I 24 PHYSIOLOGICAL CHEMISTRY. 



3. Boas' Reagent. 1 Perform this test in the same manner as 

 2, p. 123. Free hydrochloric acid is indicated by the production 

 of a rose-red color which becomes less pronounced on cooling. 



4. Congo Red, 2 



NH 2 SO 3 Na 



X s 



NH 2 



Conduct this test according to the directions given under i or 2, 

 page 123. A blue color indicates free hydrochloric acid, a violet 

 color indicates an organic acid and a brown color indicates com- 

 bined hydrochloric acid. Congo red paper, made by immersing 

 ordinary filter paper in the indicator and subsequently drying, may 

 be used in this test. 



5. Tropaeolin OO, 3 



NH(C 6 H 5 ) -C 6 H 4 -N =^ N-C 6 H 4 -S0 3 Na. 



Place 2 drops of the solution to be tested and i drop of the indicator 

 in an evaporating dish and evaporate to dryness over a low flame. 

 The formation of a reddish-violet color indicates free hydrochloric 

 acid. 



This test may also be conducted in the same manner as 2, page 

 123. 



6. Phenolphthalein, 4 



C 6 H 4 OH 

 / 



C-C G H 4 OH 

 / \ 

 C 6 H 4 O 



\/ 



C 

 \ 

 O 



Add the indicator directly to the solution, or apply the test ac- 



1 Boas' reagent is prepared by dissolving 5 grams of resorcin and 3 grams of 

 sucrose in 100 c.c. of 95 per cent alcohol. 



2 This indicator is prepared by dissolving 0.5 gram of congo red in 90 c.c. of 

 water and adding ID c.c. of 95 per cent alcohol. 



3 Prepared by dissolving 0.05 gram of tropseolin OO in 100 c.c. of 50 per cent 

 alcohol. 



4 This indicator is prepared by dissolving i gram of phenolphthalein in 100 c.c. 

 of 95 per cent alcohol. 



