EARLY HISTORY OF LIFE 



49 



calcium 



Fig. 2-19. Stable and unstable emulsions. >) is a stable emulsion of oil-in-water where the polar and non-polar 

 ends of the stabilizer (sodium soap) are "satisfied"; C, likewise is a stable emulsion of water-in-oil where both 

 the polar and non-polar ends of the stabilizer (calcium soap) are "satisfied." B is an unstable emulsion where 

 the stabilizer (a mixture of calcium and sodium soaps) forms a film separating the water from oil. 



for the change. In the oil-in-water emulsion 

 the stabilizer was soap, which is produced 

 by the action of a sodium or potassium salt 

 on a fatty acid. The resulting soap molecule 

 is polar at the end bearing the sodium or 

 potassium atom, the bulkier end, and non- 

 polar at the end which is composed of the 

 long chain of carbon and hydrogen atoms 

 (Fig. 2-19A). Such a molecule may be con- 

 sidered to be conical in shape; therefore, 

 when lying side by side their combined ef- 

 fect would form a film that would curve 

 away from the thickened ends. In a water- 

 in-oil emulsion, the heavy polar ends of the 

 molecules would reside in the water while 

 the lighter non-polar ends would lie in the 

 oil. In this condition the soap molecules 

 have satisfied both their polar or non-polar 

 ends, tlius producing oil droplets in water. 

 Once these are formed they tend to stay 

 that way; hence an emulsion remains stable 

 indefinitely. 



Now what took place when the calcium 

 solution was added? It so happens that the 

 calcium ion requires two chains of fatty 

 acids in order to satisfy its electrical needs; 

 therefore, the resulting calcium soap has 

 two wings to it, shaped something like a V, 

 both attached to the calcium ion (Fig. 2- 



19C). Again the long CH chains are non- 

 polar and the calcium end is polar. When 

 these molecules lie side by side they form 

 a sheet or film that is curved in the direction 

 opposite to the one formed by the sodium 

 soap molecules. This time when in water 

 and oil, the flared ends are emersed in oil 

 and the calcium end is in water, thus cap- 

 turing small droplets of water in oil. The 

 phases have been completely reversed, and 

 the response of such an emulsion is differ- 

 ent from the former case. Such reversals 

 happen continuously in protoplasm and ac- 

 count for some of the activities displayed 

 by this material. 



One might wonder what would happen if 

 there was neither a preponderance of so- 

 dium nor calcium soap molecules, but an 

 equal number. Under ideal conditions a 

 completely flat film should form, separating 

 oil from water, as if the soap were not pres- 

 ent. This can happen, but the molecules 

 may also form layers that curve various 

 ways, producing a continuous wavy film 

 separating water from oil (Fig. 2-19B). In 

 this condition the emulsion does not behave 

 as the oil-in-water or the water-in-oil emul- 

 sions. In both of these last two cases the 

 colloidal particles move rather freely among 



