22 BULLETIN 784, U. S. DEPARTMEIN'T OE AGRICULTURE. 



Sources of inforiTiation. — Farmers' Bulletin 295 ; Office of the Secre- 

 tary Circular 106; Department Bulletin 468; bulletins from State 

 college of agriculture. 



Illustrative Tnaterial. — Construct a chart showing the composition 

 of the potato; another showing the food value of the potato when 

 compared with other foods. Samples of potato starch, alcohol, 

 potato flour, and other products obtained from the potato. 



Class exercises. — The following topics are suggested for attention 

 in this lesson : 



1. Composition of the potato — Water, starch, protein, crude fiber, 

 fat, ash. Use iodin test for starch ; use nitric acid and ammonia test 

 for protein. Put a bit of potato on a piece of paper and put it into 

 the oven or on top of a stove which is not hot enough to burn the 

 paper. After heating hold pap6r up to light and see whether you 

 can note any evidence of fat. 



2. Uses of the potato — Potato starch, industrial alcohol, potato 

 flour, glucose, siriip, mucilage, stock feed, and human food. Study 

 briefly the minor uses mentioned above and the methods of making 

 the products. Primarily, the chief attention should be given to the 

 use of the potato as a human food. 



3. The potato as a human food — {a) Food values, chiefly a 

 starch food, but contains some protein and mineral matter. 



(&) Advantages as a food — Furnishes an abundant supply of 

 nutrients at a relatively low price; supplies nutrients in an easily 

 digestible form ; adds bulk to the food eaten. 



{c) Textures of flesh in cooked potato — Soggy, usually rather low 

 in starch and relatively high in protein ; waxy, a greater proportion of 

 starch to protein ; mealy, starch content high, protein relatively low. 



{d) Place in the general diet — Potatoes represent 3.9 per cent of 

 the total cost of food, furnish 5.3 per cent of the total calories, 4.2 per 

 cent of the total protein, 8.7 per cent of the total phosphorus, and 

 13.5 per cent of the total irpn. Since phosphorus and iron com- 

 pounds are as important to include in the dietary as protein and fuel 

 foods, it is seen that for the small percentage of money expended for 

 potatoes a generous supply of nutrients is obtained. 



(e) Cooking — (1) Effects of cooking; transforms water into 

 steam, expanding breaks down starch cells and free starch grains, 

 coagulates the protein, affects minerals only slightly. Baking and 

 steaming from all points of view are the best methods of cooking 

 potatoes. (2) Losses in cooking; in paring, both by cutting away 

 valuable material and exposing the soluble substances to the action of 

 the water; in exposing a large amount of surface to the water; in 

 soaking before cooking ; in the use of cold water at the beginning of 

 the cooking. (3) Recipes for using potatoes. Here a number of 



