116 SOAPS AND PROTEINS 



It is such increase in the number of hyd rated salt particles 

 with increasing concentration of the added salt that explains 

 the progressive increase in the viscosity (see diagram C) which, 

 when the amount of water in the system is not too high, culmi- 

 nates in gelation. If the concentration of the salt is still further 

 increased, the time approaches when the number or size of the 

 Imitated salt particles becomes so great that they touch each 

 other (diagram D). When this happens a critical point has 

 been reached and there must appear a change in the system, for 

 the hyd rated salt particles now become the continuous external 

 phase while the soap particles form the internal divided phase. 

 Such change in type of emulsion even without change in the 

 quantitative relationship of the two liquids composing the emul- 

 sion is regularly followed by a change in viscosity. This situation 

 is indicated in tube E of Fig. 74. The viscosity of the system 

 now tends in the direction of the salt solution and so, with pro- 

 gressive additions of salt, falls. This is the region of secondary 

 liquefaction after the region of gelation in our experiments. At 

 this point, however, the soap system also shows the first evidences 

 of becoming turbid. This is because more and more water has 

 been taken from the soap and as this becomes dehydrated its 

 index of refraction changes. Being different from that of the 

 dispersion medium the mixture appears milky. The dehydrated 

 soap particles, being possessed of a lower specific gravity than 

 that of the alkaline solution or salt solution constituting the 

 dispersion medium, now begin to float to the top as indicated 

 over F in Fig. 74. When enough salt has been added to the 

 system, the soap is entirely dehydrated, as shown in diagram (7. 1 



3. On the " Salting-out " of Different Soaps 



The preceding pages have made clear the general laws which 

 underlie the salting-out of a soap by different salts. We have 

 now to consider the question of how different soaps behave when 

 subjected to the salting-out effects of a single salt. 



1 It is self-evident that what has been here written of the salting-out 

 process as observed in soap manufacture holds with equal force for the salting- 

 out processes of many other technological procedures as in aniline dye, cheese, 

 and butter manufacture. For the application of these principles to certain 

 phenomena of "coagulation" as observed in milk, blood, muscle juice, etc., 

 see page 233. 



