PHYSICAL FORCES INVOLVED IN BIOLOGICAL ACTIVITIES 157 



uniformly distributed or dispersed, is considered a homogeneous system. 

 It is also a one-phase system because its components are not mechanically 

 separable or physically different. On the other hand, colloidal solutions 

 (see colloids and crystalloids) consisting of components which are 

 physically different and mechanically separable form a heterogeneous 

 system. Such a system or solution is therefore either diphasic or 

 polyphasic. 



A true solution, composed of two substances, may have one sub- 

 stance regarded as that dissolved and the other as the dissolving agent. 

 If table salt is dissolved in water, the salt would be regarded as the 

 substance dissolved in water as the dissolving agent. In this case, salt 

 would be the solute and water the solvent. However, just the converse 

 may be equally true: water dissolved in salt. Colloidal solutions 

 are somewhat different because they consist of fine or very small par- 

 ticles in suspension or emulsion. In such solutions, therefore, the 

 suspended particles in solution (called suspensoids) or emulsified 

 particles in solution (called emulsoids) are the substances distributed or 

 dispersed in a medium or menstruum. The particles are called the 

 disperse phase and the medium or menstruum the dispersion means. 

 Together they constitute a heterogeneous system, dispersoids, also a 

 polyphasic system. Some colloids approximate very closely ionic and 

 molecular solution. 



A diagram (Fig. 100) will aid in understanding. 



Solutions 



r i 



True Colloidal 



Ionic Ionic Purely colloidal Suspensions 



and molecular and not easy and emulsions 



molecular of easily 



' 1 mechanical ' separated 



separation mechanically 

 Gaseous Liquid Solid 



I I 



Gaseous Liquid Solid 



FIG. 100. 



