434 Dr. Waller's Experiments on the 



In the action of iodine on bismuth, the influence of the 

 physical condition of metallic surface is very manifest. The 

 crystalline texture of this metal may be perceived, and the 

 difference of its hardness admits, to a certain point, of being 

 measured by the difference of the colour of the films that are 

 formed on various points ; while most parts are yellow, there 

 exist others of an angular outline which remain still unat- 

 tacked ; the same difference is remarked in the other stages 

 of the combination. 



Iodine 'with Mercury. 



It is impossible to estimate the affinity between mercury 

 and iodine by means of the coloured films, because, on com- 

 bining, these two substances merely cause a dirty white ap- 

 pearance on the surface of the latter. Their combining af- 

 finity appears to be considerable, for when exposed together 

 with silver the action produced with both was red at the 

 edges, little altered in colour; on the rest of its surface a dull 

 white film, in the midst of which were seen several dark 

 spots, where the metal was apparently unaltered. 

 Bromine with Mercury and Copper. 

 J~ Mercury . , . gold colour. 

 1st. "^Copper t . . slightly darkened. 

 , f Mercury . . . blue. 

 ld, \ Copper . . . dark red. 



, J Mercury. . . green on some parts. 

 3rd, ^c op p er , # t w hite. 



After this the copper underwent its usual changes of colour 

 on prolonging the action of the vapour of bromine, but the 

 colour of the mercury suffered no further change. 



Chlorine with Mercury and Copper. 



Mercury ... a slight film. 



Copper ... no alteration of colour. 



Mercury . . . deep gold colour. 



Copper . . . deep red on some parts, blue on others. 



Mercury . . . red tinged with blue. 



Copper . . . blue, white. 



Mercury . . . blue. 



Copper . . . same as before. 

 With respect to the bromide and chloride of mercury, it is 

 necessary to view them obliquely in order to perceive all the 

 changes of colour they undergo; for if looked at perpendicu- 

 larly, there is seen on both a dull uneven film of white which 

 reflects none of the above colours; consequently, to avoid any 

 error, the copper must be inspected under the same angle. 



