58 LIFE: ITS NATURE AND ORIGIN 



Mixtures vs. Pure Substances 



Apart from the effects of colloidal protection, mixtures of sub- 

 stances often show surprising properties. A small percentage of 

 carbon (probably forming iron carbide) converts iron into steel. 

 Though pure tin melts at 232° C and pure lead at 327° C "half- 

 and-half" solder melts at 220° C. Very pure iron and vanadium 

 have properties quite different from those tabulated for the 

 ordinary "chemically pure" elements. 



H. G. Bungenburg de Jong and H. R. Kruyt 38 found that when 

 certain hydrophilic sols are precipitated by a variety of methods, 

 e.g., by salts, by removal of solubilizing salts, by temperature 

 change, and especially by addition of oppositely charged sols, the 

 "precipitate" often forms viscous droplets which aggregate into a 

 fluid mass called a coacervate, instead of forming a solid phase. 

 The phenomenon, termed coacervation, had been observed by F. 

 W. Tiebackx, 39 who remarked that the gelatin/gum arabic coagula 

 resembled casein. Strongly adsorbed shells of water are supposed 

 to surround the droplets and to prevent their aggregation. In 

 the water-dispersible emulsions of asphalt now much used in road 

 and airfield construction, the protective aqueous films commonly 

 consist of dispersions of soaps or of colloidal clays. 40 



Practical cooks know that by working butter, lard, or hydro- 

 genated oil into baked goods (pie crusts, cookies, etc.) they are 

 made "short" or tender; and the fats are known as "shortening." 

 The fat gets in between the layers of flour dough and so weakens 

 the final product that it breaks off "short," or is flaky, the latter 

 being especially desirable in pie crust. On the other hand, tech- 

 nologists often use a colloidal substance to make a mixture 

 stronger or more cohesive, e.g., starch, glue, or rosin size in paper. 

 B. W. Zweifach reported 41 that cells in the walls of capillaries are 

 bound together by a calcium protein compound, and that diffu- 

 sion takes place through this intercellular cement rather than 

 through the cells themselves. 



Development of Structures in Living Units (Bionts) 



Even in a single cell numerous chemical substances are being 

 produced catalytically, and as these are liberated in the nascent 

 state they are likely to be affected by other newly formed neigh- 

 bor substances, or by other molecules or particulate units afloat 

 in the cytoplasm of the cell. The chemical or physical combina- 



