264 REPORT-—1890. 
Todine water.—Two series of experiments were made with solutions 
of iodine; in the first carbon dioxide occupied the space above the liquid. 
The mean result of six experiments shows that 8:3 per cent. of the total 
iodine in the solution had been converted into hydrogen iodide. In the 
second series the carbon dioxide was replaced by air; the mean of four 
experiments shows that 14-2 per cent. of the total iodine was present as 
hydrogen iodide. 
Table showing the Decomposition of Water by Iodine in Sunlight, eaposed 
Fourteen Months. 
che Se Free iodine eae ae Total iodine | Per cent. free | Per cent. com- 
z ee | in grms. germs. in solution iodine bined iodine 
SERIES 1.—CO, ABOVE THE LIQUID 
5:0 grms. 032 0031 035) 90°80 9-2 
3-4 3 “039 “0027 “042 93°63 6°37 
16 A 038 “0049 043 89°55 11-45 
OP =; 034 0033 037 91:14 8°86 
0-4 oy ‘032 “0038 “036 89°35 10:65 
OulGe 030 0014 O31 96°34 3°66 
SERIES 2.—AIR ABOVE THE LIQUID. 
3:0 grms. 057 0:0129 “070 83°63 18°39 
ISO tas 042 0:0060 048 87:28 12:72 
1:8 , “032 0:0046 037 87°66 12°34 
003 =, "025 0:0039 029 86:96 13°04 
Further experiments have been made on the oxidation of gaseous 
hydrogen bromide in sunlight. The presence of free bromine exercises 
a retarding influence on the decomposition. This was shown to be the 
case where a mixture of hydrogen bromide, bromine, and oxygen were 
exposed to light. After a given period 1 per cent. of bromine was set 
free from the hydrogen bromide, whilst in a second experiment, in which 
no free bromine had been added, 10 per cent. of bromine was liberated. 
(The exposure to light was the same in both cases.) It has already been 
stated that the decomposition of hydrogen chloride is retarded by the 
presence of free bromine. With regard to the oxidation of aqueous 
solutions of hydrobromic acid by light, it is observed that in a 7 per cent. 
solution bromine is set free, whilst in a more dilute solution no oxidation 
occurs. 
Rise in temperature facilitates the oxidation of gaseous hydrogen 
bromide, and it was found that when a mixture of the moist bromide 
with moist oxygen was exposed to light at a temperature between 
75° and 85° much bromine was set free, as was shown by the deep red colour 
of the gas; whilst in a corresponding experiment conducted at the ordi- 
nary temperature (15°-25°) only a faint yellow colour was observed. 
With hydrogen chloride, on the other hand, decomposition appears to 
be retarded by rise in temperature; thus moist hydrogen chloride and 
oxygen gave 10 per cent. free chlorine when heated to 75°-85°, and 29 
per cent. free chlorine when exposed at the ordinary temperature. Fresh 
and fuller experiments are being made on this part of the subject with a 
view to further verifying these results. 
ee 
