196 COMPOSITION OF THE DIGESTIVE JUICES. [CH. VIII. 



A. Total acidity. (Ex. 243.) 



B. Total chlorides. (Ex. 244.) 



C. Mineral chlorides. (Ex. 245.) 



D. Active hydrochloric acid. (B C.) 



E. Free hydrochloric acid. (Ex. 246.) 



F. Combined hydrochloric acid. (D E.) 



G. Abnormal acidity. (A - D.) 



It is usual to express all these results in terms of grams, 

 of hydrochloric acid per cent. 



Total acidity is determined by titration with 0*1 N. 

 soda, the indicator being phenol-phthalein. 



Total chlorides is obtained by adding i cc. of a saturated 

 solution of sodium carbonate to 100 cc. of the nitrate, 

 evaporating on the water bath, heating to a dull red heat 

 and estimating the total chlorides by Volhard's method. 



Mineral chlorides are determined in a similar way, 

 except that the sodium carbonate is not added. Most 

 of the free hydrochloric acid is evolved on heating to 

 dryness. On incineration the protein matter is destroyed 

 and any hydrochloric acid combined with it is evolved. 

 The only chloride left is that which was originalry present 

 in the form of non-volatile chlorides of sodium, etc. The 

 difference between this and the former estimation is a 

 measure of free hydrochloric acid plus that combined with 

 proteins, the sum of these being known as " active hydro- 

 chloric acid." Since active hydrochloric titrates with soda 

 to phenol phthalein, the difference between total acidity 

 and active hydrochloric is a measure of the abnormal acids 

 present, generally lactic acid. 



In a few cases the author has observed that the active hydrochloric acid 

 is greater than total acidity. This puzzling result is probably due to the 

 presence of small amounts of ammonium chloride, which is volatile at a low 

 red heat, and would be removed in the estimation of mineral chlorides. After 

 treatment with sodium carbonate, the ammonium chloride would be con- 

 verted to sodium chloride. In such a case, the mineral chlorides work out too 

 low and the active hydrochloric proportionally too high, and in the absence of 

 lactic acid the active hydrochloric acid will exceed the total acidity. 



Free hydrochloric acid. The only satisfactory clinical 

 method for the estimation of this is b}^ use of Gunzberg's 



