128 
PRACTICAL PHOTO-MICROGRAPHY. 
duce with good contrasts, the plan most useful is to 
reduce slightly, so as to remove any trace of fog from 
the shadows or non-actinic parts of the image, and then 
to intensify. 
To Reduce the Density. 
Soak the plate for a few moments in a fresh solution 
of sodium hyposulphite, such as is used for fixing, and 
then in a cup or measure mix with the hypo a dram or so 
of a weak, say five per cent., solution of potassium ferri- 
cyanide, or ferridcyanide — not ferrocyanide. This 
mixture applied to the plate, and kept moving over it, 
will in a short time reduce the density, clearing up the 
image all over, but specially the thin parts. As soon as 
the desired action has taken place the negative is well 
washed, as after the fixing bath. If, in order to get a 
considerable increase of contrast, we propose to in¬ 
tensify after reducing, the washing must be thorough, 
and the plate, after washing, should be immersed for 
some minutes in the acid alum bath mentioned on 
page 124. 
Ammonium persulphate five per cent, solution is a 
reducer which acts more strongly on the dense parts of 
a negative, a valuable quality. After treatment in this, 
soak the plate in a solution of sodium sulphite, and 
wash. The “Agfa” reducer also works well and safely. 
Bothamley reports that the action of this reducer is 
“ proportional to the opacity of the image.” 
To Intensify the Negative. 
Make a saturated—at ordinary temperature—solution 
in water of mercury perchloride (corrosive sublimate), 
