148 
Proceedings of the Eoyal Society 
peroxide. On adding a portion to a solution of iodide of potassium 
acidified with hydrochloric acid iodine is set free. After drying at 
a temperature of 100° C. it still retains its properties. It gives off 
oxygen on heating (from one sample of about J of a gramme we 
collected 15 cc. of oxygen) ; on treatment with strong hot hydro- 
chloric acid it gives off chlorine, it oxidises acid solutions of ferrous 
sulphate. These properties it retains almost undiminished after 
prolonged exposure to a temperature of 140° C. 
In preparing the zinc compound we used a solution containing 5 
grm. of zinc sulphate to the cc. To a 100 cc. of this solution 450 
cc. of a solution of ammonia (0037 NH 3 to the cc.) was added, and 
the whole filtered to remove the small quantity of precipitate left 
undissolved. To 100 cc. of the filtered solution 350 cc. of a dilute 
solution of peroxide of hydrogen was added, which produced a 
copious precipitate. This was collected on a filter, and washed 
rapidly with cold water on the Bunsen pump, and then dried on a 
water bath. The substance thus obtained is a yellowish-white 
powder, which on ignition yields protoxide of zinc, water and 
oxygen being evolved. It dissolves readily in cold dilute acids, and 
this solution gives, on shaking it up with chromic acid solution and 
ether, the blue coloration characteristic of peroxide of hydrogen. 
In order to estimate the peroxide oxygen, we dissolved weighed 
portions in standard solution of ferrous sulphates acidified with 
sulphuric acid, and then titrated with standard solution of perman- 
ganate of potash. The percentages of oxygen estimated in this way, 
in three different portions, were 6*92, 6*92, and 6 - 42 respectively. 
On ignition the substance lost 20 '9 per cent. 
The composition, and notably the percentage of oxygen, vary very 
considerably when the method of preparation is slightly modified. 
We prepared three portions, A, B, and C, in different ways. 
A. 100 cc. of the ammoniacal solution of zinc were poured into 
250 cc. H 2 0 2 solution, 100 cc. H 2 0 2 solution added, and the precipi- 
tate filtered, and washed with a very dilute solution of H 2 0 2 . 
B. 350 cc. of H 2 0 2 solution were poured into 100 cc. zinc solu- 
tion and filtered, and the precipitate washed with very dilute H 2 0 2 
solution. 
C. 350 cc. H 2 0 2 solution were poured into 100 cc. of the same 
zinc solution, and the precipitate filtered and washed with cold water. 
