332
ELEMENTS OF MATERIA MEDICA.
So'dee Ace'tas. — Ac’etate of Soda.
History. —This salt was first described by Baron, in 1747 (Thomson’sChemist, of Inorg, Bod. vol. ii. p. 464): but according to Dulk ( die Preuss.Pharm. iibers. u. erldut.) its real discoverer was F. Meyer, in 1677. Itwas formerly called terra foliata tartari crystallisata, or terra foliatamineralis.
Preparation. —It may be readily procured by saturating carbonate ofsoda by distilled vinegar (as directed in the Dublin Pharmacopoeia),evaporating the solution and crystallizing. In this process the aceticacid expels the carbonic acid with effervescence.
On the large scale acetate of soda is obtained by manufacturers ofpyroligneous acid by the following process :—Rough or impure pyrolig-neous acid is saturated with either slacked lime or chalk. In this waythere is formed an impure acetate of lime (commonly termed pyrolignateof lime). To the clear solution is added sulphate of soda. Doubledecomposition takes place : sulphate of lime precipitates, and acetate ofsoda remains in solution. The clear liquid is then evaporated and crys-tallized. The impure acetate of soda thus procured is purified bydrying, solution in water, re-crystallization, fusion in an iron pot, expul-sion of the water of crystallization by heat, incipient carbonization todecompose the impurities of the salt, re-solution, and re-crystallization.
Properties. —The primary form of the crystals of this salt is theoblique rhombic prism. Geiger ( Handb. d. Pharm. 1 Bd. 150, 3 Aufl.)says that a saturated solution of this salt does not readily crystallizewhen cooled in a tall glass vessel unless some pointed or angular body beintroduced. Its taste is cooling, saline, and bitterish. Exposed to theair, at ordinary temperatures, the crystals undergo little change ; but indry and warm air they effloresce and become anhydrous. When heatedthey first undergo the watery fusion, then give out their water of crystal-lization, and afterwards undergo the igneous fusion. At a red heat theyare decomposed, and give, as a residue, a mixture of charcoal and carbo-nate of soda. They are soluble in about 3 parts of cold water; and areslightly soluble in alcohol.
Characteristics. —As an acetate it is recognized by the tests beforementioned (p. 222) for this class of salts. That the base is soda is shewnby the characters already described (p. 310) for the soda salts.
Composition.— The following is tbe composition of this salt: —
Soda . 1 . . . . 32 ... . 23-36 .... 22 94
Acetic acid.1 . . . . 51 ... . 37'22 .... 36'95
Water . 6 . . . . 54 ... . 39'41 .... 4011
Crystallized Acetate of Soda. . 1 . . . . 137 .... 99’99 .... lOO’OO
Purity. —It should be white and perfectly neutral to test-papers(litmus and turmeric.) The presence of sulphuric acid may be recog-nized by chloride of barium, which occasions, with this acid, a whiteprecipitate insoluble in nitric acid. If nitrate of silver cause a white pre-cipitate insoluble in both water and nitric acid, but soluble in ammonia,