26 PHYSICOCHEMICAL BASIS OF PHYSIOLOGICAL PROCESSES 



occurs in the epithelium of the intestine out of the fatty acid and glycerol 

 absorbed from the intestinal contents, it is possible that the last men- 

 tioned process occurs. In other cases the substance may be carried 

 away by the blood or lymph or urine as fast as it is formed. 



The Law of Mass Action as Applied to the Measurement of H-ion 

 Concentration. — Let us now return to the reaction or H-ion concentration 

 of substances in solution. As the standard of neutrality, pure water is 

 chosen. Let us consider, then, how the laws- of mass action can be 

 applied in order to enable us to determine the H-ion concentration of 

 pure water. It has been stated above that chemically pure water is in- 

 capable of conducting the electric current. This however is not strictly 

 the case, for it conducts to a very slight degree. According to the dis- 

 sociation hypothesis, it must therefore be represented as containing 

 molecules of H,0 and ions of H- and OH -, and according to that of mass 

 action there must be a balanced reaction between the molecules and ions 

 represented thus: 



H.O<=>H • + OH • oi J FTjTVi ~ = K. 



Since the concentration of H- and OH- is extremely small, there must 

 always be such an overwhelming preponderance of H 2 molecules that 

 no changes in the concentration of H- and OH • will be capable of appre- 

 ciably affecting the concentration of H 2 ; in other words, one may omit 

 the denominator of the equation and write it [H-] x [OH-] = K. If 

 then we know the value of K, it will only be necessary to measure the 

 concentration of either H- or OH- in order to express in numerical terms 

 the reaction of the solution. It has been found that the value of K is 

 about lxlO 14 ,* and since the concentrations of H- and OH- are nec- 

 essarily equal in pure water, it follows that [H] = [OH] = \'lxlO" 14 , 

 i. e., each ion has a concentration of 1 x 10" 7 . This means that water con- 

 t.iins approximately 1 gram mol. each of H- and OH- ions, or 1 gram 

 H- and 17 grams OH- ions, in 10 7 or 10.000,000 liters. A consequence 

 of the above law is that no matter how much the concentration of one 

 ion is increased by adding another substance, the solution must still 

 contain some of the other ion. Tims, in acid solutions eon. H- must 

 increase and con. OH- must decrease in such proportion that the two 

 multiplied together equals about 1 x 10 ll . The H-ion concentration can 

 be used there fore to crprrss Hie reaction of neutral, acid and alkaline 

 solutions. 



In place of water, let us substitute decinormal hydrochloric acid 



*The sign 10"" is simply a convenient way of expressing the degree of dilution. It gives the 

 number of times the value standing in front of it must be multiplied by 10 in order to find the. 

 .degree of dilution. 



