ADVANCED PHYSIOLOGICAL CHEMISTRY 447 



Estimation of Hydrochloric Acid present (Method of Morner and 

 Sjoqvist). 10 c.c. filtered gastric contents are placed in a silver 

 basin (although a good porcelain evaporating dish may do), and mixed 

 with pure powdered barium carbonate. The barium combines with the 

 hydrochloric acid to form barium chloride; and with a lactic acid to 

 form barium lactate. The whole is carefully evaporated to dryness on the 

 water bath, and the residue is incinerated over a free flame. By this 

 treatment the barium lactate is oxidized to barium carbonate, whereas 

 the chloride remains unchanged. After cooling, the residue is treated 

 with boiling water and filtered. The filtrate contains the barium 

 chloride. It is acidified with sulphuric acid and boiled, whereby 

 the barium is precipitated as barium sulphate. When the precipitate 

 has settled it is collected on an ash-free filter, dried, incinerated in 

 a platinum crucible, and the barium sulphate thus obtained weighed. 

 One molecule BaS0 4 equals two molecules HC1, or, expressed gravi- 

 metrically, 233 parts BaS0 4 correspond to 73 parts hydrochloric acid. 



As was mentioned on p. 222 the chief function of HC1 in the gastric 

 juice is to assist the action of pepsin. In doing so, the acid combines 

 with the proteid. The avidity of proteoses and peptones for the acid 

 is much greater than is that of native proteids; consequently, as 

 artificial digestion proceeds, and proteoses gradually accumulate in 

 the digest, the free acid gets less and less in amount. If the gastric 

 contents be removed, by means of a stomach tube, during the first 

 two hours after a proteid meal, however, no free HC1 can be detected 

 in them, but gradually makes its appearance later. This is because 

 the gastric glands continue to secrete HC1 till an excess is present, 

 whereas in an artificial digest no such addition is made. 



The usual method for quantitatively estimating the free acid is to 

 titrate it with a decinormal alkali using Glunzberg's reagent as indi- 

 cator. A much more accurate method, 1 however, is to compare the 

 amount of inversion measured by the polariscope of a cane sugar 

 solution which a measured quantity of filtered juice can produce with 

 the inversion which a known quantity of acid produces on a similar 

 cane sugar solution (i.e., of the same original dextro-rotatory power). 

 If the solutions be of the same volume, and both be incubated for the 

 same length of time, the calculation of the free acid in the unknown 

 solution is by simple proportion. 



Inversion in known sol. : Invers. in unknown sol. : : HC1 in known 

 sol. : X the amount of acid in unknown sol. 



1 This method depends on the fact that only free acid can exercise this catalytic 

 action which causes the inversion of cane sugar. The method was originally 

 worked out by Hofmann on Ostwald's suggestion. Details of its simpler appli- 

 cation are given in the Lancet, Vol. CLXV., p. 313. 



