270 Prof. E. Wartmann's third Memoir on Induction, 



§ XII. On the Lines of Chemical Affinity. 



104. The phaenomenon which I now propose to describe 

 is not the result of an inductive action, I however mention it 

 here on account of the connection which it appears to me to 

 have with the preceding facts. 



105. The sulphates of copper of commerce vary much in 

 purity. Amongst others, there is one which, when dissolved in 

 common water, gives a greenish opaline liquid, which becomes 

 blue and limpid by filtration. If a soft iron cylinder is placed 

 in this solution, we perceive, as soon as its contour is reddened 

 by the deposit of copper, very minute filaments, of a pale blue, 

 produced radiating all around its immersed surface. These 

 filaments increase rapidly in number and dimensions. They 

 soon attain forty to sixty millimetres in length, and then pre- 

 sent the appearance of stamens with corrugated filaments, ter- 

 minated by heads or elongated anthers, distributed over a very 

 regular circumference (fig. 10). The development of this 

 curious figure depends on the concentration of the liquid, the 

 capacity of the vessel which contains it, and perhaps on other 

 causes, such as the differences of density between the upper 

 and lower layers produced by the substitution of the sulphate 

 of iron for the sulphate of copper, the increase in density of 

 the surface layers owing to evaporation, &c. Be this as it may, 

 the relative opacity of the heads contrasts with the limpidity 

 of the liquid around the iron. When the decrease in the 

 amount of copper has reached a certain limit, indicated by the 

 grass-green tint which the solution takes, the deposit agglo- 

 merates gradually and subsides to the bottom of the vessel, 

 which it had not before done, and the reaction is terniinated. 



106. The phaenomenon becomes more instructive when 

 manifested under the action of two centres (fig. 11). Then 

 the rays which diverge arrive perpendicularly one against 

 another, following the line of the shortest distance. Beyond 

 that, they meet following directions more and more oblique. 

 They never invade each other's domain : they are devoid of 

 any power of penetrating into the interstices of each other. 

 These domains are separated by a perfectly straight line, 

 which intersects rectangularly the middle of the line of the 

 smallest interval. The rays which, from one part and another, 

 stop at this right line, there undergo an inflexion, the more 



simple or double rotation is ensiiy olitained. We may thus, as Mr. Grove 

 has told me he had repeated it, cause little cork boats to circulate around 

 a bar of iron suspended to a powerful magnet, and immersed in dihite 

 sulphuric acid, &c. I am told tiiat Mr. Christie had also noticed this ro- 

 tation, but I believe his observation is unpublished. (October 1.) 



