248 PHYSIOLOGICAL CHEMISTRY 



4. Nitrogen. Mix a small portion of casein or meat with 

 soda lime in a test tube and warm gently in the flame. (Soda 

 lime is prepared by mixing solid sodium hydroxide and calcium 

 hydroxide and heating the mixture.) Nitrogen is liberated in the 

 form of ammonia. To detect this compound, moisten a piece of 

 litmus paper with distilled water and hold it in the mouth of the 

 tube. It should turn blue. 



Sulphur. Sulphur may be present as "loosely combined," 

 that is, unoxidized sulphur, or in oxidized form as sulphate. 



5. To detect loosely combined sulphur suspend a small amount 

 of casein in water, add sodium hydrate and a few drops of lead 

 acetate and boil. "Loosely combined" sulphur is split off, and 

 combines with the lead to form lead sulphide, which causes the 

 liquid to turn dark brown or black. Add sufficient hydrochloric 

 acid to make the solution acid, and hold in the mouth of the test 

 tube a strip of filter paper moistened with lead acetate solution. 

 The acid liberates hydrogen sulphide gas, which will precipitate 

 lead sulphide as a shiny dark material on the filter paper. 



6. Oxidized sulphur is usually present as sulphate. It is 

 detected by precipitation as barium sulphate. Sometimes sulphate 

 can be extracted from a tissue with water or dilute acid. Some- 

 times it is liberated only when the material is destroyed. ( See be- 

 low under the analysis of special tissues.) 



II. Prepare extracts of the following important tissues or 

 fluids and test them for inorganic constituents. Other tissues 

 may be substituted if desired. Directions for the specific tests 

 will be found in Section III, immediately following the methods 

 of preparing the extracts. 



Prepare each material for analysis, and so far as is possible, 

 complete the tests upon it before beginning work on another 

 material. 



7. Preparation of Muscle Extract. Heat 100 c.c. of distilled 

 water to boiling and add a small teaspoonful of chopped meat. 

 Dilute about 2 c.c. of 10% acetic acid with about 18-20 c.c. of 

 distilled water. The resulting acid will be about 1%. Acidify 

 the water and meat mixture by adding 2-3 drops of the 1% 



