The book has been written for college Freshmen, and, as its title implies, it is intended to serve as an introduction to general chemistry. In consequence we have aimed to present a continuous and connected story in teachable form and have not attempted to give extensive descriptive and numerical data where such matter is of little interest to the student or is not needed for the development of important principles.
Inasmuch as the choice and arrangement of topics in the earlier part of this book depart noticeably from the familiar order, some explanation seems necessary. We shall therefore sketch briefly the plan of the less conventional chapters, together with the "philosophy of arrangement" which has resulted in the scheme presented.
The first chapter, which is brief, deals with the measurement of gases and the gas laws. In the next five chapters the most fundamental concepts of the science of chemistry are developed. These include: indestructibility of matter, idea of a pure substance, decomposition of pure substances, elements, analysis of substances and percentage composition, the law of definite composition, derivation of formulae.
Chapter V shows how chemical formulae are derived from a knowledge of percentage composition and gas or vapor density. This development keeps as close as possible to the arguments of Avogadro and Cannizzaro and shows how formulae are obtained by methods independent of the atomic-molecular hypothesis.
Reference, at this stage, to combining weights and chemical equivalents is purposely avoided, for the reason that the history of chemistry between the time of Avogadro and that of the epoch-making paper of Cannizzaro (1858) shows the fallacy of trying to develop formulae and fix atomic (symbol) weights by any method other than that proposed by Avogadro and elucidated by Cannizzaro.
The sixth chapter introduces the use of equations before the atomic-molecular hypothesis is studied. This plan has the great advantage of fixing in the student's mind the fundamental relationship between equations and the quantitative experimental data such equations represent.
Chapters II to VI inclusive form a compact division of the subject, in which the argument, illustrated at every step by experimental data, is substantiall continuous. In these chapters, we have aimed at a logical development of the subject without the introduction of any matter that does not serve to illustrate the topics under discussion.
The next three chapters, VIIi," Acids,Bases, and Salts" I"; VIIi,"Water and Solutions"; and IX," Acids, Bases, and Salts" II," are introduced at this point for very definite reasons.
In the first place, it is obvious to every teacher that much of the beginner's work will deal with acids, bases, and salts and their solutions. It is our opinion that a knowledge of these topics is best obtained by studying them directly and specifically, both in the classroom and in the laboratory. Our plan provides for laboratory work by the student, following closely the content of these three chapters.
This laboratory work is interestint go students, since they like to make and crystallizea variety of salts. It also gives good trainingin technique and is not difficult either experimentally or theoretically, while at the same time it offers a wealth of material for practice in writing equations and solving problems. The most important reason, however, for the introduction of the early study of acids, bases, and salts is to supply the indispensable data needed later for the understanding of the ionic hypothesis.