Susceptibility of Iron in Colloidal Solution. 267 



3. Susceptibility of Colloidal Solution of Iron. 



The cell was next filled with some of the colloidal solution 

 which had been prepared in another portion of the same sample 

 of methyl alcohol. A difficulty soon presented itself because the 

 strong magnetic field soon pulled some of the iron to the bottom 

 of the cell, so that a protracted series of readings could not be 

 made. Weighings were therefore made so as to get exactly the pull 

 due to one certain field — that with 7 '9 amperes through the 

 magnet. With the cell freshly filled with colloidal solution the 

 difference between the counterbalancing weight when there was 

 no current in the magnet and that with 7*9 amperes, was determined 

 as quickly as possible. The cell was then emptied, rinsed out and 

 refilled with fresh solution and the counterbalancing weight with 

 no field on was again found. By the help of the former reading 

 the balance could be set approximately at the weight required to 

 counterbalance the cell with the magnetic field on. In this way 

 the required weight was obtained in a few seconds and so the 

 error introduced by coagulation of the particles was nearly 

 obviated. 



It was found that the pull due to a field of 10140 units on the 

 cell full of colloidal solution was — '0565 gram. From Table IV we 

 see that the pull exerted by this field on the glass cell alone is 

 + '0100 gram. The pull on the colloidal solution is therefore 

 — '0665, from which, by use of the formula 



*~ AH*' 

 we find that k = - 4"83 x 10~ 7 . 



4. T owns end for mida for Colloidal Solution of Iron. 



60 c.c. of the above solution gave "035 gram of Fe 2 3 , which 

 gives the weight of iron per c.c. to be 44 x 10 -6 grams. 



Assuming the same form of equation as that given by Towns- 

 end for ferric solutions we have 



10 7 k = C ,w+ [susceptibility of solvent (kg)]. 

 For the particular case here given we have 

 A; = -4-83 x 10" 7 , 

 k s = - 6-30 x 10- 7 , 

 w = 44 x 10 _<i . 

 From which we get 



G= 33,400. 



This value of C is 13 times the corresponding number for ferric 

 solutions and 16 times that for ferrous solutions. 



