Now, Epsom Salt is also a 'salt' but instead of being made of magnesium, oxygen and carbon, as is the case with the carbon salt, its constituents are magnesium, oxygen and sulphur.Chemically it is known as Magnesium Sulphate.ow, Epsom Salt is also a 'salt' but instead of being made of magnesium, oxygen and carbon, as is the case with the carbon salt, its constituents are magnesium, oxygen and sulphur.