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SEWAGE PURIFICATION WITH REFERENCE TO 
COLLOID CHEMISTRY. 
By Epwarp Arvern, D.Sc., F.1.C., Chief Chemist, Rivers 
Department, Manchester Corporation, 
Although the problem of sewage purification, as it is known 
to-day, dates back to the introduction of the water-carriage 
system in the early part of the nineteenth century, the signifi- 
eance of colloid chemistry in relation thereto has only been 
observed within comparatively recent years. 
Even at the present time, although certain theories have been 
elaborated with respect to the fate of the colloid matter during 
the purification process, in the main such theories have been 
established by analogy from the known characteristics of organic 
colloids and their behaviour under certain conditions rather than 
from any systematic study of the colloid matter actually present 
in sewage. So far as the writer is aware, no reliable data are 
available with respect to the separation, estimation and identifi- 
cation of the actual colloids present originally in the sewage and 
during the various stages of the purification process. 
With the view, therefore, of indicating the present position in 
regard to the subject it is proposed (a) to state briefly the problem 
and (b) to give a résumé of the chief theories advanced with 
respect to the mechanism of the changes involved in the purifica- 
tion process, with special reference to the points of contact with 
colloid chemistry. 
Briefly, ordinary domestic sewage may be said to be the water 
supply polluted by human excremental matter, kitchen and other 
domestic waste products. As in the majority of cases a combined 
drainage system is adopted, road detritus and washings must 
be added. 
The character and strength of domestic sewage varies very 
considerably, dependent on the following factors :— 
(i) The extent to which the water carriage system has been 
adopted. 
(ii) The water consumption per head of population con- 
nected to the sewer. 
(iii) Whether a combined, separate or partially separate 
system is in vogue. 
