tion of sulphur in steel by evolving the sulphur
as hydrogen sulphide, precipitating cadmium sulphide by passing the
liberated hydrogen sulphide through ammoniacal cadmium chloride
solution, and decomposing the CdS with acid in the presence of a
measured amount of standard iodine, the following data are obtained:
Sample, 5.027 grams; cc. Na_{2}S_{2}O_{3} sol. = 12.68; cc. Iodine
sol. = 15.59; 1 cc. Iodine sol. = 1.086 cc. Na_{2}S_{2}O_{3} sol.; 1
cc. Na_{2}S_{2}O_{3}= 0.005044 gram Cu. Calculate the percentage of
sulphur. (H_{2}S + I_{2} = 2HI + S.)

!Answer!: 0.107%.

66. Given the following data, calculate the percentage of iron in
a sample of crude ferric chloride weighing 1.000 gram. The iodine
liberated by the reaction 2FeCl_{3}+ 2HI = 2HCl + 2FeCl_{2} + I_{2} is
reduced by the addition of 50 cc. of sodium thiosulphate solution and
the excess thiosulphate is titrated with standard iodine and requires
7.85 cc. 45 cc. I_{2} solution = 45.95 cc. Na_{2}S_{2}O_{3} solution;
45 cc. As_{2}O_{3} solution = 45.27 cc. I_{2} solution. 1 cc. arsenite
solution = 0.005160 gram As_{2}O_{3}.

!Answer!: 23.77%.

67. Sulphide sulphur was determined in a sample of reduced barium
sulphate by the evolution method, in which the sulphur was evolved as
hydrogen sulphide and was passed into CdCl_{2} solution, the acidified
precipitate being titrated with iodine and thiosulphate. Sample, 5.076
grams; cc. I_{2} = 20.83; cc. Na_{2}S_{2}O_{3} = 12.37; 43.45 cc.
Na_{2}S_{2}O_{3} = 43.42 cc. I_{2}; 8.06 cc. KMnO_{4} = 44.66 cc.
Na_{2}S_{2}O_{3}; 28.87 cc. KMnO_{4} = 0.2004 gram Na_{2}C_{2}O_{4}.
Calculate the percentage of sulphide sulphur in the sample.

!Answer!: 0.050%.

68. What weight of pyrolusite containing 89.21% MnO_{2} will oxidize
the same amount of oxalic acid as 37.12 cc. of a permanganate
solution, of which 1 cc. will liberate 0.0175 gram of I_{2} from KI?

!Answer!: 0.2493 gram.

69. A sample of pyrolusite weighs 0.2400 gram and is 92.50% pure
MnO_{2}. The iodine liberated from KI by the manganese dioxide is
sufficient to react with 46.24 cc. of Na_{2}S_{2}O_{3} sol. What is
the normal value of the thiosulphate?

!Answer!:: 0.1105 N.

70. In the volumetric analysis of silver coin (90% Ag), using a
0.5000 gram sample, what is the least normal value that a potassium
thiocyanate solution may have and not require more than 50 cc. of
solution in the analysis?

!Answer!: 0.08339 N.

71. A mixture of pure lithium chlorid