PYRO-AMMONIA The use of pyro with ammonia as a developer dates from 1862, and it had its origin in America, where ammonia was first used for fuming dry plates before the application of an acid solution of pyro. Major Russell, the author of the tannin process, was the first (in 1863) to publish full working particulars. The composition of an average developer, ready for use, is much as follows : Pyro . . . 15 grs. 3'5 g.
Ammonium bromide 14 ,, Liquor ammonia: (88o) 3o mins. 6 ccs.
Water . . . so oz. I,000 The following are two-solution developers : A. Nitric acid . . 2 rains. 4 cc.
Water . . . so oz. x,000 ccs.
Then add pyro . 20 grs. 4.5 g.
B. Liq.ammoni(88o) 12o grs. 28 g.
Potassium bromide 3o 7 ,, Water . . . so oz. x,000 ccs.
Use equal parts of each.
A developer which nearly corresponds to to per cent. solutions is the following, given by Sir William Abney : A. Pyro . . . 5o grs. 11.5 g.
Sodium sulphite . I50 34'5 ,, Citric acid . . so 2-3 Water . . . I oz. so° ccs.
B. Potass. bromide . 5o grs. 11.5 g.
Water . . .I oz. xoo ccs.
C. Liq.amraonix (.88o) 2 firms. 25 ccs.
Water . . . 2i OZ. 225 Take of A 20 mins., B 3o mins., C 6o mins., and water 2 oz. ; I oz. of the mixed developer contains approximately x gr. of pyro, I grs. of potassium bromide, and 3-1- ruins. of am monia.
Pyro-ammonia is largely used for developing lantern slides because of the excellent brown tones which it yields. The J. A. Hodges formula is excellent : A. Pyro . . . I oz. x so g.
Sodium sulphite . 4 11 11 Citric acid . . 2 drms. 25 ccs.
Water . . . so oz. I,000 B. Liq.ammonize (-88o) I oz. soo ccs.
Water . . . so I,000 C. Ammonium bromide I oz. x so g.
Water . . . To s,000 ccs.
D. Ammon. carbonate I oz. II° g.
Water . . . 10 i,000 ccs.
This will give brown tones on a plate made for black tones if the exposure is prolonged. A mixture of 3o mins. each of A and B and 6o rains. each of C and D should give a rich brown inclining to purple. Increasing D and decreasing B gives warmer and more reddish tones.
It should be noted that, while in some formula: an alkaline bromide is recommended, it is rarely necessary for modern dry plates.
J. B. B. Wellington's two-solution formula gives rich sepia tones : A. Pyro . . . 24o grs. 55 g Sodium sulphite . 2 OZ. 220 Water to . . 10 i,000 ccs.
B. Am. carbonate . 48o grs. iio g.
Potassium hydrate 36o 82 Am. bromide . 240 ,, 55 ,,Water to . . 10 oz. I,000 ccs.
Take i dram of each, and add water to make i oz.