ALCOHOLS. 307 



are compound ethers, others aldehydes, but most of them are hydro- 

 carbons or oxidized hydrocarbons, belonging to the benzene-deriva- 

 tives, where they will be considered. 



41. ALCOHOLS. 



Constitution of alcohols. The old term "alcohol" originally 

 indicated but one substance (ethyl alcohol), but is now applied to a 

 large group of substances which may be looked upon as being derived 

 from hydrocarbons by replacement of one, two, or more hydrogen 

 atoms by hydroxyl, OH. 



Any hydrocarbon may be converted jnto an alcohol radical by 

 removal of one or more hydrogen atoms ; methane, CH 4 , for instance, 

 is converted into methyl, CH 3 , which, upon combining with hydroxyl, 

 forms methyl alcohol, CH 3 OH. 



It has been shown before that the higher members of the paraffin series are 

 capable of forming a number of isomeric compounds. Eunning parallel to the 

 various series of hydrocarbons (and their isomeres) we have homologous series 

 of alcohols. The isomeric alcohols also show properties different from one 

 another, and yield different decomposition products. The isomeric alcohols are 

 distinguished as normal or primary, secondary and tertiary alcohols ; a normal 

 alcohol is derived from a -normal paraffin, and contains hydroxyl in the place 

 of a hydrogen atom in a methyl group, the constitution of normal ethyl 



CH 2 .OH 

 alcohol being, for instance, represented by the formula I 



CH 3 . 



If hydroxyl replaces but one atom of hydrogen in a hydrocarbon, 

 the alcohol is termed monatomic ; diatomic and triatomic alcohols are 

 formed by replacement of two or three hydrogen atoms respectively. 

 (Diatomic alcohols are also termed glycols.) As an instance of a 

 diatomic alcohol may be mentioned ethylene alcohol, C 2 H 4 (OH) 2 , 

 while glycerin, C 3 H 5 (OH) 3 , is a triatomic alcohol. 



QUESTIONS. 391. How do hydrocarbons occur in nature, and by what pro- 

 cesses are they formed in nature or artificially? 392. State the general physical 

 and chemical properties of hydrocarbons. 393. What is the general composi- 

 tion of the paraffins ? 394. State the composition and properties of methane, 

 and also the conditions under which it is formed in nature. 395. What is coal, 

 what are its constituents, from what is it derived, and by what process has it 

 been formed? 396. What is crude coal-oil, what is petroleum ether, and what 

 is petrolatum ? 397. How is illuminating gas manufactured, and what are its 

 chief constituents ? 398. Mention some of the important substances found in 

 coal-tar. 399. Explain a method by which the flashing-point of coal-oil can 

 be determined. 400. Which substances are termed volatile oils, and what are 

 their properties? 



