496 AMPHOTERIC COLLOIDS. IV 



The second possible explanation is based on the assumption that the 

 equality of conductivity is due to the fact that both types of solu- 

 tions in equal concentration and for the same pH possess an approxi- 

 mately equal number of charges. 



The identity of equivalents combining with gelatin demands that 

 twice as many gelatin molecules must combine with one atom of Ca 

 as with one atom of Na. For the sake of simpHfication we assume 

 that one Na atom combines with one gelatin atom. This would 

 mean that calcium gelatinate exists in the form of Ca gelatino or Ca2 

 gelatin4 or Cas gelatine, and sodium gelatinate in the form of Na gela- 

 tin. In this case all phenomena will find their explanation if we as- 

 sume that in the dissociation of Ca2 gelatin4 the four gelatin ions re- 

 main aggregated in one group with four negative charges 



Ca2 2elatin4 ^ Ca -H Ca -(- [gelatin] 4 



Such a dissociation would therefore yield three ions, one of which 

 contains an aggregate of four negative gelatin ions. In order to ob- 

 tain the same number of charges, four molecules of Na gelatin would 

 be required, dissociating into four positive Na ions and four separate 

 negative gelatin ions, making eight ions in all. This would demand 

 a ratio of osmotic pressures for the two gelatin solutions of v3: 8, which 

 is slightly less than the ratio observed. The electrical charges would 

 be the same for the two solutions and the conductivities would only 

 show the difference due to differences in the ionic mobihties. 



If the dissociating complex in the case of calcium gelatinate is Cas 

 gelatine resulting in the formation of three Ca ions and one aggregate 

 gelatine anion carrying six charges, the same number of charges would 

 be carried by six molecules of sodium gelatinate dissociating into twelve 

 ions. This would yield exactly the ratio of 1 : 3 for the osmotic pres- 

 sure of solutions of calcium gelatinate and sodium gelatinate of the 

 same concentration and conductivity. 



If the aggregates consist of eight gelatin anions with four Ca ions 

 the ratio of osmotic pressures would be 5: 16 which is also approxi- 

 mately 1:3. 



It is m reality only necessary to assume the existence of com- 

 pounds of the form Ca gelatin2, the two anions of which form one ag- 

 gregate of two gelatin anions, and to assume further that two, three, 



