This section is from the "Elixirs And Flavoring Extracts. Their History, Formulae, & Methods of Preparation" book, by John Uri Lloyd. Also available from Amazon: Elixirs and flavoring extracts,: Their history, formulae, and methods of preparation;
Ammonio-citrate of bismuth is not always entirely soluble in water, owing to the fact that it parts with ammonia and assumes a partially insoluble condition. It is well, therefore, to remember that a little ammonia water will facilitate the complete solution of ammonio-citrate of bismuth, unless the decomposition has proceeded beyond a certain limit.
In consideration of the above fact, elixirs containing excess of acids are incompatible with it, and the same is true of solutions of salts of the mineral acids. However, excess of acetic acid does not decompose it immediately, and salts of acetic acid are compatible with solutions of ammonio-citrate of bismuth, which is one reason why in elixir formulae we use acetic acid in making solutions of alkaloids.
If an elixir containing ammonio-citrate of bismuth in connection with pepsin is not alkaline in reaction, or at least neutral, decomposition of the salt results, followed by precipitation. If it is alkaline, destruction of the pepsin follows.
If an elixir containing ammonio-citrate of bismuth and salts of the alkaloids is alkaline, the alkaloids are likely to precipitate; and if acid, precipitation results from decomposition of the bismuth salt. These incompatibles can only be associated by carefully avoiding any considerable excess of either acid or alkali. The alkali to be used in order to effect neutralization is ammonia water, and the acid, acetic acid.
We call attention occasionally to the above facts, in connection with special combinations which we are forced to consider, and we trust that the repetition will be excused, as we prefer to repeat rather than omit a word of warning where it may be necessary.