GASTEIO TESTS. 87 



blue color is produced, read from the burette the amount of the 

 dichromate solution used. Calculate from this the amount of 

 acid in the gastric juice. The reactions which occur are 



2HC1 + BaCO s BaCl 2 + CO 2 + H 2 

 when the acid is neutralized by the carbonate, and 



2BaCL + K 2 Cr 2 T + H 2 = 2BaCr0 4 + 2KC1 + 2HC1 



when the barium salt is precipitated by the dichromate. 



One molecule of potassium dichromate, weighing 294, pre- 

 cipitates two molecules of barium chlorid containing four atoms 

 of chlorin. These four chlorin atoms were derived from four 

 molecules of hydrochloric acid weighing 4x36.4. Therefore, for 

 every 294 parts by weight of the dichromate used, 145.6 parts by 

 weight of hydrochloric acid were present. One cubic centimeter 

 of the dichromate solution contains 0.00735 gramme, and is, there- 

 fore, equal to 0.00364 gramme of hydrochloric acid. 



The weight in grammes of the hydrochloric acid pres- 

 ent in the gastric juice in the free state or combined with 

 the albuminous compounds is, therefore, obtained by multi- 

 plying the number of cubic centimeters of dichromate used 

 by 0.00364, and, taking the weight of 1 cubic centimeter 

 of gastric juice as 1 gramme, the percentage can be cal- 

 culated. If 10 cubic centimeters of juice were used, it is 

 only necessary to multiply the weight of HC1 in this by 10 

 to give the percentage. 



201. VOLUMETRIC DETERMINATION OF THE FREE ACIDS 

 AND ACID PHOSPHATEIS. To 10 cubic centimeters of filtered 

 gastric juice 1 add 5 cubic centimeters of concentrated calcium 

 chlorid solution and a few drops of phenol-phthalcin as an indi- 

 cator, then Vio normal sodium hydrate until it is neutralized, 

 when the color is a faint pink. The amount of alkali used cor- 

 responds to the total acidity of the juice. Then take 15 cubic centi- 



*A mixture of HC1 and phosphates may be used if juice 

 cannot be obtained. 



