322 SALTS SULPHATES. 



(b.) Evaporation gives regular crystals, whose form is that of six 

 sided prisms, sometimes crowned by six sided pyramids. 



2. HISTORY. Long known, and had formerly a multitude of 

 names,* which were banished when it received its present denomina- 

 tion. 



3. PROPERTIES. 



(a.) Taste, acrid and bitter sp. gr. 2.29, or 2.40, easily pulve- 

 rized. 



(b.) At 212, requires five times, and at 60, sixteen times its 

 weight of water for solution. 



(c.) Not affected by the air. On burning coals, or red hot iron, it 

 decrepitates. 



(d.) Contains no water of crystallization. 



4. COMPOSITION. Acid, 45.45 ; potassa, 54.55, or acid, 1 propor- 

 tion, 40 ; potassa, 1 proportion, 48 = 88, which is its equivalent number. 



5. DECOMPOSITION. 



(a.) By acids. Although the sulphuric acid has a stronger affinity 

 for potassa, than any other acid has, still the nitric and muriatic acids, 

 in large quantities, decompose it in part ; the products are much bi- 

 sulphate of potassa, and some nitrate and muriate of potassa. 



Not owing to the capriciousness of chemical attraction, but accord- 

 ing to Berthollet, to the influence of quantity, compensating for infe- 

 rior force of attraction. 



!b.) By barytic and strontitic water, attracting the sulphuric acid, 

 c.) Also, by nitrate and muriate of lime, by double elective at- 

 traction. 



(d.) By heating it with charcoal powder, when it becomes a sul- 

 phuret, and can be decomposed in the palm of the hand, by vinegar 

 or other weak acid, thus fulfilling Stahl's boast, but not as it was in- 

 tended by him, that others should understand it. 



(e.) Other processes. Saw dust substituted for charcoal, and py- 

 roligneous acid for the vinegar, and the acid is afterwards decom- 

 posed by heat. Dundonald. 



Sulphate of potassa, 100 parts, chalk 100, charcoal 50, heat 

 them sulphuret of lime is formed, and the alkali being liberated, 

 may be obtained by lixiviation.f 



6. USES, &ic. Called in the shops, vitriolated tartar, and used 

 as a purgative or alterative dose, half an oz. or less ; the effect less 

 transient than that of sulphate of soda. The sal polycrest of the old 

 physicians was made by deflagrating nitre and sulphur, and was a 



* Vitriolized and vitriolated tartar, sal de duobus, arcanum duplicatum, sal pol- 

 ycrest, salt of Glazer, vitriol of potash, vitriolated vegetable alkali, &c. but vitri- 

 olated tartar was the most general name. Hence, and from similar cases, the ne- 

 cessity of the new nomenclature of the salts. 



t Ann.de Chim. Vol. XIX. 



