568 MINERALOGY 



and other alkali earths, is collected in a te*st tube ; to this solution a 

 few drops of ammonia are added, then ammonium oxalate; boil 

 and let the precipitated calcium, barium, or strontium oxalates 

 settle, when the clear solution is tested with another drop of am- 

 monium oxalate to insure complete precipitation. The filtrate 

 from the calcium oxalate should be concentrated, either on the bath 

 or by gently boiling in a test tube to 2 cc., when if it is not per- 

 fectly clear it is filtered through a small filter. 3 cc. of strong 

 ammonia is now added, then 20 drops of sodium phosphate, shak- 

 ing the solution between each drop ; let stand in the cold. A 

 white crystalline precipitate, ammonium magnesium phosphate, 

 NH 4 MgP0 4 . 6 H 2 O, indicates the presence of magnesium. 



Illustration. Heat a fragment of brucite, Mg(OH) 2 , in O. F. ; 

 after cooling moisten with a drop of cobalt solution and ignite 

 again in the O. F. strongly for some time ; after cooling observe that 

 it has turned a delicate pink or flesh color. Moisten the ignited 

 fragment on turmeric paper and observe that the alkaline reaction 

 is rather weak. Dissolve some of the mineral in HC1 and precipi- 

 tate magnesium as directed in c above. 



GROUP III 



Metals precipitated as hydroxides by ammonia and by hydrogen 

 sulphide in alkaline solutions. 



I. Common elements, aluminium and chromium. 



II. Rare elements, beryllium, thorium, zirconium, yttrium, 

 cerium, lanthanum, didymium, titanium, tantalum, columbium. 



Aluminium, Al. Atomic weight, 27.1. Fusing point, 657 C. 



a. Cobalt solution. Light-colored minerals are ignited in the 

 O. F., after cooling are moistened with cobalt solution, and again 

 strongly ignited in the O. F., when if they contain much aluminium 

 the ignited residue will be bright blue on cooling. Silica and min- 

 erals which fuse will yield a blue color which is not due to alumin- 

 ium, but the glassy slag is colored blue with oxide of cobalt. Very 

 hard minerals as topaz must be finely ground before ignition. 



Illustration. Heat a small splinter of cyanite, Al 2 Si0 5 . In 

 O. F. when cool moisten with a drop of cobalt solution and ignite 

 again in a hot O. F., holding the fragment just without the tip of 

 the blue cone ; after cooling, the blue color due to the presence of 

 aluminium will appear. 



b. Wet test. Insoluble compounds and silicates are treated as 



