Potential diPfcrences and coagulation of collodion partióles, etc. 475 



Table I jaivas the valué of this P. D. in cliíTerent concentrations ofdif- 

 ferent salts and at the hydrogenion concentration of pll 4.7. The col- 

 lodion particles were generally negatively charged, the P. D. rising at first 

 with the addilion of KCI, XaCl, LiCl, NaoSO^, and Na,l'XCi\j,- to a má- 

 ximum of about 70 niillivolts and then diminishing again with a further 

 increase in the concentration of the salt until it approached zero. In the 

 case of LaCl.,, the concentrations of the salt beyond a molecular concen- 

 tration of M/64 made the charge of the particles slightly but increasingly 

 positiva. 



Table I. 



Potential Difference between Collodion Particles and Aqueous So- 

 lutions in Millivolts at p H 4. 7. The Particles are generally Negati- 

 vely Charged but the Minus Sign is Omitted in the Table. 



LiCl 31 



NaCl 26 



KCI 



NagSO,! 



Na4Fe(CX),.. 



MgCla 



MgSO, 



CaCl, 



La cu" 



42 48 



47 



57 I 50 



34 j 30 



35 28 



35 i 32 I 28 ' 26 



14 10 I 8 I 4 



36 

 30' 

 30 

 26 



13 

 1 1 



15 

 10 



+ 3 



22 17 

 20 14 



2\ 14 



'9 13 



9 



9 

 12 



+ 6 



The figures in the second column of Table II are the minimal concen- 

 trations of salts required for rapid precipitation or coalescence of the 

 small particles into larger masses which sink more rapidly to the bottom 

 of the test-tube. The figures in the fourth column give the maximal con- 

 centrations of different salts at which coagulation no longer occurs. In 

 these latter concentrations the suspensions remain cloudy for weeks while 

 in the concentrations mentioned in the second column the water be-co- 

 mes entirely clear inside of twelve hours (at about 18° C), all the suspen- 

 ded particles havin(j fallen to the bottom of the test-tube. i'he pH of the 

 Solutions was about 5. 8. 



