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.
Hot "soda water," so-called, is not water impregnated with carbonic acid gas. It is simply hot water flavored with such syrups as coffee, chocolate, ginger, etc. Sometimes wine syrup or punch extracts are substituted. The water may be heated in a copper boiler of various makes with a gas or oil stove, and the pressure obtained from the city mains, or, if there are no water works in the town, an ordinary soda fountain at a low pressure will do. It can be dispensed from the draught-tube of a dispensing apparatus, with syrups kept in the ordinary way.
By dispensing hot beverages in the winter season quite a lucrative trade may be done.
Formulas for "Hot Soda-water Syrups" will also be found later on among the "Chemical Ingredients of Saccharine Beverages". To obtain a supply of hot water always at the proper temperature - that is, nearly the boiling point (say 200° F.) - is the desideratum. For this purpose various kinds of boilers have been devised. The apparatus should either be supplied with a safety valve, so that when the pressure exceeds a certain number of pounds the accumulating steam can escape, or the heat should be regulated by the amount of water drawn. When there is but little demand for drinks the heat must be abated. But it must be borne in mind that the demand for "hot" drinks requires instantaneous dispensing, and to serve a drink of "hot soda" lukewarm, is worse than serving none at all.
This difficulty has made the dispensing of such beverages inconvenient and otherwise unsatisfactory.
The devices employed for the preparation of these beverages should be constructed to obviate all these difficulties, by properly regulating the inflow of cold water, the escape of steam, and by proper connection with the draught tube.