This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
This is by far the most agreeable method of exhibiting citrate of potassa, and is particularly adapted to cases in which the stomach is irritable. independently of its diaphoretic and refrigerant properties, it is one of the most effectual anti-emetic medicines. I know nothing equal to it in cases of fever with a hot skin, and a disposition to frequent vomiting. To produce, however, its best effects, it must be carefully prepared.
i have always preferred it made with fresh lemon-juice, when this could be had of good quality. it should be expressed from the lemon at the time when used. A solution of carbonate of potassa containing two drachms of the salt in four fluidounces of water, or a solution of the bicarbonate of potassa, with three drachms in four fluidounces, must be prepared. A tablespoonful of lemon-juice is to be expressed, and diluted with an equal measure of water; a tablespoonful of one of the above solutions is to be added; and the whole stirred together. if the materials are of the right quality, a brisk effervescence takes place; and, in this state, the dose should be swallowed. it need scarcely be said that the effervescence is owing to the escape of carbonic acid. The mucilaginous matter of the juice detains the acid gas for a short time, and thus increases the quantity of it swallowed. Sometimes no effervescence takes place. This is almost always owing to weakness of the lemon-juice, in other words, to its deficiency in citric acid. There is not enough of this to decompose the whole of the carbonate of potassa, and the consequence is that the liberated carbonic acid, instead of escaping with effervescence, goes to the undecomposed portion of the carbonate, and converts it into bicarbonate. This does not, however, happen, if the solution of the bicarbonate is used in preparing the draught. There can be no such appropriation of the liberated acid in this case, and if there be any acid in the lemon-juice, there will be effervescence of course. Some prefer the bicarbonate on this account. But it is not undecomposed bicarbonate of potassa that is wanted; it is the citrate; and a brisker effervescence cannot compensate for a deficiency of this. The carbonate of potassa has the advantage of indicating, by this want of effervescence, the deficiency of citric acid in the lemon-juice, and thus enables us to correct it by the addition of a little more of the juice, or as much as may be necessary duly to excite effervescence. With the bicarbonate the deficiency passes undetected. I prefer, therefore, the carbonate of potassa in making this preparation. if fresh lemons are not to be had, a solution of citric acid may be substituted, of the same strength. (See II. 92.)
The dose as above prepared should be administered every hour, two, three, or four hours. Every two hours is generally sufficient. To this, as to the neutral mixture, additions may be made to meet coexisting indications, as tartar emetic to increase its sedative powers, sweet spirit of nitre to obviate nervous symptoms, and one of the liquid forms of opium, especially the solution of sulphate of morphia, to obviate diarrhoea and quiet nervous irritation.