350 



FOOD AND NUTRITION 



products, jn cheese and butter, and in eggs. The skin, hair, and 

 nails contain protein substances. Wool and leather, glue and 

 gelatin also contain protein substances. The white of egg is 

 nearly pure protein mixed with water. Milk is a mixture of pro- 

 tein, fat, carbohydrate, mineral matter, and water, while cheese 

 is a mixture of the same substances but with less water. 



The proteins are the most expensive of the food principles. 

 Animal bodies are generally rich in proteins and poor in car- 

 bohydrates,, while the cereals are relatively poorer in proteins 

 but rich in carbohydrates. 



Exercise 78. Tests for Proteins 



1. THE BURNING TEST. Because of the nitrogen they contain, 

 protein substances burn with a characteristic odor, that of burnt 

 hair. Burn a little wool and note the odor. Compare it with the 

 odor arising from burning cotton. Heat a 

 little wheat flour and dried beef in separate 

 evaporating dishes or crucibles. Note the 

 odor of the burning materials. 



2. THE AMMONIA TEST. When protein 

 substances are heated with lime (calcium hy- 

 droxide, not the solution, but the dry ma- 

 terial) ammonia is produced. The ammonia 

 may be identified either by its odor or by 

 the fact that it turns moist red litmus paper 

 blue. Place small equal amounts of dry gela- 

 tin and lime in a test tube and mix them. 

 Heat the mixture strongly, holding a piece 

 of moist red litmus paper in the gases escap- 

 ing from the tube (Fig. 246). Be careful 

 that the paper does not touch the side of the 

 tube where it may meet lime which would turn the paper blue just 

 as the ammonia does. When you get a strong test for ammonia, note 

 the odor of the gases escaping from the tube. Disregard the odor of 

 burnt hair and give attention only to the ammonia. Ammonia was 

 formerly made almost entirely by heating animal products with lime. 

 The ammonia was called SPIRITS OF HARTSHORN because the horns 

 of the hart deer were frequently used as the animal substance. (See 

 Art. 194.) 



3. THE NITRIC ACID TEST. Place a little dry gelatin in a test 

 tube and moisten it with a single drop of concentrated nitric acid. 



FIG. 246. Test for 

 proteins. 



