303
In this process the volatility of the ammonia, joined to the affinity ofthe carbonate of potash for more carbonic acid, causes the decompositionof the sesquicarbonate of ammonia: the ammonia with a small portion ofcarbonic acid is disengaged, while the remaining acid converts the car-bonate into the bicarbonate of potash.
Properties. —It is a crystalline, colourless solid, the primary form ofwhose crystal is, according to Mr. Brooke, a right oblique-angled prism.It is inodorous, has an alkaline taste, and re-acts very feebly as an alkalion vegetable colours. It is soluble in four times its weight of water, at60° F., but is insoluble in alcohol. When exposed to the air it under-goes no change. When exposed to a red heat it gives out half its carbo-nic acid, and becomes the carbonate.
Characteristics. —The presence of carbonic acid and potash in thissalt is known by the tests for these substances before mentioned. Fromthe carbonate of potash it is best distinguished by a solution ofbichloride of mercury, which causes a slight white precipitate with it:whereas with the carbonate it causes a copious brick-dust precipitate.Sulphate of magnesia will not recognise the freedom of bicarbonate fromcarbonate, as I have before stated (p. 301.)
Composition. —The composition of this salt is as follows :—
Eq.
Eq.Wt.
Per Cent.
Berard.
Potash..
.I .
. . 48 . .
. 47-58 . .
. 48-92
Carbonic Acid. . . .
.2 .
. . 44 . .
. 43-60 . .
. 42-01
Water.
.1 .
. . 9 . .
. 8-82 . .
. 9-07
Crystallized Bicarbonate Potash 1 .
. . 101 . .
. 100-00 . .
. 100-00
Impurities. —The presence of chlorides and sulphates may be recog-nized in the way described when speaking of carbonate of potash.Bichloride of mercury may be employed to detect any carbonate ofpotash, with which it would form a brick-dust coloured precipitate.
Physiological Effects. —The effects of this salt are similar to thoseof the carbonate of potash, except that its local action is much lessenergetic, in consequence of the additional equivalent of carbonic acid;while the alkaline effect on the system is equally energetic, so that it is anexceedingly eligible preparation in lithiasis and other cases where wewant its constitutional, and not its local, action.
Uses. —-It may be employed for the same purposes that we use causticpotash (v\<1q potash), except that of acting as an escharotic. Thus it isused as an antacid, to modify the quality of the urine, in plastic inflam-mation, in glandular diseases, affections of the urinary organs, &c. Butits most frequent use is that for making effervescing draughts, with eithercitric or tartaric acid. The proportions are as follows:—20 grains ofbicarbonate of potash will saturate about 14 grains of the citric acid ofcommerce, 15 grains of tartaric acid, or Siijss. of lemon juice. In theshops, a preparation, called lemon and kali, is kept: it is composed ofsugar, dry citric acid, and the bicarbonate of potash. It is used as anextemporaneous effervescing draught. As it abstracts water from theatmosphere, it must be kept in a well-stopped bottle.
Where there is great irritability of stomach, I believe the effervescingdraught, made with bicarbonate of potash and citric acid, to be moreefficacious than that made with carbonate of soda and tartaric acid, theresulting citrate of potash being, in my opinion, a much milder prepara-