_To show that Carbohydrates contain Carbon, Hydrogen, and Oxygen._—Place one half teaspoonful of powdered starch in a test tube and heat strongly. Observe that _water_ condenses on the sides of the tube and that a black, charred mass remains behind. The black mass consists mainly of _carbon_. The water is composed of hydrogen and oxygen. These three elements are thus shown to be present in the starch. The experiment may be repeated, using sugar instead of starch. _To show that Proteids contain Carbon, Hydrogen, Oxygen, Nitrogen, and Sulphur._—Place in a test tube some finely divided proteid which has been thoroughly dried (dried beef or the lean of hard cured bacon). Heat strongly in the hood of a chemical laboratory or some other place where the odors do not get into the room. First hold in the escaping gases a wet strip of red litmus paper. This will be turned blue, showing _ammonia_ (NH3) to be escaping. Next hold in the mouth of the tube a strip of a paper wet with a solution of lead nitrate. This is turned black or brown on account of _hydrogen sulphide_(H2S) which is being driven off. Observe also that _water_ condenses in the upper part of the tube and that a black, charred mass remains behind. Since the products of decomposition (H2O, NH3, H2S, and the charred mass) contain hydrogen, oxygen, nitrogen, sulphur, and carbon, these elements are of course present in the proteid tested. _To show the Presence of Mineral Matter._—Burn a piece of dry bread by holding it in a clear, hot flame, and observe the ash that is left behind. This is the mineral matter present in the bread. *Tests for Nutrients.* _Proteids._—Cover the substance to be tested with strong nitric acid and heat gradually to boiling. If proteid is present it turns yellow and partly dissolves in the acid, forming a yellow solution. Let cool and then add ammonia. The yellow solid and the solution are turned a deep orange color. Apply this test to foods containing proteid such as white of egg, cheese, lean meat, etc. _Starch._—_(a)_ Place a small lump of starch in one fourth of a pint of water and heat gradually to boiling, stirring well. Then add enough water to form a thin liquid and fill a test tube half full. Add to this a few drops of a solution of iodine. (Prepare by dissolving a crystal of iodine in 25 cubic centimeters (1/20 pint) of a solution of potassium iodide in water and add water to this until it is a light amber color.) The starch solution is turned blue, _(b)_ Cut with a razor a thin slice from a potato. Place this in a weak solution of iodine for a few minutes and then examine with the microscope, using first a low and then a high power. Numerous starch grains inclosed in cellulose walls will be seen (Fig. 60).