HOW MOLECULES MAKE MASSES 53 



indicated in Exodus V. Philippine natives, when panning for 

 gold, often squirt the juice of "gogo bark," which they chew, into 

 the pan to deflocculate and wash away the accompanying clay. 

 About forty years ago, E. G. Acheson obtained patents for "Egyp- 

 tianizing" clay by using alkaline tannin solutions, etc. The aurum 

 potabile of the alchemists was made by reducing solutions of gold 

 (chloride) in the presence of stabilizing ethereal oils, and as early 

 as 1794 silk was dyed with colloidal gold. In his "Lehrbuch" 

 (1844) Berzelius gives recipes for making several shades of col- 

 loidal gold; and as early as 1821 isinglass, egg albumen, and 

 starch were used for this purpose. 



What Professor Richard Zsigmondy (Nobel prize, 1927) considered 

 to be the first example of protective action, recognized as such, 21 was 

 referred to by Thomas Graham. 22 He stated that crude caramel, por- 

 duced by heating raw sugar to 210-220° C, when dialyzed, allows a 

 colored substance to pass through, while the material richest in carbon 

 remains behind in the dialyzer. A 10 per cent solution of this residue 

 is gum-like and forms a weak jelly, which is completely soluble in 

 water. Evaporated in a vacuum, it yields a tough, black, elastic, 

 shining mass, which, when thoroughly dry, can be heated to 120° C 

 and still remain completely soluble. If, however, the first solution is 

 evaporated to dryness on a water bath, it becomes insoluble. Both 

 the soluble and the insoluble caramel have the same empirical for- 

 mula. Liquid caramel is tasteless, neutral in reaction, and extremely 

 sensitive to crystalloid reagents. Traces of mineral acids, alkali salts, 

 and alcohol make it pectous, and the brownish-black, powdery sub- 

 stance yielded by the precipitated caramel is insoluble in both hot 

 and cold water, though it may be rendered soluble again by dilute 

 potash. 



Graham then states: "The presence of sugar and of the intermediate 

 brown substances protects the liquid caramel in a remarkable degree 

 from the action of crystalloids and accounts for the preceding prop- 

 erties not being observed in crude caramel." Incidentally, Graham 

 refers to the analogy between caramel and anthracite: "Caramelization 

 appears to be the first step in that direction — the beginning of a col- 

 loidal transformation to be consummated in the slow lapse of geo- 

 logical ages." This recalls Dopplerite, a brown, amorphous, elastic 

 or jelly-like substance found in peat-beds, and also the so-called 

 "mother-of-coal" sometimes found in mines. 



In 1856 Michael Faraday 23 reported the discovery of "jelly" 

 (evidently gelatin or isinglass) as a protective colloid for colloidal 

 gold; and in 1898, Zsigmondy, 21 then unaware of the preceding 



