This section is from the book "Monograph on Flavoring Extracts With Essences, Syrups, and Colorings", by Joseph Harrop . Also available from Amazon: Monograph On Flavoring Extracts With Essences, Syrups And Colorings.
Water (sufficient to make).........
Wash the Irish Moss with Water, to free from impurities; add one (1) pint of Water and boil for five (5) minutes or heat in a water bath for fifteen (15) minutes, or macerate in cold water for twenty-four (24) hours, with occasional stirring; filter through purified cotton, on a muslin strainer, in a hot water funnel.
This mucilage, it is claimed, has no more taste than mucilage of Gum Arabic, and is said to keep much better.
It can be used with soda syrups, in the proportion of from two (2) to four (4) ounces of the Irish Moss to one (1) gallon of the syrup.