COLIXHDS 



and a negative colloid are mixed in Buch | 



charges are neutralized, precipitation usually i 



we can tell tli«' nature of the electric chi if an unki 



its behavior when a colloid of known electric Bign if 



example, it' ferric hydroxide (positive causes .1 i ipil 



when it is added to an unknown colloidal solution, the el< 

 i)!' the Latter musl be negative; if it does nol i»i««-i 1 «i v 

 hydroxide, but does so with arsenious sulphidi 

 posil i\ ••. 



5. Brownian Movement. Like tin- parti. -Irs in fin.- mechanical 



si"iis. those "t' colloidal solutions, ( . v] i.-i 1 1 \- when • 



microscopically, exhibit the so-called Brownian movements, 



I. >'.'ii described as "dancing, 1 1 < « j ► j > i 1 1 i_r and Bkippii I • 



occur in straighl lines, which are suddenly changed in >; 



are quite independent of external sources of energy, Buch 



temperature (although tiny become quicker as tl 



siiliitii.ii is raised . earth vibrations, chemical <•! 



charge of the colloid. The mo\ ements I"- le a apid the sma 



particles, and they become sluggish as • 



creases. Addition of electrolytes decreases the movemenl \<\ caus . 



particles to clump together. The density and visc< 



si.Hi medium, the electric charge >>( the dispersoid ami 



Brownian movements, arc the forces which operal 



sedimentation of the particles in a colloidal solution. 



6. Osmotic Pressure. As one of the distinguishing pi 

 loids we have seen that their diflfusibility, as in' 



lies, is extremely slow when compared with thai 



This does nol mean, however, that colloids are 



diffusibility if lefl long enough. Indeed th< 



movemenl indicates that such diffusion >" 



Bhould lie possible, by the application of the same prii 



w hich govern molecular Bolutioi 



Inane , in measure the osmol ic pr< 



.Man.\ studies "f the osmotic property 

 undertaken, especially bj th..>e v ho 



that tin lloids of hi I serum Berum albumin and 



ate aii osmotic pressure I f this Bhould 



ii\ for tl wnotic 



pressure BUch as that supplied l>.\ the 

 the various physiologic pi 

 through cell membranes as in tin 

 For measuring the osmotic 



