ELECTROLYTES AND THEIR ACTION 



203 



the fact that the electrolytic dissociation of water rises more quickly with 

 temperature than that of sodium bicarbonate does. 



Compared with mixtures of the alkaline and acid phosphates, the H* ion 

 concentration in blood varies between relative proportions of the two phosphates 

 between 6 to 4 and 1 to 0. Since it is to be presumed that variations of this 

 magnitude are innocuous, it will be seen that in the presence of phosphates, 

 protoplasm possesses an efficient mechanism for avoiding any considerable change 

 in reaction. All the phosphate must be converted into the acid salt before the 

 hydrogen ion concentration can rise beyond that due to this salt, or into the 

 alkaline salt before the alkalinity can become greater than that of solutions 

 of Na 2 HPO 4 . 



"Buffers." The effect of such substances as bicarbonates, phosphates, amino- 

 acids, etc., in " soaking up," as it were, excess of hydrogen or hydroxyl ions 

 was compared by Fernbach and Hubert (1900, p. 295) to that of "tampons." 

 Sorensen (1909) adopted the word and, in the translation of his paper into 

 German, it was rendered " Puffer " and thence into English as " Buffer." This 

 latter word does not seem to me to be a very descriptive one nor to convey 

 correctly the meaning of the original " tampon." A railway buffer does not absorb 

 the engine itself, as the substances referred to absorb ions. A word more 

 suggestive of a sponge would probably be better, but is not easy to find. 



The Practical Use of Phosphate Mixtures. In certain cases it is of much 

 importance to be able to obtain a solution of a definite but very small con- 

 centration in hydrogen ions, as also to possess the means of maintaining constant 

 this value in a system in which chemical changes, sensitive to change of reaction, 

 are going on. Such cases are the action of enzymes, or the solutions used for 

 perfusion of living organs. The bicarbonates are the most appropriate for the 

 latter purpose. For the making of standard solutions as well as for use with 

 enzymes, the phosphate systems are most valuable. 



These phosphate mixtures are most readily prepared by the addition of standard 

 sodium hydroxide in different proportions to standard phosphoric acid solution. 

 The following table, from the paper by Prideaux (1911) with additions, will be 

 found useful : 



The mixtures are diluted to 100 c.c. since the hydrogen ion concentration refers 

 to solutions which are decimolar in PO 4 . 



The equation by which any other required hydrogen ion concentration can be 



