THE NEW CHEMISTRY. 399 



might be written as containing different compound radicles under dif- 

 ferent conditions. 



The fault of the old chemistry was that more attention was paid to 

 symmetrical formulae than to reactions ; the merit of the new con- 

 sisted in bringing the student once more back to nature. 



And the appeal to nature was answered, and answered abundantly. 

 The new conception of compound radicles was rich in results ; from it 

 there was developed first, the theory of types, and, subsequently, the 

 wider theory of valency, which has led to that of atom-linking, and 

 these in their turn have reacted on the older and more fundamental 

 notions of the science, and have given a new meaning to such terms as 

 " chemical " and " mechanical actions," " compounds " and "mixtures," 

 etc., while, at the same time, they point the way to the chemistry of 

 the future when we shall have gained a definite conception of the 

 inner mechanism of the molecule, and of the laws which regulate the 

 combinations of molecules in groups, and the decompositions of mole- 

 cules with subsequent formations of new atomic systems. 



Let us shortly examine these ideas. If sodium be thrown on to 

 water, caustic soda is produced, a substance made up of hydrogen, 

 oxygen, and the simple radicle sodium ; by another reaction a sub- 

 stance can be obtained consisting of hydrogen, oxygen, and the com- 

 pound radicle nitryl (NOJ. These two bodies have analogous for- 

 mulas, Na OH and (N0 2 ) OH, they may both be regarded as derived 

 from water, H HO, by the replacement of otfe half of the hydrogen by 

 a radicle ; in one case by Na, in the other by N0 2 . Again, the whole 

 of the hydrogen in water may be replaced by sodium, with production 

 of the compound sodium oxide, Na 2 0. ; but in many of its reactions 

 this compound is the analogue of common ether, which is also a com- 

 pound of oxygen with a (compound) radicle ethyl, and has the for- 

 mula (C 2 H 5 ) 2 0. Now, these substances, Na OH, (NO) OH, Na 3 0, 

 and (C a H 5 ) 2 0, both on account of the methods by which they are 

 produced, and because of their general reactions, may be classed to- 

 gether as derivatives of water, or may be said to belong to the water- 

 type. Similarly, other types have been instituted, and large groups of 

 compounds have been brought into the same class as being all refer- 

 able to one parent type. This step in advance is evidently an out- 

 come of the theory of compound radicles ; without that conception a 

 system of classification by types would have been impossible. 



But it was found that while such compound radicles as C 2 H B or 

 N0 2 were capable of replacing but one part by weight of hydrogen in 

 water, other compound radicles, such as CO or C 2 H 4 , were capable of 

 taking the place of two parts by weight of hydrogen. Comparing to- 

 gether these two sets of radicles, it might be said that CO = 2 N0 2 or 

 C a H 4 = 2 C 2 H 6 , so far as the power of combining with hydrogen was 

 concerned. This conception of binding power being extended to the 

 elements, and being deepened and widened by laborious experimental 



