THE COLLOIDAL CONDITION 203 



fusibility is a condition of matter when in minute subdivision, or in 

 solution, in some liquid, as contrasted with its state, or condition, 

 when existing alone. That is, the state of a substance may be 

 either gaseous, liquid, or solid; and its condition when in solution 

 may be either crystalloidal or colloidal. Substances which are in 

 crystalloidal form, in true solution, exist there in molecular or 

 ionized condition; but, as will be pointed out below, when in the 

 colloidal condition they exist in aggregates which are somewhat 

 larger than molecules, but not large enough to be visible as indi- 

 vidual particles under the ordinary microscope, even under the 

 highest magnification which has yet been obtained. Colloidal 

 particles are, however, generally visible under the Zigmondy 

 " ultramicroscope." (See below.) 



The use of the word " colloid " as a noun, or as the name for a 

 substance which is in the colloidal condition, is of the same nature 

 as the use of the words " gas," " liquid," and " solid," in such 

 statements as " ice is a solid," "water is a liquid," or " steam is a 

 gas," etc. ; i.e., the noun represents a state or condition rather than 

 an actual object or thing. Hence, the expression " enzymes are 

 colloids," means only that enzymes exist in the colloidal condition, 

 and not that enzymes represent a definite type of substances having 

 the group name " colloids." 



THE COLLOIDAL CONDITION A DISPERSION PHENOMENON 



When one substance is distributed through the mass of another 

 substance, the mixture is said to be a " two-phase system," com- 

 posed of the dispersed phase, or substance, and the dispersion 

 medium, or continuous phase, through which the other substance is 

 distributed. The following examples illustrate the possibilities 

 of such two-phase systems: 



(1) Dispersion medium a gas. 



(a) Disperse phase a liquid mist in the air. 



(6) Disperse phase a solid smoke or dust in air. 



(2) Dispersion medium a liquid. 



(a) Disperse phase a gas foams. 



(6) Disperse phase a liquid emulsions. 



(c) Disperse phase a solid suspensions. 



(3) Dispersion medium a solid. 



(a) Disperse phase a gas solid foams, pumice stdne, etc. 

 (6) Disperse phase a liquid liquid inclusions in minerals, 

 (c) Disperse phase a solid alloys, colored glass, etc. 



