CHEMISTRY OF THE NINETEENTH CENTURY. 617 



to these newer views, by far the greater number of chemical actions 

 resulting in production of salts and other compound bodies consist 

 not in the simple conjunction of groups of atoms, but in an exchange 

 between already existing larger groups. This will be understood by 

 comparing with Berzelius's symbol for saltpetre, the following symbolic 

 representation of what takes place in the contact of nitric acid with 

 potash. 



Nitric acid Potash. 



or nitrate of hydrogen. 



NO 3 JH KiHO j Before the reaction. 



N 3 K . HHOl Afterthereaction . 



Nitrate of potassium. Water. ) 



By the dotted line we here indicate that the hydrogen and the po- 

 tassium atoms change places, thus forming the products shown in the 

 second line of symbols, viz., nitrate of potassium and water. The 

 elimination of water in such reactions is a fact which was long over- 

 looked. 



Another development of the atomic theory is the doctrine of " com- 

 pound radicals ; " that is, groups of atoms are conceived as performing 

 all the functions of single atoms by entering into and leaving combi- 

 nations. Thus a group formed by the union of one atom of carbon 

 with one of nitrogen will perform the function of a single atom of 

 chlorine, forming a parallel series of compounds. The compound 

 radical (CN) is named cyanogen, and as we have hydrochloric acid, 

 HC1 ; potassium chloride, KC1, etc., etc., so we have hydro-cyanic acid 

 H(CN) ; potassium cyanide, K(CN), etc., etc. The number of com- 

 pound radicals now recognized is extremely great; indeed, there is 

 no limit to the number that may be supposed. 



About the end of the seventeenth century we find some chemists 

 considering apart the substances derived from the mineral, animal, and 

 vegetable kingdoms respectively. About the beginning of the present 

 century it became customary to divide the study of chemistry into two 

 great divisions, called respectively "organic "and "inorganic "chemistry. 

 The provinces assigned to these branches of the science will be under- 

 stood (from Berzelius' definition of organic chemistry, 1827) as the che- 

 mistry of animal and vegetable bodies, or of those substances which are 

 found under the influence of the vital forces. It was supposed that an 

 impassable barrier existed between the mineral and organic substances 

 in this respect : that whereas the former could be formed from their 

 ultimate elements by the chemist in his laboratory, the latter, the 

 organic substances, could arise only in the living bodies of plants and 

 animals, where the vital actions were supposed to control the chemical 

 tendencies in some peculiar manner. Lavoisier had announced that 



