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 IV ATOMIC WEIGHTS, SYMBOLS, FORMULA, AND EQUATIONS We have repeatedly called attention to the quantities of the substances taking part in chemical changes, and particularly to the constant relation between the weights of each element in a given substance (pp. 17-18). This matter is of great importance in chemistry. If a cargo of copper ore is to be purchased, we do not wish to pay for the rock that all specimens of the ore contain in larger or smaller proportion. So we secure a fair sample of the ore and have an analysis made by a chemist. The analysis, in this case, is a measurement of the proportion of the valuable metal in the sample. The price will then depend largely upon the proportion of the copper per ton of ore. The making of analyses — that is, chemical measurements — plays a very large part in all industries which involve the consumption or manufacture of materials. Quantitative measurements, aside from their theoretical interest, are therefore of the greatest practical importance. Hence we must now discuss them once more. The Compositions of Substances. — Our present purpose is to compare the proportions by weight of the elements composing several compounds, in order to see whether the numbers are really as irregular as, in the examples we have heretofore given, they have appeared to be, or whether there is any way of relating and simplifying the numbers. In order to have a fair sample of these proportions, we shall include the compositions of a few substances for which the data have not yet been given. Potassium hydroxide (p. 35) has the composition: potassium (a metal) 39.1, oxygen 16, hydrogen 1.008, in a total of 56.108 parts. Water (oxide of hydrogen) contains: oxygen 16 and hydrogen 2.016 parts by weight. When iron burns in chlorine, which is...