When these substances are introduced in water in which salts are 
already in solution the results are sometimes not in agreement with those 
obtained when the substances are in solution alone. CO, renders some 
salts less toxic. One salt often renders another less toxic or may neutral- 
ize its effect. On the other hand, combinations are sometimes more toxic 
than the individual constituents alone. Wells found that a little HCl 
reduced the toxicity of common salt to about one-third. Ammonia salts 
are harmless to some fishes in the absence of carbonates but toxic in 
their presence. This subject is too complicated and knowledge too 
meager to justify inferences as to the effect of mixtures of salts in 
streams. Organic compounds are often more toxic in the presence of 
salts. For data on this subject see Clowes, 17; Lillie, 12; Loeb, ’06, ’12; 
Osterhout, ’14, ’14a, 16; Powers, 18; and Spaeth, ’17. Osterhout (14a) 
has constructed important curves showing some of the most antagonistic 
mixtures of salts. = 
The toxicity of residuals of partial recovery may be determined 
directly if the process of treatment is in operation; if not, and if the 
character of the residuals is not known it is necessary to take a series of 
the representative constituents in a pure state, and to make tests of their 
toxicity. When this has been done it will usually be possible to foresee 
the toxicity of any residual of a proposed method of treatment (Shelford, 
lia) 
Determination of Hydrogen Ion Concentration, that is, its Acidity 
or Alkalinity.—This is best done by indicators (McClendon, 16; Clark 
and Lubs,’17). The addition of substances to sea water demands some 
special attention, as precipitation of calcium and magnesium carbonates 
precedes any marked increase of hydroxyl ions due to the addition of 
alkalies (Whitley, ’05; Haas, ’16). They settle out as a white precipitate. 
Treatment of Water during Low-water Stages—Aeration of the 
effluent after considerable dilution will always help to render it less dan- 
gerous. Some of the aerating devices used in the activated-sludge proc- 
ess of sewage treatment will serve. (Porter, 17; Bartow, ’17.) 
V.-Do animals turn back from the polluting substance and thus 
escape destruction; or do they swim into it and die? 
Fresh-water fishes swim into nearly all coal-gas waste constituents, 
and on returning to clear water avoid it because intoxicated, and die. 
This fact of course increases many times the danger from these sub- 
stances. Fishes often react in this way to SO,, which may be a source of 
danger in the Miles acid process. The most important reactions of this 
kind are probably those of fish which run on shore. The great sensitive- 
ness of herring in reactions to small quantities of CO, in sea water sug- 
gests that the erratic runs of this fish on our Pacific coast may be due to 
some such negative reaction. Likewise the great historical failure and 
alleged migration of the herring in Europe which contributed to the 
decline of the Baltic towns of the Hanseatic League and to the rise of 
Amsterdam may have been due to a similar cause. 
