SALIVARY DIGESTION. 57 



turn, with alcohol and ether. Finally dry the precipitate, remove it 

 from the paper and make the following tests on the mucin : (a) 

 Test its solubility in the ordinary solvents (see page 23), (b) 

 Millon's reaction, (c) dissolve a small amount in KOH, and try 

 the biuret test on the solution, (d) boil the remainder, with 1025 

 c.c. of water to which 5 c.c. of dilute HC1 has been added, until 

 the solution becomes brownish. Cool, render alkaline with solid 

 KOH, and test by Fehling's solution. A reduction should take 

 place. Mucin is what is known as a conjugated protein or glyco- 

 protein (see p. -87) and upon boiling with the acid the carbohydrate 

 group in the molecule has been split off from the protein portion 

 and its presence is indicated by the reduction of Fehling's solution. 



8. Inorganic Matter. Test for chlorides, phosphates, sulphates 

 and calcium. For chlorides, acidify with HNO 3 and add AgNO 3 . 

 For phosphates, acidify with HNO 3 , heat and add molybdic solu- 

 tion. 1 For sulphates, acidify with HC1 and add BaCl 2 and warm. 

 For calcium, acidify with acetic acid, CH 3 COOH, and add ammon- 

 ium oxalate, (NH 4 ) 2 C 2 O 4 . 



9. Viscosity Test. Place filter papers in two funnels, and to 

 each add an equal quantity of starch paste (5 c.c.). Add a few 

 drops of saliva to one lot of paste and an equivalent amount of 

 water to the other. Note the progress of filtration in each case. 

 Why does one solution filter more rapidly than the other ? 



10. Test for Nitrites. Add 1-2 drops of dilute H 2 SO 4 to a 

 little saliva and thoroughly stir. Now add a few drops of a potas- 

 sium iodide solution and some starch paste. Nitrous acid is formed 

 which liberates iodine, causing the formation of the blue iodide of 

 starch. 



11. Thiocyanate Tests. (a) Ferric Chloride Test. To a little 

 saliva in a small porcelain crucible, or dish, add a few drops of 

 dilute ferric chloride and acidify slightly with HC1. Red ferric 

 thiocyanate forms. To show that the red coloration is not due to 

 iron phosphate add a drop of HgCl 2 when colorless mercuric thio- 

 cyanate forms. 



(b) Solera's Reaction. This test depends upon the liberation 

 of iodine through the action of thiocyanate upon iodic acid. Moisten 



1 Molybdic solution is prepared as follows, the parts being by weight : 



i part, molybdic acid. 



4 parts, ammonium hydroxide (Sp. gr. 0.96). 

 15 parts, nitric acid (Sp. gr. 1.2). 



