APR V.] SYSTEMATIC STUDY OF REACTION. 497 



exhibit it, and that unless the quantity of acid present be extra- 

 ordinarily small, the red colour of the dried stain is seen to be due 

 to extremely slender microscopic crystals. 



A solution of Resorcin, employed in the same manner as Giinz- 

 burg's reagent has been recommended by Boas 1 , and can be employed 

 in its stead. It is only influenced by free mineral acids and not by 

 the compounds of hydrochloric acid with the albuminous substances 

 or with organic bases. The solution employed is made by dissolving 

 3 grms. of resorcin and 3 grms. of cane-sugar in 100 grms. of spirits 

 of wine. 



2. ON THE SYSTEMATIC USE OF CERTAIN COLOUR REACTIONS IN 

 DETERMINING THE PRESENCE OF MINERAL AND ORGANIC ACIDS 

 IN THE STOMACH CONTENTS, AND ON THE QUANTITATIVE 

 ESTIMATION OF THE 'TOTAL ACIDITY' AND OF THE 'ACIDITY 

 DUE TO FREE ACIDS ' (MARTIUS AND LUTTKE) 2 . 



1. Determination of Reaction. Is hydrochloric acid present ? 



1. Litmus The contents of the stomach are tested with delicate 



blue litmus paper. It is, as has been said, only most 

 rarely that the reaction is found to be neutral or alkaline. 



If the reaction be acid, it may be due (a) to HCl only: (b) to 

 organic acids: (c) to a mixture of HCl and organic acids : (d) to acid 

 salts, or to a mixture of the latter with the acids previously referred 

 to. 



2. Congo- If paper stained with congo-red does not assume a 



blue colour, free acids are absent ; it follows that an 

 acid reaction previously observed with litmus must have been due to 

 .acid salts 



If congo-red is turned blue, the stomach contents contain either 

 free hydrochloric acid or free organic acids, or both. 



To determine whether hydrochloric acid is present, the phloro- 

 glucin-vanillin test should be employed. 



3. Phioro- If this reagent furnishes a negative, whilst congo- 

 giucin-vaniiiin. re( j f urn i s hed a positive, reaction, the acid or acids 

 present must be organic and no free hydrochloric acid be present. 



If the reaction be positive, the presence of free hydrochloric acid 

 is proved, whilst the simultaneous presence of organic acids is not 

 excluded. A judgment on the latter point can only be arrived 

 at, according to Martius and Liittke, by determinations of (1) total 

 acidity ; (2) the acidity due to free acids ; (3) the total quantity of 

 chlorine present; (4) the quantity of chlorine present as chlorides. 



1 Boas, 'Ein neues Reagens fiir den Nachweis freier Salzsaure im Mageninhalt,' 

 <Centralbl. f. klin. Med. 1888, No. 45. 



2 Op. cit. pp. 66, 67 and 115. 



G. 32 



