68 Dr. E. J. Mills. On Chemical Repulsion, [Jan. 15, 



January 15, 1880. 



THE PRESIDENT in the Chair. 



The Presents received were laid on the table, and thanks ordered for 

 them. 



The following Papers were read : — 



I. " On Chemical Repulsion." By Edmund J. Mills, D.Sc, 

 F.R.S. Received January 8, 1880. 



While engaged in some researches on the propagation of chemical 

 'change, I have incidentally enconntered a new order of phenomena, 

 which the title " chemical repnlsion " may serve provisionally to 

 designate. A brief outline of the experiments is given in the follow- 

 ing paragraphs. 



Upon a glass plate, laid in a horizontal position, is poured enough 

 solution of baric chloride to cover it completely to a considerable 

 depth. On this solution is placed another glass plate, provided with a 

 small central perforation ; when the two plates are firmly pressed 

 together with the hands, most of the solution is extruded, and only 

 a very thin layer of it left between the plates. All excess of the 

 solution having been removed from the outer surfaces of the plates 

 as well as from the perforation, some dilute hydric sulphate is now 

 introduced into the perforation. This reagent attacks the baric 

 chloride, throwing down a white precipitate of sulphate ; and, pro- 

 ceeding partly by diffusion, partly by flow, does not cease to widen in 

 every direction its figure of advance, until the edges of the plates 

 are attained. If the perforation is circular, the figure of advance is 

 circular ; in other words, the chemical development of a circle is a 

 circle. 



Let us now suppose the two plates to be square and equal, and let 

 the upper one have two circular perforations, equidistant from the 

 centre of the square, and situated upon its diagonal., Let also two 

 circular developments of baric sulphate be caused to proceed, as before, 

 from the two perforations simultaneously. At first, nothing remark- 

 able is observed ; but in a short time, the two growing circles begin to 

 exercise a visible retardation on each other's progress ; so that the figure 

 of advance is no longer circular, but oval. [This retardation is of 

 course observed only between the perforations ; and not outside them, f 

 where the motion is entirely free.] As the development of the figures 



