22 BIOLOGY 



LABORATORY WORK WITH ORGANIC COMPOUNDS 



PROTEIDS 



Albumen. Separate a little of the white from the yolk of an egg and 

 dilute with three times its quantity of water. With this solution make 

 the following tests: 



1. Place a little of the albumen solution in a test tube and boil, noting 

 that a precipitate appears; that is, the albumen coagulates. Repeat this 

 test, heating the albumen in a test tube in a water bath, determining, 

 by a thermometer placed in the test tube, at what temperature the coagu- 

 lation occurs. 



2. Add a little strong HNOs to some of the albumen in a test tube. 

 A precipitate appears. Boil, and the precipitate will turn yellow. Allow 

 it to cool and add enough ammonia to neutralize the acid and it will turn 

 a deep orange. This is known as the xanthoproteic test for proteids. 



3. To a weak solution of albumen add a few drops of NaOH and a 

 few drops of a 1% solution of CuSO 4 ; heat gently and the solution will 

 turn blue if ordinary proteids are present, but if peptones are present it 

 will show a reddish color. 



Gluten. Place some flour in a large piece of cheesecloth, and gather- 

 ing up the edges of the cloth, wash thoroughly in a pail of water. Much 

 of the bulk of the flour will wash away, but the gluten will finally be left 

 in the cloth, as a sticky mass that will not wash out. 



Remove a little of the wash water from the pail in a test tube and add 

 a few drops of iodine to it. If it turns blue it will indicate the presence 

 of starch. 



Casein. Add a little 2% HCL to a few c. c. of milk. A curd will form 

 which can be separated from the liquid by allowing it to drain through 

 cheesecloth. The curd is the proteid, casein. 



Myosin. Soak some chopped beef in cold water for half an hour; 

 stir and filter through cheesecloth. Boil the filtrate, and a mass of myosin 

 will appear, which was dissolved in the cold water but is coagulated by 

 heat. 



Fibrin. This is a proteid formed from blood. It may be obtained by 

 collecting freshly drawn blood and stirring it immediately with a piece 

 of wire gauze for about ten minutes. A mass of fibrin will collect on the 

 wire, and it will be found that the blood will not subsequently clot, the 

 removal of the fibrin preventing it. 



CARBOHYDRATES 



Starch. Rub up a little starch (potato starch is best) in an evaporating 

 dish with a considerable quantity of water. Place a few drops in a test 

 tube and add a little iodine solution. The starch will turn blue. 



