Section III, 1922 [109] Trans. R.S.C. 



Use of the Centrifuge in Coagulation of Electrolytes 



By E. F. Burton, F.R.S.C. and J. E. Currie, B.A. 



Presented by Professor Burton 



(Read May Meeting, 1922) 



In the experiments on the coagulating power of electrolytes 

 added to colloidal solutions, difficulty is always found in comparing 

 the results of different workers; this circumstance is due essentially 

 to the long interval of time which must often elapse before judgment 

 can be passed on the coagulation. In the following paper are given 

 quantitative results of the coagulation of arsenious sulphide sol by 

 electrolytes, in which the centrifuge was employed to increase the 

 rate of sedimentation after the addition of the electrolyte. 



The Centrifuge 



A Hearson electric centrifuge having a four-armed rotater was 

 used and samples of the colloidal solution were held in glass tubes 

 fitted into the four pivoted metal cups of the rotater. Graded 

 amounts of the electrolyte were added to four different samples for 

 each test and each set of four tubes were centrifuged for 20 minutes 

 at 2750 R.P.M. At the end of this time the amount of solid deposited 

 at the bottom of each tube was determined. 



Preparation of the Solution 



A colloidal solution of arsenious sulphide was used for these tests. 

 About two and one-half litres of distilled water was heated and 

 hydrogen sulphide gas bubbled through; when the temperature 

 approached 90°C. about 30 grams of white oxide of arsenic was added 

 slowly, with constant stirring of the solution. After some time the 

 whole was cooled, pure hydrogen was bubbled through to free the 

 sol from hydrogen sulphide, and the solution then filtered. This 

 method gives a very stable sol of rather high sulphide content: 

 analysis of the final solution gave 0.2342 grams of arsenious sulphide 

 per 100 CCS. of sol. 



Coagulation Experiments 



The coagulant used was aluminium sulphate which has a trivaient 

 metal ion and has, consequently, a powerful effect on arsenious 



