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............... ½ gr.
Water.............................. 2 oz.

The prints are of a brilliant purple or violet color.

2.--Gold chloride...................... 1 gr.
Sulphocyanide of potassium......... 10 gr.