278 CONSIDERATION OF CARSON COMPOUNDS. 



In a strictly systematically arranged text-book of chemistry organic 

 compounds 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 instruction 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 has never yet been fused 

 or volatilized, while hydrogen, oxygen, and nitrogen are colorless 

 gases which can only be converted into liquids with difficulty. More- 

 over, hydrogen is very combustible, oxygen is a supporter of combus- 

 tion, whilst nitrogen is perfectly indifferent. Finally, hydrogen is 

 univalent, oxygen bivalent, nitrogen trivalent, and carbon quadri- 

 valent. These elements are, therefore, capable of forming a greater 

 number and a greater variety of compounds than would be the 

 case if they were elements of equal valence and of similar proper- 

 ties. 



It will be shown later that carbon atoms have, to a higher degree 

 than the atoms of any other element, the power of combining with 

 one another by means of a portion of the affinities possessed by each 

 atom, thus increasing the possibilities of the formation of complex 

 compounds. 



General properties of organic compounds. The substances 

 formed by the union of the four elements just mentioned have prop- 

 erties in some respects intermediate to those of their components. 



