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.
Updated March 30, 2017. The vernal equinox is the first day of spring, on March 20 or 21 each year. âVernalâ and âequinoxâ are Latin terms meaning âspringâ and âequal nightâ respectively. The idea is that on the first day of spring there are exactly 12 hours of daylight and 12 hours of darkness, but it rarely works out that way. There is always a time each spring, and again each fall, when the hours of light and darkness are equal, but it usually occurs before the vernal equinox and after the autumnal equinox.