476 



Jacques Loeb 



Table II. 



Minimum concentra- 



tion required for pre- 



cipitation 



P. U. 



in millivülts 



Maxiraal concentra- 

 tion at which suspen- 

 sión remains stable 



P. I). 



in millivolts 



I.iCl 



XaCl 



KCl 



Na,S04.... 

 Na¡Fe(CN), 



MgCls 



MgSO,..., 



CaClj 



La CU 



M/2 



M/2 



M/4 

 M/4 

 M/16 

 M/16 

 M/16 

 M/32 

 M/2,048 



(10) 

 10 

 14 

 13 



13 

 ) I 



14 



14 



M/4 

 M/4 

 M/8 

 M/8 

 M/32 

 M/32 

 M/32 

 M/64 

 M/4, 096 



14 



2 1 



19 

 21 



'5 

 '9 

 17 



In the third column are found the valúes for the P. D. in the solutions 

 where precipitation occurred and in Column 5 ^re the valúes for the 

 P. D. where precipitation was no longer possible. It is obvious that in 

 the solutions where coagulation or coalescence of the partióles occurred 

 the P. D. was always below 15 millivolts, with the exception of MgSO^ 

 where it was I 5 millivolts. The reader must, however, remember that the 

 possible error in the P. D. may be 2 millivolts and that the actual P. D. 

 may have been in this case 14 or 13 millivolts. 



On the other hand, the P. D. in the solutions where the suspensión 

 was stable was always above 1 5 millivolts with the exception of NaCl 

 where the charge was 14 millivolts. It is quite possible that the real 

 P. D. was in this case also 15 or 16 millivolts. 



These measurements lead then to the conclusión that there exists a 

 critical P. D. for the stability of the suspensión of collodion partióles in 

 aqueous solutions. This critical P. D. is about 1 5 millivolts. \\'hen the 

 P. D. falls below this valué the particles upon colliding are no longer 

 repelled but may adhere to each other and coalesce (agglutinate or coa- 

 gúlate) into larger particles which rapidly sink to the bottom of the test- 

 tube. If the P. D. is larger than 15 millivolts the particles will repel 

 each other upon colliding with sufficient forcé to prevent coalescence. If 

 this critical valué is exceeded the stability of the suspensión is not in- 

 creased when the charge is increased. I have noticed that there is no dif- 

 ference in the rate of settling of a suspensión of the collodion particles 

 when the charge varies between 20 and 70 millivolts. 



The collodion particles are generally negatively charged, except in 



