1079 
K,C,0, + HgCl, = 2HgCl + 2KCI + 2CO,, 
If to this mixture of oxalate and mercuric chloride one adds a 
ferrous salt, one gets a slight precipitate of ferrous oxalate and at 
the same time mercurous chloride is formed. A solution of ferrous salt 
cannot reduce mercuric chloride at the ordinary-temperature, but in 
presence of an oxalate it becomes a better reducing agent, and reduces 
mercuric chloride to the mercurous state, and at the same time the 
potential reducing power of an oxalate is activated in bringing forth 
the reduction of mercuric chloride to the mercurous state. Evidently 
the reducing power of the ferrous salt as also that of the oxalate 
is activated by their mutual presence. Tartrates and citrates behave 
in a similar manner in presence of ferrous salts. 
Wintuer (Zeit. wiss. Phot. 1909, 7, 409) has brought forward 
argument to show that the light sensitiveness of a mixture of an 
oxalate and mercuric chloride is due to the presence of iron and 
the investigator suggests that the purest mixtures of an oxalate and 
mercuric chloride so far prepared have contained iron. In absence 
of iron the mixture is not sensitive to visible rays. It seems to me 
that the real function of iron, if it is present, is not that of a 
photoferment or photocatalyst, as suggested by Winrner, but that 
of an inductor. The ferrous salt in presence of an oxalate reduces 
the mercuric chloride to the mercurous state and at the same time 
activates the potential reducing power of the oxalate in inducing 
the reduction of mercuric chloride to the mercurous state. This 
induced reaction takes place also in the dark. Evidently the Winrarr 
hypothesis seems to be doubtful. 
Chemical Laboratory Muir Central College 
Allahabad India. 
