GLYCOPROTEINS III 



c. Test for loosely combined sulphur in collagen. Heat with the alkali 

 until the large piece of collagen used is partly decomposed, then add one or 

 two drops of lead acetate and again heat to boiling. 



d. Try Millon's reaction, the biuret test, the xanthoproteic reaction, and 

 the Hopkins-Cole reaction. 



e. Formation of gelatin from collagen. Transfer the remainder of the 

 collagen to a casserole, fill about two-thirds with water, and boil for several 

 hours, replacing enough of the water that is lost by evaporation to keep the 

 pieces well covered. Filter and cool. Collagen is transformed into gelatin 

 and the characteristic gel is obtained. Try this experiment also with some 

 cartilage from the trachea and with some 0.2 per cent. HC1 extracted bone. 



/. The properties of gelatin. Try the solubility as in a above on some 

 gelatin furnished by the instructor. Try the solubility also in hot water. 



g. Try the tests for loosely combined sulphur. Try Millon's Hopkins- 

 Cole, and the biuret reactions. Try the solubility in artificial gastric and 

 pancreatic juices. 



8. Elastin. a. Preparation of Elastin. Cut the ligamentum nuchce of, 

 the ox into strips and run it through a meat chopper. Wash the finely 

 divided material with salt solution and in running water for some hours. 

 Transfer it to a flask and add about 200 c.c. of half-saturated lime-water and 

 extract for forty-eight hours. Filter off the lime-water which has dissolved 

 the mucoid present, saving the filtrate, and wash the residue and tendon with 

 water. Boil the material in dilute acetic acid for some hours to convert the 

 collagen present into gelatin. Wash the residue thoroughly with water. It 

 may be dried by washing it with boiling alcohol, pressing it out between 

 filters, and manipulating it in the air. 



b. Try the solubility of elastin as in a. Test for loosely combined 

 sulphur. Try Millon's, biuret, and the Hopkins-Cole reactions. Try the 

 solubility in artificial gastric and pancreatic juices. 



c. Make a table comparing the properties of keratin, collagen, and elastin. 



GLYCOPROTEINS. 



9. Mucoid. a. Unite the lime-water of filtrates obtained in the extraction 

 of the tendons in the preceding experiment and acidify them with dilute 

 acetic acid until precipitation occurs. The mucoid is precipitated. Avoid 

 adding excessive acid or the mucoid will again go into solution. Allow the 

 mucoid precipitate to settle and decant the supernatant fluid and filter off 

 the precipitate. 



b. Try the biuret test on a portion of the mucoid. 



c. Place the remainder of the mucoid in a beaker, add about 25 c.c. of 

 water and 2 c.c. of dilute hydrochloric acid; boil until the solution becomes 

 dark. To a portion of the mixture add a few drops of barium chloride. A 



