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Acid Phosphate
American Acid Phosphate is unexcelled. It should be dispensed from an essence bottle, about one dram or teaspoonful to a tumbler, after drawing the desired syrup.
This is a dispensing instruction rather than a full formula: it tells the fountain man how much acid phosphate to add to any syrup he has already drawn. The proportions still work.
- A dram, in practiceThe apothecary fluid dram is about 3.7 mL, which is why the text glosses it as a teaspoonful. Treat it as one level teaspoon; nothing here depends on the difference.
- Essence bottleA small stoppered bottle kept on the fountain counter for concentrated flavourings and acids, often fitted with a dropper or dash top. A dropper or dasher bottle does the same job, and matters because acid phosphate is meant to go in by the teaspoon, not the pour.
- TumblerThe size is not given; fountain glasses of the period were commonly in the 8 to 12 oz range. Work from a single teaspoon of phosphate per 8 oz finished drink and scale from there.
- The order of operationsThe text is explicit only that the phosphate goes in after the syrup is drawn; the soda would then follow. Adding the acid before the syrup makes the sweet-sour balance harder to judge.
- What acid phosphate isA solution of phosphoric acid partly neutralised with calcium, magnesium and potassium salts. It gives sourness with no fruit flavour and a faintly dry, mineral finish, which is the whole point of using it instead of lemon or citric acid. Food-grade acid phosphate is still made for bartenders and is not interchangeable with hardware-store phosphoric acid.
- Syrup quantity, unstatedThe original assumes the reader knows the house measure. Period fountain manuals commonly give something in the region of 1 to 1.5 oz of flavouring syrup per glass; start at 1 oz with 1 teaspoon of phosphate and adjust.
- YieldOne drink. Better not to batch the phosphate into the syrup for storage, since acid gradually inverts sucrose and the syrup will not keep as you expect.
Acid phosphate belongs to the decades when the American soda fountain was as much a pharmacy counter as a sweet shop, and its wares were sold on the promise of being restorative as well as refreshing. The commercial trade is generally traced to Horsford's Acid Phosphate, made by the Rumford Chemical Works in Rhode Island from formulations by the chemist Eben Horsford, and marketed for headache, dyspepsia and "mental exhaustion" as much as for flavour. Competing brands followed, and "American Acid Phosphate is unexcelled" reads more like trade puffery than analysis. The appeal to dispensers was practical: phosphate delivered a clean sourness that sharpened any syrup on the shelf without arguing with its flavour, which is why the entry gives no syrup and no name for the finished drink. Phosphates faded with the soda fountain itself, and the ingredient survived mainly with a few regional bottlers before cocktail bartenders revived it in the 2000s.