86 THE GASTRIC JUICE. 



acts with free hydrochloric acid, with organic acids, and 

 with acid phosphates ; that is, with everything except com- 

 bined hydrochloric acid. Consequently A B represents 

 the acidity due to the hydrochloric acid combined in the 

 organic form. Dimethyl-amido-azobenzene is affected only 

 by free hydrochloric acid, and this is shown in C. B G 

 gives the acidity from the acid phosphates, plus the or- 

 ganic acids. 



Calculate from the amounts of sodium hydrate used 

 the percentages of each of these, remembering that one 

 cubic centimeter of the alkali contains 0.004 gramme and 

 neutralizes 0.00364 gramme of HC1. The amounts of acid 

 phosphates and organic acids must be expressed in terms 

 of an equivalent amount of HC1. 



200. DETERMINATION or PERCENTAGE OF FREE HYDRO- 

 CHLORIC ACID (SJOQVIST'S METHOD). To 10 cubic centimeters of 

 filtered gastric juice in a porcelain, nickel, or better a platinum 

 crucible add enough pure barium carbonate to neutralize the free 

 acid. Evaporate with a small name to dryness; cautiously burn 

 the residue and heat it to a low, red heat. After cooling add 

 10 cubic centimeters of water, pulverize the residue, and pour oft' 

 through a filter the water containing the dissolved barium chlorid. 

 Repeat with successive portions of water until the filtrates to- 

 gether amount to about 50 cubic centimeters. Determine in this 

 filtrate the amount of barium chlorid formed from the hydro- 

 chloric acid in the following manner: Make a solution of 10-per- 

 cent, acetic acid and 10-per-cent. sodium acetate in water and add 

 3 to 4 cubic centimeters of this to the filtrate to be tested. Add 

 also to the liquid one-fourth to one-third its volume of alcohol. 

 The latter is to make the barium precipitate more completely, the 

 former solution to prevent the presence of free hydrochloric acid. 

 Add from a burette a solution of potassium dichromate containing 

 7.35 grammes per liter until it is in excess. This is shown by 

 taking out a drop from time to time on a glass rod and putting it 

 on a piece of tetra-methyl-paraphenylene dianiin paper. An ex- 

 cess of the dichromate is denoted by a blue color. When a faint- 



