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428 COMMENTS
with. It is a recognition of good work well done that is due to him,
an inspiration to his successors and an incentive to those who are
just entering upon public service. We will never see the time
when public office will bring the income that private business affords,
but we can strive with some hope of success to secure for those who
discharge public duties ably and constructively a permanent recog-
nition of what they do. The character of the works used in water
supply particularly adapts them for receiving memorial tablets
commemorating the services of these able men.
John M. Goodell.
THE RELATION OP COLLOIDS TO WATER PURIFICATION AND SEWAGE
DISPOSAL
The colloidal state of matter is a subject that has received con-
siderable attention from scientists during the last decade, but the
application of the laws established by research to practical prob-
lems has been far too limited. The extremely broad field to which
the study of this subject is applicable may be perhaps some excuse
for the slow advance, but it is probably also due to the lack of con-
tact, and possibly interest, which the research worker usually has
in applied science. To those who are so fortunate as to have a good
working knowledge of the fundamentals of colloidal phenomena and
physical chemistry in general, and who also are confronted with
practical problems in which this knowledge may be utilized, the
opportunities for contributing to the advancement of the arts are
unparalleled. In agriculture, medicine, sanitation and hundreds of
industries, many of the unsolved problems are those relating to
matter in the colloidal state.
In the field of water purification and of sewage disposal, there
is a great need for an intelligent application of the principles involved
in colloidal chemistry. We know far too little why some turbid
waters are more easily coagulated than others. We know compara-
tively little of the inhibitory effects which various substances and
chemicals may have in preventing effective coagulation of suspen-
soids. We have only a limited and decidedly empirical knowledge
of the influence of temperature upon coagulation of natural waters.
In water softening we are confronted with several problems in
which colloidal and physical chemistry must eventually provide the
practical solution. For example, how may the precipitation of
COMMENTS 429
calcium salts be hastened where caustic lime alone, or the latter
together with soda ash are used; how may the sludge from such
plants be best utilized in the freshly treated raw water to facilitate
these reactions; how are the solubilities of the calcium and magne-
sium carbonates and of magnesium hydroxide affected by the pres-
ence of other salts in solution, and how much actual effect does the
temperature of the water have on the chemical reactions taking
place and the physical changes which follow the latter? The answer
to these questions must be found in a knowledge of the solubility
products of the salts and compounds in question; in the laws relat-
ing to equilibrium which must exist between dissociated and undis-
sociated compounds, and between undissociated compounds and the
precipitated solids; in the nature and effect of surface tension; in
the phenomenon of adsorption, and in the velocity of chemical
reactions.
The unsolved problem in sewage disposal is what to do with the
sludge. The physical condition of this residual matter varies, of
course, with the process employed; but in every case the sludge is
colloidal in character, and its manipulation is made difficult by all
of those properties which are inherent to colloids. The problem is
much more difficult where trade wastes are involved. In the latter
we have oftentimes gelatinous material of the most offensive type
and which, because of its colloidal condition, does not yield to any
form of treatment to which it may be reasonably subjected.
Structures cannot be intelligently designed and built for treating
water and sewage unless the principles which govern the changes in
the solid and liquid substances contained in them are understood.
If these principles are still undiscovered, then we must resort to
experimental studies, and base our designs on more or less empirical
formulas. Nevertheless, this lack of knowledge is no reason for
not using that which is available, and endeavoring to apply in prac-
tice what is now known. Imitation and rule of thumb do not ad-
vance the art of engineering. Many chemists have but a hazy idea
of colloidal and physical chemistry, and to the average engineer the
terminology of the subject is practically unknown.
J. W. Ellms.