HOMOLOGOUS SERIES. 341 



is obtained from potassa or oxide of potassium, although 

 by a different process. 



What were the 862. It is but a few years since the 

 grounds of be- met f 10( i o f producing ethyle was discovered, 



hef vn the ex- & J 



of but chemists believed in its existence al- 

 most as confidently before, as now. They 

 co-eery? reasoned that ether, which possesses the 



properties of an oxide, must have its radical, as Sir 

 Humphrey Davy reasoned that potassa, soda and lime, 

 must each contain its metal. 



863. HOMOLOGOUS SERIES. Certain of 



What are ho- .<>'' 



moiogous these compound radicals sustain to each 

 other a curious numerical relation. They 

 form a series in arithmetical progression, differing from 

 each other in composition, by a common difference. 

 Two atoms of carbon with two of hydrogen forms the 

 common difference of the series referred to. Methyl, 

 the radical of wood spirit, begins the list with two atoms 

 of carbon and three of hydrogen. Ethyle follows its 

 composition being expressed by the addition of the 

 common difference to the last. Margaryl, a radical 

 contained in certain fats, is the seventeenth member of 

 the series. Each of these radicals has, like ethyle, its 

 own oxide or ether, its hydrated oxide or alcohol ; also 

 its aldehyde and its acid. A series of radicals, ethers, 

 alcohols, aldehydes and acids, each in arithmetical pro- 

 gression, is thus produced. Such series are called ho- 

 mologous. 



864. PRODUCTION. There are many saps 



How are the * *- 



different mem- in most of the series, but the law of their 

 bersproduccd? progression is so we]1 established, that no 



