trouble with the transparency, except to mount it after it becomes dry.
Where it is not entirely successful I put the plate into a solution of
citric acid, four ounces to a pint of water, for about one minute, and
have in nearly all cases succeeded in getting a beautifully-clear plate.
The picture must not be left long in the citric acid solution, or it
will float off; neither do I like using citric acid until after trying
the alum, for a similar reason.

I may mention that I recommend a short exposure in the printing-frame
and slow development, in order to get sufficient intensity. Of course
the exposure is always made to a gas or petroleum light. I also still
prefer the old method of making the ferrous oxalate solution, pouring
it back into the bottle each time after using, and using it for two
or three months, keeping the bottle full from a stock bottle, and
occasionally putting a little dry ferrous oxalate into the bottle and
shaking it up, allowing it to settle before using next time. By treating
it in this way it retains its power fairly well for a long time; and as
it becomes less active I give a little longer exposure, balancing
one against the other. Making the ferrous oxalate solution from two
saturated solutions of iron sulphate and potassium oxalate has not
succeeded so well with me for transparencies. The tone of the picture is
not so black as when developed by the old method; and I do not like gray
transparencies for the lantern. I also recommend very slow gelatine
plates, about twice as sensitive as wet collodion--not more, if I can
help it.

I have demonstrated, I hope to your satisfaction, the possibility of
producing lantern slides from commercial gelatine plates of a most
beautiful quality--ranging from clear glass to deep black, and
giving charming gradation of tones, showing on the screen a film as