C 99 3 



A. a. The magnefia, contained in the water, 

 may be detected by means of a folution of cauftic, 

 vegetable, or foffile alkali. The cauftic alkali 

 unites with the fixed air, is rendered mild, and 

 remains diffolved in the water, while the magne- 

 fia is precipitated 



b. By "fufpending apiece of reddened* litmus 

 paper in it, it will loofe the red colour given it 

 by the vinegar, being blue again. And that this 

 is only owing to the magnefia, will be farther 

 proved, by evaporating the water half away, 

 the remaining liquor will be found to poffefs 

 no power of changing the colour of the reddened 

 litmus paper, and the fixed air having efcaped, 

 the magnefia is precipitated in a white powder, 

 and the liquor will be found to be water only. 



c. If the piece of paper, that is made ufe of, 

 be ftained with the tinclure of Brazil wood, in- 

 ftead of litmus, it will be changed from a red to 

 a violet colour. 



d. Or if a folution of foap be added, a$ 

 mentioned (page 56, e.) The foap is de coin pol- 

 ed, the alkali of the foap uniting with the fixed 

 air, and the oil with the magnefia, forming an 

 earthy foap. 



B e. The acid bafis will be detected to be fixed 

 air by evaporation, in a clofe veflel, as defcribed 

 (page 46, e.) The fixed air, as it flies off, may be 

 forced into lime water, which it will decom- 

 pofe. 



* Firft ftain the paper with a little infufion of litmus, then wet 

 it with vinegar. 



GYPSUM 



