1128 
Moreover, it will be shown that these reductions are markedly 
accelerated by oxidizing agents (e.g. KMnO,, Na,S,0,, H,O, etc.) so 
here light serves the same purpose as these oxidizing agents. 
It has been found out that in presence of sunlight a solution of 
sodium hyposulphite can reduce cupric chloride to metallic copper 
but in darkness the cupric salt is reduced to the cuprous state only. 
KAHLBAUM's pure sodium hyposulphite was dissclved in oxygen 
free water and a ee solution was prepared. The observations were 
carried out at 30°. 
1) 5 ee. cupric chloride containing 0.2194 gram of CuCl, and 
M ; ; 
35 C.C. 0 sodium hyposulphite were exposed for 90' minutes to bright 
sunlight; after a few minutes’ exposure metallic copper began to 
separate out. The reduced copper was estimated as CuO, which 
weighed 0.0277 gram i.e. 28°/, of the cupric salt is reduced to 
metallic copper by 90 minutes’ exposure to sunlight, whilst in the 
dark no metallic copper was formed in the same interval. 
; M 
2) 5 ce. of the same cupric chloride and 20 c.e. — sodinm hypo- 
o 
sulphite were exposed for 25’ minutes to bright sunlight. The amount 
of CuO obtained from the reduced copper weighed 0.0123 gram i.e. 
9°/, of the cupric chloride is reduced to the metallic state. 
Bennet (Jour. Phys. Chem. 16, (1912), 782 has shown that in 
presence of light a dilute ether solution of hydrazine hydrate can 
reduce ammoniacal copper sulphate solution. Evidently it is clear 
that the effect of light is superposed on the effect due to the reducing 
agents and thereby making possible reductions, which would not take 
place in the dark. 
It has also been observed that the velocity of reduction of gold 
chloride (H AuCl,) by oxalic acid, tartarie acid, citric acid, lactic 
acid, malic acid, formic acid ete. is greatly accelerated by light. 
The reduction by oxalic acid takes place according to the following 
equation : 
EN, 
2H Au Cl, +3. GOO =8 HOI 4600, + 2 Au. 
Moreover Vanino and SEEMAN (Ber. 32, (1899) 1968) have shown 
that hydrogen peroxide in alkaline solution immediately precipitates 
gold from gold chloride as finely divided metal : 
2H AuCl, +3H,0, + 8KOH=8K Cl-+-8H,0+ 30, + 2 Au. 
Now it has been found that a mixture of gold chloride and hydrogen 
