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.
The first day of spring is commonly associated with the vernal (spring) equinox. For 2016, the vernal (spring) equinox took place on March 20th, 2016 at 12:30 am. The equinox is the time when neither the Northern or Southern hemisphere is tilting away from the sun.