_Developing Collodion Process._--I use to develope my collodion pictures M.
Martin's plan, _i. e._ a solution of common copperas made a little acid
with sulphuric acid. This answers very well and gives to the pictures,
after they have been exposed an hour or two to the atmosphere, a
silver-like appearance: but this copperas solution seems to destroy the
_glass_ for using _a second time_, inasmuch as a haziness is cast upon the
glass, and its former enamel seems lost, not to be regained even by using
acids. The hyposulphite also seems to be affected by this manner of
developing the {605} pictures after a short time, which is not the case
with pyrogallic acid. The hypo., when thus affected with the copperas,
appears also to throw a mist over the picture, which new hypo. does _not_.
I should esteem it a favour if any of your numerous readers could inform me
the cause of this.