Precipitation of Colloids. 579 



In order to test the validity of the equation it was uecessarj 

 to plot values of log N against values of log ( \ 



It was difficult to find a scries of concentration values of 

 sufficient length to make an experimental verification possible. 

 Failing an independent determination of a series of values 

 for which the author had not sufficient time, an attempt was 

 made with some results of Oden's, given below, on the 

 precipitation of colloidal sulphur, the latter being negatively- 

 charged. The left-hand column shows the minimal concen- 

 tration of cation in gm. atoms per litre required to efVed 

 precipitation in a given time. The anion in every case 

 is CT :— 



Table I. 



Colloid :- Sulphur 18°-20° C. 



Minimal 

 Cation. concentration 

 with Cr 

 anion. 



Log 10 . 

 Minimal 



concentration. 



Minimal 



concentration 



with N0 3 ' 



anion. 



Atomic 

 number. 



L °gio- , 

 Atomic 

 number. ! 



H' 60 



Li* -913 



Na ' • 1 53 



0-778 

 1-960 



r-185 



•163 



1 



3 



11 



13 

 19 

 20 

 29 

 37 

 55 

 56 







•477 

 1041 

 1114 

 1-279 ' 

 1-301 

 1-462 

 1-568 

 1-740 

 1-748 



Al*" 0044 



3-643 — 

 2-322 -022 

 3-613 



K- -021 



Ca • ' -U04 L 



Cu' 1 008 



. 3-903 

 2201 

 3954 

 3-322 



•0175 

 •0096 



Kb* -016 



Cs* -009 



Ba" -0021 









On plotting the values of log minimal concentration of the 

 cations associated with CI' anions (C) against log atomic 

 number (N), it will he seen that the values of the univalent 

 ions, with the exception of that of potassium, lie approxi- 

 mately upon a straight line to which the equation is 



C 1= =5-9 N" 1 ' 64 . 



In the case of the divalent ions the values are too few to 

 be of any use in. deducing a relation. If, however, we 

 assume that the equations will he of the same form, i. e. that 



the 



expression 



is constant for sulj 



)liur, a 



nd that haiiu: 



