CONSISTENCY OF COLLOIDS 73 



found, strictly speaking, are applicable to its momentary condition; 

 previously and subsequently it has different properties. Every point 

 of its life curve has a previous history and the final portions of this 

 constantly flattening curve are the aging phenomena. In con- 

 tradistinction to crystalloids every colloid is a particular individual. 



If solutions of hydrophobe colloids, e.g., arsenic sulphid, gold solu- 

 tion, etc. (without protective colloid), are permitted to stand for 

 some time, they flocculate after a short time or else after a lapse 

 of years. It may be that traces of electrolytes are responsible 

 for the flocculation. In other cases, electrolytes certainly play no 

 part ; as I shall show by a number of examples, there is an evident 

 tendency for the unstable colloids to pass over into less dispersed 

 and stable systems (see L. WOHLER'S* observation on the aging of col- 

 loidal molybdic and tungstic acid). Several years ago H. BEOHHOLD 

 and J. ZiEGLER 1 sought to prepare for therapeutic purposes, with 

 the aid of new and especially suitable protective colloids, solutions 

 of such organic substances as are insoluble in water (iodoform, iodo- 

 chloroxychinolin, camphor, etc.). They succeeded in thus preparing 

 the substances, which, however, kept only a few weeks, when they 

 would separate out in crystals. Obviously these substances are not 

 sufficiently insoluble and they exhibited the adsorption phenomenon de- 

 scribed on page 18. P. P. VON WEIMARN made analogous observations 

 on the sol of barium sulphate in which crystals appeared at the end of 

 six months. The inequality of the particles, or more correctly the 

 "specific surface," obviously militates against the stability of such 

 colloid solutions. In the majority of cases, it soon leads to the 

 "death" of the colloidal system. 



Furthermore, we must emphasize that the changes in the col- 

 loidal system need not always consist in a diminution of the disper- 

 sion. Occasionally we find that the particles become smaller with 

 the lapse of time, but this has hitherto been observed only in the 

 case of hydrophile colloids (glycogen, benzopurpurin, hemoglobin, 

 lecithin, etc.) (W. BILTZ and L. GATIN-GRUSZEWSKA,* LEMANISSIER,* 



E. RAHLMANN,* 1 R. ZsiGMONDY* 2 ). 



Under some circumstances even electrolytes may act disruptively. 

 Thus B. G. MOORE and H. E. ROAF* observed that minutest traces 

 of electrolytes are absolutely necessary for the stability of an albumin 

 solution, as was frequently pointed out by E. JORDIS for hydrophile 

 sols. W. BILTZ and H. VON VEGESACK* observed, however, that in 

 the case of dye solutions, merely with the lapse of time, marked in- 

 crease in viscosity occurs. 



It may be pointed out in connection with the aging of jellies, that 

 1 As yet unpublished. 



