478 DIGESTION. 



in a free state. For the details of this process, consult Bidder 

 and Schmidt, Verdauungssufte, u. Stoffwechsel, 1852, p. 44; or 

 Hoppe-Seyler's Handbuch d. Chemischen Analyse, third edi- 

 tion, p. 434. , 



106. Estimation of the Acid in Gastric Juice. Fill 

 a burette with dilute standard solution of soda (one part in 

 ten), letting the standard solution flow gently into it, so as to 

 avoid air-bubbles, till it is filled above the zero mark. Then 

 place it in the stand, and take care that it is perfectly vertical, 

 If any bubbles of air are present they must be allowed to 

 break or be removed by a glass rod. Let the fluid flow out by 

 pressing the clip till its level corresponds to the zero mark on 

 the burette. Measure out 10 cubic centimetres of gastric juice 

 into a beaker, and add a little litmus solution to it till a dis- 

 tinct red color is produced. Place the beaker containing it 

 under the burette, and let the alkaline solution flow gradually 

 into it at first, and at last only drop by drop, stirring all the 

 time till the red color of the litmus changes to a violet. Then 

 note exactly the level at which the surface of the fluid stands 

 in the burette. The. difference between this level and the zero 

 mark gives the number of cubic centimetres used. Calculate 

 the amount of soda contained in this quantity. One hundred 

 cubic centimetres of the original soda solution contained four 

 grammes, or one-tenth of an equivalent of soda. One hundred 

 cubic centimetres of the diluted solution, therefore, contains 

 one-tenth of this amount, 0.04 grammes, or one-tenth of an 

 equivalent. 



Let us suppose that the amount of soda solution actually 

 used to neutralize the gastric juice is 21.6 cubic centimetres. 

 Then, as 100 cubic centimetres contain 0.04 grammes ( = 0.01 

 equivalent), this quantity will contain only 0.006 grammes 

 ( = 0.00216 equivalent). The quantity of gastric juice neutral- 

 ized was 10 cubic centimetres. Had we used 100 cubic centi- 

 metres of juice instead of 10, we should have required ten 

 times as much soda to neutralize it, i.e., 0.0216 equivalent. 

 One hundred cubic centimetres of the juice, therefore, contains 

 0.0:M of an equivalent of acid, supposing that the acid be 

 monobasic. If the acid be bibasic or tribasic, an equivalent 

 of soda would only saturate a half or a third of an equivalent 

 of acid, and the proportion of acid would be 0.015 or 0.007. 



107. To Determine the Nature of the Acid. The 

 gastric juice is introduced into a large retort connected with 

 a Liebig's condenser, and distilled till the fluid in the retort 

 becomes , r ery concentrated, and clouds begin to form in it. 

 To remove the excess of water from the distillate, it must be 

 neutralized with sodium carbonate, evaporated to dry ness over 

 a water-bath, extracted with absolute alcohol and filtered. 

 The filtrate is then evaporated to dry ness on a water-bath, and 



