1G2 



THE MODERN THEORY OF CHEMICAL TYPES. 



by subtnictiiig 2 II O from (C„ H(u+2)02 ) we obtain Cu Hu, or the series of 

 hydrocarbons (I.) Ethylene is thus actually obtained from alcohol. 



Again, Irom every acid of the series Cu IIn O4 we may obtain an amide Cn 

 H(„ + ,)N02. 



The law of homology conduced strongly to the type theory by contributing 

 a better knowledge of the chemical constitution of bodies. I3y its study, radi- 

 cals containing oxygen were definitely accepted. Thus, (in series 11,) acetic 

 acid (C, II4 04) is not formed from ethylene (C4 II4) by the addition of O4, but 

 from alcohol (U4 II,j O2) by the addition of O2, and by the subtraction of H2 in 

 such manner that the radical (C4 II3O2) is formed ; which makes acetic acid (C4 

 11^ Oj) = (O4 H3 O2) II O2. As a proof of the existence of such a radical in 

 acetic acid, we may obtain its compound with chlorine by the action of oxychlo- 

 ndi.' of phosphorus upon acetate of soda, and we may restore this chlorine com- 

 pound to acetic acid by the action of water upon it.* 



(NO4) is another radical containing oxygen. By acting upon benzoic acid 

 so as to substitute (NO4) for hydrogen, we have nitro-benzoic acid — that is, C14 

 He O4 becomes Cu H5 {NO4) O4. 



These considerations have been leading us gradually to the ideas of modern 

 chemical types. Such a type is a group of atoms of which the individuals bear 

 a certain relation to each other, and forms a pattern for imagining all chemical 

 compounds, between the atoms of which a similar relation is supposed to exist. 

 It may be illustrated by certain blocks glued together, or by a cage of wire with 

 compartments, in which the blocks may be placed, thus : 



THE TYPE — WATER. 



Examples of the type of water ; 

 Sulphuretted Hydrogen. 



Hydrate of Potassa, 



* See examples of reactions by the type metliod toward the close of this article. 



