Which chemical is also known as 'Flores martis'?

Iron chloride
Iron chloride, also known as ferrous chloride, is the chemical compound of formula FeCl2. It is a paramagnetic solid with a high melting point, and is usually obtained as an off-white solid. FeCl2 crystallizes from water as the greenish tetrahydrate, which is the form that is most commonly encountered in commerce and the laboratory. There is also a dihydrate. The compound is also soluble in water; aqueous solutions of FeCl2 are yellow.

Hydrated forms of ferrous chloride are generated by treatment of wastes from steel production with hydrochloric acid. Such solutions are designated "spent acid," especially when the hydrochloric acid is not completely consumed:

Fe + 2 HCl → FeCl2 + H2
The spent acid requires treatment before its disposal. It is also byproduct from titanium production, since some titanium ores contain iron.

Ferrous chloride is conveniently prepared by addition of iron powder to a solution of methanol and concentrated hydrochloric acid under an inert atmosphere. This reaction gives the methanol solvate, which upon heating in a vacuum at about 160 °C gives anhydrous FeCl2.FeBr2 and FeI2 can be prepared analogously.

Fe + 2HCl + 2CH3OH → FeCl2 + CH4 + H2O
An alternative laboratory synthesis of FeCl2 entails the reaction of FeCl3 with chlorobenzene:

2 FeCl3 + C6H5Cl → 2 FeCl2 + C6H4Cl2 + HCl
FeCl2 exhibits convenient solubility in tetrahydrofuran (THF), a common solvent for chemical reactions. In one of two classic syntheses of ferrocene, Wilkinson generated FeCl2 by heating FeCl3 with iron powder in THF.Ferric chloride decomposes to ferrous chloride at high temperatures.