CHEMICAL APPARATUS AND PRODUCTS. 203 



elementary gas chlorine. Thus the metal potassium burns in cyan- 

 ogen, producing potassic cyanide, in a manner similar to that in 

 which it burns in chlorine to produce potassic chloride. The dis- 

 covery of this compound radical, as it was called, was followed, in 

 1842, by that of cacodyl by Bunsen ; of butyl by Kolbe, in 1847 ; 

 and of methyl, ethyl, and amyl by Frankland, in 1849. These 

 bodies differ from cyanogen in being the analogues of another series 

 of elements, of which hydrogen and the metals are types. 



Organic analysis soon showed that there were many compounds 

 possessing exactly the same composition, but differing in proper- 

 ties ; tor example, oil of turpentine, otto of roses, and oil of lemons 

 are bodies containing the same elements, and in the same propor- 

 tions, although possessing very different properties. Sometimes 

 this may be explained by the fact, that the molecules of these 

 bodies contain different numbers of atoms, when they are said to 

 \>z polymeric ; sometimes, however, the molecules contain the same 

 number of atoms, when they are said to be isomeric, or metameric. 

 This has been explained by the different arrangement of the atoms 

 in the molecules. 



In the early days of the study of organic compounds, it was 

 supposed that these bodies could only be produced by vital force, 

 and this opinion was held until 1828, when Wohler obtained urea 

 artificially. Since that time a large number of organic compounds 

 have been built up from purely mineral matter. This synthesis 

 of organic compounds has been of great service to chemistry, 

 since it has shown that the properties of the products vary accord- 

 ing to the manner in which the compounds are produced ; isomeric 

 substances being formed when the compounds are, so to speak, 

 put together differently. The study of isomeric bodies and organic 

 synthesis are at present being investigated by a large number of 

 chemists, and amongst the greatest triumphs of organic synthesis 

 is the artificial formation of alizarin, the valuable colouring matter 

 of madder, which was effected byGrsebe and Liebermann in 1870. 



The researches of Gerhardt and of Williamson upon oxidised 



