The notation  hydrated compound ânH2O , where n is the number of water molecules per formula unit of the salt, is commonly used to show that a salt is hydrated. The n is usually a low integer, though it is possible for fractional values to occur. For example, in a monohydrate n is one, and in a hexahydrate n is 6.
When does spring start? How you define the first day of spring depends on whether you follow the astronomical or meteorological seasons. This year, spring will take place between March 20 and June 21, if you use the astronomical method. But it starts slightly earlier, between March 1 and May 31, if you follow the meteorological calendar.
March 20, 2017. First Day of Spring 2017 (Northern Hemisphere) Today is the spring equinox â when the day and night are equal in length. The word equinox comes from the Latin for equal and night. Almost everywhere in the world today, nighttime and daytime are each 12 hours.