258 Prof. Challis on Hydrodynamics. 



Crystallized zirconium resists the action of oxygen at a red 

 heat ; at a white heat it becomes covered with a thin iridescent 

 layer which protects the rest of the metal; it only burns in the 

 flame of the oxyhydrogen blowpipe. In chlorine, combustion 

 takes place at a red heat with incandescence, forming chloride of 

 zirconium. Hydrate of potash in fusion is decomposed by zir- 

 conium, with liberation of hydrogen, which ceases when the 

 potash is quite dehydrated. Heated to redness with silica it is 

 reduced, forming amorphous silicon and zirconia. 



Nitric and sulphuric acids have no action on zirconium in the 

 cold, and scarcely any when they are hot and concentrated. 

 Gaseous hydrochloric acid is decomposed by zirconium at a red 

 heat, forming chloride of zirconium but no subchloride. 



Hydrochloric acid in the cold does not dissolve zirconium, by 

 which this body is distinguished from aluminium. The true 

 solvent is hydrofluoric acid, in which, whether strong or not, zir- 

 conium dissolves — a deportment in which it differs from silicon. 



Troost says in conclusion, zirconium plays, in the carbon 

 family, a part analogous to that of antimony in the nitrogen 

 family. It forms a passage between metallic silicon and metallic 

 aluminium, and justifies Sainte-Claire Deville's classification, who 

 has placed carbon, boron, silicon, zirconium, and aluminium in 

 one natural group. 



XXXV. Supplementary Researches in Hydrodynamics. — Part II. 

 By Professor Challis, M.A., F.R.S., F.R.A.S.* 



THE first Part of these Researches was devoted to considera- 

 tions preliminary to the investigation of the motions of a 

 spherical solid submitted to the action of the vibrations of an 

 elastic fluid. I proceed now to give a solution of this important 

 problem in accordance with the principles there advocated. The 

 conditions of the problem will be assumed to be such that both 

 the motion and the condensation of the fluid are symmetrical 

 with respect to an axis passing through the centre of the sphere, 

 and parallel to the direction of the incidence of the waves. The 

 equation (e), obtained in the Supplementary Number of the 

 Philosophical Magazine for December 1864 (p. 493), is appli- 

 cable to such motion, and will be employed in the present inves- 

 tigation. For greater distinctness in carrying on the subsequent 

 argument, the reasoning by which that equation was arrived at 

 will be here reproduced. 



In Part I. (September Number, p. 211) I have shown how to 

 obtain the following expressions to the second approximation for 



* Communicated by the Author. 



