i is the refractive index of the immersion liquid and n_w that of water.