This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
Aniline is a product of the heavy oil of coal-tar. It is a colorless, limpid, oily liquid. By oxidation with other chemical substances various colors and in different shades are obtained.
The aniline red crystals have a golden green hue, and this kind only should be used.
We mention only the following particularly interesting coloring to the bottlers.
Aniline-Red is formed by heating a mixture of aniline and toluidine with corrosive sublimate or arsenic acid, and is a salt of rosaniline. Roseine, fuchsine, and azaleine are the acetate, hydrochloride, and nitrate of the same base. If obtained by the action of arsenic acid the dyes usually contain arsenic. To obtain the dyes free from arsenic the oxidation is now often effected by nitrobenzol or nitrotoluol.
On exposure to light the aniline red fades rapidly. It is affected by tartaric acid and disappears in beverages where this acidifying agent is employed. If the carbonic acid gas is not carefully generated and sulphuric acid or sulphurous vapors are mixed or dissolved in the water of the fountain or condenser, the same mystification occurs. The merits of aniline-red are that it excels in brilliancy all vegetable colors, that it is cheaper, very intense and therefore but trifling quantities being necessary. Much is said against using this aniline color, and the chief objection is that it contains arsenic, but only that kind free of arsenic should be employed. Even if it should contain traces of arsenic, the proportion of coloring matter employed is so small that no injurious effect can possibly result from its use.
Rosaniline is less soluble in water, but easily in alcohol, and gives a beautiful red color. Roseine, fuchsine and azaleine are soluble in water and alcohol, with a beautiful carmine-red color of intensive coloring capacity.
Dissolve of rosaniline one ounce in sixteen ounces of diluted alcohol; of roseine, fuchsine and azaleine, dissolve one ounce in sixteen ounces of diluted alcohol or water. The commercial solutions contain frequently some glycerine or syrup. To color one gallon of strawberry or raspberry syrup, only from one to four drachms are necessary, according to the shade desired. Even if the aniline red should contain traces of arsenic we almost fail to trace it in the beverage; into one half-pint bottle entering only about from one-half to two grains of coloring, and with how many articles of food we swallow arsenic with impunity! Aniline colors should be mixed with the syrup, and thus imparted to the beverage. If mixed directly with aqueous beverages it will stain the bottles.