34 Cincinnati Society of Natural Fiistory. 
oxalate, or as it is familiarly known, the iron developer. 
Ferrous oxalate developer is composed of the neutral oxalate of 
potash and the sulphate of iron; the proportion being one part 
of a saturated solution of the sulphate of iron (which has been 
rendered acid by the addition of a sufficient quantity of sulphuric 
or tartaric acid to turn blue litmus paper red) to six parts of a 
saturated solution of the neutral oxalate of potash. ‘This devel- 
oper may be weakened, or its action restrained, by the use of a few 
drops of atwenty per cent. solution of bromide of potassium (say 
three drops to the ounce of developer), or what is to my mind bet- 
ter still, by the addition of a little water; and it may be acceler- 
ated or strengthened by increasing the proportion of the iron to 
oxalate, from one to six, to one part of the iron to four parts of the 
oxalate. But if alarger proportion of the iron is used, a yellowish, 
muddy precipitate is formed, which renders the developer unfit for 
further use. This developer, if old and weak, may be greatly 
accelerated by the introduction of a one to four solution of hypo- 
sulphite of soda, (about the strength of a fixing bath) in the pro- 
portion of one drop of the hypo-solution to an ounce of devel- 
oper. 
I have, on numerous occasions, when my developer appeared to 
have lost its active principle, dipped the end of my finger in my 
fixing bath, and transferred to the developer the small amount of 
hypo that adhered to it. In some cases the effect was magical, 
and the developer, which was before inert, took on new life, and 
the development was carried to a satisfactory termination. ‘The 
plate would almost immediately present the appearance of over- 
exposure, and an unmistakable cloud would spread rapidly over 
it. And to one who had never made the experiment, the plate 
would soon appear hopelessly fogged. But upon washing off the 
old developer and pouring on a fresh solution, the plate would 
acquire sufficient density, and upon fixing would show a negative 
of surprising pluck and brilliancy. This, however entertaining as 
an experiment, is extremely hazardous, and I would not recom- 
mend its trial upon a valued plate. In using this developer, it is 
important to remember that the iron solution must be poured into 
the oxalate—not the oxalate into the iron—for in this latter case, 
the yellowish, muddy precipitate before spoken of is sure to be 
formed, and your developer wasted. I make it a rule to filter all 
of my solutions, and when properly made and filtered, the oxalate 
