Eosin ammonium salt

Ammonium Salt of Eosin.-—Place a very stout filter paper on a flat-bottomed crystallising basin which is one-third full of concentrated aqueous ammonia solution, spread eosin to a depth of about 0-5 cm. on the paper, and cover the whole with a funnel. Very soon the light red crystals acquire a darker colour, and after about three hours they are completely converted into the ammonium salt, which forms dark red crystals having a green iridescence. When a sample of the material dissolves wholly in water the reaction is known to be complete. 

Ammonium Eosin.—Over a flat-bottom crystallising dish, filled with a concentrated ammonia solution, place a filter, of paper as strong as possible- Upon this is spread the eosin acid, in a layer about cm. thick, and the whole is covered with a funnel (Fig. 80). The bright-red crystals of the free eosin acid very soon assume a darker colour, and, after about three hours, it is completely converted into the ammonium salt, which forms dark-red crystals with a greenish lustre. The end of the reaction is easily recognized, by testing a small portion with water. If it dissolves, the conversion is complete. 

Salts of eosin are used for dyeing. Prepare some of the ammonium salt as follows Place in a desiccator about 25 cc. of con-... 

There are a number of varieties of Eosin (sometimes eosine ), but the most common are Eosin B (Cl 45400/Acid Red 91) and Eosin Y (Cl 45380/Acid Red 87) the former is the sodium or ammonium salt of the dibromo derivative of dinitrofluorescein, while the latter is the disodium salt of tetrabromofluorescein. Eosin Y was discovered by Caro in 1871, Eosin B by Caro in 1875 and Baeyer in 1876 Colour Index, 1971). 

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