We said there was a scientific method of determining just when to stop development. This method was the result of constant study and experiment on the part of an amateur photographer, Mr. Alfred Watkins, of England, the inventor of the Watkins Exposure Meter. By faithfully following Mr. Watkins' method you need lever have an over or under-developed negative. This method is applicable to nearly all developers and should you use a developer which is not in the accompanying table, then you will first have to determine the factor by experiment. The method consists in timing the nega-tive from the moment the developer is flowed upon the plate until the first image appears and multiplying that number of seconds by a known factor and the product will be the length of time for total development. The factors which Mr. Watkins has figured out for the various developers are as follows:

 Kind of Developer. Factor. Pyro Soda, 1 grain of Pyro to the ounce .............................. II Pyro Soda, 2 grains of Pyro to the ounce .......................... 6 Pyro Soda, 3 grains of Pyro to the ounce ....................... 5 1/4 Pyro Soda, 4 grains of Pyro to the ounce ........................ 4 1/2 Pyro Soda, 8grains of Pyro to the ounce ........................ 4 3/4
 Kind of Developer. Factor. *Carbutt's Pyro Developer ............................... 7 Hydrochinon, causitc soda or carbonate .............. 5 1/2 Eikonogen .......................................................... 9 Metol...................................................... 28 Amidol, 2 grains per ounce ............................... 18 Pyro-Metol................................................. 9 Rodinal ........................................................... 40 Metol-Hydrochinon .................................... 13

Let us see how the factor works in practice. Suppose we are using Carbutt's Pyro developer and the image appears in 15 seconds. We know the factor is 7 so we multiply 15 by 7.

15 x 7 = 105 sec. = 1 3/4 minutes. This will be the total time required to complete development on an average plate. If the plate has been a trifle over-exposed then the first image will appear in a shorter time and development will not be so long and if it was a trifle under-exposed then vice versa. The factor remains the same in all instances except where bromide is added, and in this event the factor will have to be varied. If you are using a developer whose factor is given in the above table and the result should give you a negative not entirely satisfactory to you, then use a higher or a lower factor until the results are satisfactory, and then note down the factor and work by it. If you do this, your negatives will be very even and will all print in about the same time. Some people like great contrasts or blacks and whites in their negatives, while others prefer a softer negative, and so the factor may be increased or diminished to suit your individual taste.

* This factor was figured out by Mr. Carbutt.

There are a great many developers used by both amateur and professional photographers, but the Pyro developer is probably the most popular to-day. The following are the principal developers used at the present time:

## Seed's Pyro-Soda Developer

No 1. Distilled or good well water----16 oz.

Sulphite of Soda (Crystals).....4 oz.

Pyrogallic Acid................. 1 oz.

Sulphuric Acid..............10 drops.

No. a. Water...........................16 oz.

Sal Soda (Crystals)............. 4 oz.

To Develop Take

No. 1..............................1 oz.

No. 2..............................1 oz.

*Water...........................8 oz.

## Seed's Pyro Developer By Hydrometer Test

No. 1.

Of a clear Sulphite of Soda solution to test 60 with hydrometer, take....................18 oz.

Pyrogallic Acid.................. 1 oz.

Sulphuric Acid..............10 drops.

No. 2.

## Sal Soda Solution, Hydrometer Test 40

To Develop Take

No. 1..............................1 oz.

No. 2..............................1 oz.

*Water ..............8 oz

Remarks. - More water gives flatness and less water contrast. Useless water in cold weather. Nos. 1 and 2 are known as stock solutions.

## Stanley's Pyro-Soda Developer

No. 1.

Water............................80 oz.

Sulphuric Acid..............1/2 dram.

Pyro........................1 oz. Troy.

No. 2

Pure Water............... 80 oz. fluid.

Sulphite of Soda (Crystals).6 oz. Troy Carbonate of Soda (Cryst.).6 oz. Troy.

*For Double-coated plates use 18 ounces of water. If you use Aristo paper for your prints increase No. 2 to 1 1/2 ozs. and the water to 10 ozs.

To Develop take equal parts of No. 1 and No. 2.

## Stanley's Pyro Developer By Hydrometer Test

Carbonate of Soda, Hydrometer test 200.......................................40 oz.

Sulphite of Soda. Hydrometer test 200...........................................40 oz.

Mix the two for alkaline solution and use pyro solution as above.

## Hammer's Pyro Developer

No. 1.

Pure Water.....................27 oz.

Oxalic Acid.....................20grs.

Dissolve and add pyrogallic acid 1 oz.

No. 2.

Pure Water.................... -.32 oz.

Sulphite Soda Cryst............. 8 oz.

Carbonate Soda Cryst........... 4 oz.

To Develop Take

No. 1..............................1 oz.

No. 2..............................1 oz.

Water............................6 oz.

## Hammer's Pyro Developer By Hydrometer Test

No. 1.

Sulphite Soda solution testing 60 by hydrometer.

No. 2.

Carbonate soda solution testing 30 by hydrometer.

To Develop Take

No. 1 Sulphite solution...........1 oz.

No. 2 Carbonate of Soda solution.............................1 oz.

Pyro Solution.....................1 oz.

Water.............................6 oz.

To get an accurate test with hydrometer the temperature of the solutions should be always the same. 650 Fahr. is about right.

## Carbutt's Pyro-Soda Developer

No. 1.

Distilled or Ice Water..........10 oz.

Oxalic Acid.....................15 grs.

Bromide Potass................30 grs.

Then add Pyro 1 oz. and Water to make 16 fluid ozs.

No. 2.

Water............................10 oz.

Soda Sulphite Crystals.......... 4 oz.

Soda Carb. Crys. (or dry gran. 1 oz)............................. 2 oz.

Potash Carbonate............... 1 oz.

Dissolve, and add Water to make measure 16 fluid ozs.

No. 3.

Bromide of Sodium or Potassium, 1/2 oz. Water, 5 oz.

To Develop Take

No. 1..............................1 oz.

No. 2.............................1 oz.

Water............................4 oz