Standard formula for dry plates and films:

Water.........           16 ounces

Tolidol. .......           24 grains

Sodium sulphite ....... 72 (144) grains

Sodium carbonate...... 96 (240) grains

The figures in parenthesis are for crystals. It will be seen that in every case the weight of sulphite required in crystals is double that of dry sulphite, while the weight of carbonate crystals is 2.5 times as much as dry carbonate.

For tank development Dr. John M. Nicol recommends the standard formula diluted with 6 times the amount of water, and the addition of 1 drop of retarder to every ounce after dilution.

To obtain very strong negatives:

Water........               16 ounces

Tolidol....... 50 to 65 grains

Sodium sulphite ....... 80(160) grains

Sodium carbonate..... 120 (300) grains

On some brands of plates the addition of a little retarder will be necessary.

If stock solutions are preferred, they may be made as follows:

Solution A

Water...........        32 ounces

Tolidol..........           1 ounce

Sodium sulphite..     1 (2) ounce

Solution B

Water...........         32 ounces

Sodium sulphite.. 2 (4) ounces

Solution C

Water...........         32 ounces

Sodium carbonate 4 (10) ounces If preferred, stock solutions B and C can be made by hydrometer, instead of by weight as above. The solutions will then show:

Solution B Sodium sulphite.... 40

Solution C Sodium carbonate .. 75 Or if potassium carbonate is preferred instead of sodium:

Solution C Potassium carbonate 60

For standard formula for dry plates and films, mix

Solution A......... 1 part

Solution B......... 1 part

Solution C......... 1 part

Water............. 7 parts

For strong negatives (for aristo-platino):

Solution A.....1.5 to 2 parts

Solution B.....          1 part

Solution C.....          1 part

Water.........4 to 4.5 parts

For tank development:

Solution A......... 1 part

Solution B......... 1 part

Solution C......... 1 part

Water............ 35 parts

For developing paper:

Solution A......... 2 parts

Solution B......... 2 parts

Solution C......... 1 part

The reading of the hydrometer for stock solutions is the same whether dried chemicals or crystals are used. No water is used.

Pyrocatechin-Phosphate Developer

Solution A

Crystallized sulphite of soda......... 386 grains

Pyrocatechin...... 77 grains

Water............ 8 ounces

Solution B

Ordinary crystal phosphate of sodium........... 725 grains

Caustic soda (purified in sticks)... . 77 grains

Water............ 8 ounces

Mix 1 part of A with 1 part of B and from 1 to 3 parts of water. If the exposure is not absolutely normal we recommend to add to the above developer a few drops of a solution of bromide of potassium (1.10).