on of the coloring matter depends also very essentially upon the
emulsion. If the emulsion contains iodide of silver, it has a greater
sensitiveness for light blue and blue-green light. At all events, the
iodide combination must not amount to more than one or two per cent., a
small quantity of iodine acting much better upon the total sensitiveness
of the plates than can be obtained by pure bromide of silver emulsion.

Methyl violet, rose bengal, and azalein act perceptibly in 1/10000 per
cent. upon yellow sensitiveness. Eosine and its varieties, eosine yellow
shade, or eosine J, pyrosine J, erythrosine yellowish, may all be noted
as very good sensitizers for green, yellow-green, and eventually for
yellow. The bluish shades of eosine colors, on the contrary, have an
absorption band further in the yellow. This is also the case with the
blue shade eosine (eosine B) and the most bluish of all eosines, the
bengal rosa. Of both eosines, yellow shade and blue shade, the latter
gives a little more intensity.

Although the eosine permits a large limit in the quantity, it will reduce
the sensitiveness greatly in larger quantity.

If eosine solution is mixed with bromide of silver emulsion, which is
entirely free from nitrate of silver, no eosine silver can form; it acts,
therefore, only as an optical sensitizer.

Of the several kinds of cyanin, chlorosulphate, nitrate, and iodide, the
latter acts best, as stated by Eder.

Schumann has already said that one drop of cyanin solution, 1 to 2,500 to
61/2 c. c. emulsion, already acted as sensitizing in orange; five to ten
drops cyanin. 1 to 1,500 to 15 c. c. emulsion, even gave red action.

There are two ways to color the gelatine film with a suitable coloring
matter: by mixing the latter directly before filtering into the ready
made emulsion, to produce at once colored plates; or to bathe dry
emulsion plates for one to five minutes in a solution containing the
sensitizing coloring matter. The plates have previously to be soaked for
a few minutes, whereupon they are bathed in an aqueous alcoholic solution
(with eosine yellow shade and eosine blue shade, in a solution of 1 to
3,000; but with cyanin in a diluted solution of 1 to 5,000). A mixture of
1/10 cyanin and 9/10 eosine yellow shade (of above concentration) acts as
a very favorable sensitizer. Lohse recommended bathing of the gelatine
plates in a solution of 0.03 eosine and 10 c. c. ammonia in 100 parts of
water. He found tha