He first slakes 1 1/2 oz. lime by covering it with water overnight, in a wide-mouthed bottle. He then pours it- into a mortar and grinds the lime to a paste, which is next diluted with water and the whole decanted into a 2-gal. bottle. Any remaining sediment can be ground, diluted, and decanted in the same way. When the whole has been added, the 2-gal. bottle is filled to 2 gal. with water, the solution is shaken well and allowed to stand for an hour to settle. It is then filtered, and is ready for immediate use. The strength of the solution should now be tested, which is done by first making a solution of 3 1/2 oz. water and 1/2 oz. acetic acid. Into 2 oz. of the lime water (in which is placed a piece of blue litmus paper) 1 dr. and 20 m. of the acid solution is poured. This should just turn the litmus paper red, and will be a standard test. The strength of the lime solution will remain uniform, no matter what the temperature may be - a point of great importance. The solution will keep any length of time.
To prepare the developer, for 1 or 2 days' use, take 40 oz. of the filtered lime water and add 1 oz. of an 80-gr. solution of ammonium bromide. To develop, pour into a graduate 6 oz. of the bromo-lime water, add a small mustardspoonful of dry pyrogallic acid, shake, and pour over the plate laid ready in the developing tray. The image will soon appear and gain strength. If the plate was over-exposed, add a few drops of the bromide ammonium solution and a few grains of pyro. Very clean, clear, chocolate-coloured negatives are produced with this developer. Any tendency to fog may be overcome by the addition of a little more ammonium bromide.
(5) Where the photographer intends to travel, and develop on the route, it is very desirable to reduce his chemical outfit to the smallest bulk and to the fewest liquids possible. G. Cramer, the dry plate manufacturer, gives the following formula for a developer, which he considers gives the best of results, and at the same time has the advantage of extreme portability: -
Ammonium bromide .. 1/2 oz.
Potassium bromide .. .. 1 1/2 oz.
Pyrogallic acid .. .. 2 oz.
Dissolve in distilled water 32 oz.
Add sulphuric acid (c. p.) 120 m.
Aqua ammonia (strongest) 3 oz.
Water to make up bulk to 40 oz.
The sulphuric acid and aqua ammonia should be measured very exactly. Instead of 3 oz. of crystals, 2 oz. of granular soda sulphite may be substituted to produce the same effect. Dilute a sufficient quantity for one day's use as follows: For ordinary purposes, 1 part in 11; for very short exposures, 1 part in 3-6; for over-exposed plates, or in all cases where great intensity and contrast are desirable, 1 part in 20, This developer may be used repeatedly if it is always returned immediately to the pouring bottle, which should be provided with a tight-fitting rubber stopper. As long as the solution remains transparent, it is good; but when it looks muddy, its use should be discontinued.
(6) Henry J. Newton has lately discovered a new solution, which, when added to the ordinary soda carbonate developer, increases its developing power fivefold, thereby allowing sensitive plates in the camera to be exposed a much shorter time than is usual. He makes the following solution : 4 oz. water, in which is dissolved mercury bichloride 60 gr.; into this solution is poured a solution of 90 gr. potassium iodide; 1 oz. water. To every 2-3 oz. of the soda developer he adds 2-3 m. of the above solution. Clear negatives of good tone and quick printing quality are produced. Details in the shadows are brought out with greater facility. It is especially useful in the development of plates which have had an instantaneous exposure. He also found 2-3 m. of a solution of 150 gr. sodium iodide to 1 oz. water had a quickening effect, but not so much as the mercury solution.
(7) For preserving from discoloration, 2 oz. of sulphite is quite sufficient for 1 oz. of pyro. The formula then will run: Pyrogallic acid, 1 oz. Dissolve in water containing 30 gr. citric acid, and add solution of soda sulphite, as above, 4 oz. Then make up the whole to 10-20 oz., according to the operator's usual plan. You have then a stock solution easily made, always in order after the lapse of months, and capable of developing a negative perfectly free from the well-known yellow colour of pyro.
Various samples of the sulphite do not exhibit much difference in their respective effects; but it will be well to point out that, as this salt is not found in every chemist's shop, stress should be laid upon the fact, when ordering, that sulphite, not sulphate or sulphide, is wanted. Chemists are so used to their customers' ignorance of chemical nomenclature, that they might think an error had been made in asking for a little-known chemical.
The special kinds we tried were the commercial and the recrystallised sulphite, the latter costing 4-5 times as much as the former. The latter is a nicer-looking and a purer salt; it possesses no superiority in its colour-preventing properties, but may be decidedly recommended on the grounds of its probable greater uniformity.
(8) In reference to excessive contrast, presuming the exposure to be correct, the fault lies more in the developing than in anything else. A slow development, with the cautious addition of the ammonia as required, tends to produce a far more harmonious picture than the usual way of pouring the strong ammonia solution at one operation over the plate. A method well suited for interior work is as follows: -
Pyro Solution (keeps good for about a month), Pyrogallic acid .. ., 72 gr.
Citric acid ...... 24 gr.
Potassium bromide .. .. 32 gr.
Water ........ 1 oz.
Dissolve the citric acid in the water before adding the pyro.