PROTOPLASM 



35 



in the dispersions medium (Fig. 14), and the measure in which the dis- 

 persions medium is bound by the micelles. 



The stability of a liquid colloidal system with a solid disperse 

 phase depends largely upon the similar electric charge carried by the 

 suspended particles. The addition of an electrolyte neutralizing the 

 charges brings about a precipitation of the particles. In a liquid-in- 





4 



>.p' 



N^ 



-.-'/v 



Fig. 14. — Diagram to show the various appearances observable in a two-phase colloidal 

 emulsion. A, suspended droplets well separated, giving an alveolar appearance. B, 

 droplets crowded, giving continuous phase a reticular appearance. C, D, aspects due to a 

 proportionally smaller amount of the originally continuous phase and a coalescence of the 

 droplets, both phases becoming continuous. 



Fig. 15. — Photograph of an 

 oil-water emulsion. {After Seifriz, 

 1930a.) 



Fig. 16. — A torn Fticus 

 egg. Compare with Fig. 

 15. (After Seifriz, 1930o.) 



liquid system the matter is more complicated. A relatively coarse 

 oil-water emulsion will serve to illustrate some of the principal facts. 

 When olive oil and water are beaten up together, the oil forms droplets 

 suspended in the water. If the mixture is allowed to stand, the two 

 constituents quickly separate. If, however, one includes in the original 

 mixture a third substance having a certain effect upon surface tension (an 

 "emulsifier," or "stabilizer"), the resulting emulsion is stable, since the 

 emulsifier enters the interface between the oil and the water and prevents 

 the coalescence of the droplets (Fig. 15). Mayonnaise dressing is an 



