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The change of the color to red indicates an acid substance; an alkali would turn the reddened litmus paper to blue, and the mauve and Georgina test-papers to green. Take a sheet of test-paper of the same dimensions as the document to be examined, moisten it, and cover it underneath with a sheet of Swedish filter-paper.
The whole is then laid between two quires of paper, covered by a weighted board, and left in this condition for about an hour. At the end of this time examine the test-paper to see if it has partly or altogether changed color.
This examination finished, put the test-paper in contact with distilled water, to be afterwards removed and tried by appropriate tests to discover the nature of the alkali or acid present. Silver nitrate is also used to discover whether the paper has been washed with chlorine or chlorites. A paper in that way becomes acid.
The presence of ozone in any vessel or in the atmosphere, may be detected by a test-paper which has been moistened with a solution composed of 1 part of pure iodide of potassium, 10 parts of starch, and 100 parts of water, boiled together for a few moments. Paper so prepared turns immediately blue when exposed to the action of ozone, the tint being lighter or darker according to the quantity.
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