48 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



in a porcelain dish. Free acid is shown by a rose or vermil- 

 ion color. 



/XX /(OH), 



6. Alizarin, C 6 H 4 < >C 6 H< 



XXX \S0 3 Na 



Add 2 or 3 drops of the indicator directly to the solution. 



The color will be yellow in acid and acid salt solutions, but 

 red to violet in alkaline. This indicator is especially suited 

 for the determination of the acidity of the urine by titration. 



/C 6 H 4 OH 



7. Phenolphthak'in, C 6 H 



Add 4 drops of the indicator directly to the solution. 



The indicator is colorless in neutral and acid reactions, but 

 becomes red in the presence of alkalies. It shows the pres- 

 ence of free, combined, mineral, and organic acids, and acid 

 salts of all kinds. It therefore gives the total acidity. It 

 may indicate an acid reaction when dimethylaminoazoben- 

 zene shows alkaline. Explain this. 



The Inverting Action of HCL f 



To 5 c.c. of a 5 per cent cane-sugar solution add 5 c.c. of 

 1 per cent HC1 and place the mixture in the water-bath for 

 an hour at 40 C. At the end of this time cool, neutralize, 

 and test the reducing power of the mixture. Explain the 

 result. 



LACTIC ACID, CH 3 .CH(OH)-C^ OH - 



Although this substance is commonly considered as an 

 abnormal constituent of the stomach contents it may exist 



