CONTENTS. Elements-Notation-Nomenclature-Laws of Combination -Valency-Electrical Relations-Reactions-Radicles - Nature of Organic Bodies - Transformations and Decompo- sitions-Isomerism and Other Relations-Classification, Methanes - Alcohols - Aldehydes-Fat-Acids-Methenes- PAGE COMPEND OF CHEMISTRY. ELEMENTS. Chemistry is the science that investigates the composition of matter and the changes that take place in it. Matter is anything that occupies space and has weight. Changes may be physical or chemical. Physical change is in general that which occurs without change of composition. The most frequent instances of true physical change are those known as change of state. Matter exists in at least three states-the solid, liquid and gaseous. The conversion of a body from one of these conditions to the other takes place under the influence of change of temperature, and is not necessarily attended by any alteration of composition. Such is the case in the conversion of ice into water, or water into steam, or the reverse. The development of magnetic properties in iron is another example of a true physical change. In many cases the conversion of a solid into a liquid, or of a liquid into a gas is attended by change of composition, and, therefore, is not merely a physical change. Chemical change is that attended by alteration of composition. The rusting of iron, burning of coal, rotting of animal and vegetable matter, are familiar instances of chemical change. Forms of Chemical Change.-These are combination, decomposition and re-arrangement. Combination is the association of bodies to form a new substance. Decomposition is the separation of a body into new sub. stances. Re-arrangement refers to cases in which new bodies are formed without combination or decomposition. Decomposition cannot be carried on indefinitely. No matter what substance is taken for experiment, there will ultimately be reached bodies which are incapable of further decomposition by any method known to us. For example, chalk may by heat be decomposed into two substances, one a colorless gas, called carbon dioxide; the other a white powder, called calcium oxide, or, more commonly, lime. These products are different from the chalk and from each other, but they do not represent the limit of decomposition, for by special methods each can be made to yield two substances. The lime yields a solid (called calcium) and a gas called oxygen; the carbon dioxide yields a solid (called carbon) and a gas which is the same as that from the lime, namely, oxygen. The substances obtained in this second step are incapable of further decomposition by any known process. By proceeding in this way with all known substances chemists have determined the limits of decomposition, and have established that all material objects may be regarded as formed from a limited number of undecomposable substances. These are called elements. So far as at present known these elements are entirely independent forms, and are incapable of conversion into one another. About seventy-five elements are now known, and the number is from time to time increased by the discovery of new ones. Every substance must be either one of these elements or the result of a combination of two or more of them. Consequently all bodies are divided into two classes, elementary and compound. The main object of chemistry is to discover what elements are present in any body and what are the laws governing the action of the elements upon one another. Analysis and Synthesis.-When the composition of a body is determined by separating the elements contained in it, the process is called analysis; when bodies are produced by combining elements the process is called synthesis. Nature of the Elements.-A table of all the elements at present definitely known will be found at the end of the book. For the purpose of preliminary study it will be necessary to enumerate only a few, as many of the elements occur only in rare substances. For scientific purposes they are usually arranged in groups in which those bearing the closest resemblance are brought together. The following gives some of the more important groups, and the student will find it advantageous to commit these to memory, as the arrangement will aid in the study of compounds : : |