few minutes. This was, in fact, sensitive bromide of silver mixed with
a very small quantity of gelatine (about five per cent.), and could, I
found, be treated in the same manner as a bromide precipitate from
an aqueous solution; it might be washed, either by decantation or by
filtration, easily dried, and doubtless could, when dry, be kept for an
indefinite time, and be at any time used by mixing with gelatine and
water in any proportion thought fit.

I found that a less amount of gelatine than four grains to the ounce was
sufficient to carry the bromide down, while five grains to the ounce
carried it down in something which I considered too near an approach to
a plastic mass.

It will be noticed that in the experiments which I have described the
emulsion had not been boiled, so that the sensitiveness of the bromide
was probably not great. As the experiment was done in daylight it was
of no practical use for making emulsion; but I have since made several
batches in this manner and have found them most satisfactory.

When sensitiveness is sought by boiling I rind it necessary to add a
small quantity of gelatine after boiling and before precipitating, as
that which has been kept for some time at a high temperature seems to
have lost the viscosity necessary to carry down the silver bromide in
such a form that it can he easily separated from the alcohol and water.

The practical manner of making an emulsion by this method may be as
follows. Make up the following mixtures:

I.
Silver nitrate...........................................400 grains.