Mr. W. Crookes on Thallium. 317 



suggest some interesting questions for further observation and study. 

 On the 22nd of July the southern snow was a large patch, meeting 

 the limb by its diametral line. It must then have had a radius of 

 500 miles at least : in the later observations it was reduced to less 

 than half this measure. 



One of the drawings nearly corresponds to longitude 180° on 

 the author's scale, and represents the specially dark short band 

 which distinguishes that aspect of the planet (fig. 3). Two corre- 

 spond nearly to fig. 1, and contain the remarkable deep angular bay 

 which extends so far towards the north pole. In these and the re- 

 maining three drawings, general resemblances and special differences 

 appear on comparison with the sketches of Prof. Phillips and Mr. 

 Lockyer. The differences affect principally the grey southern parts, 

 and are remarkable enough to justify serious doubts whether any of 

 our drawings of those parts are much to be trusted as representing 

 permanent physical boundaries. Nor should this be thought sur- 

 prising ; owing to the high inclination of the axis of Mars to the plane 

 of his orbit, the regions round each pole are presented alternately to 

 the sun through periods somewhat less than our whole year. The 

 effect is seen in the vast outspread of snows round the cold pole, and 

 the contraction of those white sheets to a small glittering ellipse 

 round the warm pole. The enormous transfer of moisture from one 

 hemisphere to the other while the snows are melting round one pole 

 and growing round the other must generate over a great part of the 

 planet heavy storms and great breadths of fluctuating clouds, which 

 would not, as on the quickly rotating mass of Jupiter, gather into 

 equatorial bands, but be more under the influence of prominent land 

 and irregular tracts of ocean. 



February 19. — Dr. William Allen Miller, Treasurer and Vice- 

 President, in the Chair. 



The following communication was read : — 



"On Thallium." By William Crookes, Esq. 



After discussing the occurrence and distribution of the new metal 

 in different parts of the globe, the author proceeds to describe the 

 method adopted by him for extracting it from its ore. Thalli- 

 ferous pyrites is distilled at a bright red heat, in quantities of about 

 1 cwt. at a time, in cast-iron retorts. The resulting sulphur, vary- 

 ing from 13 to 17 per cent, of the pyrites taken, is then dissolved 

 in aqueous caustic soda, which leaves the sulphide of thallium as 

 an insoluble black precipitate ; this is filtered off, dissolved in acids, 

 and the thallium precipitated in the form of iodide. This is then 

 converted into sulphate, and the metal reduced from the solution by 

 electrolysis. It is obtained in the coherent form by fusion under 

 cyanide of potassium. 



The physical characteristics of thallium are then described. In 

 appearance it most resembles tin and cadmium, but has a distinct 

 colour of its own ; it has a brilliant metallic lustre, and is susceptible 

 of taking a very high polish ; it oxidizes in the air with almost the 

 rapidity of an alkaline metal, but when coated with oxide, the metal 



