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Updated: May 4, 2025
Just suppose two ammonia groups, NH and NH . If we rob those nitrogen atoms of their hydrogen atoms, we should leave two unsatisfied nitrogen atoms, atoms with an exceedingly keen appetite represented in terms of hydrogen atoms as N * and N *. We might suppose a group, though of two N atoms partially satisfied by partial union with each other, thus N:N . Now this group forms the nucleus of the azo-colours, and if we satisfy a nitrogen at one side with an aniline, and at the other with a phenol, or at both ends with anilines, and so on, we get azo-dyes produced.
Black urine is generally caused by the ingestion of pigmented food or drugs, such as carbolic acid and the anilines. Amatus Lusitanus, Bartholinus, and the Ephemerides speak of black urine after eating grapes or damson plums. The Ephemerides speaks of black urine being a precursor of death, but Piso, Rhodius, and Schenck say it is anomalous and seldom a sign of death.
It is to be feared that the palmy days of cochineal are over, and that its chief office, besides staining liqueurs and tooth-powders, will be to keep down the price of the chemicals. With regret I see this handsome and harmless colour being gradually superseded by the economical anilines, whose poisonous properties have not yet been fully recognised by the public.
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