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Updated: May 22, 2025
Another extremely sensitive indicator is the coal-tar dyestuff known as "Congo red"; the colour changes produced by it are exactly the inverse of those produced in the case of litmus, that is, it gives a blue colour with acids and a red colour with alkalis.
He dropped a piece of litmus paper into an acid, when it changed instantly to red, and on floating it in an alkali it turned as quickly to blue. "The litmus paper is still the litmus paper," he enunciated in the formal manner of the lecturer. "I have not changed it into something else. Then what did I do? I merely changed the arrangement of its molecules.
"The tube is filled to the partition line a, with tincture of litmus. The must to be examined, before it has begun to ferment is then poured into the tube, until it reaches the line 0. The blue tincture of litmus, which would still be blue, if water had been added, is turned into rose-color by the action of the acids contained in the must.
Steep Brazil dust in vinegar, with alum. Or, dissolve litmus in water and add spirit of wine. Or, steep cochineal in water, strain, and add gum. Yellow. Dissolve gamboge in water; or French berries steeped in water, the liquor strained, and gum arabic added. Horses, black. Black lightly laid on, shaded with Keating's black and bistre, heightened with masticot. Horses, chestnut brown.
Touch a few drops of blood fresh from the finger, with a strip of dry, smooth, neutral litmus paper, highly glazed to prevent the red corpuscles from penetrating into the test paper.
You might think from the river winding through our town that we are malarial, but, no, sir! Repeated experiments made both by the Government and local experts show that our air contains nothing deleterious nothing but ozone, sir, pure ozone. Litmus paper tests made all along the river show but you can read it all in the prospectuses; or the Santonian will recite it for you, word by word.
It is the great neutral centre of the Continent, where the fiery enthusiasms of the South and the keen fanaticisms of the North meet at their outer limits, and result in a compound that turns neither litmus red nor turmeric brown. It lives largely on its traditions, of which, leaving out Franklin and Independence Hall, the most imposing must be considered its famous water-works.
Half fill with dilute hydrochloric acid three large test tubes, labelled A, B, C. Add to each a few grains of pepsin. Boil B, and make C faintly alkaline with sodic carbonate. The alkalinity may be noted by adding previously some neutral litmus solution.
Solutions of the latter strength yield more accurate results when small percentages of acid or alkali are to be determined. These substances employed as indicators are usually organic compounds of complex structure and are closely allied to the dyestuffs in character. The indicators in most common use for acid and alkali titrations are methyl orange, litmus, and phenolphthalein.
This rule holds good for all poisons. On cloth the stain may be cut out, boiled in water, the solution filtered, and tested with blue litmus and other tests. Post-Mortem Appearances. Where the acid has come in contact with the mucous membranes there are dark brown or black patches.
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