118 Journal of the Mitchell Society [February 



S04.13H«0. This indicates a hydrolysis in the second stage of one 

 out of four molecules of ZrO.S04. The velocity of this reaction 

 diminishes with decreasing temperature, and it has been found that 

 only 67 p.c. of the sulphate originally used go to the formation of 

 this product. The condition of the remainder in this case is unknown. 

 The crystalline basic sulphate just mentioned and other compounds 

 of like character show partly colloidal properties and have therefore 

 been classed by Hauser as half-colloids. 



Again, the existence of an equilibrium reached in the hydrolysis 

 is indicated sometimes in measuring conductivity changes. Thus 

 in the case of the hydrolysis of a one-fourth normal solution of ZrOCU. 

 8H2O at 18° the change for the first sixty minutes is at an average 

 rate of 67 x 10-^ ohms per cc. per minute. For the next 168 hours 

 it averages only 0.014x10-^ ohms per minute, indicating the slow 

 breaking down of a more stable compound or the retarding effect of 

 the liberated acid. This retarding effect of free acid is w^ell known. 

 It can be inhibitory or even cause a reversal of the reaction. Thus 

 the addition of slilphuric acid to a partially hydrolyzed zirconyl sul- 

 phate solution when it reaches a certain concentration will bring about 

 the separation as crystals of the original zirconyl sulphate. Normal 

 zirconium sulphate crystalUzes unhydrolyzed from sulphuric acid 

 containing only a few per cent of water. This inhibitory and reversal 

 effect is produced also by the presence of the salts of strong bases 

 like the alkalies. Anhydrous zirconium fluoride, for instance, is very 

 slowly and difficultly soluble in water. In solution it is hydrolyzed, 

 ZrF4=ZrOF2.H2F>.3H20. This recrystalfizes from water unchanged. 

 If considerably diluted, an amorphous basic zirconyl fluoride is pre- 

 cipitated. This formation of an acid salt with the liberated acid has 

 been noticed in a number of cases. If the water present is in small 

 amount, the hydrolysis is checked. If a salt of a strong base is added 

 (usually in excess) there is formed a double salt or complex which 

 does not hydrolyze. With potassium fluoride three complexes are 

 formed. First, we have KF.ZrF4.H2O, which can be formed only in 

 the presence of a large excess of zirconium fluoride and is decomposed 

 on re-solution in water. It should probably be written KF.ZrOF2. 

 H2F2, lacking enough potassium fluoride to inhibit hydrolysis when 

 much water is added. The second salt, 2KF.ZrF4, crystallizes with- 

 out water of crystallization. It is very stable, giving off hydrofluoric 

 acid only at a red heat, and can be repeatedly recrystallized from 

 water. It is regarded as a salt of fluozirconic acid and, under that 



