674 THE POPULAR SCIENCE MONTHLY. 



Any common event, then, which may be selected by way of illus- 

 tration, will furnish two elements open to scientific study matter 

 and motion. The distinction between the two is more convenient 

 than essential, for we are unacquainted with matter devoid of 

 motion, and the idea of motion divorced from matter is similarly 

 unthinkable. However, the distinction is convenient, so that it 

 will be well to follow it. The study of the analysis and synthesis 

 of matter is the field of chemistry. The study of those varied 

 motions which give to matter its apparent properties belongs to 

 the domain of physics. The two sciences are commonly made the 

 objects of separate study. It would be more true to nature to 

 consider chemistry simply as a branch or subdivision of physics, 

 for it is impossible to make any change in the constitution of 

 matter without at the same time disturbing the physical equilib- 

 rium. Heat is either given out during the reaction or it is taken 

 in. If it be chemical combination, heat is commonly disengaged ; 

 if a chemical disunion, heat is commonly involved. So general is 

 the truth of this statement that we are able to predict what will 

 occur chemically if the physical conditions are known. If there 

 be two or more reactions possible, that one will take place which 

 will liberate the greatest amount of heat. It is, indeed, the dis- 

 tinctive character of the so-called New Chemistry that it takes 

 cognizance of the physical reaction which invariably accompanies 

 the chemical. If the labors of Crookes, Roscoe, Hunt, and other 

 eminent contemporary chemists count for anything, it is from 

 such joint study as this that the best secrets of chemistry are to 

 be evolved. With the view of lessening difficulties, this necessary 

 interdependence between the chemical and physical is frequently 

 omitted in presenting the science to young students ; but the prac- 

 tice of teaching errors or half-truths, in order that the truth itself 

 may afterward be apprehended, has as little excuse in science as 

 it has in religion, for generally it is the error which proves obdu- 

 rate, and the subsequent truth has no chance whatever. It robs 

 the science, moreover, of an element of vitality which is one of its 

 chief attractions. 



In selecting our illustrations of chemical action, the more 

 commonplace the event the better. The affairs of every-day life 

 present such excellent objects for study that it would be as un- 

 necessary as it would be uselessly distracting to go in search of 

 the unusual, until the fundamental principles have been learned 

 from a study of that which is familiar. That coal will burn, 

 that milk will sour, that iron will rust, that cider will turn into 

 vinegar, and that wood will decay, are all well-known facts of 

 every-day life. But they are also facts of chemistry, for they in- 

 volve a change in the composition of matter. It needs no scientist 

 to perceive that the original coal, milk, iron, cider, and wood have 



