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.
The spring equinox, the point at which the length of day and night is equal, falls on 20th March this year and usually marks the beginning of spring. However, the date of the spring equinox varies slightly from year to year. It can fall as early as 19th March or as late as 21st. Since spring (and other seasons) can begin on different days each year, it can be hard to compare seasons from year to year. To standardise the length and start of the seasons, in meteorology, the 12 months of the year have been split up into four, 3-month periods. Therefore, meteorological spring begins on 1 March every year and ends on 31 May, allowing weather forecasters to accurately make comparisons between different springs.