6O PHYSIOLOGICAL CHEMISTRY. 



tubes place 4 c.c. of starch paste and J4 c.c. of one of the solutions 

 named below. Shake well, add ^4 c.c. of saliva to each tube, thor- 

 oughly mix, and place on the water-bath at 40 C. for 10-20 

 minutes. Show the progress of digestion by means of the iodine 

 and Fehling tests. Use the following chemicals : Metallic salts, 

 10 per cent plumbic acetate, 2 per cent cupric sulphate, 5 per cent 

 ferric chloride, 8 per cent mercuric chloride; Neutral salts, 10 per 

 cent sodium chloride, 10 per cent magnesium sulphate, 3 per cent 

 barium chloride, 10 per cent Rochelle salt. Also try the influence 

 of 2 per cent carbolic acid, 95 per cent alcohol, and ether and chlor- 

 oform. What are your conclusions? 



19. Excretion of Potassium Iodide. Ingest a small dose of 

 potassium iodide (0.2 gram) contained in a gelatin capsule, quickly 

 rinse out the mouth with water and then test the saliva at once for 

 iodine. This test should be negative. Make additional tests for 

 iodine at 2 minute intervals. The test for iodine is made as fol- 

 lows : Take i c.c. of NaNO 2 and i c.c. of dilute HoSCV in a test- 

 tube, add a little saliva directly from the mouth, and a small amount 

 of starch paste. If convenient, the urine may also be tested. The 

 formation of a blue color signifies that the potassium iodide is 

 being excreted through the salivary glands. Note the length of 

 time elapsing between the ingestion of the potassium iodide and 

 the appearance of the first traces of the substance in the saliva. 

 The chemical reactions taking place in this experiment are indicated 

 in the following equations : 



(a) 2NaN0 2 + H 2 S0 4 = 2HN0 2 + Na 2 S0 4 . 



(b) 2KI + H 2 SO 4 = 2HI + K 2 S0 4 . 



(c) 2HN0 2 + 2HI = I 2 + 2H 2 + 2NO. 



20. Qualitative Analysis of the Products of Salivary Diges- 

 tion. To 25 c.c. of the products of salivary digestion (saved from 

 Experiment 12 or furnished by the instructor), add 100 c.c. of 

 95 per cent alcohol. Allow to stand until the white precipitate has 

 settled. Filter, evaporate the filtrate to dryness, dissolve the resi- 

 due in 5-10 c.c. of water and try Fehling's test (page 27) and the 

 phenylhydrazine reaction (see Dextrose, 3, page 24). On the dex- 

 trin precipitate try the iodine test (page 44). Also hydrolyze the 

 dextrin as given under Dextrin, 4, page 48. 



1 Instead of this mixture a few drops of HNO 3 possessing a yellowish or 

 brownish color due to the presence of HNO 2 may be employed. 



