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.
December 21, 2012, at 6:12 am EST starts the first day of winter 2012/2013 (often just listed as winter 2012). Winter 2013/2014 (winter 2013) would begin on December 21, 2013, at 12:11 pm EST. In astronomy, each year in the Northern Hemisphere can be defined as beginning with the spring (vernal) equinox in March.