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. 



Y 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 -fa heavy metal but not the completed fish. 2 Many observa- 

 tions indicate that the egg is more permeable after fertilization than 

 before. 3 



Appendix :\ Determination of the Reaction of a Solution. The 

 reaction of the solution, in which a chemical reaction takes place, plays 

 an important r61e 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 



where CH, COH represents the concentration of the H and OH ions, 

 CH Z O the non-dissociated water molecules and KI a constant. As CH*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 CH and COH can be 

 calculated, if the other is known. As it is more convenient to determine 

 CH than COH> therefore CH is also ordinarily determined for solutions 



1 Pfluger's Arch., 88, 68 (1901). 



2 Science, 34, 653 (1911). 



8 Lillie, Amer. Journ. of Physiol., 27, 289 (1911); McClendon, ibid., 27, 240; 

 Science, 32, 122, 317; Lyon and Shackell, ibid., 32, 249 (1910). 



