938. Note

Note. The salts used for collodion should keep and react neutral. Cadmium salts thicken the collodion; alkaline salts make it thinner. Three to four parts of iodine compound are generally taken to one or one and a half parts of bromine salts; 166 parts of iodide of potassium are equal to 186 parts of iodide of sodium, or 145 parts of iodide of ammonium, or 134 parts of iodide of lithium; 119 parts of bromide of potassium are equal to 139 parts of bromide of sodium, or 98 parts of bromide of ammonium, or 172 parts of bromide of cadmium. Calcium salts work the slowest; cadmium the quickest, and are also the coarsest. Iodide of potassium soon discolors the collodion containing it, and does not keep well. Bromine and iodine make the collodion gelatinous. Excess of bromine gives a blue film, and iodine a gray film.

939. Special Developer For Negatives

Special Developer For Negatives.

Protosulphate of Iron (saturated solution).

.....2 ozs.

Acetic Acid

1 oz.

Water ....................................

20 ozs.

940. Negative Varnish

Negative Varnish.

Alcohol .....................

.................60 ozs.

Sandarad ....................

.................10 ozs.

Camphor

1 on

Caster Oil

2 ozs.

Venetian Turpentine .........

....................1 oz.

941. A Simple Negative Varnish

A Simple Negative Varnish.

Standard

2 ozs.

Venetian Turpentine

1/2 oz.

Oil of Turpentine

1 oz.

Alcohol (825)

..................20 ozs.

This varnish is of a pale color and gives a very hard film, rhe plate must be warmed previous to coating.