The picture, which has been exposed at a distance of 1.5 feet for about 8 to 10 seconds, is developed in the customary manner and fixed in an acid fixing bath composed of

Distilled water.. 1,000 cubic centimeters

Hyposulphite o soda........ 100 grams

Sodium sulphite         20 grams

Sulphuric acid.. 4 to 5 grams

First dissolve the sodium sulphite, then add the sulphuric acid, and finally the hyposulphite, and dissolve.

Blue tints are obtained by laying the picture in a bath composed as follows:

A

Uranium nitrate..... 2 grams

Water...... 200 cubic centimeters

B

Red p r u s siate o f

potash... 2 grams Water...... 200 cubic centimeters

C

Ammonia-iron-alum 10 grams

Water...... 100 cubic centimeters

Pure hydrochloric acid...... 15 cubic centimeters

Immediately before the toning, mix Solution A.. 200 cubic centimeters Glacial acetic acid... 20 cubic centimeters Solution B.. 200 cubic centimeters Solution C.. 30 to 40 cubic centimeters

Brown tints. Use the following solutions:

A

Uranium nitrate..... 12 grams

Water......1,000 cubic centimeters

B

Red prussiate of potash... 9 grams

Water......1,000 cubic centimeters

And mix immediately before use Solution A. . 100 cubic centimeters Solution B. . 100 cubic centimeters Glacial acetic acid... 10 cubic centimeters Pictures toned in this bath are then laid into the following solution:

Water......1,500 cubic centimeters

Pure hydrochloric acid...... 5 cubic centimeters

Citric acid. . 20 grams

To Turn Blueprints Brown

A piece of caustic soda about the size of a bean is dissolved in 5 ounces of water and the blueprint immersed in it, on which it will take on an orange-yellow color. When the blue has entirely left the print it should be washed thoroughly and immersed in a bath composed of 8 ounces of water in which has been dissolved a heaping teaspoonful of tannic acid. The prints in this bath will assume a brown color that may be carried to almost any tone, after which they must again be thoroughly washed and allowed to dry.