Another characteristic protein test easily made at home is burning the substance. If it burns with the odor of burning feathers or leather, then protein forms part of its composition.[4]
A test of the cotyledon of a bean for protein food with nitric acid and ammonium hydrate shows us the presence of this food. Beans are found by actual test to contain about 23 per cent of protein, 59 per cent of carbohydrates, and about 2 per cent oils. The young plant within a pea or bean is thus shown to be well supplied with nourishment until it is able to take care of itself. In this respect it is somewhat like a young animal within the egg, a bird or fish, for example.
Beans and Peas as Food for Man.—So much food is stored in legumes (as beans and peas) that man has come to consider them a very valuable and cheap source of food. Study carefully the following table:—
| Nutrients Furnished for Ten Centsin Beans and Peas at Certain Prices per Pound | |||||
|---|---|---|---|---|---|
| Ten Cents will payfor— | |||||
| Food Materials as Purchased | Prices per Pound | Total Food Material | Protein[TN1] | Fat | Carbo- hydrates |
| Cents | Pounds | Pounds | Pounds | Pounds | |
| Kidney beans, dried | 5 | 2.00 | 0.45 | 0.04 | 1.19 |
| Lima beans, fresh, shelled | 8 | 1.25 | .04 | — | .12 |
| Lima beans, dried | 6 | 1.67 | .30 | .03 | 1.10 |
| String beans, fresh, 30 cents per peck | 3 | 3.33 | .07 | .01 | .23 |
| Beans, baked, canned | 5 | 2.00 | .14 | .05 | .39 |
| Lentils, dried | 10 | 1.00 | .26 | .01 | .59 |
| Peas, green, in pod, 30 cents per peck | 3 | 3.33 | .12 | .01 | .33 |
| Peas, dried | 4 | 2.50 | .62 | .03 | 1.55 |
A series of early stages in the germination of the kidney bean.
Germination of the Bean.—If dry seeds are planted in sawdust or earth, they will not grow. A moderate supply of water must be given to them. If seeds were to be kept in a freezing temperature or at a very high temperature, no growth would take place. A moderate temperature and a moderate water supply are most favorable for their development.
Bean seedlings. The older seedlings at the left have used up all of the food supply in the cotyledons.