cannot speak from experience on this point, it will, I have no doubt,
keep for an indefinite time so long as light is kept from it.

If it be desired the ammonio-nitrate method may be used instead of the
boiling one, although in my hands it does not give such sensitiveness.
If it be desired to use this method, solution Nos. I, II., and IV. are
made up exactly as for the boiling method, except that No. II. is not
acidified. Liquid ammonia is then poured with stirring into the silver
solution, until it blackens and again clears. Emulsification is
performed exactly as described above, but instead of boiling, the
emulsion is kept at a temperature of about 100 deg. Fahr. for half an hour,
when it is poured into the alcohol, no addition of gelatine being
previously made.

I think I may claim for the method which I have just described that it
is less troublesome and more certain than either the ordinary washing
method or the usual one of precipitating with alcohol, while it affords
an easy method of making sensitive silver bromide in such a form that it
can be more easily stored and afterwards manipulated than if it were in
the form of pellicle. The whole of the soluble salts are eliminated,
and also any gelatine which may have been destroyed in the cooking.
The amount of alcohol used is comparatively small; in fact, to prepare
silver bromide for a pint of emulsion very little more than a pint of
methylated spirit is required. Besides this I do not think that I would
be wrong in saying that the chance of green fog is reduced to a minimum.

Let me take this opportunity of thanking Captain Abney for his prompt
reply to my question about the connection between the proportion
of bromide to gelatine in emulsions, and the density of resulting
images.--_W. K. Burton, in British Journal of Photography_.