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Updated: June 22, 2025
Such a test would be useful in confirmation. Copper. Sometimes, as in the neighbourhood of copper mines or of some copper pyrites deposits, a water may be contaminated with small quantities of copper. The yellow prussiate once more forms a good test, but to ensure the absence of free mineral acids, it is first well to add a little acetate of soda solution.
The chemical he employed to saturate the paper was a solution of nitrate of ammonia and prussiate of potash, which left a blue stain on being decomposed by the current from an iron contact or stylus. The signals were the short and long, or 'dots' and 'dashes' of the Morse code.
It is said that a solution of cyanuret or prussiate of potash, is used instead of nitric acid in applying mercury to copper plates, and that it is still better, there being then no trouble with the green spots of nitrate of copper. A good amalgamated copper plate is considered as serviceable as a bed of quicksilver of equal size, and it is very much cheaper and more convenient to manage.
Five cubic centimeters hydrochloric acid are now added, and the solution tested with red prussiate of potash for protoxide of iron, and the boiling continued till near dryness, when all the nitric acid is commonly driven off. Should nitrous acid still show itself, some more hydrochloric acid is added and the boiling continued.
They were beside themselves in the lonely, dark office; but, while the men were fumbling for matches, which would not go, Cogs's sister, Nydia, a sweet blind girl, who had learned Bain's alphabet from Dr. Howe at South Boston, bent over the chemical paper, and smelt out the prussiate of potash, as it formed itself in lines and dots to tell the sad story.
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