308 PHYSIOLOGICAL CHEMISTRY 



normal as possible. In fact the conditions are somewhat similar to 

 those which surround the temperature regulation of the body. Here 

 again the body attempts to maintain a normal temperature. A given 

 man before a blast furnace, for example, shows a body temperature very 

 similar to that exhibited by the same man in the ice floes of the north. 

 Any considerable deviation from normal in the temperature of our body 

 is associated with failing health and possible death. 



The popular conception of water is that of a fluid which is neutral 

 in reaction. As a matter of fact, however, in ordinary tap water 

 we have a solution more alkaline than blood, whereas, distilled water, 

 which is our standard of neutrality, is considerably more acid than is 

 the blood. A change in the reaction of the blood equivalent to the 

 very slight difference between the reaction of tap water and distilled 

 water would be fatal to the organism. 



Just a word in review as to the physico-chemical methods of ex- 

 pressing the reaction of a solution. A neutral solution is, of course, 

 one which contains equal numbers of hydrogen and hydroxyl ions while 

 an acid solution contains an excess of hydrogen ions and an alkaline 

 solution contains an excess of hydroxyl ions. The extent to which an 

 acid ionizes or liberates hydrogen ion determines the efficiency of 

 that acid in altering the reaction of a solution. Thus tenth normal 

 solutions of hydrochloric and acetic acids, for example, each contain 

 the same amount of reacting hydrogen per liter. However, 91 per cent 

 of the hydrogen of the hydrochloric acid dissociates and forms hydrogen 

 ion whereas only 1.3 per cent of the reacting hydrogen of acetic acid 

 is thus dissociated. Therefore, the decinormal hydrochloric acid is 

 70 times as strong as the decinormal acetic acid. 



Pure water is a 1/10,000,000 N acid and a 1/10,000,000 N alkali 

 as well. If we take a normal solution of an acid and an alkali we may 

 dilute each until the hydrogen and hydroxyl ion concentrations ap- 

 proach that of water. Instead of expressing the hydrogen ion con- 

 centration of water as 1/10,000,000 N it is customary to use the logarith- 

 mic notation and express it as io~ 7 N or rather better to drop the io~ 

 and express it as pH 7 or P H 7 or P H 7. This then represents the 

 hydrogen ion concentration of a neutral solution. Exponents above 7 

 indicate alkaline solutions whereas exponents below 7 indicate acid 

 solutions. 

 Thus PHI is the hydrogen ion concentration of N/io acid. 



P H 6 is the hydrogen ion concentration of N/ 1,000,000 acid. 



P H 7 is a neutral solution. 



P H 8 is the hydroxyl ion concentration of N/ 1,000,000 alkali. 



P H i3.2 is the hydroxyl ion concentration of N/io alkali. 



