This table is to show the molecular composition of different electrolyte: when recommended concentrations of electrolytes for etching are given, the numbers stated are often not saying whether it is with or without crystal water. For example, a mol of ferrosuphate (FeSO4) usualy has 7 mol of crystal water i.e. FeSO4.7H2O. Hence an amount of 100g of FeSO4.7H2O is actually only 55g FeSO4 and 45 g water (H2O).