July 27, 1917] 



SCIENCE 



79 



bonic acid and bicarbonate, if the ratio of 

 acid to salt be 10 the concentration of hy- 

 drogen ions must be 50, if the ratio be 1 

 the concentration will be 5, and if the 

 ratio be 0.1 the concentration will be 0.5. 



Thus we can see why carbonate solu- 

 tions are almost alwaj^s nearly neutral 

 (e. g., 100 > (H) > 0.01), and, taking ac- 

 count of the universal distribution of free 

 and combined carbonic acid in the ocean, 

 in lakes and streams, and in all organisms, 

 we understand the primary cause of the 

 approximate neutrality of nearly all nat- 

 ural solutions, both organic and inorganic, 

 upon the earth. In blood the concentra- 

 tion of hydrogen ions is about one third of 

 the present unit, hence the ratio of free to 

 combined carbonic acid must be less than 

 1:10. 



In general it is evident that when the 

 value of k for an acid is nearly 1 solutions 

 containing that acid and its salts will be 

 nearly always neutral ; but that if the value 

 of k differs largely from 1 such solutions 

 will be nearly always appreciably acid or 

 alkaline. 



Beside carbonic acid, there is but one 

 biologically common acid substance, viz., 

 phosphoric acid after one hydrogen has 

 been neutralized by base as in acid sodium 

 phosphate, that possesses the value of k 

 nearly equal to 1. Most weak acids have 

 a value hundreds or thousands of times 

 greater. Phosphate solutions are therefore 

 commonly nearly neutral, and they share 

 with caiibonate solutions the function of 

 preserving the constant alkalinity of the 

 body. 



It is easy roughly to demonstrate the gen- 

 eral character of such acid-base equilibria 

 with the help of the phosphates. Thus, 

 for example, a solution of acid sodium phos- 

 phate has a faintly acid reaction, a solution 

 of ordinary sodium phosphate an alkaline 

 reaction, but almost any mixture of the 



two salts is neutral to ordinary indicators, 

 and will take up strong acids or alkalis 

 in large quantities without apparently 

 changing its reaction. Of course every 

 drop of acid or of alkali does change the 

 reaction, but the change is so slight that it 

 can not be detected by ordinary means. 

 This depends upon the fact that strong 

 acids and bases combine quantitatively with 

 the alkaline or acid phosphate: 



HCl 4- Na^HPO, = NaCl + NaH~PO„ 

 NaOH + NaH.PO. = Na,HPO, + H^O. 



Accordingly, there is only a change in the 

 ratio between the concentrations of the two 

 phosphate salts, and of hydrogen ion con- 

 centration in due proportion, according to 

 the analysis already given. 



If the solution is supposed to contain 

 bicarbonates, as well as phosphates, the 

 above experiment fully illustrates the gen- 

 eral character of the process by which acids 

 are immediately neutralized in the body. 

 The proteins, to be sure, are also involved, 

 but their share in the process is small, 

 though not physiologically insignificant. 



Upon this physico-chemical basis the phys- 

 iological processes are erected. It is as a 

 means of restoring bicarbonate and alkaline 

 phosphate from the products of reaction 

 of these substances with acids, or as a means 

 to neutralize acid, and thus prevent its 

 reaction with bicarbonates and phosphates, 

 that ammonia is produced in the meta- 

 bolism. 



In like manner the acidity of the urine 

 is the result of the reversal in the kidney of 

 the reaction by which acids have been neu- 

 tralized in the body. In the renal function 

 phosphates almost alone are concerned. 

 Therefore the process may be described as 

 foUows: In the blood, as the result of the 

 production of acid, a certain amount of al- 

 kaline phosphate has been converted into 

 acid phosphate, so that the ratio of acid 

 phosphate to alkaline phosphate has been 



