CONSTITUTION OF ORGANIC COMPOUNDS. 245 



different scientists and at different times, to represent the struc- 

 ture of acetic acid, but it should be remembered that these 

 formulas are not intended to represent the actual arrangement 

 of the atoms in space, but only, as it were, their relative mode 

 of combination, showing which atoms are combined directly 

 and which only indirectly, that is, through the medium of 

 others. 



QUESTIONS. 



361. What is organic chemistry, according to modern views? 



362. Mention the four chief elements entering into organic com- 

 pounds, and name the elements which may be made to enter into 

 organic compounds by artificial processes. 



363. State the reasons why the four elements carbon, hydrogen, 

 oxygen, and nitrogen, are more apt to form a larger number of com- 

 pounds than most other elements. 



364. State the general properties of organic compounds. 



365. Why does a qualitative analysis of an organic compound, in 

 most cases, not disclose its true nature? 



366. By what tests may the organic nature of a compound be estab- 

 lished ? 



367. By what tests may the presence of carbon, hydrogen, and 

 nitrogen be demonstrated in organic compounds? 



368. State the methods by which the elements carbon, hydrogen, 

 oxygen, sulphur, and phosphorus are determined quantitatively. 



369. By what general method may a formula be deducted from the 

 results of a quantitative analysis? 



370. What is meant by an empirical, molecular, and constitutional 

 formula ; how are they determined, and what is the difference between 

 them ? 



38. CONSTITUTION, DECOMPOSITION, AND CLASSIFICA- 

 TION OF ORGANIC COMPOUNDS. 



Radicals or residues. The nature of a radical or residue has 

 been already stated, but the important part played by residues 

 in organic compounds renders it necessary to consider them 

 more fully. 



A residue is an unsaturated group of atoms obtained by re- 

 moval of one or more atoms from a saturated compound. It is 



