1839.] 



On Chemical Tests, 



339 



same, but strontia is distinguished from lithia by its giving a precipitate 

 with the carbonated alkalies which lithia does not. 



h. Strontia is found in nature always combined with an acid, see 

 39£, c. 



113. SULPHURIC ACID; and sulphates— Sulphuric acid, free or in 

 combination is best detected by barytes, see 40. To detect the presence 

 of sulphuric acid in the sulphates which are either insoluble or very 

 sparingly soluble both in water and in acids, such as the sulphates of 

 barytes, strontian, lime, and protoxide of lead, it is necessary to boil 

 the compound in a solution of carbonate of potash or of soda. The so- 

 lution is filtered from the undissolved residue, and after being super- 

 saturated with muriatic acid, is mixed with a solution of chloride of 

 barium. This immediately produces a white precipitate of sulphate 

 of barytes, provided the insoluble substance contained sulphuric acid. 



a. Before the blow-pipe, sulphuric acid is detected in the sulphates, 

 and especially in those which do not contain a metallic oxide, by the 

 following experiment : a portion of the salt is added to a clear colour- 

 less bead formed by the fusion of soda with silica on charcoal, and the 

 whole is heated in the inner flame. The colour of the bead is thereby 

 rendered dark brown, or with small quantities and when it is cold red. 

 "When a sulphate is melted with soda, on charcoal, in the inner flame, 

 and the mass is taken from the charcoal, laid on a bright piece of silver, 

 and moistened with water the silver acquires a black or dark yellow 

 stain. 



b. The specific gravity of pure sulphuric acid should be 1.848 at 60° 

 Fah. If it be heavier, there is reason to suspect the presence of some 

 impurity. If a sediment occur on adding distilled water it contains 

 sulphate of lead. If iron be present it may be detected by diluting the 

 acid and adding a little carbonate of potash and then prussiate of po- 

 tash, or tincture of galls, see 55. For detecting copper, test by ammo- 

 nia, see 51. 



c. All sulphates in solution may be decomposed by acetate of bary- 

 tes ; see 40 g. 



d. The sulphates are an important class of salts: the greater part 

 are soluble in water. -Insoluble sulphates may be mixed with 3 times 

 their weight of carbonate of soda, and ignited ; they then form soluble 

 sulphates of soda, and may be tested by barytes. The sulphates of 

 potassa, soda, lithia, lime, baryta, and strontia resist a white heat with- 

 out decoinposi lion : the other sulphates evolve when heated intensely, 

 sulphuric acid, sulphurous acid and oxygen. Many of them are decom- 

 posed at high temperatures by the action of hydrogen, which carries 



