440 CONSIDERATION OF CARBON COMPOUNDS. 



to that time had been believed to be formed in the animal system exclusively. 

 As potassium cyanate may be obtained by oxidation of the cyanide, and as the 

 latter can be made by passing nitrogen over a heated mixture of potassium 

 carbonate and carbon, it follows that urea can be made from the elements. 



The conversion of ammonium cyanate into urea is due to a rearrangement 

 of the atoms within the molecule, thus: 



Ammonium cyanate. Urea. 



An organic compound, according to modern views, is simply a 

 compound of carbon generally containing hydrogen, frequently also 

 oxygen and nitrogen, and sometimes other elements. As this defini- 

 tion would include carbonic acid and its salts, such as marble, CaCO 3 , 

 spathic iron ore, FeCO 3 , and others i.e. 9 substances which we are 

 accustomed to look upon as belonging to the mineral kingdom it is 

 better to omit carbon dioxide, carbonic acid, and carbonates, and 

 define organic compounds as compounds containing carbon in a com- 

 bustible form. 



The definition usually given is : Organic chemistry is the chemistry 

 of the hydrocarbons and their derivatives. Hydrocarbons, as the name 

 implies, are compounds of carbon and hydrogen, which are to organic 

 chemistry what the elements are to inorganic chemistry. 



In a strictly systematically arranged text-book of chemistry organic com- 

 pounds should be considered in connection with the element carbon itself, 

 but as these carbon compounds are so numerous, their composition often so 

 complicated, and the decompositions which they suffer under the influence of 

 heat or other agents so varied, it has been found best for purposes of instruc- 

 tion to defer the consideration of these compounds until the other elements and 

 their combinations have been studied. 



Elements entering- into organic compounds. Organic com- 

 pounds contain generally but a small number of elements. These 

 are, besides carbon, chiefly hydrogen, oxygen, and nitrogen, and 

 sometimes sulphur and phosphorus. Other elements, however, enter 

 occasionally into organic compounds, and by artificial means all 

 metallic and non-metallic elements may be made to enter into organic 

 combinations. 



Here the question presents itself: Why is it that the four elements 

 carbon, hydrogen, oxygen, and nitrogen are capable of producing 

 such an immense number (in fact, millions) of different combinations? 

 To this question but one answer can be given, which is that these 

 four elements differ more widely from each other, in their chemical 

 and physical properties, than perhaps any other four elements. 



Carbon is a black, solid substance, which can scarcely be fused 



