like, with the same letters; yet nature compounds them all of the same atoms of carbon, hydrogen, and oxygen, but in different proportions and in different orders. Chemistry is all-potent. A mechanical mixture of two or more elements is a simple affair, but a chemical mixture introduces an element of magic. No conjurer's trick can approach such a transformation as that of oxygen and hydrogen gases into water. The miracle of turning water into wine is tame by comparison. Dip plain cotton into a mixture of nitric and sulphuric acids and let it dry, and we have that terrible explosive, guncotton. Or, take the cellulose of which cotton is composed, and add two atoms of hydrogen and one of oxygen, and we have sugar. But we are to remember that the difference here indicated is not a quantitative, but a qualitative one, not one affecting bulk, but affecting structure. Truly chemistry works wonders. Take ethyl alcohol, or ordinary spirits of wine, and add four more atoms of carbon to the carbon molecule, and we have the poison carbolic acid. Pure alcohol can be turned into a deadly poison, not by adding to, but simply by taking from it; take out one atom of carbon and two of hydrogen from the alcohol molecule, and we have the poison methyl alcohol. But we are to remember that the difference here indicated is not a quantitative, but a qualitative one, not one affecting bulk, but affecting structure. In our atmosphere we have a mechanical mixture of nitrogen and oxygen, four parts of nitrogen to one of oxygen. By uniting the nitrogen and oxygen chemically (N_{2}O) we have nitrous oxide, laughing-gas. Ordinary starch is made up of three different elements--six parts of carbon, ten parts of hydrogen, and five parts of oxygen (C_{6}H_{10}O_{5}). Now if we add water to this compound, we have a simple mixture of starch and water, but if we bring about a chemical union with the elements of water (hydrogen and oxygen), we have grape sugar. This sugar is formed in green leaves by the agency of sunlight, and is the basis of all plant and animal food, and hence one of the most important things in nature.