Pyrogallic acid1 ounce.
. .
Nitric acid .. 20 drops.
. .
Water, up to. . . 6 ounces.
.
No. 2.
Carbonate of soda (common washing-soda) 6 drachms. Water, up to .1 pint.
No. 3.
No. 2. . . 1 ounce.
. .
Water .. 19 ounces.
. .
Or, No. 1.
Pyrogallic acid. . . . 1 ounce.
Bromide of ammonium. . 600 grains.
Nitric acid. .
. . 20 drops.
.
Water, up to .. 6 ounces.
. . .
No. 2.
Caustic potash. . . 3 drachms.
Water, up to .. . 1 pint.
.
.
No. 3.
No. 1. . 1 ounce.
. .
. .
Water. . . . 19 ounces.
. .
These solutions are used precisely as the ordinary solutions.
Hydrokinone Developer.
Two or three years ago Captain Abney recommended hydrokinone as a developer instead of pyrogallic acid. At that time the substance was so clear as to prohibit its being used except experimentally. Now it is compara tively cheap, and the developer is becoming a popular one. It may be used without a restrainer, and when first it was described it was claimed for it that it would enable plates to be worked with from one-half to one third the exposure required when the ordinary developer is used.
It would appear that this is a mistake ; nevertheless some prefer the developer to any other. It is at least worthy of a trial by those who are of an experimental turn.
Solutions may be mixed as follows :— No. 1.
Hydrokinone . ounce.
Nitric acid . . 20 drops.
Water, up to . 9 ounces.
No. 2.
Strongest liquor ammonia •880) . SO minims.
Water 1 pint.
No. 3.
No. 1 1 ounce.
Water . 19 ounces.
No. 4.
Bromide of ammonium 1 otmce.
Water, up to . . 10 ounces.
Nos. 2 and 3 are used as with the ordinary developer when exposure is normal. No. 4 is only to be used in cases of over-exposure when a few drops are added to the developer.
This may be a good place to illustrate and briefly describe " MacDougald's Patent Developing Tubes." These consist of two glass tubes with closed ends and fitted into a solid block of wood, so that they can be carried in the pocket or sent per post without fear of breakage. One contains the "stock solution" No. 1, given on page 36. The other contains—in a concentrated form —the " stock solution " No. 2, given on the same page. It is simply necessary to break the tubes and to dilute the solutions with water, when we have all ready for imme diate use—the stock solutions Nos. 2 and 3 of page 36. The tubes are made of two sizes. In the case of the smaller size the contents of each tube is diluted to six ounces with water, in the case of the larger to twelve ounces.
When travelling at a distance from home, or even when near home, in the case where we wish to develop in the field, these tubes will be found specially useful, it being difficult or inconvenient to carry the solutions in the ordinary form.