Part 6

Six month later (April 20, 1893) an analysis of the same material showed a ratio of manganese to available oxygen of

1.300 : 1.000

This result was confirmed Mʳ Walker who made repeated analyses of the substance at the same time.

Another sample of manganese oxide was prepared in the same manner as that used in the previous experiments and placed under water. An analysis made after

Eight days gave a ratio of Mn : available O = 1.013 : 1.000 Twenty ” ” ” ” ” ” ” ” = 1.037 : 1.000 Forty three ” ” ” ” ” ” ” ” = 1.040 : 1.000

The results here recorded clearly indicate that the brown oxide of manganese which is prepared by the reduction of potassium permanganate by manganese sulphate undergoes a spontaneous decomposition involving a loss of oxygen. This loss of oxygen or the effect of varying conditions upon this decomposition of manganese dioxide is now being investigated by Mʳ Walker of this laboratory.

The Effect of Varying Quantities of Manganese Oxide on Potassium Permanganate.

The following experiments were made for the purpose of determining the effect of varying quantities of manganese oxide on the time required for the reduction of potassium permanganate.

A. In the presence of nitric acid. The ratio of manganese to available oxygen in the material used for these experiments was determined and found to be

1.018 : 1.000

The experiments were conducted after the same manner as those previously described.

Different portions of the manganese oxide were weighed out and treated in the flasks used in the previous experiments with the quantities of permanganate which were found by calculation to have the desired molecular ratios to the oxide.

A quantity of N/10 nitric acid equivalent to the potassium of the potassium permanganate was added. The flasks were then immersed in the bath of boiling water and the time required for the disappearance of the permanganate color noted.

The ratios of the oxide to the permanganate and the times required for the reduction of the latter are embodied in the following table.

Molecular Ratio } Oxide to KMnO₄ } 1:1 2:1 3:1 4:1 5:1 6:1 7:1

Time of decolorization in minutes

1 ” 120 68 2 ” 110 65 3 ” 150 65 4 ” 150 80 5 ” 120 75 6 ” 120 75 7 ” 175(?) 78 53 8 ” 160 79 54 9 ” 145 41 30 10 ” 120 50 36 11 ” ? 47 32 12 ” 110 37 30 13 ” 64 {20(?) {20(?) 14 ” 72 5(?) 5(?) 15 ” 85 5(?) 5(?)

Decolorized before time was taken.

The results appearing in the table on the same horizontal lines are those of experiments made simultaneously, that is, the flasks in these experiments were immersed at the same time and in the same water-bath. These, that is the results appearing on the same horizontal line, and these only are comparable, since it was found that very slight differences in the temperature of the bath were of great influence on the length of time required for the reduction of the permanganate.

It is clear that the rate of the reduction of the permanganate is greatly increased by increasing the quantity of the manganese oxide.

After reduction of the permanganate, the contents of the flasks were in every case filtered and the filtrate tested by Crum’s reaction for the presence of manganese. No manganese was found. The absence of manganese in the filtrate shows that the reduction of the permanganate was not due to the formation of manganese nitrate, though it will be clear from the results of subsequent experiments that the presence of nitric acid exerts an influence on the rate of the reduction.

B. In neutral solution.

The condition were the same as under A, except that the nitric acid was omitted. Those flasks containing potassium permanganate and one, two and seven molecular equivalents respectively of the manganese oxide were immersed in the water-bath as before.

No. I {containing one molecule of oxide and {one molecule KMnO₄ was reduced in 57 hours

No. II {containing two molecules of oxide and {one molecule KMnO₄ was reduced in 35 hours

No. III {containing seven molecules of oxide {and one molecule KMnO₄ was reduced in 2¾ hours

C. In alkaline solution.

The conditions were the same as under B, except that five molecules of potassium hydroxide were added for each molecule of the permanganate.