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.
Facts about Spring Begins. 1  In 2015 the beginning of spring is Friday, March 20th. 2  The First Day of Spring is also called the Vernal Equinox. 3  The Vernal Equinox is the day of the year where there are exactly 12 hours of daylight and 12 hours of dark in the Northern Hemisphere.