16 INTRODUCTION. 



DEFINITION.* CHEMISTRY is THAT SCIENCE WHICH INVESTI- 

 GATES THE COMPOSITION OF ALL BODIES, AND THE LAWS BY WHICH 

 IT IS GOVERNED. 



Remark. This, of course, includes every possible combination 

 and decomposition. 



Chemistry, taking into view the properties discovered by Natural 

 Philosophy, begins its appropriate work where the sister science stops. 



The distinction between chemistry and natural philosophy is illus- 

 trated by the familiar examples of 



1. Water, 



2. The atmosphere, 



3. Gunpowder. 



Thus, water is composed of the bases of two gases ; the air of at 

 least two, and gunpowder of combustible and metallic matter and the 

 ponderable part of gases. 



Natural History, Natural Philosophy and Chemistry are all ne- 

 cessary to complete the scientific history of any thing. 



Natural History explains the external appearance of bodies ; 



Natural Philosophy the mechanical properties ; 



Chemistry the constitution. 



This general position is easily illustrated by reference to amber, 

 tool, calc-spar, fossil salt, and other familiar bodies. 



Chemistry is distinguished as an art or a collection of arts, from 

 chemistry as a science : the former is empirical, the latter is guided 

 by established principles, and they are now, in numerous instances, 

 happily united, in the hands of both practical and scientific men. 



Chemical arts are numerous ; glass and soap-making, have been 

 already mentioned, and pottery, metallurgy, and dyeing, may be ad- 

 ded ; the latter depends on the affinity of coloring matter for fibre, 

 or for the mordant, or for both. 



The vinous fermentation produces cider, wine, perry, bear, me- 

 theglin, &ic. Carbonic acid gas is evolved, while alcohol is formed, 

 and the rapidity of the process depends on the temperature. 



Leather, is formed from skins and tannin contained in the astrin- 

 gent vegetables; the tannin of the latter uniting with the gelatine of 

 the skin. 



Bread, is produced by a peculiar fermentation : its sourness, ow- 

 ing to excessive fermentation, is corrected by an alkali and the carbon- 

 ic acid which is evolved, renders it lighter than before. 



* For various definitions the student may see the principal authors, Thomson. 

 Fourcroy, Henry, Murray, La Grange, Thenard, Davy, Brande, Turner, Hare and 

 others. 



