1921] The Chemical Behavior of Zirconium 121 



In the preparation of certain compounds by precipitation methods 

 it has been found that the precipitate forms sometimes only after a 

 considerable lapse of time or upon heating the solution. This is 

 especially the case where weak acids, such as the organic acids, are 

 concerned. The compounds thus formed are found to be more or 

 less highly basic zirconyl salts or mixtures of such. It seems reason- 

 able to infer that the acid radical of the precipitant used formed only 

 soluble compounds with the less hydrolyzed salts and insoluble ones 

 with the more basic. It is possible also that in some cases these are 

 not true chemical compounds but adsorption compounds in which 

 the acid radical has been absorbed by the colloidal hydroxide. Some 

 of these products are distinctly gelatinous and can be washed and 

 filtered with difficulty. On the other hand, some are granular and 

 some distinctly crystalline. The hypothesis of colloidal compounds 

 is especially probable wherever the acid radical can be practically 

 removed or greatly reduced in amount by repeated washings of the 

 precipitate, as is true with iodic acid and some organic acids. When, 

 however, analysis reveals the same basic compound as being formed 

 under varied conditions of dilution, etc., as is the case with the basic 

 chromate, it may fairly be assumed that a definite chemical compound 

 has been formed. 



There has been little system in the assignment of formulas to the 

 basic zirconyl compounds. Some have written them simply in the 

 ratio of the zirconia to the acid anhydride as 2Zr02.S03. Others 

 report this basic zirconyl sulphate as Zr02.ZrOS04. Perhaps the 

 most common formula is Zr203.S04. Such formulas fail to make 

 clear the known facts. These substances are often gelatinous and, 

 when hydrolysis is far advanced, the solutions become opalescent. 

 On dialyzing the solutions leave zirconyl hydroxide as a hydrogel. 

 Even the crystalline basic salts dialyze with difficulty and show partly 

 colloidal properties. They have been called half-colloids. Elec- 

 trolytic dissociation shows often a migration of the zirconyl radical 

 as an anion or a partition of the zirconium between the anions and 

 cations. It is well known that the migration of a colloid is largely 

 influenced by the medium. Furthermore, there is practically always 

 water of hydration or crystallization present. Considering these 

 facts, it is suggested that the most suitable formula for these basic 

 salts would have to include the zirconyl hydroxide. Thus ZrOj. 

 ZrOSOi becomes ZrO(OH)2.ZrOS04 and Zr203Cl2 becomes ZrO(OH)2. 

 ZrOCh. This reveals at a glance the stepwise formation of the 



