54 



Dr. J. BOTTOMLEV on 



On the equation to the Instantaneous Surface gene- 

 rated by the dissolution of an Isotropic Solid. By- 

 James Bottomley, D.Sc. 



(^Received February ^th, iSSp.) 



I. T/ie Subject considered geometrically. 

 Although the phenomenon of dissolution of a solid is 

 one of the most striking in chemistry, it does not, as a 

 general problem, seem to have been the subject of exact 

 enquiry ; nor do the text books of chemistry supply an 

 answer to the following question : — Given the form of an 

 isotropic solid placed in a menstruum capable of dissolving 

 it, what will be the surface at any subsequent time bounding 

 the undissolved portion. Considering the infinite variety 

 of forms which the primitive solid may have, whether 

 bounded by continuous or discontinuous surfaces, the subject 

 might seem to be impracticable. After some reflection on 

 the matter, two propositions occurred to me which seem to 

 be of sufficient generality to include every case which may 

 present itself The first of these propositions is as follows : 

 If lines normal to a curve be cut by a second ciirve at a 

 constant distance from the first, then these lines will be 

 normal to the second cnrve. The proof is not difficult ; let 

 X, Y be co-ordinates of a point P on the first curve, and 



