324 



On Chemical Tests. 



[Oct 



a. The alkaline earths baryta, stronlia, &c. also restore the blue co- 

 lour. To discover whether alkalies, or their carbonates, or alkaline 

 earths have acted on the test, add sulphuric acid to the solution, the 

 earths will be precipitated; but the alkalies will not. 



79. MAGNESIA. Pure magnesia is a white powder, infusible by 

 heat, and nearly insoluble in water. If laid on reddened litmus paper 

 and moistened, it changes the colour to blue. 



The following tests indicate magnesia. 



Potash. A voluminous flocculent precipitate in neutral solutions. 

 Muriate of ammonia may diminish or prevent this precipitate, according 

 to quantity. 



Ammonia. A bulky precipitate in neutral solutions, which entirely 

 disappears on adding muriate of ammonia. 



Carbonate of potah. The same. If muriate of ammonia be previ- 

 ously present, no precipitate occurs in this, or the last case. If the 

 solution however be boiled, a precipitate occurs. 



Phophate of soda added to caustic, or carbonated ammonia produces 



a precipitate in neutral solutions. 



Sulphuric acid 

 Hydrofiuosilic acid 



Oxalic acid ! AT . , 



Binoxalate of potash > f No precipitate, 



Hydrosulphuret of ammonia J 

 Prussiate of potash. J 



a. Magnesia is precipitated from its solutions by the pure alkalies as 

 a bulky hydrate, which is soluble in dilute sulphuric acid. This latter 

 circumstance distinguishes magnesia from other alkaline earths, their 

 sulphates being very sparingly soluble. 



b. Magnesia in neutral solutions is distinguished from alkaline salts 

 by its producing white precipitates with caustic ammonia, and carbonate 

 of potash; and from solutions of baryta, stronia and lime by caustic 

 ammonia, which does not precipitate those three earths. 



c. Magnesia in acid solutions may be distinguished from the salts of 

 potash, soda, or ammonia by producing a white precipitate with phos- 

 phate of soda after having been supersaturated with ammonia. From 

 the salts of lithia, magnesia may be distinguished by giving a precipi- 

 tate with an excess of potash, especially when the mixture is boiled. 

 From baryta, and strontia, it may be distinguished by producing no 

 precipitate with sulphuric acid : and from lime t^y its giving no preci- 

 pitate with oxalic acid. 



d. Suppose baryta, strontia, lime, and magnesia to be held together 

 in solution, they may be thus distinguished : add ammonia; if the so- 



