INSTIMMIATS AM) < IIKMICAL TESTS 



under magnesia, c. The hydroxides precipitated \vith ammonia 

 containing the .iliiininiiiiu are .-craped (rum the paper and boiled 

 iti :i tot tube with sodium hydrate, t he aluminium hydroxide dis- 

 solves, and the insoluble hydroxides, generally iron, are filtered off 

 and washed. The filtrate is acidified with IK '1 and the aluminium 

 is reprecipitated with ammonia, filtered, dried, ignited, and tested 

 for the blue color with cobalt solution. 



Chromium, Cr. Atomic weight, 52.1. Fusing point, 1515 C. 



a. Bead test. When oxide of chromium \s dissolved in the 

 borax bead in O. F. it will color the bead yellow while hot, becoming 

 greenish yellow on cooling. If more oxide is dissolved in the bead, 

 it becomes red while hot, yellowish green while cooling, and finally 

 green when cold. 



In the S. Ph. bead, when in sufficient quantity, chromium 

 yields a fine emerald green in both flames. Vanadium yields a 

 green bead very similar to chromium, except in S. Ph., in O. F. The 

 vanadium bead is yellow when cold. As there are several oxides 

 which yield green beads, in case of doubt the wet test for chromium 

 must be applied. 



Illustration. Use Cr 2 O 3 , and a very pure O. F. to obtain the 

 yellow described above, otherwise the bead will be green on cool- 

 ing. 



6. Wet test. The very finely ground mineral is fused on wire 

 with four parts of soda and two parts of borax ; while the fused 

 bead is still hot it is touched to a small grain of potassium nitrate 

 and fused once more in the O. F. If much chromium is present, 

 the cold bead will be yellow, due to the sodium chromate, Na^CrO*, 

 formed in the oxidation with KNOs. The fusion is dissolved in 

 2 cc. of water and acidified with acetic acid ; if not now clear it is 

 filtered. To the clear solution 3 drops of lead acetate are added, 

 when, if chromium is present, a bright yellow precipitate of lead 

 chromate, PbCrO 4 , will form ; this may be filtered off and tested for 

 the green bead. 



Illustration. Fuse powdered chromite, FeO, Cr 2 C>3, and proceed 

 as directed above. 



Titanium, Ti. Atomic weight, 48.1. Fusing point, 3000 C. 



a. Bead test. The distinctive bead reaction for titanium is the 

 violet color, in R. F. and S. Ph. when cold, especially marked 

 when reduced with tin on coal. When this bead reaction is ob- 

 scured by the presence of other oxides, the wet test must be applied. 



Illustration. Use very finely ground rutile, Ti0 2 , and heat the 



