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.
Many folks assume the first day of spring in the Northern Hemisphere â also known as the vernal equinox â has always come on March 21. But this year seems to be an exception, for in 2013 the first day of spring comes on Wednesday, March 20 at 11:02 UT, or 7:02 a.m. EDT/4:02 a.m. PDT. Now this doesn't seem right.