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.
Most mark the official beginning of summer with the summer solstice in June. There will be several first days of summer in 2016. If you live in the U.S., the first day of summer will be June 20. In Europe, Asia, Australia and parts of Africa it will fall on June 21. Then again, meteorologists may celebrate the first day of summer on June 1.