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of pyro solution may be added in order to gain opacity more quickly.

      PYRO-SODA DEVELOPMENT.

      When sodium carbonate is used as the alkali in place of ammonia the developer acts somewhat more slowly and is less liable to produce fog, especially with very rapid plates, and there is very little tendency to produce green fog. On the other hand, variations are not so easily made in the composition of the developer. Some people find the absence of the smell of ammonia a decided advantage.

      

Stock Pyro Solution. The same as for Pyro-Ammonia. Dilute Pyro Solution.2
Stock pyro-solution	1	oz. or	10	parts
Water	10	oz. or	100	parts
Soda Solution.
Sodium carbonate, crystallised.	1	oz. or	10	parts
Sodium Sulphite	1	oz. or	10	parts
Potassium bromide	10	grains or	0.23	part
Water to make up to3	10	oz. or	100	parts

[2] No more of the dilute pyro solution should be made up than is likely to be used during the same day, but it will keep well enough for a day or two.

[3] The sodium sulphite and carbonate are dissolved, with the aid of heat, in about 8 oz. (80 parts) of water, the bromide added, and the liquid when cold made up to 10 oz. by adding water.

      For use mix equal parts of dilute pyro solution and soda solution and pour over the plate.

      If the exposure has been correct the image will begin to appear in about a minute, and development is then allowed to go on with occasional rocking of the dish, until the negative is sufficiently opaque.

      If the plate behaves as if it were under-exposed, at once dilute the developer with an equal bulk of water and pour it back over the plate. If the high-lights continue to increase in opacity, but the rest of the image does not appear, add some more of the soda solution with or without some more water. Should parts of the plate still remain blank, apply some of the soda solution to them with the aid of a brush as described under pyro-ammonia (page 32).

      If the rapid appearance of the image indicates that the plate is over-exposed, at once pour off the developer into a measure or mixing glass and rinse the plate well with water. Add to the developer a small quantity of potassium bromide solution (1 in 10 of water) which should be kept at hand for this purpose. A small quantity of pyro stock solution may also be added. The developer is then poured over the plate again. When the over-exposure seems to have been considerable, the amount of potassium bromide added may amount to 4 grains (or 40 minims of the 1 in 10 solution) per ounce of the developer, but this proportion should not be exceeded; even small quantities of bromide in the pyro-soda developer have a marked influence in retarding development.

      When there is reason to suspect over-exposure, not more than half the soda solution should be added at the beginning of development, and the rest may be added or not, as the case may require.

DEVELOPMENT WITH ORTOL. Ortol Solution.
Ortol	130	grains or	1.5	parts
Potassium metabisulphite4	65	grains or	0.75	part
Water to make up to	20	ounces or	100	parts
Soda Solution. The same as for pyro-soda.

[4]See foot-note to page 30.

      Mix equal parts of ortol solution and soda solution.

      This developer behaves in much the same way as pyro-soda and gives very similar results. It has the advantage, however, that it does not stain the fingers, and has practically no tendency to produce either fog or stain on the plates. Moreover the same quantity of solution can be used for several plates; when the action becomes perceptibly slower or weaker, part of the old solution is poured away and an equal quantity of freshly mixed ortol and soda solutions is added.

      The chief differences to be observed are (1) that the different parts of the image follow one another more rapidly than with pyro-soda, even though the plate may have been correctly exposed, and (2) the colour of the reduced silver is somewhat bluer than with pyro-soda, and therefore in order to obtain the same degree of printing opacity, as distinct from visual opacity, development must be carried a little further.

      Apart from these differences, what has been said of pyro-soda holds good for ortol soda and need not be repeated.

DEVELOPMENT WITH HYDROQUINONE (QUINOL). Quinol Solution.
Hydroquinone	90	grains or	2	parts
Sodium sulphite	1	oz. or	10	parts
Water to make up to	10	oz. or	100	parts
Alkali Solution.
Potassium carbonate (dry)	1	oz. or	10	parts
Potassium bromide	20	grains or	0.46	parts
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