ipW. :0.olntm. 



Fig. 60. 



and Laboratory Methods. 1^'^^ 



VI. Potassium Antijnonyl Tartrate precipitates, from solutions containing 

 Barium^ a Double Tartrate of Barium and Antimony!. 



BaCla + 2[K(SbO)C4H40e • l/'iHjO] = [BaC^H^Og • {^"oO) ,_^Q, ^YL ^O ^• 



2H20J+2KC1. 



Method. — To the neutral and moderately concentrated drop to be tested add 

 a small drop of acetic acid. Place close to the test drop a drop of distilled 

 water containing the reagent. Warm the reagent drop, and stir until all the 

 tartar emetic has dissolved. Warm the test drop, 

 and while both drops are warm cause the reagent 

 to flow into the solution being examined. On 

 cooling, crystals of the double tartrate will separate 

 in masses near the edges of the drop. As soon as 

 crystals appear draw a platinum wire through one 

 of the crystal masses, and thence across the drop. 

 This will induce crystallization along the path of 

 the wire and will lead to the formation of well 

 formed single crystals. When this procedure is 

 followed, beautiful, clear cut, thin, transparent, color- 

 less crystals of the orthorhombic system are obtain- 

 ed. The usual forms are rhombs and hexagons (Fig. 60) ; the latter result 

 from the cutting ofiE of the acute angles of the rhombs. Multiple twins are 

 frequent. There is a great tendency toward the formation of aggregates. 



Remarks. — Free mineral acids must be absent. 



It is unfortunate that this neat reaction is of quite limited application. 



Strontium may be precipitated in like forms if the conditions are favor- 

 able. 



Calcium interferes, as do also members of Group I, and of the magnesium 

 group. 



When dealing with small amounts of barium in a mixture, it is necessary, 

 owing to the solubility of the barium double salt, to concentrate the solution to 

 such a point as to render it practically impossible to obtain satisfactory results, 

 because of the crystallization of other compounds. 



Lead forms a double antimonyl tartrate isomorphous with that of barium and 

 strontium. * 



Of the other heavy metals, silver is the only one which will yield a crystal- 

 line precipitate with the reagent, but under the conditions of the test as described, 

 the precipitate with silver is usually amorphous. 



Exercises for Practice. 



Dissolve a little of the reagent, and allow it to crystallize. Study the crystal 

 forms, and determine their optical properties. 

 Try the reaction on BaClg ; CaClo ; SrC^- 

 Test mixtures of Na and Ba ; Mg and Ba; Ca and Ba. 

 Try action of the reagent on salts of Pb. 



* Traube, Zeit. Kryst. 26: if 



