Obviously, the suppression of the sulphide-ion may be accomplished by the addition of hydrochloric, sulphuric or any other strong acid to the zinc sulphate solution in the first place, and then hydrogen sulphide should fail to precipitate any zinc sulphide at all. In fact, if to 50 c.c. of the 0.1 molar zinc sulphate solution 2 c.c. of hexamolar hydrochloric acid is added,[411] hydrogen sulphide does not precipitate even a trace of zinc sulphide (‹exp.›). We have found, then, that 0.1 molar zinc sulphate solution, acidified with a small excess of hydrochloric acid, fails to produce a precipitate of zinc sulphide, when it is saturated with hydrogen sulphide. We must conclude that, under these circumstances, the product of the ion concentrations is smaller than the solubility-product constant for zinc sulphide: ([Zn^{2+}] × [S^{2−}] / ‹x›) < K_{ZnS}, the new concentration of the sulphide-ion being represented by the symbol [S^{2−}] / ‹x›. It would follow, from these considerations, that the action of hydrochloric or sulphuric acid, in preventing the precipitation of zinc sulphide, depends on their producing a sufficiently high concentration of the hydrogen-ion, to keep the concentration of the sulphide-ion, in a mixture of zinc sulphate and hydrogen sulphide, below the point where the solution could become supersaturated with zinc sulphide. [p208] ‹For exactly similar reasons, none of the sulphides of the zinc group is precipitated by hydrogen sulphide in (sufficiently) acid solutions.› It is evident, further, that, if a solution of zinc acetate (without the addition of any acid) is substituted for the zinc sulphate solution and is treated with hydrogen sulphide, an entirely different result, quantitatively considered, must be obtained. By the action of hydrogen sulphide on the acetate, acetic acid is liberated, according to Zn(CH_{3}CO_{2})_{2} + H_{2}S ⥂ ZnS ↓ + 2 CH_{3}COOH. As a ‹weak› acid, acetic acid produces much less hydrogen-ion than is formed in equivalent solutions of sulphuric acid. Consequently, ‹a much slighter suppression of the sulphide-ion› and a much more ‹complete precipitation of zinc sulphide› from the acetate, than from the sulphate solution, must result. Such is the case. Zinc sulphide is, indeed, precipitated ‹quantitatively› by hydrogen sulphide from the ‹acetate› solution.