encompassed with difficulty." This publication attracted a great deal of
attention, and gave me occasion to again call attention to my process,[3]
and point out that it was not only the first practical solution of this
problem, but the only truly isochromatic process ever discovered. Dr.
Vogel's new process was not only no better in any respect, but the plates
were insensitive to scarlet and ruby-red, and therefore would not
photograph all colors in the true proportion of their brightness.

[Footnote 3: _Photo. News_, London, September 5, 1884, p. 566, and _Year
Book of Photography_ for 1885, p. 111.]

My method consists in treating ordinary collodio-bromide emulsion plates
with blue myrtle chlorophyl solution, exposing them through the yellow
screen, and then developing them in the usual manner. The emulsion which
I have employed is made with an excess of nitrate of silver, which is
afterward neutralized by the addition of chloride of cobalt; it is known
as Newton's emulsion. I now prepare the chlorophyl from fresh blue myrtle
leaves, by cutting them up fine, covering with pure alcohol, and heating
moderately hot; the leaves are left in the solution, and some zinc powder
is added, which helps to keep the chlorophyl from spoiling. I have a
bottle of this solution which was prepared about six months ago, and now
appears to be as good as when first made.[4] A glass plate is flowed with
the emulsion, and as soon as it has set, the chlorophyl solution is
applied for a few seconds, after which the plate is washed in pure water
until smooth, when it is ready for exposure.

[Footnote 4: I originally recommended chlorophyl extracted from dried
leaves, because I had not yet learned how to preserve the solution for
more than a few weeks; and at some seasons it would be difficult, if not
impossible, to obtain fresh leaves. The tea organifier which I