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.
Today is the spring equinox, aka the vernal equinox. It is the first official day of spring and it begins when the sun crosses directly over the earthâs equator. For 2017, the spring equinox occurs at 6:29 a.m. EDT in the northern hemisphere. However, today is only the first day of the astronomical spring. The meteorological spring started on March 1.