Home › At the Fountain › Citrate Magnesia To Dispense from Soda Apparatus
Citrate Magnesia To Dispense from Soda Apparatus
Magnesia Carbonate. 6¼ Troy ounces Citric Acid . 12/½ Troy ounces Syrup Citric Acid, 30. fluid ounces Bicarbonate Potash 1¼ Troy ounces Dissolve citric acid and carbonate magnesia in 3¼ pints water; filter, if necessary. A clear, light yellow liquid is obtained. Use no heat. Then prepare syrup citric acid.
This is a pharmacy preparation dispensed over a soda counter rather than a flavoured drink, and the figures below are given so the original can be read accurately, not so it can be reproduced.
- Why this one is off the tableSolution of magnesium citrate is a saline cathartic — a purgative — and this formula makes something over two and a half quarts of it with no dose stated anywhere. Served by the glass at fountain volumes it could easily deliver a laxative dose, with the fluid and electrolyte loss that follows. Anyone wanting magnesium citrate today should buy the labelled, dosed pharmacy product.
- The potassium is the real problemThe potassium -- About 39 g of potassium bicarbonate is dissolved into the batch, far beyond any food-seasoning quantity, though spread through the whole batch it comes to roughly a gram in a fountain glass. The recipe does not state its purpose.
- Troy ounces, not avoirdupoisDruggists weighed by the troy ounce, 31.1 g rather than the familiar 28.35 g. So 6¼ troy oz of magnesium carbonate is about 194 g, 12½ troy oz of citric acid about 389 g, and 1¼ troy oz of potassium bicarbonate about 39 g. Reading these as kitchen ounces understates every one of them.
- The liquid measures3¼ pints is close to 1.5 litres, and the 30 fluid ounces of citric acid syrup roughly 890 ml. Note that the syrup is a second preparation entirely — the entry tells you to prepare it but not how, presumably because a syrup formula was given elsewhere.
- "Use no heat"The instruction is real chemistry, not caution for its own sake. Citric acid and magnesium carbonate react with visible effervescence as the carbonate is decomposed, and warming the mixture drives off carbon dioxide, encourages the solution to go cloudy and shortens its keeping. Cold dissolution gives the clear, faintly yellow liquid the text describes.
- Why it looks like a soda recipeThe finished liquid was charged and drawn like any other fountain product, which is exactly why it appears in a soda book rather than a dispensatory. The delivery method is a soda; the contents are a drug.
The American drugstore soda fountain is often traced to the pharmacy counter, though confectioners and mineral-water sellers had a hand in it too, and formulae like this one are the seam where the trades met. Solution of citrate of magnesia was an official preparation of the United States Pharmacopoeia from the later nineteenth century into the early twentieth, sold in stoppered bottles as a mild purgative, and a dispenser who already owned a carbonating apparatus could make it himself. Sweetened with citric acid syrup and served cold and fizzing, it went across the same marble counter as a phosphate or a soda, a reminder that the fountain fixture was as much a dispensing station as a place of refreshment, and that the modern soda shop kept the fixtures long after it dropped the pharmacopoeia.