_Sulphur_ is present in protein and we get a sufficient supply from milk, meat and legumes. The element sulphur is quite inert and harmless, but some of its acids and salts are very poisonous. Sulphur dioxide is freely used in the process of drying fruits, as a bleacher. In this form it is poisonous, and for that reason it would be well to avoid bleached dried fruits. We need some sulphur, but not in the form of sulphur dioxide or concentrated sulphurous acid, both of which are used in the manufacture of food. _Sodium_, in its elementary state, which is not found in nature, is a white, silvery metal. It is found in great abundance in the succulent vegetables, and is present in practically all foods. As sodium chloride, or common table salt, it is taken in great quantities by most people. Those who have no salt get along well without it, which shows that it is not needed in large amounts. If but a little is added to the food, it does no perceptible harm, but when sprinkled on everything that is eaten, from watermelons to meat, it is without doubt harmful. By soaking foods, they are deprived of much of their soda: The two sodium salts that are very abundant are sodium chloride, or common salt, and sodium carbonate, generally called soda. _Chlorine_ is ordinarily combined in our foods with sodium or potash, forming the chlorides. It is essential to life. He who gets enough sodium also gets enough chlorine. In its elementary form it is an irritating gas, used for bleaching purposes. _Fluorine_ is present in small quantities in the body, appearing as fluorides in the bones and teeth. It is supplied by the various foods. In its elementary form it is a poisonous gas. _Potassium_ is found in the body in very small quantities, but it is very important. It is mostly in the form of potassium phosphate in the muscles and in the blood. It is necessary for muscular activity. It is found in most foods in greater abundance than is sodium, which indicates that it plays an important part in development. Like sodium, it is easily dissolved out of foods which are soaked in water, and this is one of the reasons that vegetables should not be soaked and the water thrown away. It is very peculiar in its metallic state, being a silvery metal, very light in weight, which burns when thrown upon water. That is, it decomposes both itself and the water with the liberation of so much heat that it fires the escaping hydrogen, which burns with a violet flame. Pure potassium is not found in nature.