Dalton wondered why the heavier and lighter gases in the atmosphere did not separate as oil and water do. He finally concluded that the constituent of gases must exist in the form of  21  particles or atoms and that these must be completely mixed together in the  22 . This threw a new light in the laws of definite proportions. It was  23  necessary to suppose that the atoms could combine into small groups of uniform  24  and so form more complex substance;  25  the mystery of this law was solved. Dalton suggested, for example, that carbon monoxide is formed by the one with one  26  of atoms of carbon and oxygen,  27  carbon dioxide results from a single  28  of carbon uniting with two atoms of oxygen. Assuming this to be true, then the definite proportions of Prouts's low  29  all chemical compounds the different constituents always enter in unvarying proportions would naturally unit the relative weights of the many  30  kinds of atoms.