s impossible to produce a slaty gray image. The result of
prolonged toning is merely an image of an engraving black color. Of this,
however, we shall say more hereafter. We wish first of all to refer to an
elaborate series of experiments by Lionel Clark on the effects of various
toning baths used with the gelatino-citro-chloride paper.

The results of these experiments we have before us at the time of writing,
and we may at once say that, from the manner in which the experiments have
been carried out and in which the results have been tabulated, Lionel
Clark's work forms a very useful contribution to our photographic
knowledge, and a contribution that will become more and more useful, the
longer the results of the experiments are kept. A number of small prints
have been prepared. Of these several--in most cases, three--have been toned
by a certain bath, and each print has been torn in two. One-half has been
treated with bichloride of mercury, so as to bleach such portion of the
image as is of silver, and finally the prints--the two halves of each being
brought close together--have been mounted in groups, each group containing
all the prints toned by a certain formula, with full information tabulated.

The only improvement we could suggest in the arrangement is that all the
prints should have been from the same negative, or from only three
negatives, so that we should have prints from the same negatives in every
group, and should the better be able to compare the results of the toning
baths. Probably, however, the indifferent light of the present season of
the year made it difficult to get a sufficiency of prints from one
negative.

The following is a description of the toning baths used and of the
appearance of the prints. We refer, in the mean time, only to those halves
that have not been treated with bichloride of mercury.

1.--Gold chloride (AuCl_{3})........... 1 gr.
Sulphocyanide of potassium......... 10 gr.
Hyposulphite of soda............... 1/2 gr.
Water.............................. 2 oz.

The prints are of a brilliant purple or violet color.

2.--Gold chloride...................... 1 gr.
Sulphocyanide of potassium......... 10 gr.
Hyposulphite of soda............... 1/2 gr.
Water.............................. 4 oz.

There is only one print, which is of a brown color, and in every way
inferior to those toned with the first bath.

3.--Gold chloride...................... 1 g