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.
According to the calendar, the Spring Equinox marks the first day of spring â the day in March when daylight and night hours are equal everywhere on earth. But most people have a very different concept of spring. Some say it's spring when the dogwoods bloom, the first robin appears, or they can finally go outside without a jacket. You're about to embark on the adventure of tracking spring's journey north.