Dialysis

Dialysis. Graham found that animal or vegetable membranes were impervious to some substances in solution, while others possessed the power of passing through such structures. All soluble substances he thus divided into two classes, crystalloids and colloids. The latter are those to whose solutions the membrane acted as an impervious wall, and examples of such substance are the gums, glue, precipitated silica, while the crystalloids include all substances of a crystalline nature as salt, sugar, etc. A colloid can be separated therefore from a crystalloid by placing the solutions in a small cup, the bottom of which consists of parchment, and floating it in a basin of water. The crystalloid passes into the outer water while the colloid remains in the cup. By repetition of this process - Dialysis - the separation may be made complete.