PART VI. FEEDING FARM ANIMALS 



EXERCISE 84 



PLANTS AS FOOD FOR ANIMALS 



Fig. 137. The food components of shelled 

 corn 



Statement. Plant substances are the original source of nourishment for animals. The science of 

 feeding rests upon our knowledge of these substances and of the needs of animals. Animal food 

 compounds are classified as water, ash, protein, fat, nitrogen-free extract, and crude fiber. 



Object. To determine the presence of some of the food compounds in plant and animal substances. 



Materials. Potato ; white of an egg ; balances ; evaporating dish ; nitric acid ; concentrated hydro- 

 chloric acid; ammonia; iodine solution; ether or gasoline; Fehling's solution; a-Naphthol solu- 

 tion; sulphuric acid; substances containing grape sugar or cane 

 sugar; other plant and animal substances to be tested. 



Directions. 1. Water. To determine the amount of water in a 

 plant substance weigh out a ten- or twenty-gram sample and dry it 

 for two or three hours in an oven at the temperature of boiling 

 water. Reweigh the sample, place it in the oven, and heat again. 

 Reweigh and continue heating and weighing until the weight be- 

 comes constant. The loss in weight is water. Compute and record 

 the percentage of water lost. Compute the percentage of dry matter 

 in the fresh sample. 



2. Ash. The sample after being dried is burned to a white ash. 

 Weigh and compute the percentage of ash on the basis of dry 

 substance; on the basis of fresh sample. Compute by difference 

 the percentage of organic matter in the dry substance ; compute 

 the percentage in the fresh substance. Compare results with those given in Appendix. 



3. Protein. Place some white of egg in a dish or test tube and add a few drops of nitric acid. 

 Note the color which appears. Heat the mixture slightly, rinse off the acid, and add ammonia. Note 

 again the color. The colors which appear indicate the presence of protein. Place a little nitric acid on a 

 piece of finger nail. A yellow color indicates protein. Test such substances as wheat flour, meat, and 

 milk for protein. 



4. Nitrogen-free extract. Nitrogen-free extract consists in part of sugars and starches. Sugars 

 may be detected by the taste in those substances which contain a large amount. To test for grape 

 sugar place a raisin or crystals of grape sugar in a test tube or dish and add water. Shake the 

 mixture and to a little of it add a drop of Fehling's solution and heat. Note the change in color. A 

 yellow to red color indicates the presence of grape sugar. 



To test for cane sugar or glucose proceed as follows : Place a piece of cane sugar or glucose not 

 larger than a pin head in a test tube. Add 4 or 5 drops of water and 2 drops of a ten per cent solu- 

 tion of a-Naphthol in chloroform. Add 2 c.c. of concentrated sulphuric acid in such manner as to 

 allow the heavy acid to form a separate layer at the bottom of the tube. Note the color of the ring 

 which forms. After a few minutes add 5 c.c. of water. What colored precipitate forms? 



To test for starch place a few drops of iodine solution on the cut surface of a vegetable such as the 

 potato. The blue color indicates the presence of starch. Test corn kernels, wheat, flour, rice, etc., for 

 starch. 



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