1889.] 



Zirconium and its Atomic Weight. 



75 



Under these circumstances it seemed to me essential that any 

 determination of the atomic weight of this element should be pre- 

 ceded by an inquiry into the best method of preparing pure zirconia, 

 and an examination of the salts which might be made use of for the 

 purpose, especially with reference to their stability. 



Preparation of Crude Zirconia. 



The raw material consisted of about 300 grams of zircons from 

 North Carolina, for which I was indebted to the kindness of Sir 

 Henry Roscoe, and in addition to this a quantity of impure zirconia. 

 The zircons were powdered by heating them to redness, and then 

 throwing them quickly into cold water ; they were then roughly 

 powdered in an iron mortar, and finally in an agate mortar, and 

 passed through linen. Part of this was treated with hydrogen 

 potassium fluoride, the product being extracted with water and 

 recrystallised many times from hot water. Prepared in this way, 

 however, the zirconia was still impure, and showed the presence of 

 iron in small quantities, and in addition to this it was extremely 

 difficult to get rid of alkali. 



The methods of fusion with sodium carbonate or acid potassium 

 sulphate are troublesome and even less satisfactory. 



Ultimately caustic soda and sodium fluoride were adopted for break- 

 ing up the zircons as recommended by Linnemann, and a modified 

 form of the process followed out by him (' Monatsh. f. Cheni.,' vol. 6, 

 p. 337) was adopted as the most convenient. A mixture of 100 grams 

 of caustic soda and 10 grams of sodium fluoride is heated in a covered 

 silver dish over a large Bunsen burner, 25 grams of finely powdered 

 zircons are added in portions, the melt being kept stirred, and the 

 heating continued for about an hour or so long as there is any 

 effervescence. The resulting mass is broken up and extracted with 

 water, the residue consisting principally of sodium zirconate, but 

 containing also silica and undecomposed zircon, oxide of iron, &c. 

 This is now digested with dilute hydrochloric acid and filtered, 

 the residue being subjected repeatedly to the same treatment. 

 The acid solution containing the zirconium is evaporated to perfect 

 dryness, and then exhausted with very dilute hydrochloric acid, and 

 the silica filtered off. The process of solution and evaporation is 

 repeated until the residue obtained dissolves completely in the acid. 

 The impurity now present in the largest quantity is iron, and it was 

 thought desirable to remove the bulk of this first. The hydrochloric 

 acid solution is, therefore, evaporated to small bulk, and left to cool ; 

 the oxychloride of zirconium separates out in acicular crystals, leaving 

 the iron in solution. The crystals are thrown into a funnel, and the 

 liquid as far as possible removed at the pump, and the process of 

 solution and separation of crystals in this way repeated several 



