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.
In Persian culture the first day of spring is the first day of the first month (called Farvardin) which begins on 20 or 21 March. In other traditions, the equinox is taken as mid-spring. In the traditional Chinese calendar, the spring season consists of the end of winter (from 4 February) and beginning of spring (to 5 May), roughly taking the equinox as its midpoint.