Pyrophosphate of iron furnishes a line of combinations which are extensively used. It is not unpleasant to the taste, and is quite permanent, especially if in neutral or slightly alkaline solution. However, an excess of mineral acids or certain mineral salts decomposes it, and the excess even of acetic acid causes its solution to gelatinize after a time. This difficulty can be overcome by adding to the gelatinized elixir enough ammonia water to restore the alkaline reaction.

Pyrophosphate of iron is incompatible with solutions of alkaloidal salts, unless the resultant liquid is neutral or can dissolve the alkaloid and have an alkaline reaction. If this fact is remembered the pharmacist may save some expense and inconvenience. If, for example, the elixir of pyrophosphate of iron and quinine has gelatinized from escape of ammonia, the cautious addition of ammonia water will restore it to the original condition. If, upon the other hand, the elixir has been made of alkaline reaction and the alkaloid has separated, the cautious addition of acetic acid will restore the transparency.

Solutions of pyrophosphate of iron cannot be exposed to sunlight without decomposition, and the same, to an extent, is true even of daylight, without the direct rays of the sun. Those who have reason to associate pyrophosphate of iron, pepsin, and salts of the alkaloids will find that considerable skill is necessary to make presentable and reputable preparations, and often some of these combinations are very trying to the patience of the operator. The reader is referred to remarks under the head of pepsin and elixirs of calisaya bark and the alkaloids.