1 62 PHYSIOLOGICAL CHEMISTRY. 



total acid exist. Several different schemes have been pro- 

 posed by which these degrees of acidity may be measured. 

 The total acid not combined in the form of inorganic salts may 

 be most accurately found by the methods of ordinary quanti- 

 tative analysis. The total chlorine is found by precipitation 

 or by the Volhard titration. The total bases are found by 

 the usual gravimetric methods. On calculating the amount 

 of chlorine necessary to combine with these bases an excess is 

 left over which must be considered as existing in the form of 

 free acid. In very exact work the traces of phosphates and 

 sulphates present must be also determined and these first com- 

 bined with bases. The method is one which requires great 

 care in manipulation and besides does not distinguish between 

 free acid and that held as acid albumin, and this is a very 

 important point. 



The principle of another general method may be illustrated 

 in this way. Three portions of the gastric juice of 5 cc. each 

 are measured off. The first is mixed with a little pure sodium 

 carbonate, evaporated and ignited. The total chlorine is so 

 retained and may be found by the Volhard titration. The 

 second portion is evaporated slowly to dryness at a low tem- 

 perature, mixed with sodium carbonate and ignited. The 

 chlorine is determined in the residue. This represents the 

 fractions combined to proteins and to inorganic bases, as the 

 free hydrochloric acid is lost in the original evaporation at 

 low temperature. Finally the third portion is evaporated and 

 ignited without any addition. The chlorine now found in the 

 residue is that which originally existed in inorganic combina- 

 tion. With these three operations, as is at once apparent, it 

 is possible to measure the element in the three kinds of com- 

 bination. The process has been modified and improved so as 

 to be fairly exact. 



Attempts are now made to determine the acid accurately 

 volumetrically by the aid of indicators, and here, it may be 

 said, if we can neglect the lactic acid present, pretty good re- 

 sults are possible. But if the lactic acid is present in amount 



