154 PRACTICAL PHOTO-MICROGRAPHY. 
Neall, and good results may also be got with those of 
the Sandell Plate and Film Co. Even with the slowest 
gelatino-bromide slide plates obtainable reductions may 
be made in the camera with a lens at //16 by a few 
seconds’ exposure to diffuse daylight; and the exposure 
to a fishtail gas-burner at twelve inches distance, “ by 
contact,” is from ten seconds upwards. 
No developer answers our special purpose so well as 
the ferrous oxalate , the solutions of iron sulphate and 
potass, oxalate being kept as directed on page 140, and 
mixed in the proportions of one part of iron to six parts 
of oxalate, with half-a-grain of bromide to each ounce 
of developer. The process of development is very 
similar to that with bromide paper, but we must carry 
the density to a higher point, as much is lost in fixation, 
and we require a pluckier image. The washing, in 
acidulated water, after development, must not be 
omitted; and, if after fixing a scum appears on the film, 
it is to be removed by pouring on and off the acid alum 
solution. 
Sat. solution of alum in water ... ... 10 ounces. 
,, ,, of citric acid in water ... 10 ,, 
H)drochloric acid ... ... ... ••• 2 drams. 
If any tendency to frill the film is found in the use of 
this solution, the quantity of HC1 may be reduced. 
As usual after fixation in hypo, the plates must be 
thoroughly washed in running water or under the tap. 
Very neat porcelain troughs with grooves for the plates 
are to be found on the market ; each trough holds a 
dozen plates, quarter-plate or slide size, and the water 
