The solution can be heated to boiling before titrating without interfering with the result; but it is more convenient to work with the solution at about 50° C. Cold solutions must not be used. ~Effect of Varying Bulk.~--These were all titrated at about 50° C., and were like the last, but with varying bulk. Bulk 25.0 c.c. 50.0 c.c. 100.0 c.c. 200.0 c.c. "Ferrocyanide" required 20.2 " 20.4 " 20.3 " 20.4 " Any ordinary variation in bulk has no effect. ~Effect of Varying Hydrochloric Acid.~-- With 100 c.c. bulk and varying dilute hydrochloric acid the results were:-- Acid added 0.0 c.c. 1.0 c.c. 5.0 c.c. 10.0 c.c. 20.0 c.c. "Ferrocyanide" required 24.4 " 20.2 " 20.3 " 20.3 " 20.7 " ~Effect of Foreign Salts.~--The experiments were carried out under the same conditions as the others. Five grams each of the following salts were added:-- Salt added { Ammonic Ammonic Sodium Sodium { chloride. sulphate. chloride. sulphate. "Ferrocyanide" required 20.3 c.c. 20.5 c.c. 20.6 c.c. 20.4 c.c. Salt added { Potassium Magnesium Nil. { Nitrate. sulphate. "Ferrocyanide" required 20.2 c.c. 20.4 c.c. 20.4 c.c. In a series of experiments in which foreign metals were present to the extent of 0.050 gram in each, with 20 c.c. of zinc solution and 5 c.c. of dilute hydrochloric acid, those in which copper sulphate, ferrous sulphate, and ferric chloride were used, gave (as might be expected) so strongly coloured precipitates that the end reaction could not be recognised. The other results were:-- "Ferrocyanide" required. With nothing added. 20.3 c.c. " 0.050 gram lead (as chloride) 20.9 " " 0.050 " manganese (as sulphate) 25.5 " " 0.050 " cadmium (as sulphate) 23.5 " " 0.050 " nickel (as sulphate) 26.2 " ~Effect of Varying Zinc.~--These were titrated under the usual conditions, and gave the following results:-- Zinc added 1.0 c.c. 10.0 c.c. 20.0 c.c. 50.0 c.c. 100.0 c.c. "Ferrocyanide" required 1.1 " 10.2 " 20.3 " 50.6 " 101.0 " ~Determination of Zinc in a Sample of Brass.~--Take the solution from which the copper has been separated by electrolysis and pass sulphuretted hydrogen until the remaining traces of copper and the lead are precipitated, filter, boil the solution free from sulphuretted hydrogen, put in a piece of litmus paper, and add sodic hydrate solution in slight excess; add 10 c.c. of dilute hydrochloric acid (which should render the solution acid and clear); warm, and titrate.