THE GASTRIC JUICE. 121 



acids are destroyed, while the hydrochloric acid combines with the 

 barium, and can thus be estimated as barium chloride. 



To this end, 10 c.c. of the filtered stomach-contents are treated 

 with a pinch of chemically pure barium carbonate and evaporated to 

 dry ness. The residue is ignited at a moderate temperature until 

 white, and the remaining ash extracted with hot water. After 

 filtering the solution (about 50 c.c.) it is treated with an equal volume 

 of alcohol (94 per cent.) and 0.75 c.c. of a 10 per cent, solution of 

 sodium acetate in dilute acetic acid (10 per cent, solution). The 

 barium is then estimated by titrating with a standardized solution of 

 potassium bichromate, containing 8.5 grammes of the chemically 

 pure substance in the liter, and using tetramethyl-paraphenyldiamin 

 paper as an indicator, until a drop of the titrated fluid causes a distinct 

 blue coloration of the paper within one minute. From the number 

 of cubic centimeters employed to bring about the end-reaction the 

 corresponding amount of hydrochloric acid can then be calculated 

 by multiplying with 0.00405, if the bichromate solution was 

 standardized with a ^ normal solution of barium chloride. 



METHOD OF LEO. This method is based upon the observation 

 that calcium carbonate combines with free and loosely bound hydro- 

 chloric acid at ordinary temperatures to form neutral calcium chlo- 

 ride, while the acid phosphates are not affected. If then the total 

 acidity of the stomach-contents is first determined, and the acidity 

 referable to acid salts deducted from this figure, the amount of 

 physiologically active hydrochloric acid is ascertained. Organic 

 acids, of course, must first be removed by extracting with ether 

 (50-100 c.c. for 10 c.c. of gastric juice). As the monophosphates of 

 potassium and sodium, however, are changed to monocalcium phos- 

 phate in the presence of calcium chloride, which requires double the 

 quantity of sodium hydrate solution for its neutralization than the 

 corresponding; amount of the alkaline phosphates, it is either neces- 

 sary to divide the number of cubic centimeters of the sodium 

 hydrate solution which is used in the second titration by 2, or to 

 make the first titration under the same conditions as the first, viz., 

 after adding an excess of calcium chloride solution. 



To this end, then, we proceed as follows : 15 c.c. of the filtered 

 gastric contents are - treated with a pinch of dry and chemically 

 pure calcium carbonate. The mixture is well stirred and passed at 

 once through a dry filter. Ten c.c., from which the carbon dioxide 

 is expelled by a current of air, are then treated with 5 c.c. of a con- 

 centrated solution of calcium chloride and titrated as usual. The 

 resulting value is termed P, and represents the acid phosphates. 

 The total acidity is then determined in another specimen, after 

 adding the same amount of the calcium chloride solution, and the 

 result termed T. T minus A will then represent the amount of the 

 physiologically active hydrochloric acid. 



The combined hydrochloric acid may, of course, be readily deter- 

 mined with either of the two methods which have just been 



