This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.

**Developing With Different Factors Regulates Speed Of Developer**. The following formulae are given for regular pyro developers prepared by the factorial system for the developing of plates in four, ten, twenty and twenty-five minutes. For the convenience of the reader we will apply our regular universal pyro developer for use in this illustration: -

Water........................ | 6ounces |

Sulphuric Acid C. P......... | 1/2 dram |

Pyro......................... | 1 ounce |

Procure a 20-ounce bottle. Into this pour 1 ounce Stock Solution No. 1, and add 16 ounces of water.

Stock Solution No. 3.

Sulphite of soda 40 hydrometer test, or by weight, | |

Sulphite of Soda (Anhydrous) ... | .......... 1 ounce |

.......... 13 ounces |

Carbonate of Soda ( Anhydrous), 20 hydrometer test; or if by weight,

Carbonate of Soda (Anhydrous) | ....... 1 ounce |

Water.............................. | 23 ounces |

If Crystal Sodas are used, double the quantity in weight. Use only the very best chemicals. We would recommend Seeds, Cramer's or Mallinckrodt's anhydrous C. P.

**Preparing The Stock Solution**. In order to avoid early discoloration of the Pyro Stock Solution, it is advisable to acidify the water before adding the pyro; therefore, this solution should be mixed up in the regular order: Into six ounces of water pour one-half dram of sulphuric acid. This acidifies the water. Then add to this one ounce of pyro. As you have one ounce of pyro to six ounces of water, there is in each ounce of solution one-sixth of an ounce of pyro. To reduce this to grains, divide 480 (the number of grains in an ounce), by six, which gives a result of eighty. Therefore, the grain strength of the pyro per ounce of the water will be eighty; or, in other words, you will have eighty grains of pyro to each ounce of water.

464. In order to prepare this Pyro Stock Solution for use, take one ounce of this Stock Solution, and dilute with sixteen ounces of water. This makes your Solution No. 2, and you have five grains of pyro to each ounce of this solution, for in taking the above mentioned eighty grains which were in each original ounce of Pyro Stock Solution, and adding this to sixteen ounces of water, you will have about seventeen ounces of solution to eighty grains of pyro, and when uniformly distributed throughout this bulk of water there will be in each ounce 1/17 of eighty, or 4.7 grains per ounce, or very nearly five grains of pyro per ounce of solution.

465. Solution No. 3 is made up of sodium sulphite, testing forty degrees by the hydrometer, while Solution No. 4 is composed of sodium carbonate, testing twenty degrees by the hydrometer.

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