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.
In late years phosphoric acid has been introduced for acidulating beverages, thereby bringing forward a comparatively new class of drinks called "phosphates," "nerve food," etc. Their introduction brought forward quite a controversy on their relative merits and demerits. "The views expressed by different writers in regard to the degrees and mode of action of phosphoric acid are not easily harmonized," says a good authority. Indeed, we read and hear as many opinions as many different views are expressed. At any rate its extensive use in beverages is now a matter beyond dispute. Phosphoric acid is a powerful acid. Its solution has an intensely sour taste, and it affords an agreeable acidulous beverage, but contributes a sharpness totally unlike the pleasant, mild tartness produced by citric acid, and not relished by all consumers of carbonades. It is not poisonous, as some believe; its powerful acidity would render its employment in other than homeopathic quantities unnecessary, should the slightest danger attend its use.
The prevalent notion that phosphates of one sort or another contribute to the maintenance of the nerve force, doubtless arises from the fact that the solid parts of the human frame consist principally of the phosphate of lime, a salt formed by the union of phosphoric acid and lime. A man of common stature is said to have one pound of phosphorus in his bones, and as phosphoric acid is a compound of phosphorus and oxygen, the inference that anything in the shape of drink, food or medicine containing this element is beneficial, is natural, but erroneous; however, the bottler is obliged to study and cater to the consumer's wants, whether whimsical or otherwise. Phosphoric acid is a colorless, inodorous, acid liquid, having the specific gravity 1.348, containing fifty per cent, of H3 Po4. Diluted phosphoric acid corresponds in all respects to the preceding, except that it contains only ten per cent, of H3 Po4, specific gravity 1.057. The commercial phosphoric acids are seldom perfectly pure, as the operations in their manufacture are scarcely completely accomplished.
Phosphoric acid keeps fairly well in solution, but mixed with other substances may cause sediments or opalescense to appear after a time, while it quickly inverts saccharine solutions and has a tendency to alter and frequently degrade organic coloring matters.
Phosphoric acid affects the metallic parts of the apparatus it comes in contact with; we advise, in case phosphoric acid cannot entirely be dispensed with and there is an actual demand for "phosphates," to use as an average no more than two drachms of phosphoric acid to one gallon of syrup which would be at the rate of about one grain per half-pint bottle (one ounce of syrup to the bottle). Wherever possible we urge the trade to abstain altogether from its employment, and refer to our opinions expressed on "Nerve Food Extracts".