331
larly-shaped crystals, whose primary form is the right rhombic prism:but curiously enough, the crystals are frequently produced in halves.Their taste is mildly saline and bitter. Exposed to the air they slightlyeffloresce. When heated they undergo the watery fusion, evolve theirwater of crystallization, and are decomposed: the residue consists ofcharcoal and the carbonates of potash and soda. They are readilysoluble in cold, and still more so in hot water.
Characteristics. —This salt may be recognised by the shape andsize of the crystals. Sulphuric acid added to the aqueous solution throwsdown small crystals of bitartrate of potash ; perchloric acid throws downperchlorate of potash: the chlorides of barium and calcium occasionwhite precipitates, soluble in excess of water, and composed of soda,tartaric acid, and, in the one case, baryta, in the other lime: chlorideof platinum produces a yellow precipitate of the platinum-chloride ofpotassium. Nitrate of silver occasions a white precipitate (tartrate ofsilver), soluble in excess of water. When heated, potash-tartrate ofsoda is decomposed, evolves various volatile substances, and gives outthe odour of caromel. If the residuum be digested in hydrochloric acid,we obtain a solution of the chlorides of sodium and potassium: thechloride of potassium may be precipitated by chloride of platinum,leaving chloride of sodium in solution, which may be detected by thetests already mentioned for this salt (p. 310).
Composition. —The composition of this salt is as follows:—
Soda .
Potash .
Eq.
. 1 ..
Eq.Wt.
.. 32 .... 48 .... 132 .... 90 ..
Per Cent... 10-6 .... 15*6 ..
.. 43*7 .... 29'8 ..
Schulze.
.. 133 -j
:: g-
' Tartrate PotashTartrate Soda -Water.
Eq.
1 .1 .
10 .
Eq.Wt.
... 114... 98... 90
Crystl d .Sodio-Tarte. of Potash 1 .
.. 302 ..
.. 997 ..
.. 100*0
1 .
... 303
Dr. Thomson (First Principles, ii. 440) says, that when the crystals aretree from all adhering moistiue they contain only eight equivalents ofwater of crystallization, and their atomic weight is then 284.
Physiological Effects. —It is a mild, laxative, cooling salt, veryanalogous in its effects to the tartrate of potash. Sundelin ( Heilmittell.)says it is uncertain as a purgative, sometimes failing, at others actingvery slowly, but strongly, and with violent abdominal pain. He thinksit may be completely replaced in practice by a mixture of magnesia andsulphate of magnesia. Like the other vegetable alkaline salts, it under-goes partial decomposition in the system, and is converted into the car-bonate, in which state it is found in the urine. Hence its use should becarefully avoided in persons suffering with phosphatic deposits in theurine.
Uses. —It is commonly employed as a mild aperient for females andother delicate persons. It may be used with advantage by those whoare subject to excessive secretion of uric acid or the urates.
Administration. —-It is given in doses of from half an ounce to anounce. It should be exhibited largely diluted with water. A very con-venient mode of fexhibition is in combination with bicarbonate of sodaand tartaric acid in an effervescing condition {vide Seidlitz Powders,p. 329).