General Chemistry for Colleges Author:Alexander Smith Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER III INTRO DUCTOKY HI The Law of Definite Proportions, Fifth Characteristic of Chemical Phenomena. — The ways of forming or decomposing a compound, or... more » of carrying out a more complex chemical change, may be varied indefinitely. The apparatus, the mode of experiment, and the proportions of the materials, may be altered at our will. But, in spite of an enormous amount of careful work, no case of variation in the proportion of the constituents actually used or produced in a given chemical action has come to light. If too much of one constituent, for example, is taken, a part simply remains unchanged. In every sample of each compound substance formed or decomposed, the proportion by weight of the constituents is always the same. This statement of fact is known as the law of definite proportions. Another form of statement, which is applicable more directly to complex chemical actions, is: The ratio by weight of any one of the factors or products of a chemical change to any other is constant. The Measurement of Combining Proportions. — The most exact measurement of the proportions in which the elements combine to form compounds involves manipulations too elaborate to be gone into here. One or two brief statements, diagrammatic rather than accurate, will show the principles, however. If we take a weighed quantity of iron in a test-tube and heat it with more than enough sulphur (an excess of sulphur), we get free sulphur along with the ferrous sulphide (pp. 6-7), and no free iron survives. We may remove the free sulphur by washing the solid with carbon disulphide. The difference between the weights of ferrous sulphide and iron gives the amount of sulphur combined with the known quantity of the latter. As an example of the study of rusting, we may weigh a small amount of...« less