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74 GENERAL AND PHYSICO-CHEMICAL.
they die; the toxicity of the NaCl solution can be arrested by small
quantities of almost any salt with polyvalent cations. Not only the salts
of the alkaline earths, but also those of the heavy metals (for instance
zinc sulphate or lead acetate) can neutralize the toxicity of the NaCl in
proper concentration.1
The eggs can develop in solutions which kill the
completed fish.
The antagonistic action of salts upon organic structures depends,
according to Loeb, upon the fact that the salts mixed in proper propor-
tions causes a " tanning " of the protoplasmic surface of the cells whereby
the cells become impermeable for certain destructive substances to which
the salts also belong. The fertilized eggs of Fundulus can. be tanned
by NaCl +a heavy metal but not the completed fish.
2
Many observa-
tions indicate that the egg is more permeable after fertilization than
before.3
Appendix 21 Determination of the Reaction of a Solution. The
reaction of the solution, in which a chemical reaction takes place, plays
an important role in many cases. As the acid or alkaline reaction of a
solution depends upon the amount of H or OH ions it is often of import-
ance to be able to determine the concentration of these ions in solution.
These cannot be determined by titration with alkali or acid in the pres-
ence of organic salts. In this titration the existing equilibrium in the
solution is disturbed and therefore also other decompositions occur
besides the neutralization of H or OH ions. The quantity of alkali or
acid used does not therefore correspond to the original concentration
of H or OH ions.
According to the law of mass action there exists, between the H and
OH ions formed by the dissociation of the water on the one hand and
the concentration of the non-dissociated molecules on the other, the
following equation
Ch-Coh = Ki-Ch>o
where CH , Coh represents the concentration of the H and OH ions,
<
ii o the non-dissociated water molecules and Ki a constant. As Cr2 o
can only be considered as constant in certain dilute solutions we have
Ch-Coh = K) where K is called the dissociation constant of the water.
As K is a constant it follows that the figures for Cr- and Coh can be
calculated, if the other is known. As it is more convenient to determine
Ch than C’oh> therefore Cr is also ordinarily determined for solutions
1
PfliiKer’s Arch., 88, 68 (1901).
^Science, 84, 653 (1911).
3
Lillie, Amer. Journ. of Physiol., 27, 289 (1911); McClendon, ibid., 27, 240;
Science, 32, 122, 317; Lyon and Shackell, ibid., 32, 249 (1910).
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