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.
People walk past cherry trees as they blossom around the Tidal Basin on the National Mall in Washington, April 11, 2015. Mark your calendars and get ready to put away your winter coat, the first day of spring arrives March 20, the date of the vernal equinox. Sunshine and warmer weather have already started to hit many states this month. The spring equinox officially arrives that Sunday at 12:30 a.m. EDT. Astronomically, the equinox March 20 signals springâs beginning in the Northern Hemisphere, while in the Southern Hemisphere it marks first day of fall.