4 ART. S. — S. KAWAMUKA : COAGULATION OF COLLOIDAL 



colloidal aluminium hydroxide by various electrolytes lias been 

 studied with the aid of the viscosi meter, and the results obtained 

 fulfil the expectation to a remarkable degree as is shown in the 

 following pages. 



2. The Colloidal Solution of Aluminium Hydroxide. 



The colloidal solution of akiminium hydroxide employed in 

 the following experiments is the one first prepared by the English 

 chemist, Walter Crum,^ more than half a century ago. He 

 obtained a basic acetate of aluminium as a fine insoluble crystal- 

 line powder by heating a concentrated solution of aluminium 

 acetate. On prolonged boiling with water the basic salt goes 

 into solution, the acetic acid being given off Avith the steam, 

 while aluminium hydroxide remains in the colloidal state. All 

 the soluble impurities can be removed by thoroughly washing 

 the basic acetate. When the boiling is carried out in a large 

 platinum vessel, care being taken to exclude contamination from 

 the air, it is possible to get rid of the acetic acid almost com- 

 pletely. In this way a remarkably pure solution of colloidal 

 aluminium hydroxide can be prepared with great ease. It is 

 slightly opalescent, but almost clear to the transmitted light, 

 somewhat viscous and oily to the touch when concentrated. This 

 solution is very stable. Kept in a vessel of hard Jena-glass it 

 has remained apparently quite unaltered in its appearance and 

 properties during the lapse of more than three years. Parallel 

 experiments carried out with this old solution and witli a solu- 

 tion newly prepared agreed in all particulars. 



1 Jouni. Cliem. Soc. London, 4, (1853), 216. 



