"The first of these solutions, referred to as Solution A, is an aqueous solution of a water-soluble sulphate, phosphate, carbonate, silicate or other compound, such as an aluminate, molybdate, borate, chromate, malate or others so long as the anion of said water-soluble compound forms a water-insoluble. salt with the selected alkaline earth metal, or Solution A can consist of an aqueous mixture of" . . . . .