95. What weight of impure calcite (CaCO_{3}) should be taken for analysis so that the volume in cubic centimeters of CO_{2} obtained by treating with acid, measured dry at 18°C. and 763 mm., shall equal the percentage of CaO in the sample? !Answer!: 0.2359 gram. 96. How many cubic centimeters of HNO_{3} (sp. gr. 1.13 containing 21.0% HNO_{3} by weight) are required to dissolve 5 grams of brass, containing 0.61% Pb, 24.39% Zn, and 75% Cu, assuming reduction of the nitric acid to NO by each constituent? What fraction of this volume of acid is used for oxidation? !Answers!: 55.06 cc.; 25%. 97. What weight of metallic copper will be deposited from a cupric salt solution by a current of 1.5 amperes during a period of 45 minutes, assuming 100% current efficiency? (1 Faraday = 96,500 coulombs.) !Answer!: 1.335 grams. 98. In the electrolysis of a 0.8000 gram sample of brass, there is obtained 0.0030 gram of PbO_{2}, and a deposit of metallic copper exactly equal in weight to the ignited precipitate of Zn_{2}P_{2}O_{7} subsequently obtained from the solution. What is the percentage composition of the brass? !Answers!: 69.75% Cu; 29.92% Zn; 0.33% Pb. 99. A sample of brass (68.90% Cu; 1.10% Pb and 30.00% Zn) weighing 0.9400 gram is dissolved in nitric acid. The lead is determined by weighing as PbSO_{4}, the copper by electrolysis and the zinc by precipitation with (NH_{4})_{2}HPO_{4} in a neutral solution. (a) Calculate the cubic centimeters of nitric acid (sp. gr. 1.42 containing 69.90% HNO_{3} by weight) required to just dissolve the brass, assuming reduction to NO. !Answer!: 2.48 cc. (b) Calculate the cubic centimeters of sulphuric acid (sp. gr. 1.84 containing 94% H_{2}SO_{4} by weight) to displace the nitric acid. !Answer!: 0.83 cc. (c) Calculate the weight of PbSO_{4}. !Answer!: 0.0152 gram. (d) The clean electrode weighs 10.9640 grams. Calculate the weight after the copper has been deposited. !Answer!: 11.6116 grams. (e) Calculate the grams of (NH_{4})_{2}HPO_{4} required to precipitate the zinc as ZnNH_{4}PO_{4}. !Answer!: 0.5705 gram. (f) Calculate the weight of ignited Zn_{2}P_{2}O_{7}. !Answer!: 0.6573 gram. 100. If in the analysis of a brass containing 28.00% zinc an error is made in weighing a 2.5 gram portion by which 0.001 gram too much is weighed out, what percentage error in the zinc determination would result? What volume of a solution of sodium hydrogen phosphate, containing 90 grams of Na_{2}HPO_{4}.12H_{2}O per liter, would be required to precipitate the zinc as ZnNH_{4}PO_{4} and what weight of precipitate would be obtained? !Answers!: (a) 0.04% error; (b) 39.97 cc.; (c) 1.909 grams. 101. A sample of magnesium carbonate, contaminated with SiO_{2} as its only impurity, weighs 0.5000 gram and loses 0.1000 gram on ignition. What volume of disodium phosphate solution (containing 90 grams Na_{2}HPO_{4}.12H_{2}O per liter) will be required to precipitate the magnesium as magnesium ammonium phosphate?