An investigation was made, using x‐ray diffraction methods, of the nature of the corrosion products formed on zinc when immersed in hot or cold water, and of the changes occurring when zinc hydroxide and zinc oxide were kept hot or cold in air or under water. Complicated results were obtained, but it is clear that zinc oxide may be a product of the corrosion of zinc in water, especially at elevated temperatures. The significance of the results is discussed in the light of previous work on the electrochemical behavior of zinc in hot or cold waters.