10. Sulfur

Sulfur is a common and familiar substance. As an element it is not widely distributed in nature, but its compounds are found in all soils and natural waters, and in all the higher forms of animal and vegetable life. We know it as "brimstone" when fused in sticks, and as "flowers of sulfur" when sublimed in a finely divided form. Its most common commercial compounds are sulfuric acid and the sulfates of potash, soda, lime, and magnesia. This element is an essential part of some of the most important animal tissues, and is supplied in food in the form of the sulfates and in its protein combinations.

11. Phosphorus

Phosphorus occupies an important place among the elements of nutrition. In the uncombined form it does not exist in nature, as that found in laboratories is produced only by chemical means. Its compounds are found everywhere. The phosphates of calcium and magnesium are widely distributed in soils, and large deposits of calcium phosphate are known, from which is obtained the crude phosphatic rock that serves as a basis for the manufacture of commercial fertilizers. All foods in their natural forms contain phosphorus, combined in certain fats and nitrogen compounds which stand in close relation to the vital processes. It is distributed in the flesh of man and, combined with calcium and oxygen, constitutes a large part of bone.

12. Chlorine

Chlorine, which is a constituent of common salt, is essential to human nutrition. At ordinary temperatures it is, in the free state, a greenish-colored, disagreeable gas. When combined with hydrogen, it forms hydrochloric acid, a compound which is necessary to the digestion of food.

13. Potassium

Potassium, combined with oxygen and hydrogen, gives us the caustic potash of the market. The ashes of all plants contain this element, a familiar illustration of this fact being the potassium carbonate leached from wood ashes by hot water in the old-fashioned way of making soft soap. The saleratus formerly used in bread-making was a potassium compound. This element is found in the flesh of animals, mostly in the form of the phosphate, and is abundantly supplied for the purposes of nutrition by dietaries that are not too largely made up of artificially treated foods.

14. Sodium

Sodiumis the basal element of common salt (sodium chloride); and this is about the only sodium compound we need to mention, for this is the one that serves almost wholly as a source of this element to human food. Sodium plays an important part in the digestion of food, because it is the basis of certain bile salts and is concerned in other ways in the digestive processes.

15. Calcium

Calcium, when united with oxygen, forms lime, which is one of our commonest commercial articles. Large masses of lime rock, or calcium carbonate, exist in many parts of the earth's surface, and every soil contains more or less of lime compounds. As compounds of this element are always found in plants and in the milk of all animals, a mixed diet of unmodified vegetable and animal foods nearly always furnishes a supply sufficient to meet the demands of animal life. The growing child makes a generous use of lime, because in union with phosphoric acid it is the chief building material of the bony framework. A deficiency of food lime is sure to cause abnormal development of the bony structures.

16. Iron

Iron, one of the elements of living organisms, needs no description, because its common properties are familiar to every one. Iron rust and iron ore are oxides of this element, and when the oxygen is removed from these, we have the bright gray metal of commerce. Though taken uP by plants and animals in small quantities only, iron is absolutely essential to their growth and welfare, but because of its abundance the imperative character of the demand is never realized in ordinary experience. It is intimately related to the life processes of the human organism.