1357 
iV 
8) 5 c.c. gold chloride and 2 c.c. — hydrogen peroxide : gold 
5 
appears after 
Sunlight Uilfused light Darkness 
10' 14' 18' 
From the foregoing table it is clear that the reduction of gold 
chloride is markedly cataljdically accelerated by light. Moreover it 
has been shown that oxidizing agents also act as positive catalysts 
in these reactions. Therefore light and oxidizing agents play the same 
part of accelerators in these reductions. 
A solution of platinic chloride (H^PtCI,,) is not reduced by oxalic 
acid or tartaric acid even in presence of sunlight but it is slowly 
reduced by formic acid and formates 
H,PtCl„ + 2 H . COOH = 2 CO, + 6 HCl + Pt. 
'fhis change is also fonnd to be accelerated by sunlight. 
Metallic platinum begins to separate after 
Sunlight 40 
Darkness 55 
Sunlight 75' 
Darkness 360' 
10 c.c. N sodiuin formaie and 
N 
5 c.c. — HjPtCL 
10 
5 c.c. 3.87 JSF formic acid and 2.5 c.c. 
10 
H,PtCL 
It is well known that a solution of selenious acid can be easily 
reduced to selenium. 
It has been observed that reducing agents like oxalic acid, tartaric 
acid etc. even in large excess cannot reduce a solution of sodium 
selenite in the dark but in the presence of sunlight the reduction 
takes place and selenium separates out. 
Mercks pure sodium selenite was dissolved in water and it was 
standardized by weighing the selenium separated in a Gooch crucible 
when the solution is boiled with an excess of sulphurous acid. 
* if 
An exact — solution was prepared and the observations were 
made at 31° C. 
N 
1) 25 c.c. oxalic acid and 10 c.c. 
M 
— sodium selenite, selenium 
5 
separates after 40' minutes’ exposure to sunlight. 
N M 
2) 10 c.c. — tartaric acid and 5 c.c. — sodium selenite, selenium 
5 5 
separates after 330' minutes’ exposure to sunlight. 
N M 
3) 10 c.c. — citric acid and 5 c.c. sodium selenite, selenium 
5 5 
separates after 300' minutes’ exposure to sunlight. 
