THE FRACTIONAL METHOD OF GASTRIC ANALYSIS 219 



pink color is obtained and persists for about two minutes. 1 Take 

 the burette reading and calculate the total acidity. 



Calculation. Note the number of cubic centimeters of N/100 

 NaOH required to neutralize 1 c.c. of stomach contents, and 

 multiply it by 10 to obtain the number of cubic centimeters N/10 

 NaOH necessary to neutralize 100 c.c. of stomach contents. This 

 is the method of calculation most widely used. 



(6) Determination of Free Acidity. The reagent most widely 

 used, clinically, for the determination of free hydrochloric acid 

 in stomach contents is Topfer's reagent. It has been found, 

 however, that this reagent gives rather inaccurate results due to 

 the uncertain end-point. For this reason Sahli's reagent is 

 employed. This reagent contains KI and KIOs and liberates 

 iodine in the presence of free hydrochloric acid. The liberated 

 iodine is titrated by thiosulphate, using starch as an indicator. 

 It gives values similar to Topfer's reagent in average acidities. 

 Acidities other than free hydrochloric react to a certain extent 

 with Sahli's reagent, so that, for example, high results are obtained 

 after the ingestion of acid fruits. 



Procedure. Measure 1 c.c. of the strained stomach contents 

 by means of an Ostwald pipette and introduce it into a 60 c.c. 

 porcelain evaporating dish. Dilute with 10 c.c. of distilled water, 

 and add 1 c.c. of Sahli's reagent (a mixture of equal parts of 48 

 per cent KI and 8 per cent KIOs). Allow the stomach contents 

 thus treated to stand for five minutes and then titrate with N/100 

 sodium thiosulphate until only a faint yellow color remains. Now 

 add 5 to 10 drops of a 1 per cent solution of soluble starch and 

 continue the titration until the blue color disappears. In serial 

 titrations the same procedure may be employed as described in 

 note below. 



1 Procedure for Serial Titrations. When a series of titrations are to be 

 made the following procedure may be used: Arrange the numbered evapo- 

 rating dishes in rows on a tray. Introduce 1 c.c. of the proper sample into 

 each dish, dilute with 10 c.c. of water and add the indicator. Add the N/100 

 NaOH to contents of dish No. 1 at a definite rate until a point is reached 

 at which a faint pink color is obtained, as described above. Return dish 

 No. 1 to its place in the tray and place dish No. 2 under the burette. Take 

 the burette reading of No. 1. Then titrate No. 2 in the same way. Continue 

 the series. This procedure has the advantage of being speedy and accurate. 

 There is a slight error made by the rapid addition of the NaOH but it is uniform 

 and the results (titrations) are therefore comparable. 



