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THE POPULAR SCIENCE MONTHLY 



double binary or ternary compounds, 

 and when tliese were made to act on 

 each other the reaction was represented 

 as a double decomposition. This was 

 known as the dual theory of chemistry, 

 and it organized and explained the facts 

 of tlie science in the most beautiful 

 manner. Electro-chemistry lent it pow- 

 erful aid, as compounds were resolved 

 into pairs by galvanic decomposition, 

 and their elements were supposed to be 

 in opposite electrical states and to be 

 united by polar attractions. The atomic 

 theory gave a basis of philosophy to the 

 doctrine, and the admirable nomencla- 

 ture which was adapted to it gave it 

 wide currency and acceptance. Under 

 this chemical system the science grew 

 and flourished for more than half a 

 century, spread out into branches, and 

 became the guide in medicine, mining, 

 agriculture, and numberless arts and 

 manufactures. Yet this system, too, 

 was true for its time ; only true in re- 

 lation to the facts known, and is now 

 doomed to the fate of phlogiston. As 

 it grew out of a preceding stage upon 

 which it was a great improvement, so 

 it has led to a subsequent and higher 

 stage of knowledge, to which it must, 

 in turn give way. Its facts live on ; 

 its partial truths survive and are ex- 

 panded into new forms, and a system 

 of doctrine has arisen so contrasted 

 with the dual theory and so advanced 

 beyond it that it is now characterized 

 as the " new chemistry " in contradis- 

 tinction to the old which it has super- 

 seded. We are now entering upon the 

 new chemical epoch in which ideas that 

 have long simmered in the brains of 

 chemists, and were long contested, have 

 emerged into distinctness and are pass- 

 ing into predominance. Tlie simple 

 splitting and pairing theory of chemi- 

 cal change has failed, and we are becom- 

 ing familiar with the conception of uni- 

 tary structure, molecular types, and 

 transformations by substitution and re- 

 placement that leave the construction 

 and character of chemical compounds 



unaltered. The dualist appealed to anal- 

 ysis, and asked only what are the con- 

 stituents and what their proportions in 

 chemical substances. The apostles of 

 the new chemistry point to the failures 

 of analysis, and aver that it is not so 

 much what a compound is made of, as 

 how its elements are arranged, that is 

 the present concern of inquiry. And 

 chemistry was probably never so active 

 as now under guidance of the new the- 

 ories, and never before answered so 

 well to that highest test of science, the 

 prevision and prediction of chemical 

 results. There is no escape from the 

 new chemistry. It absorbs the verities 

 of the past and it is the highest truth 

 arrived at by centuries of thought and 

 labor. But it is not a finality. Its truth, 

 though priceless, is imperfect, and is no 

 doubt destined to still further and high- 

 er development. Historically regarded, 

 the science of chemistry is a striking 

 exemplification of the laws of mental 

 evolution, as the doctrine of evolution 

 is the grandest illustration of the rela- 

 tivity of truth. 



An interesting illustration of the 

 striking changes of view that have taken 

 place in modern chemistry is furnished 

 by the reversal of scientific rank as- 

 signed to those prime elements of Na- 

 ture, oxygen and hydrogen gases. Oxy- 

 gen was long enthroned both from its 

 enormous distribution in earth, sea, and 

 air, and its active participation in the 

 great changes of matter, combustion, 

 respiration, decay, all of which were 

 generalized as different forms and 

 grades of oxidation. It was supposed 

 to be the acidifying principle in Nature, 

 and was early taken as a standard in 

 chemical scales. Hydrogen was also 

 known as a widely-diffused and impor- 

 tant element, but of far inferior import 

 to oxygen, and received its name from 

 the fact that it generates water by union 

 with oxygen. But, as more was known 

 about it, it was found to be deeply Im- 



