220 MODERN SCIENCE READER 



portant discoveries showing that chlorine and other ele- 

 ments could be substituted for the hydrogen or organic 

 compounds, and that the nature of the latter was thereby 

 affected very little. But if part of the molecule of a com- 

 pound can combine with either of such electrically different 

 atoms as those of hydrogen and of chlorine, then there is 

 no reason for believing that that part is essentially either 

 electro-positive or electro-negative, and hence there is no 

 reason for believing that every compound is made up of 

 two electrically opposite parts. The more evidence to this 

 effect was brought forward, the more bitterly old Berzelius 

 adhered to the electro-chemical theory. But finally it be- 

 came evident to all that, as Liebig wrote, "the wheel of 

 time cannot stand still," and "Berzelius is fighting for a 

 lost cause ' ' ; and, thus toward the end of the thirties, elec- 

 tro-chemical dualism was overthrown. As a result of their 

 struggles against dualism, chemists then fell into the oppo- 

 site extreme and adopted a purely unitary view of chemical 

 combination. The molecule of a compound was conceived 

 to be a composite unit somewhat like the solar system, in 

 which the planets are held together by mutual attraction, 

 but which does not by any means consist of two essentially 

 different parts, endowed with two opposite forms of energy. 

 Such unitary views of combination are still prevalent in 

 chemistry to-day. But "the wheel of time cannot stand 

 still," and recent years have forced upon us theories which 

 make us feel that extreme unitarism is just as inadequate 

 as extreme dualism. The elements certainly differ in their 

 electrical properties, and chemists have even succeeded now 

 in expressing those differences mathematically. Electricity, 

 while not identical with the energy that causes the mutual 

 attraction of atoms, is yet certainly one of the factors 

 determining that attraction. At present, however, it is 

 impossible to tell what compromise between chemical unita- 

 rism and electro-chemical unitarism and electro-chemical 

 dualism will ultimately be adopted. 



ORGANIC CHEMISTRY. When the general principles of 



