On Brownian Movements. By Wm. M. Ord. 657 



but there is a further possible explanation in the fact that chemical 

 activities are at work. The instantaneous formation of the 

 membrane indicates the existence of a decided chemical inter- 

 action between the oil and the albuminous solution, and to the 

 persistence of this interaction as producing effects of surface tension 

 I am inclined to attribute the agitation of such comparatively 

 large granules. The method of observation here employed allows 

 of the introduction of new and varied conditions by which the 

 induction may be tested. And by employing such tests I am 

 able to show that the movements are more active and more per- 

 sistent in proportion as conditions prevail, which favour the 

 activity of chemical changes in the fluid, or of reactions between 

 the fluid and the oil ; and, conversely, that the movements are 

 diminished or altogether stayed by the introduction of conditions 

 which hinder such chemical reactions. I may state what I have 

 obtained in three lines of research, namely, — 



(1) As to the influence of concentration and dilution of the 

 albuminous suspending fluid ; 



(2) as to the influence of alkalies ; 



(3) as to the influence of acids. 



1. In emulsions made with equal bulks of oil and of albuminous 

 fluid of various dilution I have found great differences of activity 

 of movement. With undiluted fresh white of egg the emulsion 

 is very perfect, but the movements are sluggish or almost imper- 

 ceptible. On dilution of the albumen the movements increase in 

 vivacity until thirty or forty parts of water are added, beyond 

 which dilution leads to enfeeblement of movement. 



2. When a little liquor potassse or carbonate of potash is 

 added to the albuminous liquid before mixture of the latter with 

 the oil, an emulsion of great fineness may be obtained by a single 

 shake of the containing vessel. After a good shaking the fluid is 

 found loaded with molecules of the smallest size mixed with a 

 smaller number of granules and globules of all diameters up to that 

 of half a blood-corpuscle. The movements of these molecules are 

 remarkable as respects both range and quickness. If some of the 

 emulsion produced by a single shake be compared with the above, 

 the proportion of the smallest molecules is much less, and the 

 globules are larger, but even here globules as large as a blood- 

 corpuscle are seen moving with great freedom. When the smaller 

 molecules are in great excess, as in the first case, the movements of 

 the larger might possibly be produced by the blows of their innu- 

 merable sateUites, but where the larger are in excess their move- 

 ments must, I think, be considered as belonging to themselves. 



3. If, while an emulsion of oil and albuminous fluid with or 

 without alkali is under the Microscope, a drop of strong acetic or 

 of hydrochloric acid be allowed to run under the covering glass a 



