of precipitating the whole of gelatine with alcohol, and which would
take less time than the method of obtaining the bromide in a pure form.

My first idea was to make up the solutions used in emulsifying in a very
concentrated form, and, after emulsifying, boiling, and allowing to
cool, to add to the thin emulsion thus obtained gelatine to the amount
of twenty grains to the ounce, and to precipitate this with alcohol,
the rest of the gelatine required to make up the bulk being afterwards
added, and the whole thoroughly incorporated by warming and shaking.
I was thus successful in reducing the amount of alcohol required to
one-third of what would be necessary if the whole of the emulsion were
precipitated; but still I found that, if a reliable emulsion were
required, the pellicle as formed had to be washed to free it from the
last trace of soluble salts.

It now struck me that it might be possible to precipitate the bromide of
silver direct from a very weak solution of gelatine, and obtain it in
such a form that it might be filtered, washed, and in every way treated
as an ordinary precipitate. I tried the following experiment. I took--

1. Silver nitrate....................... 200 grains
Water............................... 11/2 ounce.
2. Ammonia bromide...................... 120 grains.
Water................................ 11/2 ounce.
Gelatine............................. 12 grains.

I emulsified the two together in the usual way, allowed the whole
to cool, and then poured the thin emulsion into about ten ounces
of alcohol, stirring the while. As I had anticipated, a flocculent
precipitate was formed, which settled to the bottom of the vessel in a