THE CHEMISTRY AND PHYSICS OF THE CELL 33 



in the amount of dissociation. Water is the best known medium 

 for causing dissociation, except possibly peroxide of hydrogen, 

 while chloroform and alcohol are relatively very weak in this 

 respect. The amount of dissociation is also increased by 

 raising the temperature. 



The importance of this process of dissociation or ionization 

 lies in the fact that with most substances no chemical reaction 

 can occur while the substance is in the non-ionized state. .The 

 chemical properties of ionizable substances are produced largely 

 by the ions they liberate on dissociation. Acids owe their 

 character to the hydrogen ion, alkalies owe theirs to the hydroxyl 

 ion. We can appreciate the difference between the ions and 

 the same substance in the non-ionized form if we consider the 

 chemical inertness of hydrogen gas, as compared with a solution 

 of acid which owes its powerful eifects to hydrogen ions. 

 Perfectly dry sulphuric acid is absolutely free from the acid 

 properties that characterize it when it contains a little water, 

 because it is not ionized when dry. It is for the same reason 

 that we can have two substances together in a dry condition 

 without reaction, that would immediately react if moist. It 

 is by means of the electrical charges of the ions that chemical 

 reactions occur, and hence ions must be present to have reactions. 

 As a consequence, the physiological eifects of electrolytes are 

 due to their ionic condition, and through the ions that are 

 present in the cell many of its various chemical processes are 

 brought about. Not all substances ionize with the same readiness, 

 which causes a great difference in their properties. The reason 

 that acetic acid is a weaker acid than hydrochloric acid is that 

 it does not ionize to such an extent, and so a corresponding 

 quantity does not introduce as large a number of hydrogen ions 

 into a solution. Larger molecules, as a rule, ionize less than 

 smaller ones of similar nature, e. g., stearic acid ionizes less than 

 acetic acid and therefore is a weaker acid. Likewise the 

 properties of a substance which depend upon its ions will be 

 less marked when it is in a solvent that produces little ionization. 

 For example, bichloride of mercury owes its antiseptic properties 

 to the Hg ions that it sets free when in solution. It is well 

 known that solutions of mercury, and for that matter most other 

 antiseptics, are much less actively germicidal in alcohol than 

 when in water, because their ionization is less in alcohol; and 

 the germicidal properties decrease as the proportion of alcohol 

 increases, until the germicidal effect of the mixture is no greater 

 than that of alcohol alone in the same strength. 



If we had no electrolytes in the cell, electric charges could 

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