On Broivnian Movements. By Wm. M. Ord. 661 



of soap into the suspending fluid quickens and makes more per- 

 sistent the movements of the suspended particles. Soap in the 

 eyes of Professor Jevons acts conservatively by retaining or not 

 conducting electricity. In my eyes it is a colloid, keeping up 

 movements by revolutionary perturbations. Indeed, soap is a very 

 typical colloid in its tendency to physical change without obvious 

 decomposition. A solution of soap, at first clear and transparent, 

 becomes usually within a few hours thicker to the eye ; and as 

 days proceed it becomes thicker and thicker, until it has almost 

 a granular look, though even then nothing is separable by filtration. 

 Curiously enough, the formation of soap is involved in all our 

 emulsion experiments. And I venture to argue that the most 

 interesting applications made by Professor Jevons in relation to 

 the detergent powers of soap illustrate the influence of the colloid in 

 causing rearrangement of particles brought within its sphere of 

 action. It is interesting to remember that, while soap is probably 

 our best detergent, boiled oatmeal is one of its best substitutes. 

 What this may be as a conductor of electricity I do not know, but 

 it certainly is a colloid mixture or solution. ^Yith Professor 

 Jevons's idea that the detergent value of soap depends upon its 

 power of causing minute molecular disturbance rather than upon its 

 chemical action, we may compare in support Mr. Eaiuey's remark- 

 able demonstration of the erosion of the surface of glass slides by 

 spheres of carbonate of hme deposited on the shdes in solutions of 

 gum. Here, again, no chemical action is involved, the erosion 

 being a result of attraction exercised upon the molecules of the 

 glass by the molecules of the carbonate sphere, the disturbing 

 influence of the colloid allowing of rearrangement, or, indeed, 

 favouring it by disturbing pre-existing relations of molecules. 



In relation to the general subject of my paper, I would argue 

 that the increased movements here visible as a result of the pre- 

 sence of colloids in the suspending fluid, are but larger forms of the 

 movements demonstrated by Mr. Eainey as occurring in crystalloid 

 matters deposited in colloid solutions. 



He has shown that colloids interfere with the molecular 

 arrangement of crystals, and compel them to take a spheroidal 

 form — this he calls " molecular coalescence." 



He has again shown that spheres formed by molecular coales- 

 cence may be broken up on being introduced into colloid solutions 

 of the same nature as that in which they were originally deposited, 

 but of diflerent density. This he calls "molecular disi^tegration," 

 and this again bears on the detergent value of soap. 



Again, the susceptibihty of different crystalloids to this sphere- 

 forming power of colloids not being equal, I have shown at various 

 times that the power of colloids to master the polarity of any 

 crystalloid is intensified by whatever tends to increase vibration in 



