ISOMERIC COMPOUNDS. 291 



difference in the aggregate number of atoms, or in the 

 mode in which those atoms have respectively arranged 

 themselves, or that peculiar physical difference desig- 

 nated by the term allotropy, has been detected. 



Oil of turpentine- and oil of lemons have the same 

 composition, each being composed of five equivalents of 

 carbon and four of hydrogen. These substances form, 

 from the striking difference perceptible in their external 

 characters, a good example of isomerism. 



The laws of organic chemistry are not, however, the 

 same as those applying to inorganic combinations. Or- 

 ganic chemistry is well defined by Liebig, as the che- 

 mistry of compound radicals ; and under the influence 

 of vitality, nature produces compounds which have all 

 the properties of simple elements.* 



When we reflect upon the conditions which prevail 

 throughout nature, with a few of which only has science 

 made us acquainted, we cannot fail to be struck with 

 the various phases of being which are presented to our 

 observation, and the harmonious system upon w r hich 

 they all appear to depend. 



When we discover that bodies are formed of certain 

 determinate atoms, which unite one with another, ac- 

 cording to an arithmetical system, to form molecules, 

 which, combining with molecules, observe a similar law, 

 we see at once that all the harmonies of chemical combi- 

 nation the definite proportions, laws of volume, and 

 the like are but the necessary consequences of these 

 simple and guiding first principles. In the pursuit of 

 truth, investigators must discover still further arrange- 

 ments, which, from their perfection, may be compared 

 to the melodious mterblending of sweet sounds, and 



-!- Liebig's Chemistry in its application to Agriculture and 

 Physiology: translated by Lyon Playfair, Ph. D. Animal 

 Chemistry, or Chemistry in its application to Physiology and 

 Pathology: by Justus Liebig; translated by Win. Giegory. 



