Crossword-Solution: GALLATE 7 letters, 2 clues 🏆 scrabble score: 8

The preparation is even sensitive enough to permit one to obtain an impression in the camera obscura in developing by the ferricyanide.” “As to the proofs in gallate (or tannate) of iron, they can be transformed into Prussian blue in a solution of potassium ferrocyanide (yellow prussiate of potash) slightly acidified by sulphuric acid.” The paper most suitable for this process is that which has been previously well sized with starch, as explained in a special paragraph of this pamphlet.

Note: Ordinarily, black ink is made from nutgalls and a solution of some salt of iron, and consists essentially of a tannate or gallate of iron; sometimes indigo sulphate, or other coloring matter,is added.

With ferric salts its solution gives a deep blue colour, and with ferrous salts, after exposure to the air, an insoluble, blue-black, ferroso-ferric gallate.

Wet the paper with this compound; the acid will discharge the colour from the last writing, while the alkali of the first, will precipitate the gallate of iron, and the writing will become black.

They are, no doubt, the earliest examples of the agency of two chemical compounds which will be co-existent with photography itself, viz., gallate of silver and hyposulphite of soda, and my use of them, as above described, will sanction my claim to be the first to take paper pictures rapidly, and to fix them permanently.