I\STIM'.M1.\T> \M) CHEMICAL TI.STS 573 



potassium sulphate. The precipitate contains tin- cerium group 

 as sulphates the filtrate contains the yttrium group. The nil- 

 phates of the cerium group may be dissolved in boiling water, 

 to which a little HCl lifts been added, and reprecipitated a- hy- 

 droxides, with sodium hydroxide. From the filtrate containing 

 the yttrium group, their hydroxides may also be precipitated with 

 sodium hydroxide. 



GROUP IV 



Metals which are precipitated with hydrogen sulphide from alka- 

 line solutions as sulphides, but not from acid solutions. Common 

 elements are zinc, manganese, cobalt, nickel, and iron; rare ele- 

 ments are uranium, vanadium, indium, thalium, gallium. 



Zinc, Zn. Atomic weight, 65.37. Fusing point, 419 C. 



a. Coat. If zinc minerals are mixed in a stiff paste with water, 

 and 4 parts soda and a little coal dust, placed in a shallow cavity 

 on coal and heated in a hot reducing flame, the zinc is reduced 

 (zinc volatilizes at the temperature of reduction so that zinc but- 

 tons are not found in the assay upon washing in the mortar), 

 volatilizes, and settles as a zinc oxide coat near the assay, which is 

 straw yellow while hot, becoming white when cold. Zinc minerals 

 are apt to contain cadmium ; in such cases the coat will be slightly 

 yellow when cold. At times it is difficult to decide whether a slight 

 coat has been obtained or whether it is only an ash, produced by the 

 burning coal. The coat, however slight, is always accompanied by 

 a bluish border, where the white coat thins out over the coal ; and 

 then, too, the ash is easily blown off the coal with a moderate 

 breath. 



b. Cobalt solution test. The zinc coat is now moistened with 

 a drop of cobalt solution, and heated in O. F. ; the assay is also 

 heated in the blue cone to volatilize a little more zinc if possible ; 

 after cooling, if the coat is zinc oxide, it will be a grass-green, at 

 least in spots. If the assay contains silica or alumina, it will be- 

 come blue with cobalt solution. This blue color of the assay is, 

 therefore, no indication of zinc. Cobalt solution serves to dis- 

 tinguish the zinc and tin coats, which are very much alike in all 

 other respects, save the zinc coat is grass-green and the tin coat is 

 blue with cobalt solution. 



Illustration. Grind some smithsonite, ZnCO 3 , mix to a stiff 

 paste with 4 parts soda, 1 part powdered borax, and a little coal 

 dust and water. Heat gently at first in a shallow cavity on coal 



