PREPARATION OF N/10 HYDROCHLORIC ACID 



15 



4. Tenth Normal Acid and Alkali. From the half normal stock 

 solutions of hydrochloric acid and sodium hydroxide, prepare 

 1000 c.c., .1 N hydrochloric acid and .1 N sodium hydroxide. The 

 solutions so obtained should be equivalent. 



This extremely accurate method depends on the fact that when 

 hydrochloric acid solution is distilled at 760 mm. pressure the con- 

 centration of HC1 in the undistilled portion approaches 20.24 per 

 cent. When this is reached further distillation yields a distillate 

 also containing HC1 of this concentration. To prepare stock HC1 

 solution for standards, add to concentrated HC1 (sp. gr. 1.2) an 

 equal volume of water and bring to a density at 25 of 1.096 

 (see " Pycnometers ") by addition of more water or concentrated 

 HC1. Distill off three-quarters of this mixture. The remaining 

 one-quarter has within 1 part in 10,000 the following composition: 



STANDARDIZATION OF OXIDIZING SOLUTIONS 



General Principle. Many substances exist in two states of 

 oxidation; i.e., iron in ferrous sulphate (FeSCU), and ferric sul- 

 phate Fe2(SO4)3, or arsenic in sodium arsenite (NasAsOa) and 

 sodium arsenate (NaaAsO^, etc. These substances may readily 



1 Medical War Manual, No. 6, 1918, p. 78. 



